| Abstract: | The effects of two consecutive LH-RH injections at 120 min intervals with either a varying first or second LH-RH dose on pituitary gonadotrophin response were investigated in 15 eugonadal women to study pituitary secretory processes. Each volunteer underwent a total of 4 LH-RH double stimulation tests. In group I (n = 8) the first LH-RH dose of each of the 4 tests was fixed at 25 microgram, whereas the second LH-RH dose consisted of either 6, 25, 100 or 400 microgram. In group II (n = 7) the first LH-RH dose varied between 6 and 400 microgram, while the second LH-RH dose was kept constant at 25 microgram. Serum gonadotrophin and serum ovarian steroid levels were determined by radioimmunoassay before and after LH-RH administration. The volunteers in both groups served as their own controls. A linear log-dose response relationship was found between the various doses of LH-RH injected and the corresponding LH and FSH elevations elicited. However, the dose of the first LH-RH injection also significantly influenced the gonadotrophin reaction after the second LH-RH injection in a linear log-dose response relationship. Serum levels of oestradiol, 17-hydroxyprogesterone and progesterone significantly increased in response to the elevated serum gonadotrophin levels after LH-RH stimulation during the 4 h test period, but the rise did not correlate to the LH-RH dose used. The results indicate that LH-releasing hormone stimulates not only the release, but also the synthesis of LH and FSH in a dose-related manner. These findings are consistent with our previously reported concept that the magnitude of LH and FSH response to the first LH-RH injection reflects the "storage capacity", while the increase observed after the second LH-RH injection represents the "synthesis capacity" of the gonadotrophs. |
