Low response of pituitary growth hormone secretion in patients with diabetes mellitus after intravenous administration of levodopa (Japanese)

Abstract

L dopa (levodopa) has been known as a drug that stimulates the secretion of growth hormone from the pituitary gland through dopamine, which is a metabolite of L dopa, without changing serum insulin levels, blood sugar values, fatty acids and amino acids concentrations in the serum of human beings. The present study was designed to assess the effect of L dopa on the pituitary glands ability to secrete growth hormone in the normal subject, the study also compares pituitary secretion of the growth hormone following the administration of L dopa between the patient with diabetes melitus and the normal subject. 5 normal subjects and 11 diabetes mellitus patients without obesity were empoyed, they received a 30 min infusion of 200 mg L dopa dissolved in 200 ml physiologic saline. In normal subjects, serum growth hormone concentration measured by radioimmunoassay started to increase within 10 min after L dopa administration, and the maximum value of serum growth hormone was obtained 60 min after. The mean value was 30 ng/ml of serum, then it declined sharply to the value of 2 to 3 ng/ml. In the patient with diabetes mellitus, on the other hand, maximum value of serum concentration of the growth hormone was only approximately 5 ng/ml of serum obtained between 45 and 75 min after the administration of L dopa. No changes in the serum concentration of IRI (immunoreactive insulin) and of blood sugar values were observed by the infusion of L dopa in normal subjects and diabetes mellitus patients. It was concluded that the ability of the pituitary gland to secrete the growth hormone was considerably impaired in diabetics, as compared with normal subjects.