Effects of 5-hydroxytryptamine uptake blockers on the concentration in brain of 5-hydroxytryptamine and 5-hydroxyindoleacetic acid in male rats, pro-oestrous rats and ovariectomized rats treated with oestrogen and progesterone

Self Cite

The effect of the 5-hydroxytryptamine (5-HT) uptake blockers on the surges of LH and prolactin has been investigated in pro-oestrous rats and various experimental models used frequently to study the effects of steroids on LH and prolactin secretion in female rats. The steroid models were: rats ovariectomized on dioestrus, injected immediately with oestradiol benzoate (OB) and at 12.00 h on the next day (presumptive pro-oestrus) with progesterone (model 1); long-term ovariectomized rats injected with a single injection of OB and 72 h later with either progesterone (model 2) or OB (model 3); long-term ovariectomized rats injected daily with OB (model 4). The uptake blockers alaproclate (3-30 mg/kg) and zimelidine (20 mg/kg) were injected and blood samples withdrawn from previously implanted intra-atrial cannulae. Plasma LH and prolactin concentrations were determined by radioimmunoassay. The present study confirmed that a surge of LH occurs at about 17.00-18.00 h of the presumptive day of pro-oestrus in model 1, at about 5 h after (approximately 17.00 h) the injection of either progesterone or the second injection of OB in models 2 and 3, and diurnally in model 4, and the simultaneous occurrence of a prolactin surge in models 2 and 4. A surge of prolactin at the same time as the LH surge was shown to occur also in models 1 and 3. Alaproclate (30 mg/kg) administered at 15.00 h delayed significantly the peak of the prolactin surge in the pro-oestrous rat and models 1, 3 and 4, and in the latter the magnitude of the prolactin surge was also significantly reduced. By contrast, the peak of the prolactin surge in model 2 was significantly prolonged by alaproclate. Alaproclate had no significant effect on either the timing or the magnitude of the LH surge in the pro-oestrous rat, and models 3 and 4. The peak of the LH surge was delayed by alaproclate in model 1 and abolished in model 2, providing further evidence for the possible importance of interactions between 5-HT and progesterone in neuroendocrine control. Zimelidine had no significant effect on either the LH or prolactin surge in the pro-oestrous rat and in models 1 and 2. These results show that normal 5-HT uptake is necessary for the normal timing and/or magnitude of the spontaneous and steroid-induced prolactin surge but is not essential for the normal timing and magnitude of the spontaneous surge of LH and the LH surge in some but not all steroid models.(ABSTRACT TRUNCATED AT 400 WORDS)

Section: Discussionmentioning

confidence: 51%

Effects of 5-hydroxytryptamine uptake blockers on the release of LH and prolactin in several different experimental steroid models in the rat

Horn¹,

Fink²

1985

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“…This effect of pCPA, however, was not confirmed by Horn & Watts (1985). We have shown that restoration of serotonin synthesis by 5-hydroxytryptophan, which does not reverse the inhibitory action of pCPA on dopamine synthesis (Coen et al 1983), depressed pro¬ lactin release.…”

Section: Discussionmentioning

confidence: 73%

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

Jahn¹,

Deis²

1987

The effect of para-chlorophenylalanine (pCPA), an inhibitor of serotonin synthesis, on prolactin release was studied in rats on the day of pro-oestrus and at the end of pregnancy (day 19). The surges of prolactin normally seen in the afternoon of pro-oestrus in intact rats and in rats ovariectomized on dioestrous day 2 and primed with oestrogen were significantly inhibited by pCPA treatment. Administration of 5-hydroxytryptophan reversed the inhibitory action of pCPA on prolactin release. Treatment with progesterone also completely reversed the inhibitory effect of pCPA on prolactin release in pro-oestrous rats and partially reversed it in ovariectomized oestrogen-treated rats. Ovariectomy on day 19 of pregnancy induced a significant release of prolactin 12 and 24 h later. Administration of pCPA on day 18 of pregnancy produced a marked increase in serum concentrations of prolactin on days 19 and 20 in rats left intact or ovariectomized on day 19. Administration of 5-hydroxytryptophan significantly reversed this stimulatory effect of pCPA on prolactin release but did not modify the release of prolactin induced by ovariectomy. Methiothepin (1-[10,11-dihydro-8-(methylthio) less than b,f greater than thiepin-10,41]-4-methylpiperazine maleate), a serotonin receptor blocker, also induced a significant increase in serum concentrations of prolactin on day 20 of pregnancy in rats left intact or ovariectomized on day 19. These results suggest the existence of different serotoninergic actions in the regulation of prolactin release at pro-oestrus and in late pregnancy. Serotonin facilitates the surges of serum prolactin released at pro-oestrus and in ovariectomized rats treated with oestrogen; progesterone enhances this effect.(ABSTRACT TRUNCATED AT 250 WORDS)

“…These results demonstrate that 5-HT stimulates gonadotrophin release by acting directly on LHRH terminals in the median eminence from pro-oestrous INTRODUCTION A physiological role for serotonin (5-HT) in the regulation of gonadotrophin secretion has frequently been suggested (Weiner & Ganong, 1978;Coen & MacKinnon, 1979;Biegon, Bercovitz & Samuel, 1980;Marko & Flückiger, 1980;Walker, 1980Walker, , 1983Horn & Fink, 1985;Horn & Watts, 1985), but has not yet been definitively established.…”

mentioning

confidence: 99%

Serotonin induces gonadotrophin release through stimulation of LH-releasing hormone release from the median eminence

Vitale¹,

Parisi²,

Chiocchio³

et al. 1986

The effects of serotonin (5-HT) on the release of gonadotrophins and LH-releasing hormone (LHRH) were examined in an in-vitro perifusion system using median eminences and/or anterior pituitaries obtained from male or pro-oestrous female rats. Animals were killed by decapitation between 12.00 and 13.00 h. A serial double-chamber perifusion system was employed. Three types of experiments were performed. In the first, median eminences were placed in the first chamber and one anterior pituitary in the second chamber. In the second group, only the anterior pituitary was perifused. In the third group, only five median eminences were perifused. In the first and second experiments, LH, FSH and prolactin were determined in the perifusion efflux by radio-immunoassay (RIA). In the third experiment, LHRH was determined by RIA. Addition of 5-HT (final concentrations 0.06, 0.6 and 6.0 mumol/l) into the first chamber containing the median eminences stimulated the release of LH and FSH from the pituitary, but did not affect the levels of prolactin in the effluent in the same experiment (pro-oestrous rats). The stimulatory effect of 5-HT was blocked by the addition of cyproheptadine (l mumol/l) in the perifusion fluid. The introduction of 5-HT (0.6 mumol/l) into the tube connecting the first and second chambers did not modify the release of LH, nor did 5-HT added to the pituitaries perifused alone.(ABSTRACT TRUNCATED AT 250 WORDS)