Various preparations of glucagon treated with chloramine-T under different conditions have been studied with respect to their immunoreactivity toward two different glucagon antisera; one specific for pancreatic glucagon and the other capable of reacting with enteroglucagon as well. The glucagon preparations exposed to chloramine-T for different periods reacted almost identically with the nonspecific antibody whether they were used as tracer or standard. On the contrary, treatment with chloramine-T under severe conditions led to reduced immunoreactivity toward the specific antibody. Inclusion of dimethyl sulfoxide (DMSO) in the chloramine-T reaction resulted in preservation of the immunoreactivity of the treated preparations. The cyanogen bromide cleaved-glucagon, (1-26) homoserine lactone, showed little cross-reactivity with the specific antibody whereas it reacted to a similar extent with the nonspecific antibody as natural glucagon did. Amino acid analysis of the hormone exposed to chloramine-T demonstrated that the methionine residue at position 27 in the glucagon molecule had been oxidized to methionine sulfoxide. In addition, tryptophan had also been affected. DMSO protected methionine and tryptophan from the oxidative action of chloramine-T. We postulate from these results that the change in the immunoreactivity toward the specific antibody of glucagon exposed to chloramine-T is mainly due to oxidation of the methionine residue at position 27 in the molecule. The usefulness of DMSO in the iodination process is also discussed.

In order to clarify whether a dietary fiber has any effect upon the intestinal absorption of sulfonylurea, changes in plasma concentration of glibenclamide were determined during a six-hour period in nine healthy volunteers who took 2.5 mg of glibenclamide together with a breakfast and 3.9 g of glucomannan in a form of konjac powder and were compared with those of the control experiment in which the same amount of the hypoglycemic agent was given without the dietary fiber. In the control, mean plasma glibenclamide level increased rapidly, reaching a peak at 60 min and decreased gradually thereafter, whereas an increase in plasma glibenclamide level was blunted in the test experiment, thus plasma concentration of glibenclamide being lower at 30, 60, 90 and 150 min compared with the corresponding value of the control (31.7 +/- 24.5 ng/ml vs 76.4 +/- 25.0 ng/ml at 30 min; 51.3 +/- 35.5 ng/ml vs 120.9 +/- 56.0 ng/ml at 60 min; 60.0 +/- 38.8 ng/ml vs 117.4 +/- 53.1 ng/ml at 90 min; 54.0 +/- 31.5 ng/ml vs 100.7 +/- 46.5 ng/ml at 150 min). Mean plasma glucose concentration was significantly lower at 30 min in the test experiment than in the control despite the lower level of plasma glibenclamide in the former. The results suggest that glucomannan may influence the intestinal absorption of glibenclamide. A dietary fiber must be prescribed in due consideration of these facts.

In order to explore whether or not the negative feedback mechanism of insulin per se on insulin secretion exists in man, changes in plasma C-peptide immunoreactivity (CPR), as an index of pancreatic B cells secretory function, were studied in 6 nonobese healthy volunteers in the presence of high circulating levels of exogenous insulin. 10% glucose was infused concurrently so as to maintain blood sugar at the basal level. The insulin-glucose infusion was maintained for 120 minutes, achieving mean plasma levels of 140-180 mu1/ml. After this period, the insulin infusion was continued at the same rate for an additional 10 minutes while the glucose was omitted. Despite the elevated level of circulating insulin, no significant change in plasma CPR concentration was observed so long as the blood sugar was maintained at the basal levels. Following cessation of the glucose infusion, the plasma CPR levels declined with a decrease in blood sugar level. Under the conditions of the present study, no inhibitory effect of exogenous insulin on the secretory function of the B cells was noticed.

In order to assess the secretory capacity of the pancreatic alpha and beta cells in patients with hyperthyroidism, the plasma glucagon and insulin responses to 1-arginine and insulin-induced hypoglycaemia in 12 patients were compared with those in 6 normal subjects. The response of beta cell to hypoglycaemia was evaluated by measuring the decrease in plasma C-peptide immunoreactivity (CPR) level. There was a negligible rise in blood glucose and plasma insulin levels in the patients, whereas a significant increase occurred in normal subjects during the arginine infusion. Although no difference in the fasting plasma glucagon concentration between the two groups was found, 30 min after the beginning of the arginine infusion, the plasma glucagon levels rose to a peak of 252 \ m=+-\35 pg/ml in the patients, a value significantly lower than 387 \m=+-\53 pg/ml in the normal subjects. The insulin-induced hypoglycaemia caused no significant difference in the peak values of plasma glucagon between the two groups. There was a significant fall in plasma CPR after the insulin injection in both groups but the per cent decrement was rather greater in the patients than in the normal subjects. Some parts of this paper were read at

No abstract