Studies on Autoregulation of Prolactin Secretion from Perifused Rat Pituitary Glands in the Basal and Thyrotropin-Releasing Hormone-Stimulated States*

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Abstract
In order to evaluate autoregulation of PRL [prolactin] secretion at the pituitary gland, spontaneous and TRH[thyrotropin releasing hormone]-stimulated PRL secretion was determined in an isolated anterior pituitary (AP) perifusion system utilizing normal and chronically hyperprolactinemic MtTW 15 [rat pituitary tumor] tumor-bearing) male rat pituitaries. Decreased AP weight in chronically hyperprolactinemic rats [5.7 .+-. 0.1 SE vs. 7.2 .+-. 0.2 mg in controls, P < 0.001] was associated with lower mean basal PRL secretion compared to controls (9.9 .+-. 1.8 vs 20.6 .+-. 2.7 ng/min per AP, P < 0.01). PRL secretion from normal AP was not altered by addition of ovine PRL (oPRL) at 10 or 100 ng/ml (19.9 .+-. 3.8 and 19.2 .+-. 2.9 ng/min per AP, respectively). TRH-stimulated PRL secretion from normal AP in the absence of oPRL was 133 .+-. 7% of baseline (designated as 100%) and this did not differ from the response observed in the presence of 10 or 100 ng/ml oPRL (134 .+-. 9 and 133 .+-. 7%, respectively). Basal PRL secretion from tumor rat AP was likewise unaffected by the presence of medium oPRL (9.9 .+-. 1.8 in the absence of oPRL and 10.0 .+-. 1.9 ng/min per AP in the presence of 100 ng/ml oPRL). TRH-stimulated PRL secretion from tumor rat AP was 149 .+-. 10% of baseline in the absence of medium oPRL and 140 .+-. 7% in the presence of 100 ng/ml oPRL (P > 0.10). Autoregulation of PRL secretion may exist, and this regulation may not be mediated directly at the pituitary gland but rather at higher, possibly hypothalamic, centers.

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