Winfried Rossmanith

Relative changes in LH pulsatility during the menstrual cycle: using data from hypogonadal women as a reference point.

The basic premise of this study is that the GnRH‐LH pulsatile activity, particularly its frequency characteristics, constitutes, in the absence of any considerable ovarian feedback, the intrinsic rhythm of the hypothalamic‐pituitary unit at its maximal rate. Thus, LH pulse attributes determined in postpubertal hypogonadal subjects may be used as a reference in assessing the degree of influence exerted by endocrine factors that modulate GnRH‐LH pulses. Accordingly, serum LH levels were determined in samples obtained at 15‐min intervals for 24 h in 20 hypogonadal women: 13 postmenopausal women (PMW) and seven women with premature ovarian failure (POF). Similar measurements were performed in 60 normally cycling women: 25 in the early follicular phase (EFP), 13 in the late follicular phase (LFP), seven at midcycle surge (LH surge) and 15 in the midluteal phase (MLP). Significant pulses were identified by the cluster algorithm utilizing factors appropriate for 24 h data series of a sampling frequency of 15‐min intervals. The results show a 24‐h mean (± SE) LH pulse frequency of 78.2±2.8 and 85.5±2.4 min per pulse for young (POF) and older (PMW) hypogonadal women, respectively. During the follicular phase of the cycle, the LH pulse frequency is not significantly different from that of hypogonadal women, but there is a significant (P < 0.05) increase from early to late follicular phases (95.4±3.3 vs 78.8±2‐2 min per pulse). However, when the sleep periods are excluded from the 24‐h data series because of the associated decrease of LH pulse frequency in EFP women, the resulting pulse frequencies are almost identical for EFP, LFP and PMW. An elevation beyond the basic pulse rhythm determined in PMW or POF is not observed in any phase of the menstrual cycle studied, including the midcycle surge. The decrease in LH pulse frequency during the luteal phase of the cycle (151.8±8.0 min per pulse, P < 0.001 vs hypogonadal women) beyond the reference pulse frequency of hypogonadal women is unequivocal. By contrast, the pulse amplitude varies markedly among the groups with the largest found in POF (36.6±4.5 IU/1). It follows, in descending order, PMW (22.7±3.1 IU/1), midcycle surge (17.3±2.8 IU/1), MLP women (7.0±1.3 IU/1) and the EFP (4.9±0.3 IU/I) and LFP (4.0 ±0.4 IU/I). These data support the concept that the changes in the LH pulse frequency during the menstrual cycle can be reduced, but do not exceed the periodicity of the basic rhythm of the GnRH‐LH pulse generator determined in hypogonadal women. Our observations also demonstrate that the pulse amplitude is subject to profound modulation by ovarian factors. Thus, the basic rhythm of GnRH‐LH pulses may serve as a meaningful reference in assessing influences by endocrine factors on GnRH‐LH pulsatile activity.

Gonadotropin Secretion during Aging in Postmenopausal Women

Although chronological aging is known to result in reduced gonadotropin secretion in women, the precise mechanisms to account for this neuroendocrine manifestation are yet obscure. To evaluate the extent to which the pituitary and/or hypothalamus are involved in the process of aging, we aimed at characterizing the unstimulated and GnRH-stimulated gonadotropin secretion in postmenopausal women (PMW) of different ages. Accordingly, 9 younger PMW (mean age: 53.8 years) in their first and 9 older PMW (mean age: 80.3 years) in their 4th decade of life after natural onset of menopause were studied. In both groups, blood was collected at 10-min intervals for 10 h, while GnRH (25 micrograms i.v.) was administered 8 h after initiation of blood samplings. Compared to younger PMW, basal serum concentrations of dehydroepiandrosterone-sulfate were lower (p less than 0.05) in older PMW, while estrogen (estradiol, estrone), androgen (testosterone, androstendione) and sex hormone binding globulin levels were similar. Lower (p less than 0.01) mean LH levels composed of attenuated (p less than 0.05) LH pulse amplitudes and pulse frequencies (as determined by the cluster pulse algorithm) were found in the 8-hour LH secretory profiles of older PMW. Furthermore, the FSH secretion of older PMW was characterized by lower (p less than 0.01) mean FSH levels with lower (p less than 0.05) FSH pulse amplitudes, but not pulse frequencies. The absolute peak concentrations attained and the total amount of LH and FSH released in response to GnRH stimulations were blunted (p less than 0.001) in older PMW.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuroendocrinology of Aging in Humans: Attenuated Sensitivity to Sex Steroid Feedback in Elderly Postmenopausal Women

