The influence of neonatal treatment with capsaicin on the control of blood pressure in adult rats in water-replete and water-deprived states.

Arterial blood pressures and heart rates were measured in water-replete and in water-deprived (48 h) conscious, adult rats that had received capsaicin (50 mg kg-1) or its vehicle neonatally. Resting arterial blood pressures and heart rates in capsaicin-treated rats were not different from the controls in either the water-replete or the water-deprived state. Inhibition of the vascular actions of vasopressin (with 1-beta-mercapto,-beta, beta-cyclopentamethylenepropionic acid, 8-D-arginine vasopressin, (d(CH2)5DAVP] had no significant effect on blood pressures in the water-replete animals but caused a significant hypotension in water-deprived rats; the magnitude of the hypotension was the same irrespective of whether the animals had received capsaicin or its vehicle. During angiotensin converting enzyme inhibition (with captopril) and ganglion blockade (with pentolinium), the vasopressin-mediated blood pressure recovery was more gradual in the capsaicin-treated animals than in the controls, but after 60 min blood pressures were similar in all groups. Collectively the results indicate that although the full development of vasopressin-dependent mechanisms following acute hypotension takes longer when a large proportion of unmyelinated afferent fibres have been destroyed by neonatal treatment with capsaicin, 48 h of water deprivation results in a normal involvement of vasopressin-dependent mechanisms in the maintenance of blood pressure.