The effect of aging on hypothalamic function in oophorectomized women

Aging attenuates the pituitary response to gonadotropin-releasing hormone

CONTEXT

Complex changes in GnRH secretion occur with aging in women, but little is known about the effect of aging on the pituitary per se.

OBJECTIVE

The aim of the study was to determine whether pituitary responsiveness to GnRH is attenuated with aging.

DESIGN AND SETTING

A GnRH antagonist and graded doses of GnRH were used to isolate pituitary responsiveness in Clinical Research Center studies at an academic medical center.

SUBJECTS

Subjects were healthy postmenopausal women (PMW) aged 48-57 yr (n = 10) or 70-77 yr (n= 9).

INTERVENTIONS

A suppressive dose of the NAL-GLU GnRH antagonist (150 microg/kg sc) was administered and was followed by GnRH doses of 25, 75, 250, or 750 ng/kg iv every 4 h.

RESULTS

The LH response to GnRH was attenuated with aging (P = 0.05) with an interaction between age and dose (P = 0.01) such that the LH amplitude was less in older PMW at the higher doses (250 ng/kg, 50 +/- 9 vs. 29 +/- 4.9 IU/liter, for young and old PMW, respectively, P = 0.02; and 750 ng/kg, 97.7 +/- 11 vs. 70.2 +/- 9.3 IU/liter, P = 0.002), but not the lower doses of GnRH. The FSH response to GnRH was also attenuated with aging in PMW (P = 0.005).

CONCLUSIONS

In studies that isolated the pituitary from endogenous GnRH stimulation, aging attenuated the LH and FSH responses to exogenous GnRH in PMW. These studies indicate that the pituitary plays a role in the decline in gonadotropin levels with aging, further supporting the potential contribution of age-associated changes in both hypothalamic and pituitary function to reproductive senescence.

Neuroendocrine physiology of the early and late menopause

Hormonal integration of the reproductive system is dramatically affected by reproductive aging. The progressive loss of ovarian follicles with normal aging is accompanied by an initial decrease in inhibin B and a concomitant increase in follicle-stimulating hormone. Subsequently, inhibin A and progesterone decrease, where as estradiol levels are maintained and often increase. In the late reproductive stage, cycles remain regular whereas the early and late menopausal transition are characterized by irregular cycles and often dramatic swings in estradiol and gonadotropin levels. Studies in younger and older postmenopausal women suggest that there are age-related changes in the neuroendocrine axis that are independent of the changing ovarian hormonal milieu of the menopausal transition but may contribute to the end of reproductive life.

Menopausal increases in pulsatile gonadotropin-releasing hormone release in a nonhuman primate (Macaca mulatta)

Reproductive function in all vertebrates is controlled by the circhoral release of the neuropeptide, GnRH, into the portal capillary system leading to the anterior pituitary. Despite its primary role in sexual maturation and the maintenance of adult reproductive function, changes in the concentrations and pattern of GnRH release have not yet been reported in any primate species during the menopausal transition and postmenopause. Such knowledge is essential for ascertaining both the mechanisms for, and consequences of, the menopausal process. Here we used a push-pull perfusion method to measure and compare the parameters of pulsatile GnRH release in adult rhesus monkeys at 8.4 +/- 1.5 yr (young adult females, early follicular phase, n = 6) and 28.8 +/- 0.3 yr (aged females, n = 4, of which two monkeys were in the menopausal transition, and two were postmenopausal). Our results demonstrate that: 1) GnRH release is pulsatile in both young and aged monkeys; 2) mean concentrations of GnRH increase during reproductive aging; and 3) GnRH pulse frequency does not differ between aged monkeys and young monkeys in the early follicular phase. We conclude that not only do GnRH neurons have the continued capacity to release GnRH in a pulsatile manner but also they can do so with enhanced GnRH levels in aged primates. To our knowledge, this is the first direct demonstration of elevated pulsatile GnRH concentrations in a primate species during reproductive senescence, a result that may have implications for menopausal symptoms.

