Parachlorophenylalanine blocks the spontaneous pro-oestrous surge of prolactin as well as LH and affects the secretion of oestradiol-17β

Abstract

The effect of the 5-hydroxytryptamine synthesis inhibitor, parachlorophenylalanine (PCPA), on the spontaneous, pro-oestrous surges of prolactin and LH was investigated in conscious female rats implanted with an intra-atrial cannula. The LH surge was blocked in all animals treated with PCPA, but the prolactin surge was blocked in six out of ten animals and unaffected in four out of ten animals. There was a significant correlation between the plasma concentrations of prolactin and oestradiol-17 beta, surges of prolactin occurred in animals with plasma oestradiol-17 beta concentrations of 120 pmol/l and above, and the LH surge was blocked in animals in which the oestradiol-17 beta concentration was less than 188 pmol/l plasma. These results show that (i) PCPA can block the pro-oestrous prolactin as well as the LH surge, (ii) in addition to a central action PCPA may depend also on its peripheral effect on the secretion of oestradiol-17 beta and (iii) on average, lower plasma concentrations of oestradiol-17 beta are required for triggering the prolactin compared with the LH surge.

A possible dual regulation of prolactin release by the serotoninergic system in rats at pro-oestrus and during late pregnancy: role of ovarian hormones

“…1). It has been shown by others that pCPA can block the pro-oestrous surges of prolactin and LH (Walker & Wilson, 1983;Horn & Fink, 1985) and also the surges of both hormones induced by administration of oestrogen or oestrogen plus progest¬ erone to chronically ovariectomized rats (Caligaris & Taleisnik, 1974;Coen & McKinnon, 1979;Iyengar & Rabii, 1983;Walker & Wilson, 1983;Meyer &Eadens, 1985). This effect of pCPA seems to be mediated by serotonin depletion or by the disappearance of the daily rhythm of serotonin (Walker & Wilson, 1983;Walker, 1984).…”

“…Never¬ theless, Horn & Fink (1985) found that administration of pCPA decreased oestradiol production by the ovar¬ ies in pro-oestrous rats, which could explain, at least partially, the inhibitory action of this drug on prooestrous prolactin release, which is oestrogen depend¬ ent. This possibility, however, may be discounted because pCPA was equally effective in inhibiting the oestrogen-induced prolactin surge in the rats ovari¬ ectomized on dioestrous day 2 (Fig.…”

“…Thus the administration of serotonin or its precursors and agonists increases serum concentrations of prolactin (Lu & Meites, 1973;Lawson & Gala, 1976Subramanian & Gala, 1976;Clemens, Sawyer & Cerimele, 1977;Ruszas, Limonta & Martini, 1982). Moreover, inhibitors of serotonin synthesis, serotonin neurotoxins or seroto¬ nin receptor blockers inhibit prolactin release at prooestrus or prolactin release induced by oestrogens or suckling (Caligaris & Taleisnik, 1974;Clemens, 1978;Clemens, Roush & Fuller, 1978; Moltz, 1978a; Garthwaite & Hasen, 1979;Horn & Fink, 1985).…”

Serotonergic 5‐HT2A Receptors Important for the Oestradiol‐Induced Surge of Lusteinising Hormone‐Releasing Hormone in the Rat

“…(1, [12][13][14][15]. While some earlier studies suggested that 5-HT inhibits LH release, the majority of data suggest that 5-HT eously ovulating mammals is triggered by a spontaneous surge of LH releasing hormone (LHRH ) which, in the rat, plays a major role in stimulation of the LH surge (14)(15)(16)(17)(18)(19). The apparent discrepancy between 5-HT inhibition and 5-HT occurs on the afternoon of pro-oestrus.…”

Rates of Release of GABA and Catecholamines in the Mediobasal Hypothalamus of Ovariectomized and Ovariectomized Estrogen-Treated Rats: Correlation with Blood Prolactin Levels

“…data]. Re cently Horn and Fink [11] also demonstrated that low blood levels of estrogen stimulate only a prolactin surge, whereas higher levels of the steroid are required to induce both, a prolactin and LH surge. The failure of the estrogen treatment used in the present study to induce LH surges is not due to a traumatization of the hypothalamus, be cause estrogens, when given subcutaneously, were able to induce LH surge in push-pull-cannula-implanted ani mals [3].…”