Mechanism of the Effects of Hypothalamic Deafferentation on Prolactin Secretion in the Rat¹

Abstract

Male rats with complete hypothalamic deafferentation had consistently lower serums prolactin concentrations than controls when the blood samples were obtained under other anesthesia. However, when rats were decapitated, both groups had similar low prolactin levels. Posterolateral deafferentation was as effective as complete deafferentation in preventing the stress-induced prolactin release, whereas anterior frontal deafferentation had only a small effect, L-Dopa (100 mg/kg body wt, ip) decreased prolactin titers in both control and deafferented animals, whereas reserpine (1 mg/kg body wt, ip) had the opposite effect. Since both drugs inhibited prolactin release from pituitaries in vitro, the decrease of prolactin levels following L-dopa in vivo might have been caused not only by stimulation of PIF release but also at least partly by the direct effect of the drug on the pituitary. However, the increase of serum prolactin following reserpine was in all probability caused by inhibition of PIF secretion. Electrolytic lesions in the median eminence of deafferented rats caused an elevation of serum prolactin which was more marked in female than in male rats. On the contrary, deafferentation in the females affected prolactin levels less than in males. It is concluded that hypothalamic deafferentation prevents ether-induced release of prolactin and that the "low" levels of the deafferented animals are probably due to a tonic release of prolactin-inhibiting factor (PIF) from the isolated island. It is though that this continuous release of PIF might be maintained by persisting autonomous activity of the adrenergic, presumably dopaminergic, neurons contained in the isolated island.

Effect of Aromatizable Androgens and Estradiol on Prolactin Secretion in Prepuberal Male Rats

“…Castration slightly decreases [13,151 or has no effect on serum prolactin levels in male rats [7,111. Castration of prepuberal rats for 10 days did not alter serum prolactin levels in this study.…”

“…Increasing evidence has accumulated over the past several years indicating that testosterone can stimulate prolactin secretion in intact or castrated rats [6,7,13,141 and in juvenile rhesus monkeys [5]. Indirect evidence to this effect has also been obtained in man [4, 121.…”

Effect of Partial Deafferentation of the Hypothalamus on Stress-Induced LH Suppression and Prolactin Release

“…Previously, we reported a biphasic effect of immobilization on prolactin release; an early stimulatory phase and late inhibitory phase [16]. Although Received: May 30, 1980 Accepted after revision: November 19,1980 there are some reports which suggest neural pathways medi ating stress information to the mediobasal hypothalamus [21, 33], the pathway is not still clear for prolactin release in response to stress. In this experiment we attempted to elu cidate the neural pathways responsible for the inhibitory in fluence of the immobilization stress on LH secretion and the stimulatory effect on prolactin secretion in ovariectom ized rats by using a neural deafferentation technique with Halasz' s knife [12],…”

The Physiological Role of Thyrotropin-Releasing Hormone in the Regulation of Thyroid-Stimulating Hormone and Prolactin Secretion in the Rat

“…It is well established that Prl secretion is tonically suppressed by dopamine either by a direct effect on the pituitary or by modulating the release of the Prl inhibiting factor. Median eminence and pituitary stalk lesions usually enhance rather than suppress Prl secretion (11,12), although this is not always observed in unstressed rats after hypothalamic deafferentation (13). In intact animals, electrical stimulation of the hypothalamic "hypophysiotropic area" (14) has been shown to increase serum TSH levels (10,15), presumably secondary to TRH release, although direct experimental evidence of enhanced TRH release is lacking.…”