EFFECTS OF TWO SUBSTITUTED BENZAMIDES, TIAPRIDE AND SULTOPRIDE, ON GONADOTROPHINS AND PROLACTIN

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Abstract
The acute effects in the human of tiapride and sultopride, 2 new substituted benzamides related to sulpiride, were studied with respect to gonadotropins (LH [lutropin] and FSH [follitropin]) and prolactin (PRL) secretion. Two different groups of 3 normal men and 3 normally cycling women received i.m. injections of either 100 mg sultopride or 200 mg tiapride. Five min after the injection of either psychotropic drug, the serum PRL concentration increased significantly (P < 0.001 by variance analysis) and reached maximal values by 30 min and remained elevated for at least 6 h; women tended to release more prolactin than men. Although tiapride (500 nM) had no direct effect on the in vitro synthesis or secretion of prolactin, the drug blocked the inhibitory action of dopamine (500 nM) on the secretion of prolactin. Rats bearing a transplantable prolactin-secreting pituitary tumor MtTW15 have extremely high serum prolactin and through an autofeed mechanism the host''s pituitary gland is suppressed. The in vitro synthesis and secretion of prolactin by these rats'' pituitary gland is decreased. In vivo tiapride administration to these tumor-bearing rats restored the in vitro secretion of prolactin to control values. The in vitro data support the concept that tiapride increases prolactin secretion directly at the pituitary level by blocking the inhibitory activity of dopamine; an additional effect at a higher level can not be ruled out. In vivo in the human, no significant modification of LH and FSH occurred after either drug, suggesting that the menstrual cycle disturbances observed during chronic treatment with tiapride might be related to hyperprolactinemia or be the result of a mechanism similar to that inducing hyperprolactinemia.

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