Morphine acts through alpha adrenergic and serotoninergic neurons to stimulate growth hormone secretion in the dog

In the awake-trained dog morphine caused a significant increase in growth hormone (GH). This response was blocked by i.v. administration of metergoline and by simultaneous infusion of phentolamine. Haloperidol did not block morphine's effect on GH. Furthermore when administered alone haloperidol caused a significant increase in GH. We conclude that alpha-adrenergic and serotoninergic receptors play a role in morphine's stimulatory effect on GH. The role of dopamine (DA) receptors requires further investigation.