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R W Rebar

Publications and source records attributed to R W Rebar.

At least 19 recordsLinked to original sources
PubMed1992

Evidence of a corticotropin-releasing hormone pulse generator in the macaque hypothalamus.

The secretion of hormones from the hypothalamic-pituitary axis is, in general, characterized by an episodic pattern of release. In the adrenal axis, ACTH and cortisol levels in peripheral blood display irregularly pulsatile ultradian patterns that are superimposed on the well characterized circadian rhythm. While it is generally accepted that CRH is released from the hypothalamus in a similar manner, very few studies have actually examined the temporal release of CRH. To examine the temporal release of CRH directly, we have established an in vitro perifusion system using the hemisectioned macaque hypothalamus. Perifusate samples were collected at 10-min intervals for 20 h and assayed for CRH by RIA. In control animals, a very regular, pulsatile pattern of hormone release was present, with a pulse interval of 90 +/- 11 min. Although this interval closely approximates the average pulse interval of ACTH and cortisol in the human, the regular pattern revealed in our study has not been demonstrated previously in the adrenal axis in vivo and suggests that factors outside the hypothalamus play a major role in controlling adrenal hormone levels. When hypothalami were perifused with dexamethasone added to the culture medium, no change in pulsatile activity was detected, indicating that a site outside of the hypothalamus may function as the primary center of feedback inhibition by adrenal glucocorticoids in the central nervous system. Because the very regular pulses of CRH that we observed bear striking similarity to the circhoral pulses of GnRH, we speculate that CRH may play a more subordinate role in regulating the adrenal axis and that other releasing factors and/or feedback effects at the pituitary level may be more important in the generation of the irregularly pulsatile, circadian patterns of ACTH and cortisol seen in peripheral blood.

Animals↗
PubMed1992

Hypergonadotropic forms of amenorrhea in young women.

Hypergonadotropic forms of amenorrhea in young women are many and varied, and the disorder is not nearly as uncommon as previously believed. It is likely that all physicians seeing women with amenorrhea will encounter this disorder. Careful evaluation is warranted to eliminate any associated autoimmune disorders. Because of the high likelihood of osteopenia in affected individuals, estrogen replacement therapy is warranted. Although pregnancy is possible in women with secondary hypergonadotropic amenorrhea, remarkably it most commonly occurs in women utilizing exogenous estrogen. Women desirous of achieving a pregnancy are best served by assisted reproductive technology utilizing donor oocytes. Success rates in such patients have been quite high. Thus, physicians today can counsel affected women that pregnancy is indeed possible, even in women with so-called "premature ovarian failure."

Adult↗
PubMed1991

Characteristics of the new progestogens in combination oral contraceptives.

This review details the characteristic features of three new progestogens which soon will be available in low-dose combination oral contraceptive agents in the United States. Available data suggest that desogestrel, gestodene, and norgestimate are extremely potent progestogens with few androgenic side effects. The smaller changes in lipids induced by these progestogens seem to confer some advantage to the use of preparations containing one of these agents. Whether this advantage is also present clinically remains to be determined.

Blood Coagulation↗
PubMed1991

A biotin-streptavidin enzyme immunoassay for detection of antibodies to porcine granulosa cell antigens.

A colorimetric solid-phase enzyme immunoassay has been developed which quantifies antibodies to porcine granulosa cell membrane antigens in rabbits immunized with porcine granulosa cells. A cell-free, particulate membrane preparation of porcine granulosa cells was used as coating antigen. A biotinylated second antibody in conjunction with a streptavidin-beta-galactosidase conjugate was utilized to amplify reactivity. The enzyme beta-galactosidase was used due to high background obtained using peroxidase, presumably due to endogenous peroxidase activity of the tissue. Sigmoidal serum dilution curves were obtained with immune rabbit sera indicating that absorbance was related to the concentration of antibodies. Assay activity was reduced by preincubation of immune serum with granulosa cell membranes. Sera from ovariectomized or pre-immune rabbits did not yield any specific binding in the assay. This assay has potential applicability for quantifying antiovarian and antigranulosa cell antibodies in women suspected of having autoimmune premature ovarian failure.

