Short communication/Kurzmitteilung
83
J. Clin. Chem. Clin. Biochem.
Vol. 25, 1987, pp. 83-85
© 1987 Walter de Gruyter & Co.
Berlin · New York
SHORT COMMUNICATION/KURZMITTEILUNG
Effect of Verapamil on Plasma Parathyroid Hormone
By E. Bogin
Kimron Veterinary Institute, Department of Biochemistry, Bet-Dagan, Israel
A. Chagnac
Hasharon Hospital, Department of Medicine — Nephrology, Petach Tiqvah, Israel
H. Jüppner
Medizinische Hochschule Hannover, Abt. für klinische Endokrinologiey Hannover, W. Germany and
/. Levi
Hasharon Hospital, Department of Medicine — Nephrology, Petach Tiqvah, Israel
(Received January 13/Aügust 22, 1986)
Summary: The effects of the Ca antagonist, verapamil, on the
behaviour of parathyroid hormone was studied in normal and
uraemic male Wistar räts.
Parathyroidectomy was by cautery. Acute uraemia was induced
by bilateral nephrectomy, and mqderate uraemia by s. c. injection of gentamicin (200 mg/kg). Ethylendiamine tetracetic acid
(50 mg/kg · d) was injected subcutaneously.
Parathyroid hormone was determined by radioimmunoassay.
The degree of üraemiä was determined from plasma urea levels.
Renal failure resulted in a significant increase in plasma parathyroid honnone (x ± SEM, ng/1) (84 ±6, n = 10, in the
control; 277 ± 39, n = 7, in the moderate uraemies and
667 ± 128, n = 6, in the acute uraemies).
Injection of verapamil significantly increased plasma levels of
parathyrpid hormone, ranging from 21% in the controls to
62% in the moderate uraemia group.
In the acute uraemies, parathyröid hormone levels were very
high and verapamil did not eause any further elevation of the
hormone in the blood.
Parathyroidectomy significantly lowered plasma paräthyroid
hormone, and verapamil resulted in a mean increase of 29%.
EDTA caused an increase of 64%, eompared with the control
group.
J. Clin. Chem. Oin. Biochem. / Vol. 25,1987 / No. 2
Introduction
Hypoparathyroidism and hyperparathroidism occur frequently
in humans and animals, and are accompanied by higher or
lower plasma levels of parathyroid hormone. Secretion of the
hormone by the parathyroid gland is regulated by, and is
inversely related to, the concentration of Ca2+ (1). The feedback
mechanism for the regulation of parathyroid hormone secretion
depends on an interaction of Ca2+ with components of the
plasma membrane of the parathyroid gland cell (2).
Synthesis and excretion of the hormone can be indirectly influenced 2+
by modifying the serum levels of free Ca2+. Chelation
of Ca with ethylene-glycol-bis(ß-aminoethyl ether)-N,N' tetraacetate (EGTA), resulted in increased parathyroid hormone
secretion intp the serum (1).
High parathyroid hormone levels, which are commonly seen in
uraemic patients (3), were shown to be toxic to many biological
Systems (4—8) and were postulated to be one of the toxic
factors responsible for some of the observed clinical Symptoms
of uraemia.
Calcium antagonists are a diverse class of organic compounds
used äs theräpeutic agents in the management of cardiac
arrhythmias and coronary disease. It is believed that they act
äs ligands,
which bind strongly to the membrane and inhibit
Ca22+ influx, thus limiting the 2+
supply of inward permeating
Cä + (9, 10). Modulation of Ca metabolism by drugs might
therefore aflfect products such äs parathyroid hormone, which
are regulated by Ca2+.
The present study describes the effect of the Ca2+ blocker,
verapamil, on the serum levels of parathyroid hormone.
Short coirununication/Kurzmitteilung
84
Materials and Mcthods
Six to seven week-old male Wistar rats weighing about 200 g
were used. The animals were fed ad libitum a regulär chow
diet. Parathyroidectomy was performed by caulery and the
success of the procedure was ascertained by a drop in the level
of serum calcium of at least 0.5 mmol/1.
Uraemia was produced by 2 different procedures:
a) acute - by bilateral nephrectomy, then maintained for 4872 h after the Operation; and
b) moderate — following the s. c. injection of Gentamicin (200
mg/kg · d) for 3 consecutive days.
Verapamil (2.5 mg/kg body weight) and ethylendiamine tetraacetic acid, disodium salt (EDTA-Na2; 50 mg/kg body weight)
were injected s. c. daily until sacrifice äs described in the results.
The controls were sham treated.
At the end of the experiment, the animals were anaesthetized
with ether and bled from the abdominal vein into cold heparinized tubes. The plasma was prepared for the determination of
parathyroid hormone, calcium and urea.
Mid-C-regional parathyroid hormone was determined by radioimmunoassay (11). Rat parathyroid hormone was shown to
run in parallel with the synthetic sequence 44—68 of human
parathyroid hormone used for Standards (12). Urea was determined enzymatically (13) and total calcium colorimetrically
(14). Only sera with normal albumin levels were used.
