AMER. ZOOL., 13:639-651
(1973).
The Chondrichthyean Endocrine Pancreas: What are its Functions?
GREGORY J. PATENT
Department of Zoology, University of Montana, Missoula, Montana 59801
SYNOPSIS. The limited studies on chondrichthyean islet function are discussed and
evaluated. The only certain effect is that of insulin-induced hypoglycemia in all
species studied. Bovine and chondrichthyean insulin preparations both have pronounced effects. The evidence also indicates that glucagon is hyperglycemic in some
species, but the source of the mobilized glucose is unknown. Blood glucose levels in
the Chondrichthyes show wide variations, even within a species, and are apparently
not closely regulated. To the present time the effects of pancreatic hormones on
carbohydrate metabolism have been investigated, but other possible effects of these
hormones on intermediary metabolism (e.g., protein and lipid) have not been studied.
The sparse information on the immunology of chondrichthyean insulins is also
discussed.
with discussing chondrichthyean blood
glucose and glycogen levels under "norDespite the numerous publications, both mal" conditions and following insulin and
old and recent, dealing with various aspects glucagon treatment, the effects of surgical
of Chondrichthyean biology, our present and chemical procedures on the production
state of knowledge regarding endocrine of diabetes mellitus, and our present knowpancreas physiology in this group of fishes ledge of the immunology of chondrichthyean insulins.
is rather meager.
This may be due, in part, to our investiBLOOD GLUCOSE
gating the "wrong" parameters. The
workers in the field have all been inNo other biochemical parameter has been
fluenced by a decided mammalian bias in
studied
more extensively than blood
their approach to the study of chondrichthyean intermediary metabolism. The most glucose (or sugar) levels in the Chondrichfrequent parameters studied are blood thyes. However, few studies have been
glucose and tissue glycogen levels. Both of systematic in their approach. Nevertheless
these carbohydrates are known to be the data in Table 1 illustrate that regardaffected by insulin and glucagon in mam- less of the species studied blood glucose
mals, so perhaps it was only natural that values range widely not only between
investigations dealing with carbohydrate species, but also within a species. It is
metabolism in the Chondrichthyes should difficult to make meaningful comparisons
begin with a study of the endocrine factors not only because many different species
were studied, but because of differences in
which might influence these substances.
An examination of the available data the analytical methods employed, lack of
indicates that the pancreatic hormones, in- standardization in handling and collecting
sulin and glucagon, may not play major the animals, and other factors which might
roles in the regulation of carbohydrate affect blood glucose levels (see Kiermeir,
metabolism in the Chondrichthyes (see 1939). The older colorimetric methods
Patent, 1970). This paper will be concerned determined total reducing substances in
the blood, of which true glucose may only
The author is grateful to the National Science
be a part. The high values reported in all
Foundation, Geigy Pharmaceuticals, and the Symstudies of the smooth dogfish, Mustelus
posia Fund of the American Society of Zoologists
for making it possible to participate in the Sym- canis, should be reinvestigated using a
posium.
glucose oxidase method.
