Effect of somatostatin on intestinal absorption of nutrients in the rat

Abstract

Effects of somatostatin on absorption of D-glucose, L-leucine and triacylglycerols by the small intestine were studied in rats after treatment with the peptide in vivo and in everted jejunal segments in vitro. Absorption of glucose was not affected in vitro by somatostatin or the analogue [ D-Trp 8, D-Cys 14]somatostatin at concentrations up to 0.006 mM. Addition of various peptidase inhibitors had no influence, suggesting that failure of somatostatins to inhibit absorption was not due to inactivation by peptidases. Glucose absorption in vitro by jejunum from rats treated with high doses of somatostatin in vivo was not different from that of untreated rats. The biguanide phenformin inhibited glucose absorption, whether added in vitro (IC 50 ≈ 1 mM) of after treatment in vivo (3–100 mg/kg per os). The blood glucose increase following oral glucose administration in fasted rats was not affected by somatostatin, but significantly suppressed by phenformin. Absorption of leucine in vitro was not affected by somatostatin (up to 0.03 mM) or [ D-Trp 8, D-Cys 14]somatostatin (0.01 mM), but inhibited by phenformin (IC 50 = 2 mM). Absorption of acylglycerols (glycerol tri[1- 14C]oleate) administered orally was significantly inhibited by somatostatin (twice 5 mg/kg subcutaneously) and phenformin (100 mg/kg per os). In rats — apparently in contrast to man — somatostatin does not decrease role of somatostatin in carbohydrate absorption remains controversial. Investigations in healthy [9] and diabetic [20] human subjects suggest that the peptide inhibits (directly or indirectly) the intestinal absorption of glucose in man. On the other hand, our results and those of others obtained in experiments in rats [4,11,21] and Rhesus monkeys [7] clearly do not support such a role in these species. Further studies are therefore needed to resolve this problem.