Animals↗
PubMed1991

Dose-response effects of exogenous pulsatile human corticotropin-releasing hormone on adrenocorticotropin, cortisol, and gonadotropin concentrations in agonadal women.

Acute activation of the hypothalamic-pituitary axis with CRH has been reported to suppress gonadotropin secretion in women of reproductive age. In this study we specifically examined the effects of increasing doses of human CRH (hCRH) on circulating concentrations of ACTH, cortisol, and gonadotropins in five agonadal women, aged 46-65 (mean, 51.2) yr. The subjects had undergone either natural menopause or surgical removal of their ovaries at least 1 yr before study. Each woman was studied on four separate occasions and received either saline or hCRH at a dose of 0.5, 1.0, or 2.0 micrograms/kg BW through an indwelling iv catheter in a randomized, single blind fashion. During each experiment, five sequential iv injections of the same dose of hCRH or saline were administered at 90-min intervals over an 8-h period, followed by a 10-micrograms iv bolus of GnRH to test for pituitary gonadotropin responsiveness. Blood samples for measurement of LH, FSH, PRL, ACTH, and cortisol were obtained at 15-min intervals through an indwelling iv in the contralateral arm. Episodic pulses of LH secretion were analyzed using the Cluster computer program. Transverse mean LH, FSH, and PRL levels did not change with increasing hCRH doses. Mean (+/- SEM) LH pulse frequency [saline, 5.2 +/- 0.4/8 h; hCRH, (0.5 micrograms/kg), 4.8 +/- 0.2; hCRH (1 microgram/kg), 5.2 +/- 0.2; hCRH (2 micrograms/kg), 5.4 +/- 0.2] and amplitude [saline, 14.4 +/- 4.2 IU/L; hCRH (0.5 microgram/kg), 14.0 +/- 2.4; hCRH (1 microgram/kg), 15.8 +/- 2.5; hCRH (2 micrograms/kg), 17.2 +/- 2.9] did not differ among groups. Although the transverse mean levels of ACTH [saline, 8.7 +/- 0.2 pmol/L; hCRH (0.5 microgram/kg), 12.4 +/- 0.3; hCRH (1 microgram/kg), 11.5 +/- 0.4; hCRH (2 micrograms/kg), 12.8 +/- 0.4] did not change with increasing doses of hCRH, the duration of cortisol peaks after hCRH was longer and accounted for the increased transverse mean at each dose [saline, 152.8 +/- 4.1 nmol/L; hCRH (0.5 microgram/kg), 265.4 +/- 10.5; hCRH (1 microgram/kg), 329.7 +/- 14.3; hCRH (2 micrograms/kg), 348.2 +/- 12.1]. These findings suggest that ever larger doses of pulsatile hCRH continue to increase adrenal output of cortisol secondary to more sustained ACTH responses. However, hCRH-induced acute hypercortisolism does not alter gonadotropin secretion in agonadal women.

Adrenocorticotropic Hormone↗
PubMed1991

Depletion of luteal phase serum progesterone during constant infusion of cortisol phosphate in the cynomolgus monkey.

OBJECTIVE: To study the impact of chronic infusions of cortisol phosphate on ovarian function in the cynomolgus monkey. DESIGN: Cortisol phosphate at doses of 5 or 15 mg/d or saline were infused for periods of up to 8 weeks using subcutaneously implanted osmotic pumps. SETTING: Animals were maintained in the Center for Experimental Animal Resources, Northwestern University. MAIN OUTCOME MEASURES: Serum total and unbound cortisol concentrations, serum total and unbound progesterone (P) concentrations, urinary P metabolites. RESULTS: Mean increases in serum cortisol of 56% and 77% above control levels were achieved. Mean serum P concentrations were not decreased with low-dose cortisol phosphate infusion during the 12 days preceding menses, but mean serum P levels were decreased by 69% to 2.3 ng/mL during high-dose cortisol phosphate infusion. No corresponding decrease in excretion of conjugated immunoreactive P metabolites was found in daily urine samples during cortisol phosphate infusion, suggesting that production rates of P were unaltered by the cortisol phosphate treatment. Unbound serum cortisol increased by a mean of 162% above control levels during high-dose cortisol phosphate infusion, but no increase occurred in the percentage of unbound serum P. CONCLUSIONS: We conclude that elevation of serum cortisol in the range observed in chronically stressed individuals may severely decrease the available P to target organs by displacement of P from plasma proteins but does not inhibit ovarian steroidogenesis or ovulation.

