A COMPARISON OF THE EFFECT OF LEVODOPA AND SOMATOSTATIN ON THE PLASMA LEVELS OF GROWTH HORMONE, INSULIN, GLUCAGON AND PROLACTIN IN ACROMEGALY

Abstract

The acute suppressive effects of L-dopa and somatostatin (growth hormone release inhibiting hormone) on the elevated plasma GH (growth hormone) concentrations of 7 patients with acromegaly were compared. In addition the effects of the 2 agents on fasting concentrations of plasma glucose, insulin, glucagon and prolactin were studied. In 6 of the 7 patients hourly samples for GH assay were taken from 08.00 to 20.00 h on a control day. Synthetic cyclic somatostatin (100 .mu.g) was infused i.v. in an albumin/saline solution over 75 min with a Harvard constant infusion pump. L-dopa 500 mg was given orally. Somatostatin infusion produced a reduction in plasma GH concentrations in 6 of 7 patients (mean reduction 55%). L-Dopa produced a reduction in plasma GH concentrations in the same 6 patients (mean reduction 52%). The minimum GH concentrations achieved in the 2 tests were comparable and did not differ significantly from the minimum GH concentrations recorded during the 12 h control study. Mean plasma insulin and glucagon concentrations were also significantly reduced during the somatostatin infusion (P < 0.025; P < 0.05 respectively). Plasma glucose concentrations did not change. L-Dopa did not alter mean plasma glucose, insulin or glucagon values. Somatostatin did not alter prolactin values but L-dopa suppressed basal values to < 2 ng/ml in 5 patients. The plasma GH change after the administration of L-dopa and somatostatin in acromegaly is comparable and confirms the pancreatic effects of somatostatin.