Central μ-, δ- and κ-opioid influences on intestinal water and electrolyte transport in dogs

Abstract

The effects of intracerebroventricular (i.c.v.) administration of opioid peptides with μ- (DAGO), μ- and δ- (DALAMIDE, DADLE) and κ- (dynorphin) properties on normal and stimulated (cholera toxin) net fluxes of water, Na + and K + through a jejunal Thiry-Vella loop were investigated in conscious dogs. Basal net water absorption was slightly, but significantly ( P < 0.05) increased during i.c.v. infusion of DALAMIDE or DAGO (0.5 ng/kg/min) but not DADLE and dynorphin-(1–13) at the same rate; DALAMIDE and DAGO also markedly reduced (by 72.3 and 79.5% respectively) the secretory effects of cholera toxin (0.4 μg/ml). Similar effects were obtained with DALAMIDE and DAGO when injected i.c.v. as a bolus (100 ng/kg) prior to cholera toxin infusion; they were suppressed after i.v. pretreatment with naltrexone (0.3 mg/kg) but also with propranolol (0.2 mg/kg). In contrast, i.v. phentolamine (0.2 mg/kg) and bilateral truncal vagotomy, were unable to block their effects. These results suggest that Met-enkephalin can act centrally to affect intestinal transport of (i) water and (ii) electrolytes in dogs. They act probably at central μ-receptors which are involved in the regulation of intestinal secretion mediated through a central or peripheral β-adrenergic pathway.