The effect of cholinergic blockade on the growth hormone response to galanin in humans.

The effect of cholinergic blockade with pirenzepine or atropine on growth hormone (GH) release after galanin administration was investigated in five normal male subjects. The mean peak GH response to an infusion of galanin (40 pmol/kg/min for 40 minutes) was significantly reduced from 17.2 mU/L to 2.9 mU/L (P less than .001) with prior administration of pirenzepine (30 mg IV). When galanin was infused at a higher dose (80 pmol/kg/min), this suppression of release by pirenzepine was partially overcome, with GH rising to a mean peak response of 8.0 mU/L (P less than .05). Repeated administration of atropine (two bolus doses of 0.6 mg IV) also failed to abolish the GH response to this higher dose of galanin in two subjects. It has been proposed that cholinergic pathways control GH release via somatostatin, and this study suggests that galanin may also act by modulating hypothalamic somatostatinergic tone either directly or by facilitating cholinergic transmission.