/ . Embryol. exp. Morpfu, Vol. 11, Part 2, pp. 369-382, June 1963
Printed in Great Britain
The Origin and Development of Smooth Muscle
and Contractility in the Ductus Epididymidis
of the Rat
by ROBERT L. VAN DE VELDE and PAUL L. RISLEY 1
From the Biology Department, University of Oregon
WITH THREE PLATES
INTRODUCTION
T H E contractile activity of smooth muscles of the epididymal duct has long been
overlooked in discussions relating to functional aspects of the epididymis and
the problem of sperm transport in the male. Benoit (1926) described the
occurrence of smooth muscle fibers, circularly arranged, surrounding the
efferent ductuli and ductus epididymidis. Young and co-workers (1929-1931)
emphasized that currents produced by vibrant cilia of the ductuli efferentes, the
continued production of sperm in the testis, and the pressure of fluids transferred across the germinal epithelium to the lumina of the efferent duct system
were responsible primarily for the movement of spermatozoa through the
epididymis to their storage place in the caudal end of this organ prior to emmission. Simeone (1933) described contractile movements in the excised epididymis
of the guinea-pig, and, although she discussed the probable occurrence also of
peristaltic action, she concluded that the activity was mainly of a segmentationlike character. On the other hand, Maneely (1958), in a histochemical study of
the epididymis of the rat, questioned the existence of circular smooth muscles in
this organ, as have other histologists and physiologists concerned with reproduction in the male.
The occurrence of in vivo rhythmic contractions in the ductus epididymidis of
the normal adult male hamster was observed in this laboratory in 1949 by
Roslansky & Risley (unpublished). Two years later Muratori & Contro (1951)
reported on the nature of these contractions in the rat, using cinematography
to record their observations with the aid of the Knisely apparatus for transillumination of organs in vivo. The work of the Italian group was unknown to Risley &
i Authors' address: Department of Biology, College of Liberal Arts, University of Oregon,
Eugene, Oregon, U.S.A.
370
ROBERT L. VAN DE VELDE AND PAUL L. RISLEY
Turbyfill (1957) when a similar method was used to follow out the problem
further, also using the rat. Risley (1958, 1959) also studied some hormonal
effects on the contractions in vivo. During the course of this work, an attempt
was made to establish the time of origin of the contractile activity and to trace
its development. However, the small size of the animals and the epididymis in
younger stages required higher magnifications and other methods. It was
possible to record minute contractions in the caput epididymidis of 10-day-old
rats with cinematographic transillumination in vivo methods.
Battaglia (1958) explanted whole epididymides from newborn rats, and small
fragments of immature and adult epididymides, in organ culture media. He
observed the occurrence of contractions in the cultured epididymides from
newborn animals after they had been in roller tube cultures for 5 or 6 days, but
did not state whether contractions also were present at the time of explantation.
The organs were maintained in culture for periods of about 12 days, and contractions in the ducts occurred at about 7-9 sec. intervals in prepuberal animals.
The present paper attempts to answer the problem of when and where the
rhythmic contractile activity originates in the development of the efferent ductuli
and ductus epididymidis, and includes a study of the histogenesis of the smooth
muscles of the Wolffian duct, together with some observations on the origin of
contractility in the Miillerian duct of the female.
MATERIALS AND METHODS
Animals used in this study consisted of pre-natal male rat embryos with
gestation ages of between 14 and 21 days, and post-natal male and female rats
ranging in age from 1 to 45 days, obtained from a rat colony, including representative laboratory strains of albino and hooded rats. Healthy females weighing between 190-270 g. were examined for estrus by vaginal smearing. Females
in late proestrus and early estrus were placed with males and examined after
12 hr. If sperm were present, the females were marked, placed in metal cage,
and housed singly.
When the appropriate gestation age was reached, the pregnant female was
injected with sodium Nembutal (0-1 c.c. per 100 g. body weight). The effects of
the anesthetic lasted for an approximate period of 1 | hr. Fetus and placenta
were removed together to a warm towel which was then placed under a binocular
dissecting microscope. Cotton which had been saturated with ether was placed
over the head of the fetus, or sodium Nembutal was injected in minimal doses.
