Regional hemodynamic responses to exogenous catecholamines and vasoactive peptides in conscious rats

The vasoactive hormones vasopressin, angiotensin II, adrenaline, and noradrenaline may all be released after central neural stimulation, but our knowledge of their relative actions on regional vascular resistances is incomplete. A comprehensive account of these patterns will help our understanding of their contributions to centrally generated patterns of blood flow. In the present study, regional blood flows and resistances of five major arteries were measured during sequential intravenous infusions of a range of doses of each substance in conscious rats. Vasopressin strongly increased superior mesenteric, hindquarters, carotid, and renal resistance but did not affect celiac artery resistance until the highest infusion rate. Both angiotensin II and noradrenaline increased resistance, although to different extents, in all vascular beds except the hindquarters, which was unaffected. Adrenaline infused at pressor rates markedly increased superior mesenteric resistance while moderately increasing renal, carotid and celiac arterial resistances. At subpressor rates, however, adrenaline increased celiac resistance but decreased hindquarters vascular resistance without significantly affecting the other beds. It is concluded that each vasoactive substance released into the systemic circulation causes its own characteristic pattern of vascular responses. This information should be useful for understanding the humoral basis of hemodynamic responses to central stimuli.