Diurnal Patterns of Plasma Glucagon and Insulin in Normal and Diabetic Subjects

Abstract

Diurnal fluctuations of plasma insulin and glucagon levels, and their relationship to glucose were examined in 5 normal subjects and 14 stable diabetics. In the normal subjects plasma glucose levels showed a steady course throughout the day, increases occurring in response to meal ingestion; plasma insulin and glucagon levels were observed to rise concurrently. The elevation of plasma insulin was greater than that of glucagon so that the ratio of insulin to glucagon (I/G) was increased, this rise being proportionate to the increase of plasma glucose.

In the diabetic patients, plasma glucose was elevated and showed much greater fluctuations following meals. The area beneath the diurnal glucose curve was almost double the normal value. In contrast, the mean diurnal patterns of glucagon showed minimal changes during meals, and the diurnal glucagon areas arid fasting glucagon levels did not differ significantly from the normal. Furthermore, the diurnal glucagon areas were lower in those diabetics who exhibited greater hyperglycemia.

In the non-insulin requiring diabetics, in spite of the presence of hyperglycemia, the magnitude of elevation of plasma insulin in response to meals was similar to the normal, as was the diurnal insulin area. Thus the plasma insulin was inappropriately low for the prevailing blood sugar, as was confirmed by the negative relationship between diurnal glucose and diurnal insulin areas. The molar I/G ratio was low and did not increase in response to elevation of plasma glucose as was found in normal subjects.

It is therefore concluded that although hyperglucagonaemia is not sufficient to produce the hyperglycemia of diabetes, a combined derangement of α and β cells of the pancreas, such as to produce a reduction in the I/G ratio, may be responsible for the biochemical features of the disorder.

Key words

Insulin - Glucagon - Diurnal Fluctuation - Normal and Diabetic Subjects

1 Correspondence and requests for reprints: Dr. R.G.A. Behrman, Metabolic Unit, St. Mary's Hospital, London, W. 2

2 Present address: Endocrine-Metabolic Section, Medical College of Wisconsin, Milwaukee, Wisconsin, U.S.A.