Animals↗
PubMed1991

Gonadotropin dynamics in women receiving immediate or delayed transdermal estradiol after oophorectomy.

A prospective study was performed in 24 premenopausal women to evaluate the gonadotropin dynamics of pharmacologic doses of transdermal estradiol-17 beta (E2) administered after bilateral oophorectomy. Patients were given 0.2-mg transdermal E2 patches for 2 weeks, followed by 0.1-mg patches for 4 weeks either immediately postoperatively (immediate estrogen replacement therapy [ERT]) or beginning 12-14 days after surgery (delayed ERT). Serum gonadotropins and E2 levels were measured serially, and postmenopausal symptoms were prospectively recorded. Administration of 0.2 mg transdermal E2 immediately after surgery suppressed the post-castration rise in gonadotropins for at least 4 days, but LH and FSH levels did increase to the menopausal range after 2 weeks despite continued therapy. Sustained circulating levels of E2 with transdermal E2 therapy were comparable to follicular phase values. Vasomotor symptoms were well controlled by 0.2 mg of transdermal E2 in the majority of patients during the clinical trial. There was no significant estrogen-related morbidity despite the large doses used. Two patients had skin irritation at the patch site causing discontinuation of therapy. These data suggest that large doses of transdermal E2 can suppress gonadotropin levels only for a brief interval. We were unable to demonstrate any long-term alteration in the hypothalamic-pituitary set point for sensitivity to exogenous E2.

Administration, Cutaneous↗
PubMed1990

Comparison of endometrial biopsy and urinary pregnanediol glucuronide concentration in the diagnosis of luteal phase defect.

To determine if pregnanediol glucuronide (PG) excretion is useful in luteal phase assessment, we compared daily first morning urinary PG concentrations during the luteal phase in nine normal and nine deficient cycles. Total luteal pregnanediol excretion (44.1 +/- 11.3 versus 64.0 +/- 11.6 area units +/- SEM) was not different. However, significantly less pregnanediol was excreted by the abnormal group during the 1st 5 days of the luteal phase (12.7 +/- 1.2 versus 18.0 +/- 1.7 area units +/- SEM, respectively). Thus, delayed PG excretion may be characteristic of luteal phase defect and measurement of urinary PG may be useful only if daily samples during the early luteal phase are obtained.

Biopsy↗
PubMed1990

Clinical features of young women with hypergonadotropic amenorrhea.

One hundred fifteen women under age 40 presenting with hypergonadotropic amenorrhea (follicle-stimulating hormone greater than 40 mIU/mL) were evaluated. Incomplete pubertal maturation and chromosomal abnormalities were more likely in the 18 women (15.7%) with primary amenorrhea than in those with secondary amenorrhea. The 97 women with secondary hypergonadotropic amenorrhea were significantly more apt to complain of symptoms of estrogen deficiency, have been pregnant before diagnosis, and have evidence of ovulation after diagnosis. Withdrawal bleeding occurred commonly (greater than 48%) in those women administered exogenous progestin. Immune abnormalities occurred with approximately equal frequency (17.4%), and spinal bone density was decreased in both groups.

Adult↗
PubMed1990

Management of problems during menopause.

Many women pass through menopause with no problems and no complaints. They should be encouraged to pursue healthy life-styles. For those who do experience difficulties or for those who are at risk for developing problems, the aforementioned treatment options can be considered. At this time, the benefits of HRT appear to outweigh the risks and offer substantial improvement in the quality of life to appropriately selected women. With the realization that women can expect to live one third of their lives after menopause, it becomes clear that it is important to discuss menopausal health issues with each women in order to make the postmenopausal period as enjoyable as possible.

Cardiovascular Diseases↗
PubMed1989

Pituitary function in isolated gonadotrophin deficiency.

