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Lack of suppression of vasopressin plasma levels by catapres
Pharmacological Research Communications, VoL 11, No. 1, 1979
39
LACK OF SUPPRESSION OF VASOPRESSIN PLASMA LEVELS BY CATAPRES
Hans-Georg Gullner, M.D.
Hypertension-Endocrlne Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
20014
SUMMARY
Receivedin final form 3 October 1978
The effect of catapres (clonidine hydrochloride), an alpha-adrenerglc agonlst with hypotensive and diuretic properties, on release of vasopressln (AVP) was studied.
Administration of Catapres to conscious rats or dogs did
not alter plasma concentrations of vasopressin.
Catapres may modulate the
effect of vasopressln by an intrarenal mechanism or by an unknown mechanism.
INTRODUCTION
Catapres, an antihypertenslve drug with alpha-adrenerglc agonlst properties (van gw~eten, 1976), has been shown to increase free water clearance (Chrysant and Lavender, 1973; Humphreys and Reid, 1975) and to decrease urine osmolallty (Humphreys and Reid, 1975) when administered to
0031--6989n9~10039--06/S02,00~
© 1979 TheltalianPharmacologicalSociety
Pharmacological Research Communications, VoL 11, No. 1, 1979
40
hydropenlc anesthetized dogs, but not when given to hypophysectomised animals receiving ~nfuslons of antidiuretic hormone. evidence, Hu~phreys and Reid release of vasopressin.
On the basis of this indirect
(1975) suggested that catapres may suppress
In order to further examine this question, we
measured plasma levels of arginine-8-vasopressin
by radiolmmunoassay before
and after administration of catapres in conscious rats and dogs.
METHODS
Thirty adult male Sprague-Dawley rats mongrel dogs of either sex, weighing
(180-230 g) were studied.
18-24 kg were used.
Six
All animals had free
access to tap water and food (Purina Rat or Dog Chow).
One-hundred fifty intraperltoneally
g/kg catapress
(clonidlne hydrochlorlde)
to conscious rats, a dose which previously had been shown to
suppress renin release without changes in blood pressure. decapitated
was given
The rats were
20 min after injection and arterial blood was collected from the
trunk into chilled heparlnlzed
tubes.
Catapres,
in concentrations
ranging
from I ng/kg/mln to 3 g/kg/min, was infused via an indwelling catheter into the femoral or Jugular vein of conscious dogs for periods of 10 mln. cent dextrose solution was infused during control periods.
Five per
Venous blood
samples were collected in heparinlzed tubes at the end of each infusion period.
Arginine-$-vasopressln
was adsorbed to bentonite,
measured by radioimmunoassay Rosenbloom and Fischer procedure.
extracted by acetone and
according to the method described by Skowsky,
(~97~) w~th minor modifications
in the radioiodination
Vasopressin antiserum was generously supplied by Professor Jan
Mohring of Centre de Recherche Merrell International
(Strasbourg,
France).
Pharmacological Research Communications, Vol. 11, No. 1, 1979 It was used in a final dilution of 1:400,000.
Arginine-8-vasopressln
gift of Dr. Jan Mulder of Ferring AB, Malmo, Sweden. iodlnation and for construction of standard curves. of the radioimmunoassay was 5 picogram.
41 was a
It was used for The limit of sensitivity
There was no cross-reaction of the
antibody with the angiotensins,
bradykinin and other structually and
biologically related peptides.
The results are expressed as picograms of
vasopressin per ml of plasma.
Plasma vasopressin concentrations
species were determined in one assay. plasma was 65 ~ 12% $.E.M.
Recovery for extraction of AVP from
All values are corrected for recovery.
Statistical analysis was performed using the paired or unpaired experiments)
Student's t-test. Table I
RAT
DOG
AVP pg/ml Control
11.7
5% Dextrose
13.5
AVP pg/ml Control 5% Dextrose
6.3 8.6
12.6
9.9
10.8
6.3
16.2
11.7
30.6 15.9 ~ 3.0 SF~I
Clonidine hydrochloride 150 ~g/kg
16.2
5.7
8.5 + i.I SEM
Clonidine hydrochloride
8.6
30 ng/kg/min
8.1
41.4
5.7
11.7
6.2
22,5
4.5
10,8 18,1 + 5.2 S ~
from each
6.6 + 0.8 SD!