Neuroendocrine aspects of aging in women

In women, the loss of ovarian function at menopause is associated with marked changes in hypothalamic and pituitary function. In addition, the steady decline in serum levels of LH, FSH, and FAS with age following menopause provides clear evidence for age-related neuroendocrine changes independent of the changes occurring owing to loss of ovarian feedback on the hypothalamic and pituitary components of the reproductive axis. An increase in the overall amount of GnRH secreted occurs despite a 30% decrease in GnRH pulse frequency with aging. This observation implies that the amount of GnRH secreted with each secretory bolus is greater in older postmenopausal women when compared with younger postmenopausal women. Thus, there may be a prominent pituitary component to the age-related decline in gonadotropin secretion. Recent studies indicate that the response to estrogen negative feedback at the hypothalamic level is preserved with aging, whereas the response to estrogen positive feedback may decrease with reproductive aging; however, the response to estrogen positive feedback in women has not been investigated with respect to aging, per se. It will be important to determine whether these age-related changes in hypothalamic-pituitary function contribute to reproductive senescence in normal women, as has been suggested for similar changes in animal models.

Developmental and endocrine aspects of normal ovarian aging

Supplies of follicles are established during early fetal life and decrease exponentially thereafter by a process called atresia. Subfertility only starts at a mean age of about 30-31 years, when the remaining follicle reserve has become a fraction of its original number. Thereafter, a further decrease in both oocyte quantity and quality dictates the subsequent reproductive events including decrease of fertility, increased abortion rate, the end of fertility, the beginning of cycle irregularity and, when almost no follicles are left, the occurrence of menopause. The same remarkable variation of age at menopause almost certainly is also present for the preceding reproductive events. When quantity and quality of antral follicles drop below a critical threshold, there is a subsequent drop in inhibine B resulting in the selective FSH rise at a mean age of 37-38 years. This FSH rise explains the accelerated follicle depletion, the increased proportion of growing follicles reaching the selectable stage, the shortening of the follicular phase and the increased incidence of dizygotic twinning. The concurring decrease of oocyte quality is in line with the increased incidence of abortions and chromosomal aberrations after age 35.

Effects of aging and gonadal failure on the hypothalamic-pituitary axis in women

OBJECTIVE

Our aim was to determine the effect of aging on the hypothalamic-pituitary-gonadal axis function.

STUDY DESIGN

We studied 9 women aged 25 to 40 years with well-defined idiopathic premature ovarian failure and compared them with 8 women aged 51 to 70 years who had age-appropriate menopause. All women underwent 24 hours of frequent blood sampling every 10 minutes before and after replacement with transdermal estradiol targeted to achieve serum concentrations of approximately 100 pg/ml.

