Neonatal capsaicin treatment impairs vasopressin-mediated blood pressure recovery following acute hypotension.

Rats were treated with a single injection of either capsaicin (50 mg kg-1 s.c.) or vehicle on day 2 after birth. When the animals were adult, they were challenged with osmotic (water deprivation) and haemodynamic (acute hypotension) stimuli that normally evoke vasopressin release. Capsaicin-treated and vehicle-injected rats showed similar body weight losses and plasma osmolalities following 48 h of water deprivation. Thus it appears that neonatal treatment with capsaicin does not impair the antidiuretic response to plasma hyperosmolality. Following acute ganglion blockade in the presence of angiotensin converting enzyme inhibition, there was some recovery of blood pressure in the vehicle-injected rats, but recovery was significantly (P less than 0.001) less in the capsaicin-treated animals. The recovery may be attributed to vasopressin since it was abolished by an antagonist selective for the pressor action of the peptide (d(CH2)5DAVP). These results suggest that neonatal treatment with capsaicin impairs vasopressin-mediated recovery of blood pressure following acute hypotension. The possible involvement of baro- or chemoreceptor afferents is discussed.