Possible involvement of endogenous opioid peptides in prolactin secretion induced by alpha 2-adrenergic stimulation in rats.
Noradrenergic mechanisms have a stimulatory role in regulating prolactin (PRL) secretion in the rat. We investigated the mechanism by which the alpha 2-adrenergic system stimulates PRL release in urethane-anesthetized male rats. Intracerebroventricular injection of norepinephrine (2 micrograms/rat) or epinephrine (100 ng and 1 microgram/rat) caused an increase in plasma PRL levels. The PRL increase induced by epinephrine was much greater than that by norepinephrine. Intracerebroventricular injection of phentolamine (1 microgram/rat), an alpha-antagonist, blunted the plasma PRL increase induced by epinephrine (100 ng intracerebroventricularly). Plasma PRL levels were increased by intravenous injection of alpha 2-agonists, clonidine (15 micrograms/100 g of body wt), and xylazine (200 micrograms/100 g of body wt). Plasma PRL increase induced by clonidine or xylazine was suppressed by intravenous injection of naloxone (125 micrograms/100 g of body wt), an opiate antagonist. These findings suggest that alpha 2-adrenergic mechanisms stimulate pituitary PRL secretion, at least partly, by activating endogenous opioid peptides in the rat.
Koshiyama
H
H
Department of Internal Medicine, Kyoto University Faculty of Medicine, Japan.
Kato
Y
Y
Shimatsu
A
A
Murakami
Y
Y
Hattori
N
N
Ishikawa
Y
Y
Imura
H
H
D000818:Animals; D002552:Cerebral Ventricles / Q000187:drug effects / Q000502:physiology*; D003000:Clonidine / Q000494:pharmacology*; D004723:Endorphins / Q000502:physiology*; D004837:Epinephrine / Q000494:pharmacology*; D007276:Injections, Intraventricular; D008297:Male; D009270:Naloxone / Q000494:pharmacology*; D009638:Norepinephrine / Q000494:pharmacology*; D010646:Phentolamine / Q000494:pharmacology*; D011388:Prolactin / Q000097:blood / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D013843:Thiazines / Q000494:pharmacology*; D014991:Xylazine / Q000494:pharmacology*
D004723:Endorphins; D013843:Thiazines; D014991:Xylazine; D009270:Naloxone; D011388:Prolactin; D003000:Clonidine; D009638:Norepinephrine; D004837:Epinephrine; D010646:Phentolamine