Results
As shown in table l, renal failure resulted in signiflcant increases of parathyroid hormone in the plasma. The control
levels were 84 ± 6 ng/1, whereas values of 277 ± 39 ng/1 were
found for moderate uraemics (an increase of 230%) and 667
± 128 ng/1 for acute uraemics (an increase of 700%).
Injection of verapamil significantly increased plasma levels of
parathyroid hormone. This was seen in all groups studied
with the exception of the acute uraemic group. The degree of
parathyroid hormone elevation by verapamil ranged from 21 %
in the control group to 62% in the moderate uraemia group.
In the acute. uraemics, parathyroid hormone levels were very
high and verapamil did not cause any further elevation of the
hormone in the blood. Parathyroidectomy significantly lowered
plasma levels of parathyroid hormone from 84 ± 6 ng/1 to
48 ± 6 ng/1 (a drop of 43%). Injection of verapamil raised
parathyroid hormone to 62 ± 7 ng/1 (an increase of 29%).
Administration of ethylendiamine tetraacetic acid caused a significant increase in plasma parathyroid hormone (a rise of 64%
compared with the control).
While verapamil and EDTA did not alter significantly the
plasma calcium levels, it caused a change in the level to parathyroid hormone in both control and moderate uraemic rats.
Parathyroidectomy, on the othef hand, caused a significant
drop (p < 0.05) in calcium. Although not significant, there was
a slight drop in plasma calcium in the acute uraemics.
Kidney function, äs evaluated by the blood urea levels, was
significantly different in moderate and acute uraemia, rising
from a level of 6.6 ± 0.2 mmol/1 to 27.3 ± 6.8 and 35.4 ±
14.1 mmol/1 respectively (tab. 1).
Discussion
There is a close relationship between parathyroid hormone and
Ca2+. While the hormone is involved in the regulation of Ca2"*"in the serum and cells, the levels of the ion are involved in the
regulation of parathyroid hormone secretion. Calcium affects
the secretion of parathyroid hormone probably through the
interaction of the ion with some coinponent of the plasma
membrane of the parathyroid cell (2). Furthermore it seems that
low levels of cellular calcium signal the increased production of
parathyroid hormone secretipn by parathyfoid gland. Lowerkig
blood calcium levels with EDTA or phosphate promptly result
in higher secretion (15 — 17). Similarly, Mayer et al. (18) working with calves have demonstrated that during hypocalcaemia,
the secretion rate of parathyroid hormone was high and during
hypercalcaemia the secretion rate was low.
The mechanism by which Ca2+ regulates parathyroid hormone
production is not clear. It is postulated that Ca2+ binds to
a ß-adrenergic receptor on parathyroid gland cells, thereby
regulating the production of cellular cyclic AMP, signalling
parathyroid hormone synthesis (2).
Calcium antagonists or Ca2+ channel blockers, such äs verapamil, are a diverse class of organic compounds. It is thought that
they act äs ligands, binding strongly to the cellular membranes,
thereby inhibiting Ca2+ influx, and limiting the supply of inward permeating Ca2+. Fleckenstein (19), working with verapamil, have postulated that verapamil and Cä2+ compete for the
common site on the membrane. Akaike et al. (20), on the other
hand, reported a non-competitive interaction between the two.
Tab. 1. Levels (x ± SEM) of mid-C-terminal parathyroid hormone, calcium and urea in plasma from normal parathyroidectomized, and uraemic rats treated with verapamil.
Group
n
Parathyroid
hormone
(ng/1)
Calcium
(mmol/1)
Urea
(mmol/1)
Control
Verapamil
EDTA
Parathyroidectomized
Parathyroidectomized + verapamil
Moderate uraemia
Moderate uraemia + verapamil
Moderate uraemia + EDTA
Acute uraemia
Acute uraemia -h verapamil
10
6
5
6
5
7
6
5
6
5
84 +
109 ±
138 ±
48 ±
62 +
277 ±
449 ±
389 ±
667 ±
684 ±
2.45
2.55
2.40
1.90
1.92
2.35
2.35
2.38
2.23
2.20
6.6 +
6.4 t
6.7 ±
6.5 ±
6.6
27.3 ±
26.8 ±
25.1 ±
35.4 ±
37.0
6
12a
12b
6b
39b
66b
74a
128a
132
+ 0.13
+ 0.11
± 0.18
± 0.11
0.13
± 0.14
± 0.17
± 0.13
± 0.15
± 0.10
0.2
0.3
0.3
0.2
0.3
6.8
7.4
6.8a
14.1a
13.6a
a - significantly different from control p < 0.05
b - significantly different from control p < 0.01
c - significantly different from its own group p < 0.05
J. Clin. Chem. Clin. Biochem. / Vol. 25,1987 /No. 2
85
Short comraunication/Kurzmitteilung
The use of Ca2+ antagonists in the present study
revealed
additional Information on this question. The Ca2+ blocking
agent, verapamil, is commonly used äs a coronary vasodilator
drug and was shown to be a good antiarrhythmic agent because
of its depressor action on the atrioventricular node (9). Verapamil was shown in the present study to significantly increase the
serum level of the Hormone. Similar results were obtained
following the administration of EDTA. While the modes of
action of the two compounds are different, the results obtained
were similar both in normal and uraemic rats.
