HINDQUARTER VASCULAR-RESISTANCE AS COMPENSATOR FOR HYPOTENSION IN CONSCIOUS RATS

The purpose of this study was to test whether hindquarter (terminal ao rtic) vascular resistance uniquely increases in order to compensate fo r interventions which result in a lowering of arterial pressure. Chang es in hindquarter resistance were compared to changes in superior mese nteric resistance after the administration of the nitrovasodilator dru g, molsidomine. Hindquarter blood flow or superior mesenteric flow was measured in conscious rats using an electromagnetic flow probe implan ted around the terminal aorta or the superior mesenteric artery, respe ctively. Twenty minutes after an intravenous bolus injection of molsid omine (1 mg/kg), ganglionic blockade with hexamethonium bromide (25 mg /kg, i.v.) significantly decreased hindquarter resistance, but not sup erior mesenteric resistance. In the absence of molsidomine, ganglionic blockade has no effect on resistance in either vascular bed. These fi ndings suggest that excitation of sympathetic vasoconstrictor fibers s upplying the hindquarters but not those supplying the superior mesente ric area occurred in response to the hypotensive effect of molsidomine . This is consistent with the hypothesis that augmenting-hindquarter r esistance is the first line of defense against hypotensive interventio ns.