INTRODUCTION
639
S. acanthias
M. rants
Kange: 15-74
Mean: 46
flange: ftO-181
"mostly between 90-110'
'considerable number
125, 125, 125
M. cams
1
31. canis
Severed caudal vessels
Cardiac puncture
Tail severed and 2 cc blood
collected at 0.5, 4.5 and G.5
minute intervals
Same procedure as above; time
intervals were 0.5, 1.5, 2.5
and 3.5 minutes
Severed caudal vessels (ft
Severed caudal vessels
Revered caudal vessels
18(1, 142, 105, 106
1(1)
M. canis
if. canis
1(1)
Carcharinvs obncurus
97
Dead for sometime
taken as soon as possible
capture
taken as soon as possible
capture
Liken as soon as possible
capture
of animals
20 minutes in lab tank following
capture: ' 'not yet fully recovered"
"Apparently normal"
Kept in lab 2 weeks
Kept in lab 2 days without, fowl
and "under as nearly as possible normal conditions"
Folin-Wu
Folin-Wu
Folin-Wu
Folin or Benedict
Folin or Benedict
Foliu-Wu
Folin-Wu
" B l « l as soon as brought in
from the t r a p s "
"Rled as soon as brought in
from the t r a p s ' '
32 hoursiu lab; "gooil comlition"
in " b a d " condition;
Sample
after
Sample
after
Sample
after
Conditio
Foli n-Wu
Severed caudal artery
29, 41, 32
SO
Picric acid
Kona'and Michael is. method
as modified by Macleod;
or Munson and Walker
"unified method"
Bona and Machaelis method
as modified by Mnclotxl;
or Munson and Wnlker
'/unified method"
Koua and Michnelis method
as modified by Macleod;
or Munson and Walker
"unified method"
Cardinal sinus
Vertebral artery caudal artery
section
Picric acid or Bert rand
Mohr-Bcrtrand (NaF-HgNO4)
Mohr-Bcrtraml (XaF-HgXO.)
Mohr-Bortrand (XaF-HgXO,)
Method of analysis
77, 50, 57, 27
8. acanthias
Cardinal sinus
Cardiac puncture
Bulbus cordis
Bulbus cordis
Source of blood
Cnrckarias lit t oralt x
51
50
Values reported
(inmg/lOOml)
Hydrolagus colliei
Number of animals
values).
3 animals had no reducing
substances, 1 showed trace
amounts, and 2 had values
of 3 and 38 mg%
22, 26, 37
ilustclus vulgans
Jtaja sp.
S. acanthias
Jiaja batis
Species
TABLE 1. Chondrichthycan blood glucose data ("normal"
White (1928)
White (1928)
Mentcn (1927)
D^uis (1922)
Denis (1922)
IVnis (1922)
Denis (1922)
Keniu (1922)
Scott (1921)
Scott (1921)
Scott (1921)
Lang and Macleod (1920)
Lang and Macleod (1920)
Fandard and Rane (1914)
Fandanl and Rane (1914)
Bernard (1877)
Fandard and Kane (1914)
M
Z
>
73
o
7)
PI
O
O
S. acanthias
10
(from above grp.)
:t(i, 138 (aortic blood of first
niiimnl was 73)
Carcharia,i obscurus
(1933)
Mean: 05
Snviano (1940)
Florkin (1036)
Amlrecu-Svedbertf
Onus (1!>32)
Orias (1932)
Fremont Smith and Dailey
(19:12)
liny 0
1
8
Hagetlorn- Jensen
and Dailey
Fremont Smith and Dailry
(1932)
Fremont-Smith
(1932)
Kisch (1929)
73, 8.7, 64.3
36.5, 10.0, 25.9
32, 10, 22
29.5, 8.7, 20.8
27, 8.7, 18.3
Within one hour of capture
Author
Ciray and Hall (10211) (fn
Kiermeir 1930)
flowing
Kiscli (1929)
Samples taken immediately after
arrival in the lab
48 hours after arrival in Inb; no
food given
1-2 days in lab tank
water
VA-A days in lab
Condition of animals
Florkin (193)5)
Folin and Svedberg
Shaffer and Jlartmann
Shaffer and Hart maim
Hagedoru-Jonsen
H aged orn-Jen sen
Method of aiialvsis
All fish en light at same time but
sampled at different times
Severed caudal vessels
Cardiac puncture
Cardiac puncture
Abdominal wall slit and blood
' ' iispi ra ted
from
vena
eava"; serum used for analysis
Abdominal
wall slit and blood
1
' aspirated
from
vena
esivn"; serum used for analysis
Abdominal wall slit and blood
' 'aspirated
from
vena
c a v a " ; serum used for analysis
Caudal vessel
Heart
Heart, caudal artery, or " Lebervene''
Source of blood
(Continued).
