Serotonin stimulates gonadotrophin release by acting directly on the median eminence

The study examined the effect of serotonin (5-HT) on gonadotrophin release and its tissue site of action using a sequential double chamber perifusion system. Cycling female rats were killed between 12.00 and 13.00 h on the day of proestrus. Median eminences and anterior pituitaries were removed and transferred to perifusion chambers. Two types of experiments were performed: a) five median eminences (ME) were placed in the first chamber and one anterior pituitary in the second chamber. b) In the second group, only the anterior pituitary was perifused. The effluent from the first chamber perifused the second chamber. The effluent from the second chamber was collected for hormone assays. Addition of serotonin (final concentration 0.06, 0.6 and 6.0 uM) stimulated the release of LH and FSH into the perifusion fluid draining the pituitary in series with the median eminences. Pretreatment with the 5-HT receptor blocker cyproheptadine (1 uM) completely inhibited the stimulatory effect of 5-HT. Serotonin was ineffective in stimulating gonadotrophin release when injected into the tube connecting the first and the second chambers (50 ul of 0.6 uM solution) or when the anterior pituitary was perifused alone. Serotonin did not affect the prolactin release in any of the experimental conditions studied. These observations demonstrate that serotonin stimulated the gonadotrophin release by acting on serotoninergic receptors at the level of the median eminence.