RESULTS

In the absence of estrogen exposure, women with premature ovarian failure demonstrated a greater 24-hour mean luteinizing hormone concentration compared with that in the older women with age-appropriate menopause (32.3+/-4.3 mlU/ml vs 19.2+/-2.4 mlU/ml, p=0.0001). Despite the lesser luteinizing hormone serum levels in the older group, the luteinizing hormone pulse frequency per 24 hours was similar (22.1+/-3.0 pulses per 24 hours in prematurely menopausal women vs 21.9+/-2.5 pulses per 24 hours in the older postmenopausal women, p=0.94). When exposed to estrogen, mean luteinizing hormone concentrations decreased to 11.6+/-2.7 mlU/ml in prematurely menopausal women versus 4.4+/-1.0 mlU/ml in older postmenopausal women, p=0.017. Both groups had suppressed mean luteinizing hormone secretion compared with their paired, non-estradiol-exposed studies, p=0.0001. Frequency of luteinizing hormone pulsations was reduced to 16.5+/-3.5 pulses per 24 hours in prematurely menopausal women exposed to estradiol (p < 0.0058, compared with non-estradiol-exposed women). Further reduction was observed in older postmenopausal women (11.5+/-1.1 pulses per 24 hours, p=0.0001, compared with nonestradiol exposure, and p=0.0125, vs prematurely menopausal, estradiol-exposed women). Pulse amplitude was suppressed in both prematurely menopausal women (5.6+/-0.5 mlU/ml to 2.3+/-0.5 mlU/ml, p=0.0001) and older postmenopausal women (3.6+/-0.4 mlU/ml to 2.3+/-0.6 mlU/ml p=0.04) in the presence of estradiol. Although luteinizing hormone pulse amplitudes were greater in the women with premature menopause in the absence of estradiol (p=0.0028) compared with those in older postmenopausal women, pulse amplitudes became similar in the presence of estradiol. Parallel changes in mean follicle-stimulating hormone were observed. Women with premature ovarian failure had a mean follicle-stimulating hormone level of 71.1+/-9.4 mlU/ml that was suppressed to 18.0+/-4.1 mlU/ml after estradiol exposure (p=0.0001); values in older postmenopausal women were 45.9+/-6.0 and 10.3+/-2.0, respectively (p=0.0001). Although the women with premature ovarian failure secreted more follicle-stimulating hormone in the absence and presence of estradiol, only the former situation was statistically significant (p=0.0008 and p=0.23, respectively).

CONCLUSIONS

These data suggest that there is an age-related decrease in gonadotropin secretion that may be hypothalamic or pituitary in origin. There is less luteinizing hormone secreted in women older than age 50. There is greater suppression of luteinizing hormone and follicle-stimulating hormone secretion by estradiol in aged women. Thus these data indicate that postmenopausal hormone changes involve central hypothalamic-pituitary alterations, as well as ovarian changes.

Modulatory effects of a synthetic steroid (tibolone) and estradiol on spontaneous and GH-RH-induced GH secretion in postmenopausal women

OBJECTIVE

Since hormonal replacement therapy (HRT) affects plasma GH levels, the present study aimed to verify the effect of tibolone, a synthetic steroid, on modulating spontaneous and growth hormone releasing hormone (GH-RH) induced GH secretion.

METHODS

Postmenopausal women (n = 30) were enrolled and randomly subdivided in three groups (n = 10 each group): (1) treated with transdermal estradiol (50 micrograms) (Dermestrill, Rottapharm, Monza, Italy) biweekly; (2) treated with transdermal estradiol (100 micrograms) (Dermestrill, Rottapharm, Monza, Italy) biweekly; (3) treated with tibolone 2.5 mg/day (Livial, Organon Italia, Rome, Italy). Patients underwent a GH-RH test (1 microgram/kg) and 15 of them underwent to a pulsatility study before and 5 weeks after treatment.

RESULTS

Mean (+ S.E.M.) GH plasma levels increased in all patients after any type of HRT. GH response to GH-RH stimulation (expressed as maximal response to GH-RH or as delta value) was similar in the three groups while significant changes occurred in spontaneous pulsatile GH release. Tibolone and both dosages of transdermal estradiol significantly reduced GH pulse frequency and increased pulse amplitude.

CONCLUSIONS

The reduced plasma GH levels observed during postmenopause are probably related to a reduced endogenous GH-RH and not to a reduced pituitary ability to respond to GH-RH. In addition tibolone, as well as transdermal estradiol, are effective in restoring the spontaneous GH episodic release.

Changes in prolactin levels with the menopause: the effects of estrogen/androgen and calcitonin treatment