Hypothalamic-pituitary function was assessed in 24 individuals with isolated gonadotrophin deficiency (IGD). Thirteen had normal olfaction (Group I) while 11 (Group II) had anosmia (Kallmann's syndrome). In response to a 10 micrograms intravenous (i.v.) bolus of GnRH, the minimal dose required to evoke a consistent gonadotrophin response in normal subjects, the patients responded with significant LH and FSH increases over baseline (P less than 0.01). In Group II patients, large doses (150 micrograms) of GnRH, which elicit maximal release of gonadotrophin in normal subjects did not increase gonadotrophin release beyond that produced by a 10 micrograms bolus. In response to two 10 micrograms GnRH doses, at times 0 and 120 min, the IGD patients responded with similar LH increases to both boluses (both P less than 0.01 compared to baseline). The maximal PRL responses to arginine infusion and to TRH in the male patients were similar to those of normal males. However, in the IGD females, the PRL response to TRH was less than in normal females. The TSH responses to TRH in IGD males and females were similar to each other and similar to normal. The IGD male GH response to arginine infusion was comparable to that in normal males. We conclude that (1) IGD patients appear to retain minimal endogenous GnRH secretion so that the IGD pituitary responds to a minimal dose of GnRH without priming; (2) IGD is a heterogeneous syndrome in which affected individuals with and without normal olfaction represent parts of the spectrum of the same disease; and (3) except for the PRL response in females, the PRL, TSH and GH responses demonstrate that the IGD pituitaries are largely intact.

Adolescent↗
PubMed1988

Differences between serum and urinary LH in hypergonadotropic states.

In an attempt to investigate the relationship between molecular configuration, immunoreactivity, radioligand binding, and biological activity, we compared the elution profiles of immunoreactive and radioligand receptor-active LH following gel filtration over Sephadex G-100 (1.6 X 100 cm column). Samples of sera and urinary acetone-insoluble material from normal cycling women during the LH surge (n = 4) and postmenopausal (n = 2) and castrate women (n = 2) were examined. One major peak of LH immunoreactivity was present in the sera and the urinary samples from all subjects. However, this peak of immunoreactive LH in the urinary precipitate consistently occurred 8-10 fractions later than the peak activity observed in the sera. Despite the differences in the profiles of immunoreactivity between sera and urinary precipitates, the major peak of radioligand receptor activity for LH was observed in the same fractions in all samples and corresponded to the major peak of immunoreactivity observed in the sera. Thus, binding activity was sometimes observed in urinary fractions containing little immunoreactivity for LH. Bioassay of selected fractions using the rat interstitial cell-testosterone assay revealed good agreement between receptor activity and bioactivity but not between immunoreactivity and bioactivity. The ratios of total radioreceptor-active to total immunoreactive LH were consistently higher in the sera than in the urinary precipitates. These data suggest alterations in molecular form during metabolism and/or excretion of LH. Whether these alterations represent differences in peptide structure or merely carbohydrate moieties remains to be determined.

Chromatography, Gel↗
PubMed1988

Molecular forms of LH subunits in hypergonadotropic states.

To determine whether differences in subunits of LH exist in various hypergonadotropic states, we compared the elution profiles of immunoreactive alpha LH and beta LH following gel filtration over Sephadex G-100 (1.6 X 100 cm column) of sera and urinary acetone-insoluble precipitates from normal cycling women during the LH surge and untreated agonadal women and those receiving estrogen replacement. The elution profiles for the alpha subunit were similar in all subjects in both sera and urinary precipitates. In contrast, the elution profiles of beta LH varied between sera and urinary extracts among the 3 groups of subjects. Sera and urinary precipitates from the individual agonadal women eluted identically, but the profiles were distinct from those in samples from each of the cycling women. Exogenous estrogen therapy had no effect on the elution profiles of immunoreactive urinary beta LH in agonadal women but altered the ratios of beta LH/alpha LH excreted to those observed in normal cycling women. These data document the existence of immunoreactive subunits of LH in sera and urinary acetone-insoluble precipitates and confirm the existence of multiple forms of immunoreactive beta LH. The data further suggest that gonadal steroids may modulate the metabolism and/or excretion of beta LH in various hypergonadotropic states.

Chromatography, Gel↗