EFFECTS OF FASTING AND GLUCAGON ON THE KINETICS OF ACTIVE HEXOSE ABSORPTION ACROSS THE RAT DISTAL ILEUM IN VIVO

Abstract

SUMMARYThe effects of starvation for 1, 2 or 3 d and the administration of glucagon to fed rats on the kinetics of active glucose and galactose absorption across the distal ileum have been determined in vivo. Fasting caused reductions in 'apparent Kt' for glucose and galactose transport together with a decrease in Jmax for glucose but not galactose absorption. Treatment with glucagon produced decreases in Kt for the absorption of both hexoses and an increase in Jmax for glucose absorption. The Jmax for galactose uptake, however, was unaltered by glucagon administration. Villus size was unaltered by starvation of up to 3 d duration, but significantly decreased by glucagon treatment. The results suggest that chronically elevated plasma glucagon levels may be a factor in the change in kinetics of hexose absorption in the distal ileum evoked by fasting.

The effect of fasting on the potential difference across the brush‐border membrane of enterocytes in rat small intestine.

“…The changes in Vm seen in the ileum in this present work, however, imply that other factors are operative since the ileum in the rat is not exposed usually to intraluminal nutrient even in the fed condition (Debnam, 1982). Raised plasma levels of glucagon may well be one factor responsible for the changes in hexose uptake induced by starvation (Rudo & Rosenberg, 1973;Debnam, 1982). A preliminary study has indicated that treatment of fed rats with pancreatic glucagon results in similar changes in Vm compared to starvation (Debnam & Thompson, 1983).…”

“…Dietary modification is known to cause rapid changes in the kinetics of intestinal hexose absorption (Debnam & Levin, 1975Debnam, 1978Debnam, , 1982. Since the rat is a nocturnal feeder Vm and hexose uptake must exhibit significant fluctuations during a 24 h cycle.…”

“…The epithelium must therefore be capable ofadaptation ifthe body is to maintain homoeostasis. Fasting is one condition which has been shown to cause rapid changes in the kinetics of hexose and amino acid absorption across the small intestine (Debnam & Levin, 1975;Debnam, 1978Debnam, , 1982. The effects of starvation, however, on absorption at the cell membrane level remain to be clarified.…”

“…The purpose of this present study was therefore to determine the E. S. DEBNAM AND C. S. THOMPSON effect of starvation on the electrical properties of the brush-border membrane during resting and absorptive conditions. A comparison of dietary-induced changes in the jejunum and ileum was carried out since, unlike the upper intestine, enterocytes in the distal region are not exposed usually to high levels of dietary sugar (Debnam, 1982), a factor which has been claimed to influence directly the absorption of hexose in the jejunum (Menge, Werner, Lorenz-Meyer & Riecken, 1975;Debnam & Levin, 1976). A preliminary account of this work has been presented to the Physiological Society (Debnam & Thompson, 1982).…”

Acute and chronic effects of pancreatic glucagon on sugar transport across the brush‐border and basolateral membranes of rat jejunal enterocytes

“…The effects of the hormone on sugar transport has attracted particular interest since the enhanced hexose absorption seen in starvation and experimental diabetes mellitus in the rat (Rudo, Lawrence & Rosenberg, 1975;Karasov & Diamond, 1983) may be due to increased levels of plasma glucagon which have been noted in these conditions (Rudo et al 1975;Potter & Morris, 1980). It is noteworthy that chronic treatment of rats with glucagon stimulates sugar absorption (Rudo & Rosenberg, 1973;Rudo et al 1975;Debnam, 1982), an effect which is due, at least in part, to changes in the maturity of the villus cell population (Thompson & Debnam, 1986a).…”