Total reducing substances,
non ferment able
reducing
substitutes, and true blood
glucose reported (left to
right, respectively)
Unlakcd Wood: 3C, 34;
Plasma, 40, 38; Corpuscles:
Range: 65-137
Menu ± SEM:
105 ± 22
Kange: 72-250
70, 70, 71
35
42
Range: 13-77
Mean: 32
Carcharias lit tomlis
Torpctto occllata
190, 157
1
19
Scyllium catalus
75
Values reported
(in mg/100 ml)
M. cants
1
Number of animals
-V. cants
Species
TABLE 1.
a
—
o
5!
a
o
n
2
w
W
>
•<
1-4
o
2
g
X
n
Species
4.
10 (f)
20
20
(Same animals ns above)
S, canicula
Da&yatis pastinaca
90 ± 49
16
•V. acanthius
Mean:
36
0.58 •+• 0.55
19.18 ± 0.89
87.3
(Range: 49-101)
74.9
06.2
Range: 13-88
Mean: 47.6
Range: 27-80
Mean: 52.9
Range: 102-164
Mean: 134
Range: 75-135
Mean: 109
Ji, astcrias
T. marmorata
(Same group as above)
(Same fish as above)
Range: 98-284
Mean: 191
216, 236, 252, 219
110, 110, 97, 93
30 ± 1, 8
29 ± 0.94
Vastjatig pastinaca
Dasyatis pastinaca
Hagedorn-Jen sen
Glucose oxidase
Anthrone
Heart
Glucose oxidase
Captured in December one week
before samples taken
1-2 days following capture
Fasting 1-3 weeks
Fasting 1-3 weeks
Plasma
Fasting 1-3 weeks
H a gedoni-Jensen
2.5-13 days after sham operation
Immediately prior to operation
Hagedorn-Jensen
Hagedorn-Jensen
Cardiac puncture; plasma used
for determinations
Cardiac puncture
Cnrdiac puncture
Cnrdiac puncture
Shaffer and Hartmanu
Fasted 7 davs
Shaffer nnd Hartmann
"Meagerly f e d "
Irfibson and Plisetsknyn (1968)
Bocquet (1967)
Boy In ii and Antkowiak (1900)
Kern (1966)
Hnrtman et al. (1944)
llartman et a). (11)44)
Abramowitz et nl. (1940)
Oppelt et al. (1963)
' ' Fed for various periods of
time"
"Well f e d "
Fasted 7 days
Miller and Van Slyke
Caudal vein
Oppelt et al. (1963)
Oppelt et al. (1963)
l^ibson et al. (1963)
Plisetskaya et al. (1904)
Miller and Van Slyke
Caudal vein
Author
Oppelt et al. (1963)
Unfe<l fall animals
Unfed fall animals
Caudal artery
Miller ami Van Slyke
Miller and Van Slyke
Caudal artery
Caudal artery
Condition of nnimnls
" F a s t e d " 1-3 days in live cars;
no food
(a) sampled
" nonfasting;"
right after capture
(b) fish on line 1-2 hours before
sampling
Cauglit by hnndline; sampled immediately
Caudal artery
Miller and Van Slykc
Hagedorn-Jensen
Hngedorn- Jensen
Glucose oxidase
Caudal artery
Bulbus cord is
Bulbus cordis
Ventral tail vein plasma
Glucose oxidase
Ventral tail vein plasma
Glucose oxidase
Ventral tail vein plasma
02.3 ± 7.8 (b)
Met11cxl of analysis
Glucose oxidase
(Continued).
Ventral tail vein plasma
Source of blood
TABLE 1.
Range: 52.5-191
Mean: 91.2 ±. 25.1
55.1 ± 4 . 0 (n)
138 •*• 13
23
X mil her of nnimals
II. ffjlantfria
S. aeanthiax
Values reported
(in nig/UK) ml)
4
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o
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S
CHONDRICHTHYEAN ENDOCRINE PANCREAS
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643
In most cases where both non-enzymatic
and enzymatic methods were used on the
same species, the results have indicated
that almost all of the reducing substance
present in the blood was true glucose, although there was individual variation in
this regard (see Patent, 1970). Of the
chondrichthyean species studied so far only
Scylliorhinns canicida (Florkin, 1936;
Bocquet, 1967) and Raja radiata (Idler,
personal communication; see also discussion to deRoos and deRoos, 1972) shows
significant amounts of other reducing sugars
in the blood. Bocquet's analysis by paper
chromatography revealed the presence in
the plasma of five sugars: glucose,
arabinose, fucose, xylose, and rhamnose,
glucose being the most abundant.
