We investigated the alterations of rat aortic alpha 1-adrenoceptors and alpha 1-adrenergic stimulated phosphoinositide (PI) metabolism in intraperitoneal sepsis. An analysis of [125I]-hydroxyethylaminotetralone (HEAT) binding to alpha 1-adrenoceptors on rat aortic membranes revealed decreased numbers of receptors without changes in affinity. The maximum number of binding sites decreased from 349 +/- 35 fmol/mg to 146 +/- 16 fmol/mg (P less than 0.05 vs. control). PI metabolism was similarly attenuated in aortae from septic rats. The norepinephrine-stimulated hydrolysis of [32P]-phosphatidylinositol-4,5-bisphosphate was significantly decreased in aortae from septic rats as was the alpha 1-adrenoceptor stimulated accumulation of [3H]-inositol monophosphate. Finally, the basal labeling of [32P]-phosphatidylinositol-4,5-bisphosphate but not of [32P]-phosphatidylinositol or [32P]-phosphatidic acid was significantly diminished. These results imply that signal transduction induced by alpha 1-adrenoceptor agonists in rat aorta is significantly altered in intraperitoneal sepsis. These findings may help define the mechanisms of depressed aortic contractility in models of sepsis and endotoxic shock.