Clonidine inhibition of pancreatic secretion in rats: A possible central site of action

The effects of clonidine on pancreatic secretion were studied in rats fined with chronic or acute fistulas. Subcutaneous and iniracerebroventricular injections of clonidine in conscious rat induced a dose-dependent inhibition of basal pancreatic secretion involving volume, bicarbonate output and protein output with an ED 50 of about 10 μg/kg. Clonidine inhibition of pancreatic secretion was not dependent on the associatcti inhibition of gastric acid output. In conscious rats. the pancreatic inhibitory effect of clonidine was completely antagonized by yohimbine and slightly by piperoxane and prazosin. Propranolol, mianserin, naloxone and cimetidinc did not antagonize the clonidine effect. Clonidine decreased the basal panereatic secretion in anaesthetized rats and this action was completely reversed by yohimbine. Clonidine inhibited the pancreatic secretion stimulated by 2-deoxyglucose This effect was reversed by yohimbine, while prazosin had no effect. Clonidine did not inhibit the pancreatic secretion induced by electrical stimulation of the vagus nerves. These results suggest that clonidine inhibition of pancreatic secretion is mediated through α 2-adrenergic receptors, and at least in part by a central nervous system mechanism. Yohimbine alone increased basal pancreatic secretion in conscious rats. This suggests that α 2-adrencrgic receptors might be involved in the physiological nerve one to the pancreas.