Effects of lesions of hypothalamic catecholamines on blood pressure, fluid balance, vasopressin and renin in the rat.

Fluid balance, systolic blood pressure (BP) and serum vasopressin (VP) and renin activity (SRA) in the basal state and in response to blood volume depletion were examined in unanesthetized rats previously given intrathecal 6-hydroxydopamine (6-OHDA) to destroy catecholaminergic (CA) input to supraoptic nucleus (SON). Sham-operated rats, unoperated ad libitum hydrated rats and rats undergoing 4 days of water deprivation served as controls. The 6-OHDA lesion resulted in adipsia, a failure to conserve administered fluids and a decrease in systolic BP. Despite decreased blood volume secondary to dehydration, and decreased systolic BP, the 6-OHDA group failed to show the expected increase in serum VP. However, when blood volume was further decreased following intraperitoneal polyethylene glycol, lesioned rats showed robust VP and SRA responses. Thus, CA input to critical target areas in the hypothalamus may be necessary for maintenance of sensitivity to stimuli that normally elicit VP release. Decreased systolic BP following 6-OHDA lesions most likely results from dehydration coupled with inadequate VP responses.