[Influence of glucagon on jejunal absorption of glucose, water and electrolytes in man (author's transl)]

Glucagon and small-bowel mucosa

Numerous functional and structural effects of pharmacological dosages of glucagon on the small-intestinal mucosa have been demonstrated. In addition, clinical conditions associated with elevated concentrations of plasma glucagon may go along with alterations of the intestinal mucosa. The physiological and pathophysiological relevance of these findings, however, is questionable in view of the heterogeneity of the findings, of the complexity of the experimental systems used and of the methodological problems involved. With respect to possible trophic effects on the small-bowel mucosa enteroglucagon is of special importance. Numerous diseases in which increased intestinal mucosal growth has been shown are associated with elevated plasma concentrations of enteroglucagon. Our results concerning radiation damage, the time course of plasma enteroglucagon levels during antimitotic treatment, the small intestinal resection and the experimental blind loop syndrome are discussed. An outlook will be given as to the use of monoclonal antibodies in the development of glucagon as well as enteroglucagon deficiency states for the study of the physiological relevance of these two regulatory peptides.

Quantitative study of mucosal structure, enzyme activities and phenylalanine accumulation in jejunal biopsies of patients with early and late onset diabetes

A study of the three-dimensional structure of the upper jejunal mucosa in diabetics has been carried out. The structural findings were related to 14C-L-phenylalanine uptake in vitro, sucrase activity in mucosal homogenates, and the enzyme content of the absorptive cells as measured cytophotometrically. A low grade mucosal transformation of the sprue-type was found, which was associated with decreased sucrase activity, and with no reduction in phenylalanine accumulation. On the other hand the specific activities of alkaline phosphatase, non-specific esterase, and succinic dehydrogenase in the surface cells remained unchanged.

[Functional and morphological studies on intestinal mucosa of the rat under chronic glucagon application (author's transl)]

Chronic application (20 days) of glucagon in pharmacological doses induces mucosal transformation of the hyperregenerative type in the small intestine of the rat. This transformation is characterized by decreased villi, and increased crypt length. The morphological changes are accompanied by a reduction in glucose absorption in vivo as well as by decreased activities of lactase, sucrase and maltase. The findings demonstrate that hyperglucagonemia is not the cause for hyperplastic mucosal transformation, which is found in the experimental diabetes in the rat.

Lowering of fasting and food stimulated serum immunoreactive gastric inhibitory polypeptide (GIP) by glucagon

The effect of intravenous glucagon infusion on serum levels of immunoreactive GIP (IR-GIP), insulin (IRI), gastrin (IRG), and on blood glucose has been investigated in six healthy volunteers in the fasting state and during ingestion of a mixed standard meal. Glucagon (500 ng/kg/min) lowered significantly serum levels of IR-GIP and IRG below the fasting values and increased the levels of IRI and blood glucose. Glucagon (50 ng/kg/min) infused 30 minutes before and continued 90 minutes after ingestion of a test meal abolished the IR-GIP response, suppressed significantly the IRG response, and left the IRI response unchanged. The same glucagon dose infused 60 minutes after ingestion of the test meal decreased significantly the raised levels of IR-GIP and IRG to fasting levels without changing IRI values. It is concluded that exogenous glucagon inhibits Gip release at the level of the GIP-producing cells.