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 radioimmunoassay (RIA). In the third experiment, LHRH was determined by RIA.
Addition of 5-HT (final concentrations 0·06, 0·6 and 6·0μmol/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 (prooestrous rats). The stimulatory effect of 5-HT was blocked by the addition of cyproheptadine (1 μmol/l) in the perifusion fluid. The introduction of 5-HT (0·6 μmol/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.
Injection of 5-HT into the first chamber (median eminences), containing tissue samples from male rats, stimulated LH release, but to a significantly (P< 0·001) lower degree than that found when samples from pro-oestrous females were used (P< 0·0001).
When median eminences from pro-oestrous rats were perifused alone, injection of 5-HT produced an immediate release of LHRH which peaked during the first 10 min of collection and lasted for 30 min; in these experiments, a clear relationship existed between dose of 5-HT and release of LHRH (P<0·02). The stimulatory effect of 5-HT was blocked by the addition of cyproheptadine (5 μmol/l) or methiothepin (5 μmol/l).
These results demonstrate that 5-HT stimulates gonadotrophin release by acting directly on LHRH terminals in the median eminence from pro-oestrous rats. Furthermore, the effect of 5-HT on LHRH release was dose dependent and was nullified by 5-HT receptor blockers (cyproheptadine and methiothepin).
J. Endocr. (1986) 111, 309–315
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