Clonidine releases immunoreactive beta-endorphin from rat para distalis.
Clonidine (10(-6), 10(-7) M) evokes the release of beta endorphin-like immunoreactivity (beta-END-LI) from cell cultures of anterior (pars distalis) but not neurointermediate (pars nervosa plus pars intermedia) lobe of the rat pituitary. This drug-induced secretion is blocked by alpha-adrenergic (phenoxybenzamine, yohimbine; 10(-5) M) but not beta-adrenergic (propranolol, 10(-5) M) antagonism. Gel filtration (Sephadex G-50) reveals that beta-END-LI released from anterior lobe cells consists of 2 major forms of immunoreactivity which coelute with beta-lipotropin or beta-endorphin standards. Conversely, beta-END-LI released spontaneously from neurointermediate lobe cells almost entirely corresponds to beta-endorphin. The data show that alpha-adrenergic stimulation by clonidine releases beta-END-LI selectively from cells of anterior but not neurointermediate lobe in vitro and suggests that the clonidine-induced release of pituitary beta-END-LI we have observed in vivo occurs in part by direct action on the corticotrophs of the pars distalis.
D000818:Animals; D002478:Cells, Cultured; D003000:Clonidine / Q000494:pharmacology*; D004723:Endorphins / Q000378:metabolism*; D008297:Male; D009928:Organ Specificity; D010643:Phenoxybenzamine / Q000494:pharmacology; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D010903:Pituitary Gland, Anterior / Q000378:metabolism; D010904:Pituitary Gland, Posterior / Q000378:metabolism; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D015016:Yohimbine / Q000494:pharmacology; D001615:beta-Endorphin
D004723:Endorphins; D010643:Phenoxybenzamine; D015016:Yohimbine; D001615:beta-Endorphin; D011433:Propranolol; D003000:Clonidine