The workers have not been consistent in
which hematological fraction is analyzed
for glucose. Some have used whole blood
which may or may not have been deproteinized, whereas others have analyzed
serum or plasma. Thus, just what "blood
glucose" represents may not be apparent in
the individual studies. (Compare, for example, Bocquet's and Kern's separate results on S. canicula in Table 1). There is
evidence to indicate that there may be no
significant difference in glucose values regardless which fraction (deproteinized
whole blood, blood plasma, or serum) is
employed for S. acanthias and H. colliei
(Patent, unpublished observations); however, we do not know if this is the case for
other chondrichthyean species.
To the present time there has been no
adequate evidence for seasonal fluctuations
of blood glucose levels in the Chondrichthyes. This is unlike the situation in many
teleost species, where seasonal fluctuations
in blood glucose levels have been found
(Nace et al., 1964). The blood glucose
values reported for S. acanthias and H.
colliei, which were collected over a 15month period, do not indicate any clearcut
seasonal cycle (Patent, 1970). In fact the
values from multiple collections and samplings during a given month during the
same year may show great variations (Table 2), thus precluding any meaningful con-
644
GREGORY J. PATENT
TABLE 2. Average blood glucose' valves for S. acanthias and H. eolliei on different days of
the same year.
Organism
S. acanthias
If. eolliei
Month
March
March
March
November
November
February
February
February
February
May
May
May
May
May
No. of animals
Average blood glucose2
(mg/100 ml)
4
4
4
5
20
40
97
58
36
65
4
65
57
80
76
48
56
53
88
65
5
6
4
5
8
8
10
11
1
2
Blood obtained 24—48 hours following cannulation of the dorsal aorta.
Glucose oxidase method employed on deproteinized (ZnSO4-NaOH) filtrates of whole
blood.
elusions regarding seasonal variations of
blood glucose values, unless large and frequent samplings are performed. Inasmuch
as the nutritional state may influence
chondrichthyean blood glucose levels
(Patent, 1970), any claims for seasonal fluctuations of blood glucose levels must be
evaluated with caution.
There also appear to be species differences in the maintenance of blood glucose
levels during long-term fasting. A population of dogfish, 5. acanlhins, maintained in
an unfed state for one month showed a
significant increase in blood glucose levels
compared with newly captured animals.
Of 24 animals collected from one location
at a single collecting period, 12 had blood
glucose values averaging 30 mg/100 ml
(deproteinized whole blood filtrates) the
day after capture. The remaining 12 animals were maintained unfed in outdoor
pens and killed 30 days later. Their blood
glucose values were significantly higher
(mean: 88 mg/100 ml) than the group
killed the day after capture. Aside from
appearing emaciated, the 30-day group
appeared "normal." Clearly, gluconeogenesis was occurring, but it was not possible
to say what factors were responsible for its
occurrence. These results are in contrast
to those of Grant et al. (1969) who found
that blood glucose values did not change
significantly in R. erinacea maintained
under fasting conditions for as long as 6
weeks. These authors state tliat "while no
distinct time pattern could be discerned,
there appeared to be a trend for glucose
levels to fall for some hours after capture
and then rise to near initial levels over a
period of days." The above observations
suggest that there may be real differences
in the control of gluconeogenesis and other
metabolic pathways in different elasmobranch species and that careful attention
should be paid to aspects of the species'
life history in evaluating the results obtained.