Studies in experimental animals have shown that the sensitivity of the hypothalamic-pituitary system to ovarian sex steroid feedback declines while aging progresses. Since similar observations are lacking in humans, we studied the gonadotropin secretion of postmenopausal women (PMW) of different ages before and following a 7-day course of oral clomiphene citrate (CC, 100 mg daily). For serial determinations of serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels, blood was sampled frequently from 5 younger PMW (mean age 55.2 years) and 6 older PMW (mean age 80.3 years) for 10 h. Eight hours after initiation of blood sampling, gonadotropin-releasing hormone (GnRH, 25 micrograms) was administered. Compared to untreated conditions, CC administration did not significantly change the serum concentrations of the estrogens (estrone, estradiol) and androgens (testosterone; androstenedione, dehydroepiandrosterone sulfate). However, CC increased the sex hormone-binding globulin levels in both younger and older PMW, suggestive of the estrogenic effects of this compound. In the unstimulated secretory profiles of younger PMW, mean LH levels decreased (p < 0.05) in response to CC, presumably a consequence of decreased (p < 0.05) pulse frequencies, but not pulse amplitudes. Likewise, by virtue of decreased (p < 0.05) FSH pulse amplitudes, FSH levels declined (p < 0.05) in younger PMW. In contrast, both the LH and FSH levels and their pulsatility remained virtually unaltered following CC administrations to older PMW. The GnRH-mediated gonadotropin release was uneffected by CC administrations in either group of PMW.(ABSTRACT TRUNCATED AT 250 WORDS)

SECRETORY DYNAMICS OF OESTRADIOL (E2) AND PROGESTERONE (P4) DURING PERIODS OF RELATIVE PITUITARY LH QUIESCENCE IN THE MIDLUTEAL PHASE OF THE MENSTRUAL CYCLE

Although the temporal relationship between pulsatile pituitary luteinizing hormone (LH) secretion and steroid hormone release from the corpus luteum has been investigated, the secretory profiles of oestradiol (E2) and progesterone (P4) during periods without any discernible LH pulsatile activity remain unknown. Consequently, blood was sampled at 15‐min intervals for 24 h from 16 women during the midluteal phases (6–8 days after midcycle LH surge) of their cycles. LH was measured in all samples and analysed for significant pulses by the Cluster pulse algorithm. Nine studies showing the lowest LH pulse frequencies and large LH pulse amplitudes were also assessed for E2 and P4 in all samples. All three hormones were released in pulsatile fashions. Pulses of E2 and P4 were found to be synchronous. While the release frequencies for E2 (mean±SEM: 8.9±0.7 pulses/24 h) and P4 (8.5±0.7 pulses/24 h) were comparable, the LH pulse frequency (4.6 ±0.4 pulses/ 24 h) was found to be significantly (P< 0.001) lower than the ovarian steroid pulse frequencies. Maximum (P<0.01) cross‐correlation coefficients were determined at positive time lags of 28.1 ± 7.7 min for LH/E2 and 31.7 ± 5.8 min for LH/P4, indicating that changes in E2 or P4 levels tended to occur within approximately 30 min following LH concentration changes. Further, the degree of concomitance between a steroid pulse and an LH peak was much higher (P< 0.001) than by chance. Maximum (P<0.01) cross‐correlation coefficients between E2 and P4 hormonal data series were found at zero time lag, suggesting that these sex steroids were secreted simultaneously. The pulse amplitudes, pulse durations and areas under the peaks of those E2 or P4 pulses preceded by large (> 5IU/1) amplitude LH pulse were significantly greater (P<0.05 or less for all comparisons) than for steroid pulses not associated with preceding LH pulses. Thus, two populations of steroid pulses were observed; one associated with preceding LH pulses and having greater magnitude of all pulse attributes (duration, amplitude, area under the peaks), and another, not associated with preceding LH pulses and having pulse characteristics of lower magnitude. This observation suggests that the pulsatile release of ovarian steroids is a result of the episodic modulating influence of LH and that pulsatile steroid hormone secretion pertains with smaller magnitude during periods of relative pituitary quiescence of LH pulsatility.

