Effect of dehydration and cardiac tamponade on superior mesenteric artery flow: role of vasoactive substances.

The role of serotonin, catecholamines, and angiotensin in the pathogenesis of mesenteric low ,jow states was investigated in anesthetized dogs by measurement of blood,fiows with electromagnetic,flow meters. During dehydration or cardiac tamponade, a disproportionate decrease in superior mesenteric artery flow was demonstrated, compared with aortic,pow, but renal artery,fiow was relatively better maintained. Depletion of serotonin and catecholamines by pretreatment with reserpine or blocking serotonin’s action with methysergide did not alter the disproportionate reduction in mesenteric,pow. Disproportionate superior mesenteric artery flow during dehydration and tamponade was associated with increased levels of circulating angiotensin and virtually was abolished by bilateral nephrectomy, by inhibition of enzymatic conversion of angiotensin I to II by Bothrops nonapeptide, and by competitive inhibition of angiotensin II with I-sar, &ala angiotensin II. Exogenous angiotensin administered intravenously to dogs not protected by drug treatment disproportionately decreased superior mesenteric artery /low with less effect on renal artery,%ow. These results are compatible with the hypothesis that increased circulating levels of angiotensin during dehydration and tamponade contribute to the disproportionate reduction in superior mesenteric arteryjow in the anesthetized dog.