The American journal of physiology
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The effect of beta-adrenergic agonists on splanchnic intravascular volume (SIV), measured with radionuclide imaging, and the subsequent influence of such volume changes on cardiac output (CO) were examined in 40 anesthetized dogs. Isoproterenol (6 micrograms/min) caused a decrease in total SIV of 12 +/- 1% (P less than 0.001). The decrease was due entirely to a decrease in splenic volume of 24 +/- 3% (P less than 0.001), since volume increased in the remainder of the splanchnic vasculature [hepatic and mesenteric volume increased 12 +/- 2% (P less than 0.001) and 11 +/- 3% (P less than 0.02), respectively]. ⋯ After subsequent alpha-adrenergic inhibition with phenoxybenzamine, terbutaline caused no change in SIV and an attenuated (P less than 0.05) increase in CO. Thus beta-adrenergic agonist administration causes a decrease in total SIV due entirely to a decrease in splenic volume. The SIV decrement is dependent on beta 2- and alpha-adrenoceptor stimulation and appears to enhance CO only if beta 1-adrenergic effects are minimized.