As soon as the anesthetic became effective, the testis with epididymis was
excised and removed to a warmed depression slide containing Hanks BSS at
approximately 36°C. The preparation was then placed on a warm stage of a
compound microscope for observation.
With a sufficient quantity of Hanks BSS in the depression slide, a coverslip
could be placed upon the specimen under observation without any noticeable
DEVELOPMENT OF DUCTUS EPIDIDYMIDIS IN THE RAT
371
effects on smooth muscle contractions. Besides providing better visibility, the
cover slip also prevented too rapid evaporation.
Because smooth muscle contractions in the ductuli efferentes and ductus
epididymidis were extremely weak during late intra-uterine development and
the neonatal period, observations were made using a 10 x ocular and a 43 x
objective. Microcinematography was used as an aid in identifying and recording
the contractions when possible. Times of contraction intervals were taken by
stop-watch, and counts of a series of contractions were made in order to determine average values.
The technique used for the fetuses was altered in post-natal animals. Better
results could be obtained when the animal was anesthetized by placing it in the
freezing compartment of a refrigerator for 15-17 min. The animals were
removed when quite stiff, and warmed under a lamp. When the first signs of
movement were detected, the testis and epididymis were removed for study.
At the conclusion of the observation period, tissues were fixed in Zenker's or
Bouin's fluid, embedded and sectioned at 5-10 /*. Harris's haematoxylin and
eosin, Masson's trichrome stain and Mollier's quandruple stain for muscle were
used to study the histogenesis of the smooth muscles of the epididymis.
OBSERVATIONS
Histogenesis of smooth muscles
Histogenesis of the male accessory sex ducts in late embryonic and early
post-natal periods appears to have received little attention in the past. This is
particularly true with respect to the development of the smooth muscle layer
which invests the ductuli efferentes and ductus epididymidis.
Ductuli efferentes
By the 14th day of gestation, the ductuli efferentes of the rat appear as tubules
with slightly open ducts surrounded by a simple cuboidal layer of epithelial
elements. They are surrounded by a typical syncytium of mesenchymal cells
(Plate 1, fig. 1). The mesenchymal cells undergo further condensation and
differentiation during subsequent stages of development to form the sheet of
smooth muscle cells which envelops the ductuli efferentes and ductus epididymidis throughout their lengths.
As muscle tissue differentiates from the mesenchyme, there is an increase in
the amount of cytoplasm which surrounds each nucleus. The cytoplasmic
processes stretch out in a direction corresponding to the elongating nucleus, and
in so doing, bring about an alteration of the cells from the stellate to a typical
lengthened spindle shape (Plate 1, figs. 2 & 3). This occurs between the 15th
and 17th days in the ductuli efferentes.
24
372
ROBERT L. VAN DE VELDE AND PAUL L. RISLEY
Ductus epididymidis
Differentiation of mesenchymal cells surrounding the caput epididymidis is
somewhat slower than in the ductuli efferentes. Elongate, spindle-shaped fibers
begin to be evident in the slightly condensed mesenchyme surrounding the upper
caput by 15 days of gestation (Plate 1, fig. 4). Condensation of mesenchymal
cells becomes more pronounced through mitoses. The rapid multiplication
brings about an increase in the number of cells and a subsequent increase in the
cytoplasm of the area. Between the 16th and 17th days of gestation three to
four layers of spindle-shaped smooth muscle fibers may be seen adjacent to the
basement membrane (Plate 1, fig. 5).
At 20 days of gestation the mesenchymal condensation has become concentrated in a small band surrounding the upper caput epididymidis, and clearly
denned smooth muscle elements are present (Plate 1, fig. 6). The width of this
investing band varies in the different regions of the caput, being less pronounced
distally. By birth, two or three layers of smooth muscle fibers also are present
in the mid-caput (Plate 1, fig. 7). By the 3rd day after birth, the investing layers
of smooth muscle are evident in the lower caput, and the upper and midcorpus (Plate 2, fig. 8).
