A Low Response of Pituitary Growth Hormone Secretion in the Patient with Diabetes Mellitus after Intravenous Administration of L-Dopa

Abstract

Recently, L-dopa has been known as one of drugs to stimulate the secretion of growth hormone from the pituitary gland through dopamine, which is a metabolic of L-dopa, without any changes of serum insulin levels, blood sugar values, fatty acids and amino acids concentrations in the serum of human being. The present study was thus designed to assess the effect of L-dopa on the pituitary gland to secrete the growth hormone in the normal subject and the study was further extended to compare the response of the pituitary secretion of the growth hormone following the administration of L-dopa between in the patient with diabetes mellitus and in the normal subject. In the present experiment, 5 normal subjects and 11 diabetes mellitus without obesity were employed and they received a 30 min infusion of 200 mg L-dopa dissolved in 200 ml physiological saline. In normal subjects, serum growth hormone concentration measured by radio-immunoassay was started to increase within 10 min after L-dopa administration and maximum value of serum growth hormone was obtained 60 min after the drug, mean values of it, 30 ng/ml of serum. Then it was declined sharply upto the values of 2-3 ng/ml. In the patients 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 both normal subjects and diabetes mellitus. From the above mentioned facts, it was concluded that the ability of pituitary gland to secrete the growth hormone was considerably impaired in diabetics when it was compared with normal subjects.