HISTAMINE AND SEROTONIN RECEPTORS ON CULTURED SMOOTH MUSCLE CELLS

Abstract

The purpose of this thesis was to pharmacologically characterize histamine and serotonin receptors linked to adenylate cyclase on cultured calf aorta smooth muscle cells. First, the effects of specific agonists and antagonists on histamine and serotonin stimulated adenylate cyclase were examined. Second, radioactively labelled compounds believed to interact with these receptors were employed to further identify and differentiate these receptors from reported sites previously examined in peripheral and central tissue.;The cultured smooth muscle cell was shown to contain adenylate cyclase activity associated with three separate and independent receptors to epinephrine, serotonin and histamine. The calf aorta serotonin receptors were insensitive to the majority of the classical serotonin antagonists and agonists. Of the serotonin antagonists tested, only methysergide could produce inhibition and this was in a non-competitive manner. LSD was not an antagonist and {lcub}('3)H{rcub}LSD binding could not be demonstrated. An investigation of the structural requirements for agonist activity demonstrated that a hydroxyl or methoxy group on the 5-position of the indole ring and modification of the amine nitrogen by methylation but not by acetylation were compatible with activity.;Characterization of the histamine receptor via its associated adenylate cyclase demonstrated it to be exclusively of the H(,2) type displaying affinities for H(,2) agonists and for H(,2) antagonists including cimetidine analogues similar to other H(,2) systems. The use of these antagonists in displacing {lcub}('3)H{rcub}cimetidine revealed that only imidazole containing antagonists were active and relative potencies of antagonists did not correspond to those found for the adenylate cyclase system. {lcub}('3)H{rcub}Cimetidine binding was high affinity and saturable but involved primarily "imizidazole like" rather than H(,2) histamine receptor sites.;The conclusions of the thesis were: (1) this cultured smooth muscle cell contains an H(,2) histamine receptor coupled to adenylate cyclase; (2) the relative simplicity of assaying for cAMP in this homogenous cell system makes it a useful model for screening putative H(,2) compound; (3) the serotonin receptor has agonist structure-activity requirements similar to other serotonin receptors, (4) the dissimilarities between the cultured calf aorta and other serotonin receptors suggest that there may be a variety of serotonin receptor types linked to adenylate cyclase.