Naloxone or vagotomy does not influence centrally octreotide-induced inhibition of gastric acid secretion in rats

Abstract

To investigate the effect of preceding naloxone injection into the third cerebroventricle or acute subdiaphragmatic vagotomy on the gastric acid secretion inhibited by the somatostatin analogue octreotide given by intracerebroventricular (icv) injection. The third ventricles were cannulated in male Wistar rats anesthetized with sodium pentobarbital. One week later, acute gastric lumen perfusion was carried out. The gastric perfusion samples were collected every 10 min and were titrated by 0.01 mol/L NaOH to neuter. On the basis of subcutaneous injection of pentagastrin (G-5, 160 micro, g/kg), icv injection of physiological saline (group A, n = 20), icv injection of octreotide (0.05 micro g) (group B, n = 20), icv injection of naloxone (2.5 micro g)+octreotide (0.05 micro g) (group C, n = 20), acute subdiaphragmatic vagotomy+ icv injection of physiological saline (group D, n = 20), or acute subdiaphragmatic vagotomy+icv injection of octreotide (0.05 micro g) (group E, n = 20) were conducted. Before and after icv injection, 1-h total acid output (TAO) was determined and compared. The experimental data were expressed in change rate (%) of TAO. The change rates (%) of TAO were 4.60% in group A, -20.35% in group B, -18.06% in group C, 5.01% in group D and -21.59% in group E, respectively. Comparison of group B or C versus group A showed that P < 0.01 and comparison between the group E versus group D showed that P < 0.01. Whereas the differences between group C and group B, group E and group B were not statistically significant (P > 0.05 for all). The results indicate that the central inhibition of gastric acid secretion by octreotide may not be mediated by the endogenous opiate substance or its receptor and the peripheral pathway for icv injection of octreotide to suppress gastric acid secretion is via extra-vagus route.