Effect of somatostatin on D-galactose transport across the small intestine of rats

Serotonin-induced changes in L-leucine transport across rabbit jejunum

The aim of the present study has been to determine the effect of serotonin (5-HT) on the absorption of L-leucine across the rabbit jejunum. The results show that serotonin significantly diminishes the uptake and steady-state tissue accumulation and the mucosal to serosal flux of L-leucine. This effect does not change with previous intestinal exposure of the mucosa to the 5-HT. Serotonin does not seem to modify amino acid simple diffusion across the intestinal epithelium. The effect on the amino acid uptake is due to an inhibition of the Na(+)-dependent system of transport, mainly through a reduction of the apparent Vmax. Moreover, this hormone, added to the incubation solution, does not affect the L-leucine uptake across brush border membrane vesicles. In presence of trifluoroperazine, TMB-8 and staurosporine, the serotonin effect disappears. These results suggest an effect mediated by intracellular processes related to protein kinase C which inhibit the intestinal absorption of L-leucine.

Effects of somatostatin on luminal transit and absorption of nutrients in the proximal gut of minipigs

A discrepancy exists on the effects of somatostatin on the absorption of nutrients: in humans, absorption was found to be reduced, whereas in rats no effects were observed. However, intestinal absorption might be influenced by the transit rate of contents. This was not considered in previous studies. Therefore, we investigated simultaneously the effects of somatostatin on the absorption of nutrients and on luminal transit. In five minipigs (44-62 kg), a 150-cm segment of the proximal jejunum was temporarily isolated by two cannulas and perfused with an oligomer diet (60% carbohydrate, 18% protein, and 22% fat). The perfusion rate was 2 kcal/min. Flow rate and mean transit time were determined by markers (Cr-EDTA and Cu-EDTA). Somatostatin was infused intravenously at rates of 0.5, 1.25, 2.5, and 5 micrograms/kg/hr. In control experiments saline was administered intravenously. Somatostatin dose-dependently diminished flow rate of luminal contents and increased the transit time. At the largest dose of somatostatin (5 micrograms/kg/hr) flow rate was reduced by 50% compared with control infusion of saline (1.0 +/- 0.4 vs 2.0 +/- 0.05 ml/min, P < 0.05), and transit time was increased 3.6-fold (39.8 +/- 4.7 vs 11.2 +/- 4.9 min; P < 0.05). Somatostatin also dose-dependently enhanced the absorption of nutrients and energy. However, the increase in absorption was small compared with the effects on flow rate and transit time. At the largest dose (5 micrograms/kg/hr) absorption of energy, carbohydrate, protein, and fat was enhanced only by 9.7%, 7.0%, 5.2%, and 15.3%, respectively (49.9 vs 40.2%, 50.9 vs 43.9%, 67.3 vs 62.1%, and 30.1 vs 14.8% during saline infusion; P < 0.05). Results indicate that the major effects of somatostatin consist in a marked reduction of flow rate and a delay of luminal transit. The small increase in absorption was caused by the delay in transit and the prolonged contact of the nutrients with the mucosa. Therefore, in absorption studies, effects on transit need to be considered.

Effect of VIP on sugar transport in rabbit small intestine in vitro

The vasoactive intestinal peptide (VIP) has shown to be widely distributed in the gastrointestinal mucosa, submucosa and nerves, and the existence of VIP receptors on the basolateral membrane of enterocytes has been recently reported for many species. The interaction of VIP with its receptors seemed to increase cyclic AMP level, and this nucleotide has been shown to be responsible for the intestinal secretion produced by VIP. The present study confirms that VIP inhibits the intestinal absorption of D-galactose. This effect seems to be due to the inhibition of the Na(+)-independent basolateral intestinal sugar transport system. RMI 12330A, described as adenylate cyclase inhibitors, blocked the VIP action. These findings suggest that cyclic AMP might be responsible for the inhibition of Na(+)-independent transport of D-galactose across the basolateral membrane. Moreover, results obtained to determine the possible role of calcium in the action of VIP suggest that Ca2+ play a part, directly or indirectly, in the inhibition of the D-galactose transport across the basolateral membrane produced by VIP.