Increased gonadotropin responsiveness to gonadotropin-releasing hormone during fasting in normal subjects

To investigate whether food deprivation affects hormone release from pituitary gonadotrophs, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) responses to intravenous (IV) administration of 50 micrograms gonadotropin-releasing hormone (GnRH) were determined in 12 healthy subjects (six women and six men) after an overnight fast and after a fasting period of 56 hours. In the female participants, these GnRH tests were performed early in the follicular phase of the menstrual cycle. Blood glucose declined during the fast from 4.4 +/- 0.1 (mean +/- SEM) to 3.3 +/- 0.1 mmol/L (P less than .001). LH and FSH responsiveness to GnRH--as reflected by hormone incremental areas--increased from 1973 +/- 256 to 3267 +/- 450 (IU/L X min) for LH (P less than .001), and from 376 +/- 44 to 705 +/- 112 (IU/L X min) for FSH (P less than .01). When control studies were carried out in nonfasted subjects in exactly the same way as in the fasted participants, the gonadotropin responsiveness to GnRH did not change significantly between the tests. To explore possible mechanisms behind the increased gonadotropin responsiveness in fasted subjects, six of the above mentioned healthy women were given nine small oral doses of glucose (each dose 0.5 g/kg) during an additional 56-hour fast to prevent blood glucose from falling significantly during the period of food deprivation. This did not change the hormone response pattern at all, since both the LH and the FSH responses to GnRH increased significantly during the glucose-supplemented fasting period.(ABSTRACT TRUNCATED AT 250 WORDS)