Physiological Levels Of Estradiol Research Articles

Involvement of Nerve Growth Factor in Female Sexual Development*

The ovary is innervated by noradrenergic and peptidergic fibers. Treatment of neonatal rats with antibodies to nerve growth factor (NGF Ab) resulted in failure of the sympathetic (noradrenergic and neuropeptide-Y) nerves to develop. Partial loss of sensory innervation, represented by calcitonin gene-related peptide fibers, was also observed. Follicular growth was stunted, and production of androgens and estradiol was reduced. The timing of first ovulation was delayed, estrous cyclicity was disrupted, and fertility was compromised. Plasma LH levels were elevated, and LH pulsatility was enhanced, suggesting primary ovarian failure. A normal appearance of tyrosine hydroxylase-, LHRH-, and neuropeptide-Y-immunoreactive neurons in the hypothalamus, as determined by immunocytochemistry, suggested that neonatal immunosympathectomy did not directly affect hypothalamic reproductive function. In vitro release of LHRH from median eminence nerve terminals in response to prostaglandin E2 was, however, reduced in NGF Ab-treated rats. Normalization of the response by prior in vivo exposure of the animals to physiological estradiol levels, suggested that the diminished LHRH output was due at least in part to estrogen deficiency. Although ovarian dysfunction induced by immunosympathectomy may be related to alterations in vascular tone, the striking loss of perifollicular noradrenergic innervation caused by NGF Ab suggests that the absence of the nonvascular norepinephrine stimulus to follicular steroidogenesis is a primary factor responsible for the alterations observed. The results indicate that development of the sympathetic innervation of the ovary is NGF dependent and that NGF, by supporting the differentiation and survival of the innervating neurons, contributes to the acquisition of mature ovarian function.

Pituitary and hypothalamic glucose-6-phosphate dehydrogenase: effects of estradiol and age in C57BL/6J mice.

Activities of glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6-PGDH) were measured in the mediobasal hypothalamus and pituitary gland of C57BL/6J mice throughout their lifespan. Activities of pituitary G6PDH, pituitary 6-PGDH, and hypothalamic G6PDH increase with age in female mice, assayed 7 days after ovariectomy, but not in intact females or males. Pituitary G6PDH specific activity is increased by middle-age (13-14 months) in females, before the onset of acyclicity, and remains elevated throughout the acyclic phases of persistent vaginal cornification and persistent diestrus. This increase in activity is ovary dependent, because it can be prevented by long term (12-month) ovariectomy. The increased activity is not linked to pituitary tumorigenesis and does not result from trapped blood cells, as evaluated by studies with 51Cr-labeled erythrocytes. Responses to physiological levels of estradiol (E2) were analyzed with a graded series of chronic polyethylene implants or after a single sc injection in ovariectomized mice aged 5-22 months. The responsiveness of pituitary G6PDH to E2 is not altered during aging. Young cycling (6 months old) and older acyclic mice (19 months old) displaying persistent vaginal cornification show equivalent increases of about 100% in G6PDH specific activity after chronic E2 treatment and similar time courses of induction after a single E2 injection. Pituitary G6PDH is maximally induced (30% increase) by 48 h after E2 injection in all age groups. In addition, the rates of decline in pituitary G6PDH specific activity after ovariectomy are similar in young and older mice (half-life, 4 days). The specific activity of G6PDH in the mediobasal hypothalamus and blood is unaffected by E2 administration. The relatively low doses of E2 used here fail to alter 6-PGDH specific activity in pituitary or brain. These findings indicate that female reproductive senescence in mice is not associated with generalized losses of sensitivity and responsivity to E2 throughout the neuroendocrine axis.

The Effect of Season on the Induction of Sexual Behavior by Estradiol in Female Rhesus Monkeys1