(for rat
Pharmacological Research Communications, VoL 11, No. 1, 192"9
42
RESULTS
Table I shows the effect of catapres on AVP plasma levels in conscious rats and dogs.
For the dog experiments one representative dose, 30 ng/kg/min,
is shown which was the highest dose which could be infused without altering blood pressure.
Concentrations above 30 ng/kg/min resulted in an initial
blood pressure increase which disappeared after 30-60 min. statistically
There was no
significant change in AVP plasma levels following administration
of catapres in either animal species at any of the doses studied.
Control
plasma AVP levels in rats were 15.9 + 3.0 S.E.M. and 18.1 + 5.2 S.E.M. after catapres administration.
In dogs, plasma concentrations
(N.S.)
of AVP were
8.5 ~ I.I S.E.M. before and 6.6 ~ 0.8 S.E.t!. (N.S.) after catapres treatment.
DISCUSSION
Humphreys and Reid (1975) proposed, volume and osmolality, dogs.
on the basis of changes in urine
that catapres may suppress AVP release in anesthetized
The results reported in the present study indicate that catapres does
not suppress circulating plasma levels of arginlne-8-vasopressin
in conscious
rats or dogs, in the absence of blood pressure changes by the drug. confirms the observations of Olsen
This
(1976) who did not find changes in the
excretion of bioassayable urinary AVP during periods of maximal diuresis following intravenous administration of catapres to conscious dogs. In some animals a slight increase in AVP plams levels could be observed after catapres administration while in others plasma AVP tended to decrease. Several explanations are possible for this finding.
The variation in plasma
AVP may be a reflection of the state of hydration of the animals at the time of plasma collection.
In addition,
the above observation may be due to the
Pharmacological Research Communications, Vol. 11, No. 1, 1979
43
reproducibility of the assay or due to the error in the extraction of the peptide from plasma.
In the present experiments,
urine flow and urinary osmolalities were not
measured since conscious animals without ureter catheters were studied.
In
similar previous experiments in anesthetized dogs, catheters were implanted into the ureters and urinary volume was measured.
Intravenous administration
of catapres to these dogs increased urine flow and decreased urinary osmolality.
However, plasma AVP levels did not change at any dose
(unpublished observations).
The demonstration that AVP infusion inhibits catapres-induced water dluresls
(Chrysant and Lavender,
1973; Humphreys and Reid
1975) suggests a
decreased AVP concentration or AVP activity within the collecting ducts of the kidney caused by catapres. ~ Grantham and Orloff isolated collecting tubule that prostaglandins effect of AVP.
In addition, Olsen
(1968) have shown in the can antagonize the cellular
(1976) showed that Indomethacln
pre-treatment abolishes the diuretic effect of catapres.
He also observed
that catapres increases urinary prostaglandin excretion in conscious dogs.
On
the basis of these results, however, it cannot necessarily be concluded that increased excretion of prostaglandlns associated with catapres.
in urine is responsible for the diuresls
Increased secretion of prostaglandlns
could be a
reflection of altered renal blood flow or of redistribution of intrarenal blood flow caused by catapres.
I wish to thank Dr. Jan Mulder, Medical Director, Ferring AB, Malmo, Sweden,
for the generous supply of arglnlne-8-vasopressin.
Drs. T. K. Keeton
and W. A. Pettinger, The University of Texas Health S~ience Center at Dallas, Dallas, Texas, provided invaluable help in the early phases of this study.
Pharmacologica! Research Communications, Vol. 11, No. 1, 1979
44
REFERENCE S
I.
Chrysant, S.G. and Lavender, A.R. (1973):
2.
Grantham, J.J. and Orloff, J. (1968):
Humphreys, M.H. and Reid, I.A. (1975):
Clin. Res. 21, 410.
3. Clin. Invest. 47, 1154.
Kidney Int. ~, 405.
4.
Olsen, U.B. (1976):
Europ. J. Pharmacol. 36, 95.
5.
Skowsky, W.R., Rosenbioom, A.A. and Fischer, D.A. (1974): J. Clin. Endocrin. Metab. 38. 278.
