Serotonin stimulates prolactin secretion in the hypophysectomized adenohypophyseal grafted rat.

Normal male, oestrogen (F2) primed male and hypophysectomized adenohypophyseal grafted male rats (HAG rats) were used in the experiments. Serotonin creatinine sulphate was injected as a bolus via an indwelling atrial cannula in the conscious free moving rat. Serotonin caused a dose-dependent increase in plasma prolactin (Prl) in normal (1, 3 and 10 mg/kg serotonin) and E2 primed (1 and 3 mg/kg serotonin) male rats that began immediately after injection and reached a peak within 12-15 min of injection. Oestrogen priming significantly increased the magnitude of the response to serotonin. To analyze the site of action of serotonin in the rat, serotonin (1 mg/kg) was injected into HAG rats. Serotonin increased plasma Prl in this rat preparation, indicating that serotonin acts directly on the ectopic pituitary.