Rhesus monkeys housed in an outdoor environment are seasonal breeders, with ovulations and concomitant sexual behavior limited to the fall and winter months. To determine if there is a seasonal difference in the capacity of physiological levels of estradiol (E2) to induce sexual behavior in ovariectomized rhesus monkeys housed outdoors, subjects living in a social group were treated with subcutaneous E2 implants in a counter-balanced design during the nonbreeding season (May-July) and during the breeding season (September-November). Serum E2 levels were monitored by obtaining blood samples twice a week. Three levels of E2 were studied: baseline (less than 30 pg/ml), follicular (100 pg/ml), and periovulatory (200 pg/ml). Two of five adult males in the group were injected with human chorionic gonadotropin (hCG) twice a week to insure that males with high testosterone levels were present during each season. Focal observations of behavior of 15 minutes' duration on each subject were conducted 5 days per week, with frequencies and durations of social, sexual, and solitary behaviors recorded. Concomitant 2-h group scans were made to record all occurrences of mounting behavior. Neither heterosexual serial mounting nor seminal plugs were ever observed in E2-treated females during the summer months. In contrast, copulation and seminal plugs were observed in subjects at both treatment levels during the fall. While E2-treated females engaged in homosexual mounting behavior during both summer and fall, E2 treatment resulted in heterosexual copulation only during the fall. Changes in patterns of social behavior paralleled changes in sexual behavior and were significantly affected by treatment and season, with more male-female interactions during the fall months.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered tubulin distribution in the hypothalamus of aging female C57BL/6J mice

The effects of age and estradiol on hypothalamic content and distribution of tubulin and calmodulin were examined by radioimmunoassay in ovariectomized C57BL/6J female mice. A small (14%) increase in particulate tubulin, but not soluble tubulin, was found in the hypothalamus of reproductively senescent mice (20 months) compared to young (8 months) controls. This alteration was limited to tubulin; calmodulin content was unaffected by age. Post-castration serum LH levels were lower in old, ovariectomized controls relative to young controls, but physiologic levels of estradiol, achieved by subcutaneous implants, suppressed LH levels in both age groups. In contrast to LH and uterine weight, hypothalamic tubulin and calmodulin were unaffected by estradiol treatment. These results suggest that the negative feedback effect of estradiol on LH secretion is exerted by a mechanism other than redistribution of hypothalamic tubulin or calmodulin, or that changes are restricted to a discrete sub-population of neurons.

Existence of multiple forms of follicle-stimulating hormone within the anterior pituitaries of cynomolgus monkeys.

Ovariectomized cynomolgus monkeys were treated with physiological levels of estradiol and progesterone. A reduction in serum levels of FSH was observed after steroid exposure. Anterior pituitary homogenates were prepared from monkeys after 0, 12, 24, or 36 h of exposure to estradiol and progesterone and quantitated for FSH activity by radioreceptor assay (RRA) and RIA. Pituitary FSH activity (expressed as RRA/RIA) increased with duration of exposure to steroids. Forms of FSH within these pituitaries were separated by the column isoelectric focusing technique, chromatofocusing. All pituitary homogenates tested contained FSH isohormones that eluted at similar isoelectric points. Each FSH isohormone exhibited a mol wt similar to that of a purified FSH standard, but differed in ability to displace labeled FSH from a biological receptor preparation. FSH forms with basic isoelectric points exhibited greater RRA/RIA values than forms with more acidic isoelectric points. The relative proportion of the more basic FSH forms increased within pituitary tissue with duration of exposure to steroids. All FSH forms were secreted by pituitary cells in culture. The biochemical basis for the microheterogeneity appears to be the degree of sialic acid incorporation into the FSH molecule. The results of these studies demonstrate that the cynomolgus monkey pituitary responds to the surrounding hormonal milieu by altering the relative proportions of FSH forms present within that gland.

ALTERATION IN THE PLASMA TESTOSTERONE: ESTRADIOL RATIO: AN ALTERNATIVE TO THE INHIBIN HYPOTHESIS

The data suggest that in the absence of the testis: (1) testosterone can maintain both FSH and LH concentrations chronically within the physiological range; (2) that estradiol preferentially suppresses plasma LH concentration, indicating that the androgenic component of testosterone modulates FSH secretion; and (3) that subphysiological testosterone concentrations accompanied by physiological estradiol levels permit FSH to escape to midcastrate levels while maintaining LH concentration at intact levels. An alteration in the testosterone: estradiol ratio can account for a selective FSH elevation when testosterone production is low. The data provide an alternative explanation for the inhibin phenomenon.

Stimulation of in vitro 3H-uridine uptake and RNA synthesis in mouse blastocysts by 17beta-estradiol.

SummaryIt was found that physiological levels of estradiol (10-8-10-10M) enhanced 3H-uridine uptake by mouse blastocysts cultured in a protein-free medium and that 10-8 and 10-9M 17β-estradiol increased the amount of RNA synthesized during the 2-hr incubation period. The volume of the blastocysts decreased during incubation, the reduction in size was partly prevented by 17β-estradiol.Financial support was received from NIH Grant GM 14370, USAID Contract CSD/2837 and the Ford Foundation. We are indebted to D. M. Hunt for drafting the figures.