Condensation is observed in the lower corpus epididymidis by the time the
animal reaches 3 days of age. Differentiation of smooth muscle cells is delayed,
however, but by 10 days post-parturition, a band three or four cells thick is
apparent (Plate 2, fig. 9).
Condensation of the mesenchymal syncytium of the cauda epididymidis does
not occur until birth (Plate 2, fig. 10). By 10 days, a well established band of
investing fibers can be demonstrated throughout the length of the cauda (Plate 2,
EXPLANATION OF PLATES
PLATE 1
All photomicrographs are x 500
FIG. 1. Cross section of the tubules of the ductuli efferentes of the rat at 14 days of gestation.
The cuboidal epithelial cells are surrounded by a typical syncytium of mesenchymal cells.
FIG. 2. Ductuli efferentes at 15 days of gestation. Note the elongation of the mesenchymal
cells, especially in the neighborhood of the ductuli.
FIG. 3. Ductuli efferentes of the rat at 17 days of gestation. Note the spindle-shaped cells
which are now quite apparent as an investing layer surrounding the ductuli.
FIG. 4. Cross section of the upper caput at 15 days of gestation. Note condensation and slight
elongation of the surrounding mesenchymal cells.
FIG. 5. Cross-section of upper caput at 16£ days of gestation. Cells which have begun to
assume the shape of smooth muscle fibers are concentrated in a circular layer, three to four
cells thick, surrounding the duct.
FIG. 6. Cross section of the upper caput at 20 days of gestation. Note the definite layer of
smooth muscle cells concentrated in a circle two to three cell layers thick surrounding the duct.
FIG. 7. Cross section of the middle caput epididymidis at birth. Smooth muscle cells, two to
three cell layers thick, can be seen surrounding the duct.
/ . Einbryol. exp. Morph.
Vol. 11, Part 2
r>r
PLATE 1
ROBERT L. VAN DE VELDE and PAUL L. RISLEY
{Facing page 372)
Vol. 11, Part 2
J. Einbryol. exp. Morph.
PLATE 2
ROBERT L. VAN DE VELDE and PAUL L. RISLEY
(Facing page 373)
DEVELOPMENT OF DUCTUS EPIDIDYMIDIS IN THE RAT
373
fig. 11). Fibers are circular in the upper cauda, but there is, however, an
indication that a layer of longitudinal smooth muscle is interspersed within the
circular layer in the extreme lower cauda (Plate 2, fig. 12).
Development of contractile function in excised ductuli ejferentes and ductus
epididymidis
After removal of the testis and adjoining epididymis to a warm slide placed
under a compound microscope, an over-all examination was made of the
epididymis to locate a suitable area for observation. A cross-sectional view
showing the lumen proved to be particularly useful since the muscle contractions were much easier to recognize. Leaving the testis intact during the period
of observation reduced the possibility of injury to the epididymis. Damage to
the epididymal duct during excision appears to result in a preparation which
lacks contractility. This is especially true of preparations of preparturition and
neonatal organs.
The testis was removed, however, from the adjoining duct in preparations of
8-day-old and older epididymides. This procedure was followed primarily to
facilitate observation, since the size of the testis by this time made observation
difficult if it remained attached. Removal of the testis by cutting the connective
tissue and ductuli efFerentes adjacent to the testis was more readily done without
evident injury to the adjoining ductuli.
PLATE 2
FIG. 8. Cross section of the upper corpus epididymis of a rat 3 days old. A slight elongation
of the nucleus and a corresponding elongation of the cytoplasm of cells surrounding the duct
is apparent. A mitotic figure can be seen in the low columnar epithelium.
FIG. 9. Cross section of the lower corpus at 10 days post-parturition showing a band of
smooth muscle three to four cells thick.
FIG. 10. Cross section of a typical upper cauda duct at birth. A condensation of the mesenchyme surrounding the duct is apparent. Elongation of these cells does not occur until a
few days later.
FIG. 11. Cross section of the upper cauda epididymidis of the rat at 10 days of age. Note the
definite elongation of those cells which immediately surround the duct.
