Catecholamine effects on cyclic AMP levels and ion secretion in rabbit ileal mucosa

Abstract

Effects of catecholamines on cyclic AMP (cAMP) levels and ion fluxes were examined in isolated rabbit ileal mucosa. The base-line cAMP level was unaffected by epinephrine (Epi), norepinephrine (Norepi), and isoproterenol. The theophylline-augmented cAMP level was decreased slightly be Epi in one series of experiments but not in another. Propranolol did not enhance this effect. The increase in cAMP level produced by cholera toxin was almost completely reversed by addition of Epi or Norepi. This reversal was prevented by phenoxybenzamine. Epi also partially reversed the increase in cAMP level produced by prostaglandin E1. Effects of Epi on ion fluxes were determined following addition of secretagogues. Epi significantly decreased theophylline-induced but not cAMP or cholera toxin-induced Cl secretion. A decrease in short-circuit current was nonetheless observed in the latter two instances. The observed discrepancies between alpha-adrenergic effects on cAMP levels and ion fluxes suggest the following possibilities: 1) ion transport-related cAMP is only a small fraction of total mucosal cAMP; 2) cAMP-induced active ion secretion is only slowly reversible, or 3) effects of alpha-adrenergic stimuli on ion transport are not due to inhibition of cAMP accumulation.