Functional effects of polyamines via activation of human β1- and β2 -adrenoceptors stably expressed in CHO cells

Polyamines mediate acute metabolic effects and cardiac hypertrophy associated with β-adrenoceptor stimulation. They may also modulate β-adrenoceptors, causing functional responses in rat atria and tracheal smooth muscle. The aim of this study was to determine whether polyamines interact with human β1- and β2-adrenoceptors and the functional consequences of such an interaction. Chinese hamster ovary (CHO) cells stably transfected with human β1- and β2-adrenoceptors were used to evaluate the effect of polyamines binding to β-adrenoceptors, cAMPproduction and morphological changes, which were pharmacologically validated by investigating the effects of the β-adrenoceptor agonists, isoproterenol and salbutamol. Polyamines interacted with human β1 and β2-adrenoceptors, as shown by the displacement of [125I]iodocyanopindolol in the binding assay. Putrescine showed higher affinity to β1- than β2-adrenoceptors. Spermidine and spermine produced partial displacement (approximately 50%) and, at the highest concentration, the effect was reversed. Putrescine and spermine acutely increased cAMP and, in a serum-free medium, induced a stellate-like form in cells, which was inhibited by propranolol, a β-blocker. A 10 to 15 h incubation with putrescine produced a spindle-like form and spatial organization via β-adrenoceptor activation, evidenced by the antagonizing effect by propranolol and lack of effect in wild-type CHO cells. Additionally, it decreased cell proliferation independently of β-adrenoceptor activation. Spermine caused cell death via fetal bovine serum-dependent and -independent mechanisms. The results suggest that putrescine may act as a non-selective and low affinity agonist of human β1 - and β2 - adrenoceptors, eliciting morphological changes. These findings may be of importance in physiology and in diseases involving β-adrenoceptor functionality.