EFFECTS OF [SAR(1)]ANGIOTENSIN-II ON PROENKEPHALIN GENE-EXPRESSION AND SECRETION OF [MET(5)]ENKEPHALIN IN BOVINE ADRENAL-MEDULLARY CHROMAFFIN CELLS

We have studied the effect of [Sar1]angiotensin II [S1-AII; a degradation-resistant analogue of angiotensin II (AII)] on the release of [Met5]enkephalin (ME) and proenkephalin A (proENK) gene expression. Short-term (15-min to 1-h) stimulation of bovine adrenal medullary chromaffin (BAMC) cells with S1-AII at concentrations from 0.1 to 100 nM had no significant effect on secretion of ME, whereas high concentrations of S1-AII (3 to 100-mu-M) produced a concentration-dependent increase in the concentration of ME in the incubation media. In contrast, long-term (3- to 24-h) stimulation with low concentrations (0.1 nM-1-mu-M) of S1-AII increased the secretion of ME in a concentration-dependent manner (EC50 = 1 nM). The intracellular level of ME was not changed by long-term treatment with S1-AII (100 nM). In addition to increased ME secretion, long-term (24-h) stimulation with S1-AII increased the expression of proENK mRNA in a concentration-dependent manner (EC50 = 4 nM). Losartan {2-n-butyl-4 chloro-5-hydroxymethyl-1-[(2'-(1H-tetrazol-5-yl)biphenyl-4-yl)-methyl]imidazole potassium salt, a type 1 AII receptor antagonist) inhibited these effects, whereas PD123319 (50-mu-M, a type 2 AII receptor antagonist) was inactive. Our results suggest that AII in BAMC cells exerts a major effect on the long-term regulation of expression of proENK mRNA and secretion of ME. These effects appear to be mediated by type 1-like AII receptors.