Pressor Sensitivity to Exogenous Vasopressin in Conscious, Adult Rats Treated Neonatally with Capsaicin

Pressor responses to exogenous arginine vasopressin were assessed in adult rats that had been treated neonatally with capsaicin or its vehicle. Measurements were made under control conditions, after inhibition of baroreflexes (with pentolinium), and after inhibition of baroreflexes (with pentolinium) and the production of angiotensin II (with captopril). Resting arterial blood pressures and pressor sensitivities to exogenous arginine vasopressin were similar in capsaicin-treated and vehicle-injected rats. Sixty minutes after the administration of pentolinium, systolic and diastolic blood pressures were reduced in both groups of rats and the pressor responses to arginine vasopressin were similarly and significantly enhanced. In both groups of rats 60 min after administration of pentolinium and captopril, systolic and diastolic blood pressures were lower than in the presence of pentolinium alone, but pressor responses were not different from those seen in control conditions. The possibility that the present results are explicable in terms of baroreflexes, the renin-angiotensin system and endogenous vasopressin interacting to influence the pressor sensitivity to exogenous vasopressin is discussed. From the present findings, it seems that our previous observation of impaired, vasopressin-mediated blood pressure recovery following acute hypotension in capsaicin-treated rats cannot be attributed to a reduced pressor sensitivity to the hormone.