Effects of Dopaminergic Blockade on the Sleep-Associated Changes of Luteinizing Hormone Pulsatility in Early Follicular Phase Women

To investigate the dopaminergic role in the sleep-associated changes of luteinizing hormone (LH) pulsatile pattern, 11 normal cycling women were studied in the early follicular phase (EF, days 3 and 4) of their cycles before and after the administration of metoclopramide (MCP), a dopamine receptor antagonist. Twenty-four-hour infusions of either saline (NaCl 150 mmol/1-50 ml/h) or metoclopramide (MCP, 30 micrograms/kg/h) were conducted in a random sequence. Pulsatile LH activities were assessed in blood samples obtained at 15-min intervals for 48 h. Sleep was electrophysiologically confirmed by EEG during night hours (23.00-07.00 h). Significant sleep-associated decreases in LH pulse frequency (p less than 0.05) and mean LH serum levels (p less than 0.001) with a concurrent increase in LH pulse amplitude (p less than 0.01) were observed during the saline control studies. MCP infusion failed to significantly modify the LH pulsatile activity during either the wake or sleep periods. In particular, it did not prevent the changes in LH pulsatility during sleep. This observation suggests that a dopaminergic mechanism does not critically contribute to the sleep-related changes in LH pulsatile activity in women during the early follicular phase.

Synchronous Pulsatile Release of Luteinizing Hormone and Immunoreactive Beta-Endorphin from the Human Pituitary in vitro.

An in vitro perifusion system employing very frequent (30 s) perifusate collectionswas utilized to investigate the relationship between pulsatile release of luteinizing hormone (LH) and immunoreactive β‐endorphin (iβ‐END) during individual perifusions of adult human anterior hemipituitaries. Each of six hemipituitaries released LH and iβ‐END in a distinctlypulsatile fashion, with pulses occurring approximately every 3.2 min for each. Power spectral analysis revealed that pulsatile release of both LH and iβ‐END occurred in a rhythmic pattern, with a periodicity of 3.1 and 3.2 min, respectively, and that the periodicity of pulsatile LH and iβ‐END release was correlated within individual perifusions. Moreover, the relative amplitudes (% change) of the synchronous LH and iβ‐END pulses were correlated. The effluent fractions from two of the perifusions were also assessed for thyrotropin, and it was determinedthat thyrotropin pulses were synchronized to both LH and iβ‐END pulses. These studies confirm that LH and iβ‐END are released from human anterior pituitaries in vitro in an intrinsically pulsatile fashion, and demonstrate that the LH and iβ‐END pulses tend to occur rhythmically and in synchrony and proportion with each other. Furthermore, correlation of thyrotropin pulses to both the LH and iβ‐END pulses suggests a common fundamental intrapituitary pulse generating mechanism.

PULSATILE GNRH-STIMULATED LH RELEASE FROM THE HUMAN FETAL PITUITARY IN VITRO : SEX-ASSOCIATED DIFFERENCES

An in‐vitro perifusion system was utilized to examine LH release from human fetal (19–24 weeks gestation) anterior pituitaries during repetitive GnRH stimulations. Pituitaries (five male, four female) were dissected into halves, and one hemipituitary of each pair was stimulated with 10‐min pulses of 1 nm GnRH administered at 60‐min intervals over 24h, whereas the matching hemipituitary received pulses of medium alone. Basal (no GnRH stimulation) LH release from female hemipituitaries was significantly (P < 0.01) greater than from male hemipituitaries, and the amplitude of LH release associated with GnRH pulses was sixfold greater (P < 0.001) with female hemipituitaries. Furthermore, the magnitude of LH release associated with individual GnRH pulses was significantly (P < 0.001) enhanced during the course of female hemipituitary perifusions, but not during perifusion of male hemipituitaries. These studies demonstrate that LH secretion by the female, but not male, mid‐gestational human fetal pituitary is increased in response to a physiological pattern and interval of repeated pulsatile GnRH stimulation in vitro.

Effects of acute hyperprolactinemia on LH pulsatile secretion in hypogonadal and early follicular phase women

To investigate the effects of acute hyperprolactinemia on the 24 h LH pulsatile pattern, 11 women in the early follicular phase (EF, days 3 and 4) and 8 postmenopausal women (PMW) were studied before and during administration of metoclopramide, a dopamine receptor antagonist. Sequential 24 h infusions of either metoclopramide (MCP, 30 micrograms/kg/h) or normal saline were conducted and pulsatile LH activity assessed for 48 hrs. In both EF women and PMW, a prompt (within 90 min, p less than 0.001) and sustained (greater than 45 micrograms/L, p less than 0.001) release of PRL was induced by MCP infusions. MCP-induced hyperprolactinemia failed to modify the LH pulsatile activity in both EF women and PMW. These observations suggest that acute hyperprolactinemia due to dopaminergic blockade has no discernible effect on LH pulsatility and that the reduced LH pulse frequency observed in association with endogenous hyperprolactinemia may result from different neuroendocrine mechanism(s) and/or is time dependent.