LIVER GLYCOGEN
The level of liver glycogen may also not
be a meaningful criterion in evaluating the
effects of pancreatic and other hormones
on intermediary metabolism in the Chondrichthyes. In general liver glycogen levels
show wide variations from animal to animal within a species and arc of relatively
low magnitude (Leibson and Plisetskaya,
1968; idler et al., 1969; Patent, 1970). The
amount of liver weight represented as
glycogen in S. acantliias ranged from 0.022.0%; the ratfish values fall in the lower
end or below the lower limit of this range.
Forced feeding results in an elevation of
both liver glycogen and blood glucose levels
645
CHONDRICHTHYEAN ENDOCRINE PANCREAS
in dogfish, and fasting dogfish are capable
of storing liver glycogen for short periods
(Patent, 1970). In ratfish, however, glycogen
is apparently not stored. Three ratfish, held
in the laboratory 1 week prior to use, were
injected with 7-9 gm glucose intramuscularly or intravascularly over a 48-hour
period. The fish were killed 3 hours following the last injection. Blood glucose levels
ranged from 771-1143 ntg/100 ml, whereas
liver glycogen levels were 18.8 ± 7.4 rag/
100 gm and muscle glycogen levels were
79.1 dz 12.1 mg/100 gm, the glycogen values being expressed as glucose equivalents. These results, even though obtained
from three animals, indicate that excess
glucose in ratfish is not deposited as tissue glycogen. Control animals had essentially the same tissue glycogen content as
glucose-injected animals, but blood glucose
values averaged 65 mg/100 ml.
INSULIN AND GLUCAGON
Few studies have been concerned with
the effects of pancreatic insulin and
glucagon on chondrichthyean intermediary
metabolism. In general the parameters
measured have been blood glucose levels
and/or tissue glycogen content. In all cases
insulin, regardless of its source and mode
of administration, produced a significant
hypoglycemia in the species examined (Table 3). The severity of the hypoglycemia
is variable between species, but it generally becomes most evident 24 hours following insulin injection and persists for several
days in most instances. The effect of insulin
on tissue glycogen levels is variable, and
it is not possible at present to state whether
the hormone has significant effects upon
li\er or muscle carbohydrate metabolism in
the Chondrichthyes (Leibson et al., 1903;
Leibson and Plisetskaya, 1968; Patent,
1970). Of interest is the observation that
dogfish injected with their own insulin recovered normal blood glucose values within 3 days, whereas dogfish injected with
bovine insulin remained hypoglycemic
(Patent, 1970). This may be due to the
different dosages employed or there may be
real biological differences in the mechanism of action of the bovine and chondrichthyean hormones.
Leibson and Plisetskaya (1968) and
Grant et al. (1969) have found that insulininduced hypoglycemia in skates typically
lasted for 5 days after which there was
usually a return to normal levels or higher.
Since the doses employed were equal to or
higher than that used in dogfish this may
reflect an inability on the part of dogfish
to inactivate the mammalian hormone.
Glucagon has been tested in only three
chondrichthyean species thus far: S.
acanthias, H. colliei, and R. eiinacea. In
general high doses were required to produce a transient hyperglycemia in dogfish;
no accompanying liver glycogen changes
were apparent, however, at the conclusion
of the experiment. The hormone had no
effect on glycemia in ratfish (Patent, 1970).
Glucagon resulted in a rapid, slight, and
transient increase in blood glucose in 7?.
crinacea (Grant et al., 1969). Relatively
low doses (200 /ng/kg) administered intra-
TABLE 3. Effect of insulin on chondrichthyean hlood sugar levels.
Species
T. paslinaca
T{. crinacea
S. acanthias
H. collioi
Insulin and dose
Bovine, 2-200 U A g
Bovine, 5 U/kg
Bovine, 5 UAg
Dogfish, 0.3 U A g
Ratfish, 2 UAg
Bovine, 5 UAg
Eatfish, 2 U A g
Dogfish, 0.3 U/kg
Blootl
Eoute1 glucose
i.p.
i.m.
i.a.
i.a.
i.a.
i.a.
i.a.
i.a.