FIG. 12. Cross section of the extreme lower cauda at 10 days of age. Note the well established
smooth muscle layer immediately surrounding the duct and the longitudinal layer on the
outside. Interspersed between the inner layers one can see occasional cross sections of
nuclei which appear to be the nuclei of longitudinal muscle cells.
Figures 13A through 13B are direct positive prints from cinematographic records
FIG. 1 3A. A photograph of the closed phase of a contractile wave passing through the midcaput epididymidis of a rat at 20 days of gestation. FIG. 13B is the open phase of the same
tubule seen in 13A. Complete dilation of the duct required only 30 sec. while completion of
the contraction phase took only 5 sec.
FIG. 14A. The closed phase of contraction of the middle caput epididymidis of the rat at
parturition. FIG. 14B shows the same duct as in 14A during the open phase. This particular
duct required 27 sec. to assume the open phase and 2 sec. to close.
374
ROBERT L. VAN DE VELDE AND PAUL L. RISLEY
14-, 15-, and 16-Day embryos
Of the thirty-six epididymides examined between the 14th and 16th days of
gestation, none exhibited any form of contraction.
17-Day embryos
A total of thirty-eight preparations of the 17-day gestation stage were
examined. Extremely weak contractions were observed in the area of the coni
vasculosi of only three 17-day embryos. None were seen in other regions of the
duct. These preparations were very good with several areas in which the tubules
were oriented in such a way that the observer could look directly into the
lumina. In one preparation, three successive extremely weak contractions were
observed, appearing approximately 60 sec. apart. In a second preparation, two
contractions were recorded with an interval of 44 sec. In the third preparation,
two contractions were again seen, this time the interval between the contractions was 71 sec. If contractions were present in the remaining thirty-five
examples, they were not recognized, although special care was taken to use
uniform techniques of handling. The use of an anesthetic on the embryos may
have reduced the incidence of contractions that were weakly beginning.
20-Day embryos
Examination of 20-day pre-natal males indicated that smooth muscle contractions were present in twelve of thirty-seven preparations observed. As in
previous preparations which exhibited motility, contractions were confined
mainly to the coni vasculosi and upper caput epididymidis. In four preparations, however, some rhythmic movements were observed distally as far as the
mid-caput. These contractions were very weak and extreme care had to be
exercised in order to see them at all.
Because of the few ductuli and their small size it was not possible to determine
if rhythmic movements of the investing muscle layer were consistent throughout
the lengths of these ducts. Intervals between successive constrictions were
measured for the region of the coni vasculosi. Times varied in different animals.
In one animal in which a number of contractions were observed the interval
between successive movements of the ducts was approximately 45 sec. for the
first 6 contractions. Subsequently, the interval between constrictions increased.
By the eighth consecutive contraction the time interval had increased to 72 sec.
No further contractions were seen.
Very weak rhythmic movements of the mid-caput were observed to occur
between 35 and 48 sec. Few successive contractions were observed, however,
four being the most that were seen during one observation period. The times
in these cases were as follows: 35 sec, 45 sec. and 46 sec. (Plate 2, figs. 13A, 13B).
Parturition
Observations of neonatal male epididymides indicated that smooth muscle
contractions appear more regularly. In a number of preparations, rhythmic
/. Embryol. exp. Morph.
Vol. //, Part 2
PLATE 3
FIGS. 15A&15B. The open and closed phases of the lower caput epididymidis at 1 day of age.
Dilation of the duct requires 26 sec.; total contraction takes 2 sec.
FIGS. 16A & 16B. The open and closed phases of the ductuli efferentes of a 10-day rat.
Twenty-one seconds were required to assume the open phase and 2 sec. to assume the closed
phase.
FIGS. 17A & 17B. Photograph of the mid-caput of a rat 10 days old. Sixteen seconds were
required to assume the open phase and 2 sec. were necessary to assume the closed phase as
depicted in 17B.
