Effect of forskolin, isoproterenol and IBMX on angiotensin converting enzyme and cyclic AMP production by cultured bovine endothelial cells

Abstract

The production of angiotensin converting enzyme (ACE) is known to be increased by glucocorticoids, thyroid hormones and converting enzyme inhibitors. We have recently reported that active cAMP analogues also stimulate production of the enzyme. The effect of stimulation of adenylate cyclase in cultured endothelial cells or of phosphodiesterase inhibition on ACE production was therefore evaluated. The phosphodiesterase inhibitor, isobutylmethylxanthine (IBMX) (10(-4) M), produced 10.5 +/- 1.3 and 1.3 +/- 0.1 (P less than 0.01 and P greater than 0.1) fold increases in extracellular and cellular cAMP levels and a 1.55 +/- 0.10 (P less than 0.0001) fold increase in ACE accumulation. The adenylate cyclase stimulator, forskolin (0.01-10 microM), acutely stimulated cellular cAMP accumulation in a dose-dependent manner, reaching a 2.8 +/- 0.1-fold increase at 10 microM. After 48 h exposure to 10 microM forskolin, significant increases in cellular (1.90 +/- 0.38-fold increase, P less than 0.0001) and extracellular cAMP (2.35 +/- 0.26-fold increase, P less than 0.0001) were also observed but ACE accumulation was unchanged (108 +/- 10% of control, P greater than 0.5). The beta-adrenoceptor agonist, isoproterenol (1-1000 nM), acutely stimulated cellular cAMP accumulation, with a threshold effect at 10 nM, an ED50 of approximately 30 nM, and a plateau effect of 2.0 +/- 0.13-fold increase by 100 nM. After 48 h exposure to isoproterenol (1 microM), extracellular cAMP levels were increased significantly (1.68 +/- 0.33-fold increase, P less than 0.01) but ACE production was slightly inhibited (83 +/- 7% of control, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)