4i
i
I
i
i
I
Author
Method
Hagedoni- Jensen
Leibson et al. (1963)
Grant et al. (1969)
Glucose oxidase
Patent (1970)
I J
* i.p. = intraperitoneally; i.m. = intramuscularly; i.a. — intra-aortally.
j
646
GREGORY J. PATENT
muscularly or intravenously or directly into
the hepatic portal vein were effective in
causing the hyperglycemia; however, no
glycogen levels were determined so it is not
possible to attribute a glycogenolytic role
to glucagon in this case. In fact, there is
no evidence to suggest that glucagon is
glycogenolytic in any chondrichthyean
species.
Grant et al. (1969) report that two hypophysectomized skates given the same
glucagon dose, however, showed a 34% increase in blood glucose levels in 1 hour,
followed by a 45% drop below base line
over the next 23 hours. This result is difficult to evaluate due to the small sample
size and lack of information regarding condition of the animals.
Chondrichthyean glucagon has not been
extracted or isolated. That the hormone
exists at all in chondrichthyean fishes is
based upon histological and histochemical
evidence (Ferner and Kern, 1964; Patent
and Epple, 1967). It appears that glucagon,
unlike insulin, shows a degree of biological
specificity in its action (see Falkmer and
Patent, 1972). Therefore it is desirable for
the sake of obtaining meaningful results
to use the animal's own hormone in biological tests. Until this is done we can only
make poor guesses as to the role of this
hormone in chondrichthyean fishes.
Additional hormones of non-pancreatic
origin have also been tested on intermediary metabolism in the Chondrichthyes
and the reader is directed to these papers
for additional information: Grant et al.
(1969), Patent (1970), deRoos and deRoos
(1972, 1973).
SURGICAL EXPERIMENTS
Two other experimental approaches have
been used to study the role of the pancreas
in the regulation of carbohydrate metabolism in the Chondrichthyes: surgical
pancreatectomy and hypophysectomy, and
the use of the cytotoxic agent alloxan.
Orias (1932) found that pancreatectomy
caused a marked hyperglycemia in M. canis
(159 ± 6 mg/100 ml blood in nine un-
operated animals compared with 402 ± 7
mg/100 ml blood in the same animals 48
hour later). Hypophysectomy plus pancreatectomy resulted in a less severe hyperglycemia than pancreatectomy alone (controls 166 ± 11 mg/100 ml; experimental
288 ± 18 mg/100 ml), suggesting that the
pituitary is the source of an "aggravating
influence" on pancreatic diabetes. Orias's
results, however, although clearcut, are
difficult to evaluate due to the stress factors
imposed upon the animals. No anesthetic
Was employed and after 48 hours the
mortality rate became "rather high."
Abramowitz et al. (1940) also used M.
canis and performed experiments similar
to that of Orias (1932). They found, interestingly, that the severity of diabetes (hyperglycemia) following pancreatectomy was
the same for "well-fed" as for "poorlyfed" animals. In addition, the degree of
diabetes was very variable among the individual fishes. Complete hypophysectomy
reduced the severity of diabetes just as
Orias (1932) found, but the removal of
the "anterior lobe" alone had the same
effect as the removal of the entire pituitary.
The most recent study on the effects of
pancreatectomy and hypophysectomy on
chondrichthyean blood glucose levels is
that of Grant et al. (1969). Twelve pancreatectomized R. erinacea maintained for
several weeks essentially showed no hyperglycemia over the long-term period. It is
not stated if the animals were fed following the operation. These results are similar
to those of Lewis and Epple (1972) who
found that pancreatectomized American
eels, Anguilla rostrata, did not become hyperglycemic by 18-20 days following the
operation. The eels were not fed at any
time. These results indicate that in these
species the pancreas may not be involved
in the etiology of classic diabetes mellitus.
