EFFECTS OF METOCLOPRAMIDE ON THE PARADOXICAL GROWTH-HORMONE RESPONSE TO GALANIN IN ACROMEGALY

Galanin is able to enhance growth hormone (GH)-releasing hormone stimu lated GH secretion in normal man. In acromegaly circulating GH levels are elevated and the GH response to GHRH may be exaggerated. Galanin h as been recently shown to decrease circulating GH levels in acromegaly . Dopaminergic drugs were the only previously known agents able to cau se a paradoxical GH fall in acronegaly. Aim of our study was to invest igate the effects of a potent central dopaminergic receptor blocker, m etoclopramide (MCP), on the galanin-induced paradoxical GH secretion i n acromegalic subjects. Two male and three female patients with active acromegaly (age range 44-66 years, body mass index range 24.6-28 Kg/m 2) were studied after 45 min iv infusion of porcine galanin (0.5 mg in 100 ml of saline) from 0 to 45 min combined with a 60 min iv infusion of a) saline (100 ml) or b) MCP (10 mg in 100 ml of saline) from -15 to 45 min. After galanin, GH values fell from baseline (27.5+/-10 mug/ L) to a mean nadir of 16.4+/-6.1 mug/L; after galanin+MCP, circulating GH levels were also decreased (mean nadir 17.3+/-8.1 mug/L) in all th e patients with respect to baseline (23.6+/-9.7 mug/L). No significant differences were found in absolute or percent of baseline GH levels a fter galanin+saline vs galanin+MCP. Our results suggest that the parad oxical GH fall after galanin in acromegalic patients is not mediated t hrough dopaminergic receptor. It can be hypothesized that galanin may interact at the pituitary level with its own receptors expressed by GH -secreting adenomatous cells.