ROBERT L. VAN DE VELDE and PAUL L. RISLEY
(Facing page 375)
DEVELOPMENT OF DUCTUS EPIDIDYMIDIS IN THE RAT
375
smooth muscle contractions were observed over a number of minutes. In the
coni vasculosi many constrictions were recorded at 45 sec. intervals. In a few
instances recordings were made of rhythmic movements 24 sec. apart, but this
was rare; more frequently the contractions were observed at 40-45 sec. frequencies. Virtually all neonatal preparations demonstrated the presence of
rhythmic movements in the initial and middle caput. They occurred more
rapidly in the middle caput where the mean interval between constrictions was
29 sec. as compared with 45 sec. in the initial caput (Plate 2, figs. 14A, 14B).
No contractions appeared in the lower caput or upper corpus.
1-Day post-parturition
By the first post-natal day, contractions were apparent in the lower caput and
upper corpus epididymidis as well as in the more proximal regions of the duct
(Plate 3, figs. 15A, 15B). The interval between contractions remained approximately the same as at birth with the exception of the coni vasculosi. In this
region, rhythmic movements of the duct occurred more frequently. At birth
they occurred at 40-45 sec. frequencies, but at 1 day the intervals decreased to
28 sec.
Of twenty-nine preparations studied, twelve showed contractions in the lower
caput, and two showed smooth muscle movements in the upper corpus
epididymidis. The mean interval between movements in the lower caput was
35 sec, and most contractions were between 33-37 sec. apart. Most annular
constrictions of the upper corpus were observed to occur at intervals of 40-45
sec.
3- to 10-Days post parturition
The period from 3 days through 10 days shows a slight but constant decrease
in the interval between successive rhythmic movements of the ductuli and upper
duct (Plate 3, figs. 16A, 16B, 17A, 17B). There seems to be a tendency for all
regions of the duct and ductuli to establish a more similar rhythmic period by
the 10th day. The intervals between contractions ranged between 18 sec. in the
mid-caput to 23 sec. in the ductuli efferentes. The other regions of the upper
duct showed intervals between these extremes.
No contractions were observed in the lower corpus epididymidis until the
20th day. To fill the gap which existed between 20-day preparations and in vivo
studies of the 56-day rat epididymis by Risley (1958), an examination was made
of the ductuli and ductus of a 45-day-old animal. In addition, it was desirable
also to see if the rhythmic activity of the smooth muscle recorded in excised
tissues and those made in vivo were in close agreement with respect to frequency.
Contractions were observed in the ductuli efferentes and along the entire
length of the ductus; furthermore, the frequency of annular constrictions in the
duct compared well with those observed by Risley in the 45-day-old rat. In
376
ROBERT L. VAN DE VELDE AND PAUL L. RISLEY
addition, we were able to observe rhythmic contractions in the cauda epididymidis where they were much slower, occurring at intervals of 2 min. and
37 sec.
By the 45th day, peristaltic waves sweep the ductuli efferentes at rates of
about ten times per minute. They appear in the caput and corpus epididymidis
somewhat less frequently, and occur about six or seven times per minute. These
time intervals between successive smooth muscle contractions were similar to
those also established for the adult (Risley, 1958). A summary of the number of
preparations showing contractions and contraction rates in the various parts of
the ductuli and ducts of preparturition and neonatal males is given in Table 1
and Table 2 respectively.
TABLE 1
Initiation of smooth muscle contraction in various regions of the ductuli efferentes
and ductus epididymidis of the rat
Preparations showing tubular contractions
Age (days)
*gestation
*14, 15, 16
•17
*20
Birth
1
3
5
10
20
45
Total
number of
epididymides
examined
36
38
37
50
29
40
40
27
10
1
Caput
Corpus
Cauda
Ejf-Coni
*
vasculosi Prox. Dist. Prox. Dist. Prox. Dist.
—
—
—
—
—
—
—
—
—
3
—
—
—
—
—
—
—
—
—
12
8
—
—
—
—
—
37
41
27
2
12
24
5
26
40
40
35
39
39
20
—
—
—
27
27
25
25
—
—
—
10
10
10
10
10
—
—
1
1
1
1
1
1
1
A
I
Total
—
3
12
41
27
40
39
27
10
1
»
^
I
>
Contractile function in the excised Mullerian duct or neonatal and post-natal
female rats
Incidental to this study, an examination of the Mullerian duct muscular
activity in embryonic and neonatal female rats was undertaken. While much
information has been acquired on the physiology of muscular action in the
adult female reproductive ducts, little has been mentioned relative to the origin
and development of contractile function in the genital ducts of the immature
female.