Grant et al. (1969) did find, however, that
hypophysectomy resulted in a drop of 2040% in blood glucose levels in skates; this
effect persisted for 1 week, the duration of
the experiment. These results tend to confirm those of Orias (1932) and Abramowitz
et al. (1910) indicating that the pituitary
CHONDRICHTHYEAN ENDOCRINE PANCREAS
is the site of a diabetogenic factor in
chondrichthyeans. However, three hypophysectomized 5. acanthias showed marked
hyperglycemia which reached levels 60%
above base line 1 week after the operation
(Grant et al., 1969). Unfortunately, no
sham-operated Squalus were used as controls. Nevertheless, it may be that R.
erinacea and S. acanthias have different
pituitary factors regulating blood glucose
levels, or possibly the same factor(s) has
different effects in the two species. Whether
these pituitary hormones affect carbohydrate metabolism directly or act via
other endocrine glands remains to be determined.
The cytological composition of chondrichthyean islet tissue has been investigated in detail with the light microscope.
In general at least three islet cell types
are recognized: A-, B-, and D-cells (see
Thomas, 1940; Epple, 1973). In addition,
the ratfish possesses a foujrth cell type,
called the X-cell (Fujita, 1962; Patent and
Epple, 1967) which may also be present
in other chondrichthyean species (Patent,
1968). Studies with the electron microscope
have shown that at least two other endocrine-appearing cell types occur in ratfish
islets (Patent, 1972, and unpublished observations). Nerve fibers have also been observed within the islets of both dogfish
and ratfish, al thought axonal-islet junctions of the type seen in teleosts (Klein,
1971; Brinn, 1973) have not yet been found.
Alloxan has been used in attempts to
destroy the islet B-cells of several chondrichthyean species, but the results have
been variable and inconclusive. No consistent changes were found in blood glucose
levels and no consistent destruction of
B-cells was seen (Saviano, 1947; Clausen,
1953; Kern, 1966; Grant et al., 1969).
Several factors influence the ability of
alloxan to destroy B-cells. The alloxan solution must be prepared immediately prior
to use and should be administered in such
a way so as to insure that the pancreas
receives the chemical before the liver and
possibly other organs are able to inactivate
it. Even so, a general toxic effect of alloxan
647
is seen, particularly at the level of the
kidney (e.g., House, 1948; Kern, 1966).
Thus, it would be difficult to evaluate the
effect the drug has on pancreatic physiology.
IMMUNOLOGY OF INSULIN
There is little information on the immunology of insulin in the Chondrichthyes,
and less information on that of glucagon.
Biologically speaking, the effect of insulin
on blood glucose levels appears to be
phylogenetically non-specific. All preparations tested so far are able to produce
hypoglycemia in the chondrichthyeans examined. Immunologically, however, there
appears to be a degree of phylogenetic
specificity as judged by studies involving
passive cutaneous anaphylaxis (Wilson et
al., 1966) and neutralizability of insulin's
biological effect on the mouse hemidiaphragm (Davidson et al., 1968) with
different insulin antisera (Failkmer and
Wilson, 1967).
Dogfish and lemon shark insulins showed
potencies of 0.13 I.U./mg and 0.87 I.U./
mg, respectively, in the mouse hemidiaphragm assay when compared with ox
insulin (29.4 I.U./mg) (Falkmer and Wilson, 1967). This assay measures the ability
of an insulin preparation to cause glycogen
deposition. However, the tests involve a
comparison of fish insulin or other insulins
with that of a mammalian insulin in a
mammalian test system. Thus, we are speaking of international mammalian units of
insulin and relating this to chondrichthyean insulins. Large amounts of both ox
and cod insulin antisera are needed to
neutralize the biological effect of dogfish
insulin on the mouse hemidiaphragm
(Falkmer and Wilson, 1967), suggesting
that these insulins do not have many antigenic sites in common.
The results of the passive cutaneous
anaphylaxis test indicate that dogfish and
ratfish insulins are immunologically more
like chicken insulin than bovine or cod
insulin (Wilson, personal communication)
(Table 4). A real comparison between holo-
648
GREGORY J. PATENT
TABLE 4. Passive cutaneous anaphylactic reaction produced in guinea pigs injected with three
insulin aniisera.'
