Prolactin responses to hypoglycemia and thyrotropin-releasing hormone in anorexia nervosa

Although prolactin (PRL) responses to thyrotropin-releasing hormone (TRH) have been described by many investigators, PRL secretion after insulin stimulation has rarely been documented in patients with anorexia nervosa (AN). We investigated PRL responses to TRH (500 micrograms) and insulin (0.1 U/kg) in 19 women with AN and 10 normal women. Levels of PRL stimulation at 60 min and later following insulin administration were significantly lower in AN than in normal women. PRL increased by at least 10 micrograms/ml after insulin in 42% of women with AN and in 70% of normal women. The maximum PRL increase (max delta PRL) did not differ after the two stimulations in the normal women. However, in AN, the max delta PRL after insulin stimulation (17.2 +/- 4.0 micrograms/l, mean +/- SEM) was significantly lower than that after TRH (49.1 +/- 6.4 micrograms/l). These findings suggest that anorectic women may have a disturbance in hypothalamic functions. Insulin-induced hypoglycemia is useful to determine the integrity of the hypothalamic-pituitary axis for PRL secretion, in combination with TRH stimulation.