Although we have not made detailed studies to date, there is no doubt in
our minds that rhythmic muscular contractions of the Mullerian duct of the
female rat, as in the Wolffian ducts of the male, are established also by a very
early age. Using techniques similar to those employed in the examination of
the epididymis, we were able to observe contractions as early as birth. The
intervals between the successive contractions seem to be less frequent than those
*17
*19
*20
Birth
1
3
5
8
10
44
39
38
24
26
20
19
20
20
Age (days)
* gestation Min.
71
71
72
67
53
45
41
39
41
Max.
60
58
46
40
28
25
21
24
23
Mean
Ductuli efferentes
and coni vasculosi
Max.
—
73
73
62
53
42
27
27
22
Min.
—
44
46
42
42
26
21
18
19
Proximal
Min.
—
39
35
20
15
—
23
19
16
Mean
—
60
58
45
44
32
21
21
20
—
51
48
43
38
—
38
34
21
Max.
Middle
—
45
39
29
23
—
24
22
18
Mean
Caput Epididymidis
—
—
—
—
29
28
27
21
20
Min.
Frequency of Contraction (intervals in seconds)
—
—
—
—
41
40
39
31
27
Max.
Distal
—
—
—
—
35
34
33
26
22
Mean
—
—
—
—
27
—
24
19
12
Min.
—
—
—
—
49
—
49
31
25
Max.
29
22
20
—
—
—
—
43
Mean
Coprus Proximal
Frequency of smooth muscle contraction in the ductuli efferentes and ductus epididymidis at different prenatal
and post-natal ages
TABLE 2
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378
ROBERT L. VAN DE VELDE AND PAUL L. RISLEY
of the epididymal duct of the male at the same age. At birth, rhythmic constrictions of the oviduct were recorded at the following intervals: 67, 69 and
72 sec. The contraction rate was virtually the same for 5- and 8-day-old
specimens. By 15 days, rhythmic contractions of the duct were recorded at
intervals of 60 sec, and by 40 days the interval between successive constrictions
of the duct were further reduced to 27 sec. As yet, no smooth muscle activity
in pre-natal preparations of the oviduct has been observed.
DISCUSSION
In vivo studies on the rhythmically active smooth muscles of the ductuli
efferentes and epididymis of the adult rat have been made by Muratori &
Contro (1952), and Risley (1958). As a result of these investigations there is
no doubt that spontaneous contractions occur from an early age through the
sexually mature phase of life.
As soon as the phenomenon of epididymal duct mobility was established, the
question arose as to the time and locus of origin of these contractions. As a
basis for a proper understanding of this question a study of the general arrangement and differentiation of the investing smooth muscle layer of the ductuli
efferentes and ductus epididymidis was considered essential.
It was noted that a gradual formation of smooth muscle tissue from the
mesonephric mesenchyme proceeds from the region of the ductuli efferentes
down the epididymal duct, differentiating in the upper caput after its appearance
in the ductuli efferentes. The smooth muscles of the middle caput, lower caput,
upper corpus, lower corpus, upper cauda and lower cauda epididymidis
differentiate sequentially in a proximal-distal order.
Before the muscle begins to differentiate, the walls of the ductuli efferentes
and ductus epididymidis consist of an epithelial lining of cuboidal or low
columnar epithelial cells, surrounded by a layer of mesonephric mesenchyme.
Smooth muscle fibers begin to differentiate by concentration of the nephrogenic
mesenchyme surrounding the ductuli efferentes and epididymis. Throughout
there is a distinct basement membrane between the epithelial cells and the
mesenchyme. Mesenchymal cells adjacent to the basement membrane flatten
out against it, and elongate to assume the typical spindle-shapes of smooth
muscle cells. Several layers of these cells are formed to establish the circular
muscle walls of the duct.
