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1 Department of Pharmacology,
The aim of the present study was to
determine the receptor subtype involved in arginine vasopressin
(AVP)-induced modulation of baroreflex function in spontaneously
hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats using novel
nonpeptide AVP V1- and V2-receptor antagonists.
Baroreceptor heart rate (HR) reflex was investigated in both SHR and
WKY rats which were intravenously administered the selective
V1- and
V2-receptor antagonists OPC-21268 and OPC-31260, respectively. Baroreflex function was assessed by
obtaining alternate pressor and depressor responses to phenylephrine and sodium nitroprusside, respectively, to construct baroreflex curves.
In both SHR and WKY rats baroreflex activity was tested before and
after intravenous administration of vehicle (20% DMSO), OPC-21268 (10 mg/kg), and OPC-31260 (1 and 10 mg/kg). Vehicle did not significantly
alter basal mean arterial pressure (MAP) and HR values or baroreflex
function in SHR or WKY rats. The
V1-receptor antagonist had no
significant effect on resting MAP or HR values or on baroreflex
parameters in both groups of rats, although this dose was shown to
significantly inhibit the pressor response to AVP (5 ng iv; ANOVA,
P < 0.05). In SHR but not WKY rats
the V2-receptor antagonist
significantly attenuated the gain (or slope) of the baroreflex curve
(to 73 ± 3 and 79 ± 7% of control for 1 and 10 mg/kg,
respectively), although AVP-induced pressor responses were also
attenuated with the higher dose of the
V2-receptor antagonist. These
findings suggest that AVP tonically enhances baroreflex function
through a V2 receptor in the SHR.
arginine vasopressin; OPC-21268; baroreceptor heart rate reflex
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