Tiisulin
for challenge
Co3rpu
Cod
Lemon shark
(Negaprion)
Dogfish I
(S. acanthias)
Dogfish I I
(S. acantlrias)
Batfish
1
Dose per guinea pig
Milli units
V%
Diam. of blue spot
(mm) with antiserum to:
Ox insulin Chicken insulin Cod insulin
20
4
2
20
0
25
0
0
25
0
40
22
1000
9
18
33
0
1C0
20
>50
n.d.
24
300
100
18
6
0
0.2
50
Died within 5 minutes
27
0
Prom Wilson (personal communication).
cephalan and elasmobranch insulins, however, would require the preparation of antisera to these insulins, and as yet there are
inadequate purified chondrichthyean insulin supplies for such a study.
Falkmer (1966) failed to identify
glucagon by radio-immunoasssy in Squalus
acanthias and Raja clavata using I131-ox-
glucagon and glucagon antiserum.
CONCLUDING REMARKS
I turn now to the question posed in the
title. At this juncture we can state that
the chondrichthyean endocrine pancreas
secretes insulin. There are histological,
biochemical, and physiological data to substantiate this conclusion. That chondrichthyean insulins function in the regulation
of carbohydrate metabolism is supported
by the observed effects on blood glucose.
We do not as yet know, however, the fate
of the glucose once removed from the
circulation.
We are less certain of glucagon's effects.
If the glucagon-induced hyperglycemia in
skates and dogfish is due to hepatic glycogenolysis, dien perhaps the negative results
with ratfish are not surprising since these
animals store virtually no glycogen in their
livers. Glucagon lias yet to be extracted
from cartilaginous fishes.
The wide variations in blood glucose
values within a species is pu/zling and
raises the question as to what glucose is
doing in these fishes. Perhaps glucose may
not be a required energy source in chondrichthyeans, although it may be of
physiologic importance and utilized for
other purposes (see deRoos and deRoos,
1972). Chondrichthyeans are able to
tolerate extremely high as well as extremely low levels of circulating glucose
with no apparent ill-effects.
Thus far, insulin and glucagon have
only been tested for effects on caibohydrate
metabolism. Perhaps we should look for
effects on lipid and protein metabolism.
Corticoid hormones affect liver fat and
glucose levels in chondrichthyeans (Patent,
1970). ACTH also has long-term hyperglycemic effects (Grant et al., 1969; deRoos
and deRoos, 1973), and catecholamine
hormones also affect lipid (Lipshaw et al.,
1972) and carbohydrate (Patent, 1970; deRoos and deRoos, 1972) metabolism. In
fact the effects of adrenalin on blood
glucose levels in all species studied so far
occurred relatively rapidly (Table 5).
Thus, it may be worthwhile to pursue in
detail the effects of this and other catecholamine hormones on intermediary metabolism in chondrichthyeans.
Considering the high levels of blood
urea found in chondrichthyeans it may be
that endocrine phenomena, pancreatic or
extrapancreatic, are involved in the regulation of this metabolite.
The concentration of fat in the livers of
chondrichthveans is also interesting:. Total
CHONDRTCHTHYEAN ENDOCRINE PANCREAS
• ^O
5
O
O
"
649
fat content may be as high as 80% of
the wet liver weight in ratfish and 70%
in dogfish (Patent, 1970). Malins and
Barone (1970) have evidence which suggests
that certain liver lipid fractions function
in the control of buoyancy in dogfish, the
ratio of triglycerides to diacyl glyceryl
ethers being the significant factor. Whether
hormones are involved in the regulation of
buoyancy is unknown.
We lack information regarding circulating levels of insulin in these fishes. Now
that radioimmunoassay methods have been
developed for insulin it would be useful to perform such measurements in
chondrichthyeans during experimental
manipulations.
Finally, we do not know what the
secretory products of the other chondrichthyean islet cell types are, or what their
functions might be.
OT
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be
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be be
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>c IO
a.
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