ADRENERGIC CONTROL OF IMMUNOREACTIVE BETA-ENDORPHIN RELEASE FROM THE PITUITARY OF THE RAT - INVITRO AND INVIVO STUDIES

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  • 1 January 1982
    • journal article
    • research article
    • Vol. 222  (1) , 103-108
Abstract
The adrenergic control of pituitary .beta.-endorphin release was investigated by testing the effects of various .alpha.- and .beta.-adrenergic drugs on the secretion .beta.-endorphin-like immunoreactivity (.beta.-END-LI) from primary cell cultures of anterior and neurointermediate lobes and into plasma in vivo. Incubation of anterior lobe cells with several adrenergic agonists (10-7-10-5 M) evoked significant release of .beta.-END-LI with the following potency order: l-epinephrine > .alpha.-methylnorepinephrine > guanfacine = methoxamine = l-isoproterenol. The epinephrine- and isoproterenol-induced release from anterior lobes were both inhibited by phenoxybenzamine but not propranolol, suggesting mediation by .alpha.-adrenoceptors. Release of .beta.-END-LI from cultured neurointermediate lobe cells was also stimualted 3-fold by epinephrine or isoproterenol (10-100 nM) but appeared to do so via a .beta.-adrenergic mechanism because propranolol blocked their effects. Administration of l-epinephrine (100 .mu.g/kg s.c.) or l-isoproterenol (200 .mu.g/kg s.c.) to rats evoked a 3- to 4-fold increase in plasma .beta.-END-LI, which peaked 30 min after injection and was dose-dependent up to 500 .mu.g/kg. Pretreatment with phenoxybenzamine (5 mg/kg i.p.) 30 min before epinephrine (100 .mu.g/kg s.c.) inhibited the drug-induced rise whereas propranolol (2 mg/kg i.p.) blocked the increase in plasma .beta.-END-LI after isoproterenol (200 .mu.g/kg s.c.). .alpha.- and .beta.-adrenergic stimulation selectively release .beta.-END-LI from cultured anterior and neurointermediate lobes, respectively. Both methanisms appear to be active in vivo.