Abnormal insulin secretion in Parkinson's disease before and during L-dihydroxyphenylalanine (L-dopa) therapy.

Abstract

SUMMARY Insulin and glucose metabolism were studied in parkinsonian patients before and during treatment with l-DOPA and in a chronically ill, elderly, control group of patients. The parkinsonian patients had a low absolute glucose disappearance rate and a low serum insulin response to intravenous glucose compared with controls, which was not altered by l-DOPA therapy. The serum glucose and insulin responses to the oral glucose tolerance tests in parkinsonian patients were similar to those of the control group. Normal immediate insulin responses were observed after infusions of tolbutamide and glucagon. l-DOPA decreased serum insulin and glucose levels during the first 90 min of the oral glucose tolerance test and produced an increase in concentration of human growth hormone in serum of some parkinsonian patients. l-DOPA therapy had no effect on intravenous tolbutamide and glucagon tolerance tests. Our results indicate a selective defect in the mechanism of intravenous glucose-induced insulin release in patients with Parkinson's disease.