Adrenergic Receptors Regulationof Insulin Secretion due to 12-O-Tetradecanoyl phorbol-13-acetate

Abstract

A possible role for the activation of protein kinase C and adenylate cyclase in the regulation of insulin secretion by monolayer islet B cells of neonatal rats was examined in a perifusion system. Stimulation of 60 min of 16.7 mM glucose secreted a first component of insulin for the first 10-min period. In the presence of 200 nM 12-O-tetradecanoyl phorbol-13-acetate(TPA), a protein kinase C activator, however, the same dose of glucose significantly increased cAMP accumulation in medium and dramatically enhanced a second component of insulin secretion in which the average secretion rate was 1.81 +/- 0.25 of insulin for the first 10-min period. In the presence of 200 nM 12-O-tetradecanoyl phorbol-13-acetate(TPA), a protein kinase C activator, however, the same dose of glucose significantly increased cAMP accumulation in medium and dramatically enhanced a second component of insulin secretion in which the average secretion rate was 1.81 +/- 0.25 of insulin for the first 10-min period. In the presence of 200 nM 12-O-tetradecanoyl phorbol-13-acetate(TPA), a protein kinase C activator, however, the same dose of glucose significantly increased cAMP accumulation in medium and dramatically enhanced a second component of insulin secretion in which the average secretion rate was 1.81 +/- 0.25 ng/ml/min for the 10-30 min (second phase IIa) and 3.39 +/- 0.18 ng/ml/min for the 30-60 min (second phase IIb) respectively. Addition of 10 microM epinephrine significantly decreased the medium cAMP content and abolished the sustained second-phase secretion, resulting in a monophasic response of approximately the same magnitude as evoked by 16.7 mM glucose alone. In contrast, joint addition of 10 microM epinephrine and 10 microM phentolamine, which activates adenylate cyclase, exerted a more pronounced increase in cAMP accumulation and the second component of insulin secretion than in the presence of TPA; the average secretion rates were 3.62 +/- 0.38 and 6.44 +/- 0.35 ng/ml/min respectively for the second phase IIa and IIb. However, no antagonistic effect of propranolol (10 microM) was found. Likewise, either phenylephrine (10 microM) or clonidine (1 microM) inhibited enhancement of insulin secretion that a combination of glucose with TPA caused, and alpha 1-adrenergic blockade of 10 microM prazosin was weak as compared to the blockade of yohimbine at the same concentration.(ABSTRACT TRUNCATED AT 400 WORDS)