The observation that the development of a smooth muscle band investing
the ductuli efferentes and ductus epididymidis proceeds in a distal direction
differs from reported observations of histogenesis of smooth muscle in other
organs. In a study of histogenesis of smooth muscle in the esophagus of the
pig, McGill (1906) states that differentiation originates in the mid-region of the
esophagus and progresses in both directions.
An examination of excised epididymides from pre-natal and neonatal rats
reveals that contractions are initiated soon after the formation of the investing
DEVELOPMENT OF DUCTUS EPIDIDYMIDIS IN THE RAT
379
smooth muscle layer. The question concerning the erratic behaviour of contractions in the ductuli of 17- through 20-day embryos is not yet fully resolved.
Although it is difficult to see just where the technique used in preparations which
showed contraction and those which gave negative results could vary, some
differences might occur: e.g., the amount of Nembutal injected into the pregnant
female or into the embryo may have affected the embryonic epididymis. A
second possibility which exists is that maternal humoral agents might exert an
inhibitory effect on the contractions in some degree prior to birth. Variabilities
between animals might be a third factor. Although care was taken in order
that the technique involved in all experiments was identical, some variations may
have been due to temperature changes, time factors, and manipulations preparatory to observation.
Inspection of contraction frequency data in the region of the ductuli efferentes
and upper regions of the epididymis indicates that the intervals between successive annular constrictions of the duct diminish with age until a relatively stable
condition is reached. Although it is probable that increase in smooth muscle
differentiation may be a factor in the phenomenon of contraction frequency
increase, a complete answer to this question is lacking. It would be desirable to
establish the action of various hormones in this respect. It is known from
observations on adult preparations that rhythmic contractility of the upper
regions of the epididymis is dependent on the hypophyseal-gonadal hormonal
system for its maintenance and development (Risley, 1958). In this way, it
differs from the lower regions of the epididymis and ductus deferens where
contractions are reported to be inhibited by male hormone but to be responsive
to estrogen (Martins & de Valle, 1939).
Most of the epididymal contractions commence in the ductuli efferentes and
pass progressively toward the cauda, although few of them reach the distal
region of the duct. They usually disappear as a visible wave at the apex of a
coil of the relatively larger duct of the lower corpus. Not all the motile behavior
is strictly peristaltic. At times, pendular and segmental dilations and contractions complicate the picture (Muratori, 1954). Segmental contractions can
often be observed in a duct adjacent to but not necessarily directly continuous
with the portion of the duct which exhibits the peristaltic movements.
According to Battaglia (1958), fragments of epididymides from neonatal
animals explanted in roller tube organ cultures begin to contract spontaneously
about 5 to 6 days after excision. By the 10th day, contractions were observed
to occur at frequencies of nine to ten per minute. This rate was about the same
as that observed by Van de Velde and Risley in the 10-day old animal in vivo,
but somewhat more rapid than that observed in excised ducts followed by
immediate examination. The slower rates observed after excision from anaesthetized or refrigerated animals may be due to effects of sodium Nembutal in
young animals where dosage was difficult to control, or to temperature effects of
refrigeration prior to excision and examination.
380
ROBERT L. VAN DE VELDE AND PAUL L. RISLEY
It is of some interest that the ability of the smooth muscle to contract is so
closely related to its histological differentiation in development. It is also
noteworthy that the initiation of contractile function occurs at the 17th day of
gestation, which is at a time when the interstitial cells of the testis also become
differentiated and presumably are capable of elaborating male sex hormones
(Roosen-Runge & Anderson, 1959).
SUMMARY
1. The smooth muscles of the ductuli efferentes and ductus epididymidis
develop from primitive mesonephric mesenchyme.
2. In both ductuli efferentes and ductus epididymidis a proliferation and
condensation of the mesenchyme occurs around the ductuli and epididymal
duct. This appears in the ductuli efferentes of the 14- and 15-day rat embryo,
and by birth it has extended to the cauda epididymidis.
