Central inhibition of basal pancreatic and gastric secretions by β-endorphin in rats

Abstract

The effects of intracerebroventricular injections of synthetic ovine β-endorphin were tested in conscious rats with gastric and pancreatic fistulas. In the range of 0.8 to 25 μg injected in the third ventricle of the brain, basal gastric and pancreatic secretions were strongly inhibited in a dose-dependent manner. Pancreatic volume, bicarbonate output, and total protein output were similarly inhibited, while the bicarbonate concentration was only slightly changed. Similar effects were noted after the administration of morphine. In the present model system, morphine was 20–30 times less active than β-endorphin on a molar basis. β-Endorphin inhibition of pancreatic secretion was reversed by naloxone, suggesting that opiate receptors are involved in this phenomenon. Gastric acid secretion participated in the pancreatic effects of β-endorphin to only a slight extent, since pancreatic inhibition by the endorphin was decreased only slightly in rats with gastric fistula in which gastric juice was diverted and did not reach the duodenum. The comparison of intravenous and intraventricular injections of β-endorphin and morphine suggested that the observed inhibitions originated in the central nervous system. No effects were detected after the administration of α-endorphin, Met-enkephalin or Leu-enkephalin, although pancreatic secretion was measurably inhibited by longacting synthetic enkephalin analogues.