Human Luteinizing Hormone in Serum During the Menstrual Cycle: Determination by Radioimmunoassay1

Human luteinizing hormone (LH) has been quantitated by radioimmunoassay in sera obtained daily from 11 subjects during 16 menstrual cycles. In each cycle, a brief surge in LH was found prior to the rise in basal body temperature. Peak serum LH concentrations, expressed in terms of the Second International Reference Preparation of Human Menopausal Gonadotropin, have ranged from 0.027 to 0.054 IU/ml. The concentration of serum LH was usually lowest at the onset of menstruation, followed by somewhat higher, relatively constant levels throughout the follicular phase. More variable LH levels were found in the luteal phase following the midcyclic peak. Sera were obtained throughout 5 cycles from 3 subjects who had a history of abdominal pain at midcycle. In each cycle, the pain was reported prior to, rather than after, the surge in LH.