Serotonin and dopamine independently regulate pituitary beta-endorphin release in vivo.
Serotonin and dopamine neurons have been shown to exert a stimulatory and inhibitory control, respectively, over pituitary release of beta-endorphin-like immunoreactivity (beta-END-LI). In the present study we sought to determine whether an interaction exists between these two reciprocal mechanisms regulating beta-END-LI in the rat. The intraperitoneal (i.p.) administration of 5 mg/kg quipazine, a serotonin receptor agonist, or 2.5 mg/kg haloperidol, a dopamine receptor antagonist, each elevated circulating levels by beta-END-LI 5-fold over control levels by 30 min post-injection. Pretreatment (1 h) with 5 mg/kg, i.p., cinanserin, a serotonin receptor antagonist, completely blocked the quipazine-induced rise in beta-END-LI without affecting the elevated levels of beta-END-LI in haloperidol-treated animals. Conversely, pretreatment (2 h) with 1 mg/kg, i.p., bromocriptine, a dopamine receptor agonist, had no effect on quipazine-induced release of beta-END-LI but did completely prevent the rise in plasma beta-END-LI due to haloperidol treatment. Gel filtration chromatography revealed that quipazine and haloperidol treatments elevated plasma levels of both beta-END-size immunoreactivity and beta-lipotropin (beta-LPH)-sized immunoreactivity though to different relative degrees. However, since circulating levels of beta-LPH serve as a marker for anterior lobe (AL) beta-END-LI secretion, serotonin and dopamine appear to exert stimulatory and inhibitory control, respectively, over AL beta-END-LI release. Further, the quipazine-induced rise in total plasma beta-END-LI primarily resembled beta-LPH in size and was blocked by cinanserin but not bromocriptine pretreatment. And conversely, bromocriptine but not cinanserin prevented the haloperidol-induced rise in circulating beta-END-LI.(ABSTRACT TRUNCATED AT 250 WORDS)
D000818:Animals; D001921:Brain / Q000502:physiology*; D001971:Bromocriptine / Q000494:pharmacology; D002928:Cinanserin / Q000494:pharmacology; D004298:Dopamine / Q000502:physiology*; D004723:Endorphins / Q000378:metabolism*; D006220:Haloperidol / Q000494:pharmacology; D008297:Male; D010903:Pituitary Gland, Anterior / Q000378:metabolism*; D011814:Quipazine / Q000494:pharmacology; D051381:Rats; D012701:Serotonin / Q000502:physiology*; D009435:Synaptic Transmission; D001615:beta-Endorphin
D004723:Endorphins; D012701:Serotonin; D001971:Bromocriptine; D011814:Quipazine; D001615:beta-Endorphin; D006220:Haloperidol; D002928:Cinanserin; D004298:Dopamine