6.
van Zwieten, P.A. (1976):
Progr. Pharmacol. i, I.
3.
39
LACK OF SUPPRESSION OF VASOPRESSIN PLASMA LEVELS BY CATAPRES
Hans-Georg Gullner, M.D.
Hypertension-Endocrlne Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
20014
SUMMARY
Receivedin final form 3 October 1978
The effect of catapres (clonidine hydrochloride), an alpha-adrenerglc agonlst with hypotensive and diuretic properties, on release of vasopressln (AVP) was studied.
Administration of Catapres to conscious rats or dogs did
not alter plasma concentrations of vasopressin.
Catapres may modulate the
effect of vasopressln by an intrarenal mechanism or by an unknown mechanism.
INTRODUCTION
Catapres, an antihypertenslve drug with alpha-adrenerglc agonlst properties (van gw~eten, 1976), has been shown to increase free water clearance (Chrysant and Lavender, 1973; Humphreys and Reid, 1975) and to decrease urine osmolallty (Humphreys and Reid, 1975) when administered to
0031--6989n9~10039--06/S02,00~
© 1979 TheltalianPharmacologicalSociety
Pharmacological Research Communications, VoL 11, No. 1, 1979
40
hydropenlc anesthetized dogs, but not when given to hypophysectomised animals receiving ~nfuslons of antidiuretic hormone. evidence, Hu~phreys and Reid release of vasopressin.
On the basis of this indirect
(1975) suggested that catapres may suppress
In order to further examine this question, we
measured plasma levels of arginine-8-vasopressin
by radiolmmunoassay before
and after administration of catapres in conscious rats and dogs.
METHODS
Thirty adult male Sprague-Dawley rats mongrel dogs of either sex, weighing
(180-230 g) were studied.
18-24 kg were used.
Six
All animals had free
access to tap water and food (Purina Rat or Dog Chow).
One-hundred fifty intraperltoneally
g/kg catapress
(clonidlne hydrochlorlde)
to conscious rats, a dose which previously had been shown to
suppress renin release without changes in blood pressure. decapitated
was given
The rats were
20 min after injection and arterial blood was collected from the
trunk into chilled heparlnlzed
tubes.
Catapres,
in concentrations
ranging
from I ng/kg/mln to 3 g/kg/min, was infused via an indwelling catheter into the femoral or Jugular vein of conscious dogs for periods of 10 mln. cent dextrose solution was infused during control periods.
Five per
Venous blood
samples were collected in heparinlzed tubes at the end of each infusion period.
Arginine-$-vasopressln
was adsorbed to bentonite,
measured by radioimmunoassay Rosenbloom and Fischer procedure.
extracted by acetone and
according to the method described by Skowsky,
(~97~) w~th minor modifications
in the radioiodination
Vasopressin antiserum was generously supplied by Professor Jan
Mohring of Centre de Recherche Merrell International
(Strasbourg,
France).
Pharmacological Research Communications, Vol. 11, No. 1, 1979 It was used in a final dilution of 1:400,000.
Arginine-8-vasopressln
gift of Dr. Jan Mulder of Ferring AB, Malmo, Sweden. iodlnation and for construction of standard curves. of the radioimmunoassay was 5 picogram.
41 was a
It was used for The limit of sensitivity
There was no cross-reaction of the
antibody with the angiotensins,
bradykinin and other structually and
biologically related peptides.
The results are expressed as picograms of
vasopressin per ml of plasma.
Plasma vasopressin concentrations
species were determined in one assay. plasma was 65 ~ 12% $.E.M.
Recovery for extraction of AVP from
All values are corrected for recovery.
Statistical analysis was performed using the paired or unpaired experiments)
Student's t-test. Table I
RAT
DOG
AVP pg/ml Control
11.7
5% Dextrose
13.5
AVP pg/ml Control 5% Dextrose
6.3 8.6
12.6
9.9
10.8
6.3
16.2
11.7
30.6 15.9 ~ 3.0 SF~I
Clonidine hydrochloride 150 ~g/kg
16.2
5.7
8.5 + i.I SEM
Clonidine hydrochloride
8.6
30 ng/kg/min
8.1
41.4
5.7
11.7
6.2
22,5
4.5
10,8 18,1 + 5.2 S ~
from each
6.6 + 0.8 SD!
