Growth hormone responses to the stimulation of hypothalamic glucoreceptors in diabetic retinopathy. Effects of catecholamine precursors and dopamine antagonists.

The effects of the stimulation of glucoreceptors located at the level of the lateral hypothalamic nuclei and sensitive to intracellular glucose deprivation on growth (GH) release are well documented in the monkey. In this study the effect of a reproducible hypoglycemic stimulatory procedure was controlled by continuously monitoring blood glucose (BG) levels in normal subjects and in a series of 120 diabetic patients. In contrast to control subjects, GH responses to similar hypoglycemic nadirs were not reproducible in diabetics (with or without diabetic retinopathy). The infusion of levodopa, precursor of both norepinephrine (NE) and dopamine, during BG decline rendered the GH response to hypoglycemia consistently reproducible. To investigate the site of action of levodopa, a group of diabetics were pretreated with a centrally active dopamine antagonist, metoclopramide hydrochloride. The pattern of GH release was similar in both groups. These data suggest that in diabetes the interaction of levodopa and adequate stimulation of hypothalamic glucoreceptor systems is mediated by an NE transmission.