Title

Characterization of the norepinephrine regulation of phosphoinositide metabolism in vascular smooth muscle

Date of Award

1990

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Pharmacology

First Committee Member

Irene Litosch, Committee Chair

Abstract

The present studies have characterized the events which occur upon norepinephrine-stimulated phosphoinositide hydrolysis in vascular smooth muscle tissue. In rat aortic segments labeled for 4 hours with ($\sp3$H) inositol, norepinephrine generated a rapid ($<$60 second) increase in ($\sp3$H) inositol phosphates (quantitated by anion-exchange chromatography) which occurred with the degradation of phosphatidylinositol-4,5-bisphosphate. High pressure liquid chromatography was used to identify the inositol trisphosphate isomers generated by norepinephrine and determine the kinetics for their production. A maximal increase in inositol-4,5-trisphosphate due to norepinephrine was observed at 15 seconds. Levels of inositol-4,5-trisphosphate declined to basal within 5 minutes. Inositol-1,3,4-trisphosphate levels increased rapidly and continued to increase in the presence of agonist. There was little accumulation of inositol bisphosphate during 5 minutes. Increases in inositol monophosphate were observed within 60 seconds of stimulation; levels continued to increase during incubation. The norepinephrine-stimuilated generation of inositol-1,4,5-trisphosphate was dose-dependent and correlated well with the dose-response for contraction due to release of intracellular Ca$\sp{2+}$, with half-maximal activation at 2 $\times$ 10$\sp{-7}$ and 2.7 $\times$ 10$\sp{-7}$ M, respectively. The pattern for norepinephrine-stimulated generation of inositol phosphates was similar in rat caudal artery segments. these results provide evidence for a primary role for the inositol phospholipid transduction system inthe activation of vascular smooth muscle. the modulation of norepinephrine-stimulated phosphoinositide hydrolysis by endothelium, cyclic adenosine monophosphate and extracellular Ca$\sp{2+}$ was also addressed. The norepinephrine-stimulated generation of inositol phosphates was unaffected by removal of endothelium. Forskolin and isoproterenol, agents which increase intracellular cyclic adenosine monophosphate levels, did not affect the levels of inositol phosphates generated in aorta. IN caudal artery Ca$\sp{2+}$ channel blockers, diltiazem and verapamil did not affect the nonrepinephrine-stimulated production of inositol phosphates. Depolarization with KCl did not stimulate inositol phosphate production. These results indicate that endothelium, cyclic adenosine monophosphate and extracellular Ca$\sp{2+}$ do not have major modulatory roles in the regulation of agonist-stimulated inositol phosphate production in vascular smooth muscle.

Keywords

Health Sciences, Pharmacology

Link to Full Text

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