The reason for parathyroid hormone elevation in the parathyroidectomized rat injected with verapamil is not clear. It could
be due to continued secretion of the hormone by remnants of
incompletely removed parathyroid gland. This possibility is
further supported by the fact that the relative increase in the
serum hormone level is greater than in the controls, which
might be explained by the additive effects of low Ca2+ and
verapamil.
Hermann-Erlee et al. (10) demonstrated in vitro that verapamil
inhibits the parathyroid hormone induced Ca2+ release from
foetal rat bone. Thus such resistance to the effect of parathyroid
hormone could induce a secondary rise in parathyroid hormone
secretion, and provide another possible explanation for the
effect of verapamil on parathyroid hormone secretion.
There are importent clinical implications to the use of verapamü. Because of the common use of Ca2+ blockers äs therapeutic
agents in the management of cardiac arrhythmias and coronary
diseases, attention should be paid to blood levels of parathyroid
hormone, especially in patients with renal failure. Parathyroid
hormone was postulated to be a uraemic toxin responsible for
a wide ränge of clinical Symptoms seen in uraemic patients.
Bogin et al. (4—8) have shown that high levels of the hormone
are toxic to biological Systems. It seems that increasing parathyroid hormone production caused by verapamil should be
avoided, especially in patients already suffering from high blood
levels of the hormone.
References
1. Blum, J. W., Fischer, J. A., Schwoerer, D., Hunziker, W. &
Binswanger, U. (1974) Endocrinology 95, 753-759.
2. Brown, E. M. (1982) Mineral Electrolyte Metab. 8, 130150.
3. Arnaud, C. D. (1973) Kidney Int. 4, 89-95.
4. Bogin, E., Massry, S. G. & Harary, I. (1981) J. Clin. Invest.
67, 1215-1227.
5. Bogin, E., Massry, S. G., Levi, J., Djaldeti, B., Bristol,
G. & Smith, J. (1982) J. Clin. Invest. 69, 1017-1025.
6. Meytes, D., Bogin, E., Ma, A., Dukes, P. P. & Massry, S.
G. (1981) J. Clin. Invest. 67, 1263-1269.
7. Bogin, E., Levi, J., Harary, I. & Massry, S. G. (1982)
Mineral Electrolyte Metab. 17, 151-156.
8. Earon, Y., Blum, M. & Bogin, E. (1983) Clin. Chim. Acta
735, 253-262.
9. Singh, B. N. (1970) Lancet /, 563-564.
10. Hermann-Erlee, M. P. M., Gaillard, P. J., Hekkelman, J.
W. & Nijweide, P. J. (1977) European J. Pharmacol. 46,
51-58.
11. Atkinson, M. J., Niepel, B., Jüppner, H., Butz, R., Casaretto, M., Zahn, H., Hehrmann, R. & Hesch, R. D. (1981)
J. Endocrinol. Invest. 4, 363 — 366.
J. Clin. Chem. Clin. Biochem. / Vol. 25,1987 / No. 2
12. Wong, G. C., Dohler, K. D., Atkinson, M. J., Geerlings,
H., Hesch, R. D. & zur Mühlen, A. (1983) Acta Endocrinol.
102, 377-385.
13. Wybenga, D. R., Di Giomigio, J. & Pileggi, V. (1971) Clin.
Chem. 77,891-895.
14. Gilford (1973>In: Gilford Instruments Laboratories Inc.
Oberlin, Ohio, USA.
15. Reiss, E., Canterbury, J. M., Bercovitz, M. A. & Kaplan,
E. L. (1970) J. Clin. Invest. 49, 2146-2149.
16. Arnaud, D. D., Littledike, T. & Tsao, H. S. (1969) In:
Calcitonin (Taylor, S. & Foster, G., eds.) W. Heinemann,
London, p. 95.
17. Sherwood, L. M., Potts, J. J., Care, A. D., Mayer, G. P. &
Aurbach, G. D. (1966) Nature 209, 52-55.
18. Mayer, G. P., Keaton, J. A., Hurst, J. G. & Haneber, J. V.
(1979) Endocrinology 104, 1778-1784.
19. Fleckenstein, A. (1977) Ann. Rev. Pharmacol. Toxicol. 17,
149-166.
20. Akaike, N., Brown, A. M., Nishi, K. & Tsuda, Y. (1981)
Br. J. Pharmacol. 24, 87-95.
Prof. E. Bogin, Ph. D.
Dept. Biochemistry
Kimron Veterinary Institute
P.O. Box 12
Bet Dagan
Israel