3. Subsequent to the condensation around the ducts, elongation of the mesenchymal cell nuclei beings, and the cytoplasm becomes aligned and extended.
This appears first in the circular layer of the caput by the 16th day of gestation,
and in the investing layer of the corpus epididymidis by the 20th day. Formation
follows lastly in the region of the cauda epididymidis, occurring by parturition
or very soon thereafter.
4. After the smooth muscle cells are differentiated, delicate pulsations or
contractions may be observed in the ductuli efferentes and ductus epididymidis.
They can be seen first at 17 days of gestation in the region of the coni vasculosi,
where they occur at intervals of 60 sec. This condition may not be representative
of all 17-day embryos as contractions were seen in but three of thirty-three
preparations studied.
5. Rhythmic movements of the ductuli and upper and middle caput epididymidis take place with regularity, occurring approximately at 40-45 sec. intervals
in the ductuli and upper caput and at 20-25 sec. in the middle caput epididymidis
at birth.
6. By the 10th day, a visible contractile wave commences in the region of the
ductuli and passes to the upper corpus where it disappears.
7. Inspection of contraction frequency data for the ductuli and upper segments of the epididymis indicates that the interval between successive rhythmic
waves diminishes with age.
8. An incidental examination of the Mullerian duct of female neonatal and
post-natal animals demonstrated that rhythmic contractions are established by
birth.
RESUME
Origine et developpement des muscles lisses et de la contractilite dans le canal de
Vepididyme et le canal de Muller du rat
1. Les muscles lisses des canalicules efferents et du canal de l'epididyme se
forment a partir du mesenchyme mesonephretique primitif.
DEVELOPMENT OF DUCTUS EPIDIDYMIDIS IN THE RAT
381
2. II se produit a la fois chez les canalicules efferents etle canal de l'epididyme,
une proliferation et une condensation du mesenchyme autour de ces formations.
Elles apparaissent dans les canalicules efferents chez l'embryon de 14 a 15 jours,
et se sont etendues a la naissance jusqu'a la queue de l'epididyme.
3. Faisant suite a la condensation autour des canaux, commence une elongation des noyaux des cellules mesenchymateuses, et le cytoplasme s'aligne et
s'etire. Ceci apparait d'abord dans l'assise circulaire de la tete de l'epididyme
le 16eme jour de la gestation, et dans l'assise enveloppante du corps le 20eme
jour. Cette formation survient en dernier lieu dans la region de la queue de
l'epididyme, a la parturition ou tres tot apres.
4. Apres differentiation des cellules musculaires lisses, on peut observer de
delicates pulsations ou contractions dans les canalicules efferents et le canal de
l'epididyme. On peut les voir en premier lieu le 17eme jour de la gestation dans
la region des cones vasculaires, ou elles surviennent a intervallesde 60 secondes.
Ces proprietes peuvent ne pas etre caracteristiques de tous les embryons de
17 jours car les contractions n'ont pas ete vues dans trois des 33 preparations
etudiees.
5. Les mouvements rythmiques des canalicules et des regions superieure et
moyenne de la tete de l'epididyme ont lieu regulierement, survenant approximativement a intervalles de 40-45 secondes dans les canalicules et la tete
superieure, et a intervalles de 20-25 secondes dans la tete moyenne, a la
naissance.
6. Le lOeme jour, une onde contractile visible debute dans la region des
canalicules et s'etend au corps superieur, ou elle disparait.
7. L'examen des resultats concernant la frequence des contractions des
canalicules et des segments superieurs de l'epididyme indique que l'intervalle
entre les ondes rythmiques successives diminue avec l'age.
8. Un examen fortuit du canal de Miiller de femelles nouveau-nees ou apres
le naissance, a montre que des contractions rythmiques s'etablissent a la
naissance.
ACKNOWLEDGEMENTS
The above work was accomplished with aid of research grants from the National Academy
of Science—National Research Council, Committee for Research in Problems of Sex. The
authors also are grateful to Jan Martan and Carol Y. Fujita for their assistance in recording
the data, making preparations, and verifying the observations.
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(Manuscript received 7 November, 1962)