Prolactin levels were evaluated over a 2-year period in three groups of postmenopausal women: group A consisted of 35 untreated women distributed according to time since the menopause; group B consisted of 17 women on a combined estrogen/androgen preparation (Gynodian depot) intramuscularly at monthly intervals; and group C consisted of 12 women on 100 units of salmon calcitonin intranasally on alternate days and 1500 mg calcium daily. The control group (group D) consisted of 11 healthy premenopausal women. Serum prolactin, estradiol, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels were measured at the onset and at 6-month intervals over 24 months. Mean serum prolactin concentrations decreased significantly during the second postmenopausal year in untreated women p = 0.0001 and p = 0.0000 after 18 and 24 months, respectively) when compared to either the levels in premenopausal women or those at the beginning of the menopause (p = 0.0007). Neither combined estrogen/androgen nor calcitonin therapy significantly influenced prolactin levels which were similar throughout the observed period. In the group on a combined estrogen/androgen preparation, physiological estradiol concentrations together with a suppression of gonadotropins during the first 6 months of therapy were achieved. In women treated with intranasal salmon calcitonin, estradiol, FSH and LH levels were unchanged. Our results show that prolactin levels decrease significantly during the second year of the menopause. Neither combined estrogen/androgen, nor salmon calcitonin therapy had any effect on serum prolactin concentrations in postmenopausal women.

Age related changes in the female reproductive cycle

OBJECTIVE

To investigate the effect of age on the control of the reproductive cycle in regularly menstruating women.

DESIGN

In this prospective study all women were seen regularly during both the follicular and luteal phases. Ultrasound scanning was used to confirm ovulation and measurements were taken to assess follicular development and endometrial thickness. Serum gonadotrophin levels on day 4 of the cycle, the maximum periovulatory oestradiol and progesterone on the seventh day after ovulation were measured and compared in different age groups.

SUBJECTS & SETTING

Fifty-six healthy, regularly menstruating women were recruited from volunteers amongst staff of the University Hospital of South Manchester.

RESULTS

Ovulation occurred later in the cycle for older women, with mean follicular phase length increasing from 13.9 days (in group 21-25 years) to 15.9 days (in group 37-45 years (P < 0.05). The mean of the maximum follicular diameter prior to rupture was significantly smaller in the older women: 16.7 mm in the 37 to 45 years old group compared with 19.6 mm, 21.6 mm and 21.3 mm in the 21 to 25, 26 to 31 and 32 to 36 years old age groups, respectively (P < 0.001). The maximum thickness of the endometrium in the luteal phase was greatest for older women: 15.9 mm in the age group 37 to 45 years compared with 12.1 mm in the age group 21 to 25 years (P < 0.001). Serum gonadotrophin concentrations during menses were higher with increased age; mean follicle stimulating hormone was 4.8 iu/l in the age group 21 to 25 years, and 8.5 iu/l in the age group 37 to 45 years (P < 0.001). Mean luteinising hormone was 4.5 iu/l in age group 21 to 25 years and 7.21 iu/l in age group 37 to 45 years (P < 0.001). Mean ovarian steroid concentrations were no different.

CONCLUSIONS

These data illustrate significant age related differences in the pituitary-ovarian axis and endometrial thickness. This has implications for the management of older women in assisted reproduction and fertility control programmes.

Aging of endometrium and oocytes: observations on conception and abortion rates in an egg donation model

OBJECTIVE

To assess the comparative contribution of endometrial and oocytic aging to the decline in fertility with age.

DESIGN

Retrospective analysis of conception and abortion rates in an egg donation program, with respect to donor and recipient ages.

PATIENTS

All oocyte recipients had ovarian failure. Donors were women undergoing in vitro fertilization who contributed up to a third of retrieved oocytes.

INTERVENTIONS

None.

RESULTS

Thirty pregnancies (28 intrauterine) were recorded in 169 reception cycles originating from 91 donation cycles. Women who conceived were younger than those who did not (median age 31 versus 37; P less than 0.046), with no difference in age of donors. There was a significant difference in spontaneous abortion rate by age of donor rather than by age of recipient. Donors to successful pregnancies were younger than donors to aborted pregnancies (median age 27.5 versus 33; P less than 0.0211), but the 11 women with aborted pregnancies did not differ in age from the 17 women with successful pregnancies.

CONCLUSIONS

In women, endometrial function as expressed by conception rate in the recipients declines with age, whereas it is oocyte age that primarily influences risk of abortion.