Comparison of single and repeated applications of a long-acting synthetic analogue of LHRH [D-Ser (TBU)6 EA10 LHRH] in the assessment of pituitary gonadotrophin secretory capacity.

Abstract

SUMMARYA long‐acting synthetic analogue of LHRH [D‐Ser (TBU)6 EA10 LHRH] was administered intramuscularly to thirteen normal women in the early‐to‐mid follicular phase of the menstrual cycle. Six women received a single injection of 5 μg of analogue and seven received 10 μg of the analogue, followed by 20 and 10 μg at 10 and 24 h after the first injection, respectively. The concentrations of LH, FSH and oestradiol in plasma were measured before, and at intervals up to 72 h after treatment. In the group receiving 5 μg of analogue the concentrations of both LH and FSH rose rapidly to a peak value five times the pre‐injection value, 5 h after injection. The concentrations of both gonadotrophins remained elevated for 10 h, but 24 h after injection had returned to control values. The concentration of oestradiol rose progressively to reach a peak value 7 h after injection. In the second group of women, receiving three injections of analogue, there was a rapid twelvefold increase in the concentration of LH in plasma within 4 h of the initial injection, and plasma concentrations remained elevated for 10 h. The concentration of FSH rose progressively to a peak value, five times the pretreatment value, 5 h after the initial injection and was still elevated after 10 h. The concentrations of both gonadotrophins remained elevated above pretreatment values for at least 34 h after the start of treatment. The concentration of oestradiol rose gradually to a peak value 7 h after the initiation of treatment and remained elevated for 34 h. These results indicate that a single injection of the LHRH analogue is effective in demonstrating pituitary secretory activity, but repeated applications are required to induce and maintain a rise in plasma LH similar in magnitude and duration to the pre‐ovulatory, mid‐cycle surge. This analogue of LHRH provides a simple means of evaluation of the secretory capacity of the anterior pituitary.