Exogenous versus endogenous pulses of luteinizing hormone-releasing hormone and secretory patterns of gonadotropins.

OBJECTIVE: Does an exogenously administered regimen of luteinizing hormone-releasing hormone (LH-RH) pulses override endogenous LH-RH? DESIGN: Pulses of LH-RH were given intravenously during 1 week with intervals of 90 (n = 5) or 120 minutes (n = 5). Before, during, and after treatment serial plasma luteinizing hormone (LH) and follicle-stimulating hormone (FSH) patterns and pituitary responsiveness to LH-RH were estimated. PATIENTS: Women with virtual absence of gonadal function (postmenopause, gonadal dysgenesis, and premature menopause). RESULTS: During treatment with the 90-minute interval, no LH pulses that were not related to injections of LH-RH were observed. Two spontaneous LH pulses were observed during treatment with the 120-minute interval. Immediately after treatment, a lowered incidence of spontaneous LH pulses was seen of 3 pulses/6 h if LH-RH had been given every 90 minutes and to 1.5 pulses/6 h after the 120-minute interval treatment. Gonadotropin responses to 100 micrograms of LH-RH were attenuated during treatment but recovered within 48 hours after discontinuation of treatment. CONCLUSIONS: (1) Exogenously administered LH-RH can override endogenous LH-RH or its effects on the release of LH in women with hypergonadotropic hypogonadism; (2) during pulsatile LH-RH treatment desensitization of the pituitary occurs to some degree; and (3) immediately after cessation of treatment with pulsatile LH-RH, spontaneous LH pulses are present but with a significantly lower incidence.

The frequency of pulsatile luteinizing hormone-releasing hormone treatment and luteinizing hormone and follicle-stimulating hormone secretion in women with amenorrhea of suprapituitary origin.

The influence of luteinizing hormone-releasing hormone (LH-RH) pulse frequency on luteinizing hormone (LH) and follicle-stimulating hormone (FSH) was studied in hypogonadotropic hypogonadal women. They received three regimens of 5 days of pulsatile LH-RH (5 micrograms/pulse) given at 30-, 90-, or 180-minute intervals, with at least 6 weeks between treatments. On day 1, LH and FSH increased in proportion to the LH-RH pulse frequency. After 5 days of treatment with the 30- and 90-minute intervals, LH was still elevated, but FSH had returned to pretreatment levels together with a decline of the FSH response. The LH response only declined during treatment with the 30-minute pulse interval. During each treatment, estradiol (E2) increased. Explanations for dissociation between LH and FSH secretion during treatment with higher LH-RH pulse frequencies could be: (1) desensitization of FSH rather than LH secretion on LH-RH; (2) a differential effect of E2 on LH and FSH; (3) nonsteroidal ovarian factors selectively regulating LH and/or FSH release.

Short-term pituitary desensitization to luteinizing hormone-releasing hormone (LH-RH) after pulsatile LH-RH administration in women with amenorrhea of suprapituitary origin.

The existence of a short-term pituitary desensitization in luteinizing hormone (LH) release to single doses of luteinizing hormone-releasing hormone (LH-RH) in the ovariectomized rat was recently disclosed. The purpose of the present study was to investigate whether this refractoriness is also present in humans. Blood from six women with amenorrhea of suprapituitary origin was sampled every 10 minutes for 300 minutes for determination of LH and follicle-stimulating hormone (FSH). A pulse of 20 micrograms LH-RH was given intravenously 90 and 210 minutes after the first blood sample, and 2 micrograms LH-RH was given 30, 150, 240, and 270 minutes after t0. The mean maximal increments of LH and FSH were compared. The LH response to a 2-micrograms LH-RH bolus given 30 (t240) or 60 (t150) minutes after a 20-micrograms LH-RH pulse was significantly decreased, compared with the initial response to this dose at t30. For both LH and FSH, the response to 2 micrograms LH-RH given 30 minutes after the 20-micrograms pulse (t240) was almost absent, compared with 60 (t150) minutes after the 20-micrograms dose. We conclude that a short-term pituitary refractoriness to LH-RH is present after administration of single pulses of LH-RH in women with amenorrhea of suprapituitary origin and pulses of LH-RH in the physiologic range (2 micrograms) given to these women do not always generate LH and FSH increments that are identifiable as significant hormone pulses.

Short-term pituitary desensitization to LH-RH after pulsatile LH-RH in the ovariectomized rat: an in vivo experiment.

The development of acute insensitivity of pituitary LH secretion to LH-RH after a short exposure to LH-RH is described. In the first experiment, ovariectomized (OVX), phenobarbital-pretreated rats were given pulses of LH-RH (1.25 or 6.25 ng/100 g body weight (b.w.), intravenously). In rats given 1.25 ng at time 0, 6.25 ng at 60 min, 1.25 ng at 80 min and 1.25 ng at 120 min, there was a substantial increase in plasma LH after the first two injections, no increase after the third injection and a relatively small increase after the fourth one. In other rats treated identically but not given a 1.25-ng dose at 80 min, the plasma LH rise in response to the 1.25-ng dose at 120 min was comparable to that seen after the 1.25-ng dose given at time 0. If the 1.25-ng LH-RH pulses given at times 0 and 80 min were replaced by a rat pituitary extract, the plasma LH rise in response to the 1.25-ng dose at 120 min was comparable to that seen after administration of pituitary extract. In the second experiment, OVX phenobarbital-pretreated rats were given 1.25 ng LH-RH/100 g b.w. at t = 0. They were then divided into three groups, each receiving 1.25, 3.75 or 6.25 ng LH-RH/100 g b.w. at t = 60 min. Each of these three groups was again divided into three groups which received 1.25 ng LH-RH/100 g b.w. at 80, 100 or 120 min.(ABSTRACT TRUNCATED AT 250 WORDS)