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

Abstract

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.