(for rat
Pharmacological Research Communications, VoL 11, No. 1, 192"9
42
RESULTS
Table I shows the effect of catapres on AVP plasma levels in conscious rats and dogs.
For the dog experiments one representative dose, 30 ng/kg/min,
is shown which was the highest dose which could be infused without altering blood pressure.
Concentrations above 30 ng/kg/min resulted in an initial
blood pressure increase which disappeared after 30-60 min. statistically
There was no
significant change in AVP plasma levels following administration
of catapres in either animal species at any of the doses studied.
Control
plasma AVP levels in rats were 15.9 + 3.0 S.E.M. and 18.1 + 5.2 S.E.M. after catapres administration.
In dogs, plasma concentrations
(N.S.)
of AVP were
8.5 ~ I.I S.E.M. before and 6.6 ~ 0.8 S.E.t!. (N.S.) after catapres treatment.
DISCUSSION
Humphreys and Reid (1975) proposed, volume and osmolality, dogs.
on the basis of changes in urine
that catapres may suppress AVP release in anesthetized
The results reported in the present study indicate that catapres does
not suppress circulating plasma levels of arginlne-8-vasopressin
in conscious
rats or dogs, in the absence of blood pressure changes by the drug. confirms the observations of Olsen
This
(1976) who did not find changes in the
excretion of bioassayable urinary AVP during periods of maximal diuresis following intravenous administration of catapres to conscious dogs. In some animals a slight increase in AVP plams levels could be observed after catapres administration while in others plasma AVP tended to decrease. Several explanations are possible for this finding.
The variation in plasma
AVP may be a reflection of the state of hydration of the animals at the time of plasma collection.
In addition,
the above observation may be due to the
Pharmacological Research Communications, Vol. 11, No. 1, 1979
43
reproducibility of the assay or due to the error in the extraction of the peptide from plasma.
In the present experiments,
urine flow and urinary osmolalities were not
measured since conscious animals without ureter catheters were studied.
In
similar previous experiments in anesthetized dogs, catheters were implanted into the ureters and urinary volume was measured.
Intravenous administration
of catapres to these dogs increased urine flow and decreased urinary osmolality.
However, plasma AVP levels did not change at any dose
(unpublished observations).
The demonstration that AVP infusion inhibits catapres-induced water dluresls
(Chrysant and Lavender,
1973; Humphreys and Reid
1975) suggests a
decreased AVP concentration or AVP activity within the collecting ducts of the kidney caused by catapres. ~ Grantham and Orloff isolated collecting tubule that prostaglandins effect of AVP.
In addition, Olsen
(1968) have shown in the can antagonize the cellular
(1976) showed that Indomethacln
pre-treatment abolishes the diuretic effect of catapres.
He also observed
that catapres increases urinary prostaglandin excretion in conscious dogs.
On
the basis of these results, however, it cannot necessarily be concluded that increased excretion of prostaglandlns associated with catapres.
in urine is responsible for the diuresls
Increased secretion of prostaglandlns
could be a
reflection of altered renal blood flow or of redistribution of intrarenal blood flow caused by catapres.
I wish to thank Dr. Jan Mulder, Medical Director, Ferring AB, Malmo, Sweden,
for the generous supply of arglnlne-8-vasopressin.
Drs. T. K. Keeton
and W. A. Pettinger, The University of Texas Health S~ience Center at Dallas, Dallas, Texas, provided invaluable help in the early phases of this study.
Pharmacologica! Research Communications, Vol. 11, No. 1, 1979
44
REFERENCE S
I.
Chrysant, S.G. and Lavender, A.R. (1973):
2.
Grantham, J.J. and Orloff, J. (1968):
Humphreys, M.H. and Reid, I.A. (1975):
Clin. Res. 21, 410.
3. Clin. Invest. 47, 1154.
Kidney Int. ~, 405.
4.
Olsen, U.B. (1976):
Europ. J. Pharmacol. 36, 95.
5.
Skowsky, W.R., Rosenbioom, A.A. and Fischer, D.A. (1974): J. Clin. Endocrin. Metab. 38. 278.
6.
van Zwieten, P.A. (1976):
Progr. Pharmacol. i, I.
3.