Pituitary response to LHRH in hypothyroid women

This study was designed to characterize pituitary function in premenopausal women during hypothyroid and euthyroid periods. Six subjects with basal thyroid-stimulating hormone (TSH) levels above 10 microU/ml were studied. Estradiol (E2), prolactin (PRL), follicle-stimulating hormone (FSH), and luteinizing hormone (LH) levels were measured by radioimmunoassay at 30, 15, and 0 minutes before infusion. Pituitary function was evaluated by rapid infusion of 10 micrograms of luteinizing hormone-releasing hormone (LHRH) every 2 hours for a total of 6 hours. Samples were then obtained for FSH and LH every 30 minutes for the duration of the 6-hour study. A significant elevation in basal gonadotropins was observed during the hypothyroid period regardless of basal E2 levels in all 6 subjects (P < .01). Basal PRL levels were not significahtly different during the 2 periods (P > .05). In all 6 patients pituitary sensitivity and reserve correlated significantly with basal E2 levels (P < .05), but were not altered by the hypothyroid condition. It is concluded that pituitary responsiveness to LHRH is not altered in hypothyroid women, but that chronic elevation of basal gonadotropins may in part explain the anovulation that so often accompanies this disorder.