Abstract
In selected β 1- (heart, lipolysis) and β 2-adrenoceptor (trachea) systems, the interaction of racemic-trimetoquinol (TMQ) and the erythro- and threo-diastereomers of 1-(3′,4′,5′-trimethoxy-α-hydroxybenzyl)-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (α-hydroxy TMQ) was investigated. Each tetrahydroisoquinoline possessed agonist activity in these β-adrenoceptor systems. The rank order of potency observed for these compounds was racemic-TMQ > erythro-α-hydroxy TMQ > threo-α-hydroxy TMQ. Using isolated fat adipocytes, a favorable correlation was observed between the elevation in c-AMP and pharmacological response for the TMQ stereoisomers and diastereomers of α-hydroxy TMQ. The rise in intracellular c-AMP produced by (−)- and (+)-TMQ in fat cells was blocked by the presence of propranolol, and not in the presence of phentolamine. Since considerably higher concentrations (>10 −4 M) of these compounds were required to produce a significant inhibition of c-AMP phosphodiesterase activity in adipose tissue, it is proposed that the lipolytic response is a result of stereoselective interaction of these tetrahydroisoquinolines at the level of membrane-bound adenylate cyclase.
Published Version
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