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Biomedical subjects

A R Midgley

Publications and source records attributed to A R Midgley.

At least 55 records · Page 3Linked to original sources
PubMed1978

Hormonal regulation of ovarian cellular proliferation.

The steroid hormone estradiol, and the glycoprotein hormones follicle-stimulating hormone (FSH) and luteinizing hormone (LH), are known to be essential for the growth and differentiation of follicles in the ovary. The present study was conducted to determine quantitatively the effects of estradiol, FSH and LH on proliferation of different ovarian cell types (granulosa and theca cells). The immature female hypophysectomized rate sequentially primed with estradiol, FSH and LH was used as the experimental model. Proliferation was assessed by examining changes in total DNA, incorporation of 3H-thymidine into DNA and labeling index in specific cell types. Estradiol and FSH each acted on follicles at different stages of development to stimulate proliferative activity of both granulosa and theca cells. Continued administration of either hormone caused a decrease in the proliferative activity of both cell types. These observations have been interpreted to indicate that estradiol and FSH can each alter the length of the specific phases of the cell cycle. A luteinizing dose of LH caused a cessation of proliferation in luteinizing granulosa cells while stimulating a limited proliferation of theca cells. Absence of the appropriate hormonal stimulus caused both granulosa and theca cells to stop proliferating and the follicles to undergo atresia. These results indicate that, depending upon the state of differentiation of granulosa and theca cells, estradiol, FSH and LH can stimulate or inhibit the ability of these cells to proliferate.

Cell Division↗
PubMed1977

Development-dependent responses of ovarian follicles to FSH and hCG.

Ovarian follicles removed from immature rats (preantral follicles) and immature rats treated in vivo with follicle stimulating hormone (FSH) (antral follicles) released progesterone in vitro in response to either human chorionic gonadotropin (hCG), hFSH, or DBcAMP in a time- and concentration-dependent fashion. Antral follicles produced approximately 20 times more progesterone than preantral follicles in response to both FSH and hCG at 10(-7) M and approximately 5 times more progesterone in response to 8 X 10(-3) M DBcAMP. After in vitro incubations, follicles were transplanted beneath the kidney capsules of recipient rats to assess their ability to luteinize after hormonal stimulation. Only antral follicles incubated with hCG, hFSH, and DBcAMP formed ectopic corpora lutea. Adenylate cyclase activity in preantral and antral follicle granulosa cells increased in response to both 10 mM KF and 10(-6) M hFSH with no major differences observed between membranes prepared from preantral or antral follicle granulosa cells. These results demonstrate that follicular maturation is associated with major changes in the ability of the granulosa cells to produce progesterone and luteinize in response to hormonal stimulation and that these changes may be, in part, independent of a functional hormone-responsive adenylate cyclase system.

Adenylyl Cyclases↗
PubMed1977

Regulation of gonadotropin receptors by luteinizing hormone in granulosa cells.

In association with luteinization, LH induces a decrease in the content of receptors for FSH and LH and an increase in that for PRL. To elucidate if the mechanism by which LH regulates its own receptors involved occupancy of sites and/or loss of receptors the effects of a luteinizing dose of LH were examined in the preovulatory follicles of immature hypophysectomized rats primed with estradiol and FSH. The measurable LH receptor content declined by 82% 24 h after LH administration. Serum concentration of the hormone declined by 24 h to 1.4% of the concentration measured 2 h after LH administration. Administration of iodinated LH to demonstrate occupancy of sites in vivo, resulted in a decline in the amount of hormone bound in vivo, over a period of time. This decline in occupancy paralleled the decrease in the number of available sites as measured in vitro. Furthermore, a large dose of highly purified hFSH administered in lieu of LH induced luteinization and an associated loss of gonadotropin receptors. These results indicate that luteinizing doses of LH and FSH induce a loss in gonadotropin receptors by mechanisms other than occupancy.

Animals↗
PubMed1976

Effect of prolactin on LH receptor in rat luteal cells.

This investigation was undertaken to determine whether prolactin might act as a luteotropic hormone in the rat by increasing the receptor for LH. Immature female rats were treated with 5 SC injections of oFSH beginning at 0900 h on day 25; luteinization was induced with a single SC injection of oLH at 1500 h on day 27. In this model, LH-receptor activity, assessed by specific binding of [125I]iodohCG to ovarian membrane fractions, increased steadily (greater than 7-fold) from day 27 to day 33; specific [125I]iodoprolactin binding rose greater than 3-fold between days 27 and 31. Serum progesterone measured at 1500 h rose from greater than 10 ng/ml on day 27 to greater than 130 ng/ml on day 34. 2-Bromo-alpha-ergocryptine (CB-154, [EC]; 35 mug) given 2 X/day beginning at the time of LH injection, blocked nocturnal increases in serum prolactin measured at 0200 h on days 29, 30, and 31, and resulted in reduced binding of [125I]iodohCG on days 31 and 33; serum progesterone was similarly reduced on days 31 and 34 in EC-treated rats. Simultaneous treatment with EC and prolactin completely reversed the effects of EC with regard to both binding of [125A]iodohCG and serum progesterone. Changes in ovarian uptake of [125I]iodohCG in vivo were similar to those of the in vitro experiments described above. EC and/or prolactin treatment did not affect binding of [125I]iodoprolactin. In summary, the data indicate that LH in the absence of prolactin can induce the formation of corpora lutea which have an increased number of prolactin receptors but which have a few LH receptors and a reduced capacity to produce progesterone. If prolactin is present during the early luteinization process, corpora lutea develop an increased capacity to bind LH and to produce progesterone. It is possible that the increase in LH-receptor and progesterone production occur as independent events both mediated by the luteotropic action of prolactin. Alternatively, LH receptor might be limiting for LH stimulation of progesterone production.

Animals↗
PubMed1976

Progesterone metabolism by the ovary of the pregnant rat: discrepancies in the catabolic regulation model.

The intraovarian site of 20 alpha-hydroxysteroid dehydrogenase activity (20 alpha-OH-SDH) was determined biochemically by measuring enzyme activity in homogenates of the whole ovary, or of isolated ovarian compartments, during the last third segment of pregnancy in the rat. In agreement, with previously reported histochemical evidence, an increase in 20 alpha-OH-SDH activity was observed in isolated corpora lutea, but not in the non-luteal compartment of the ovary. Enzyme activity in corpora lutea was low between days 16 and 22 of pregnancy, but increased markedly (4-6 fold) on day 23. Between days 17 and 20 of pregnancy, serum concentrations of progesterone declined from 130 +/- 3 to 80 +/- 3 ng/ml, while 20 alpha-hydroxypregn-4-en-3-one (20 alpha-OH-P) concentrations declined from 34 +/- 3 to 18.5 +/- 3 ng/ml. Only later, between days 20 and 22 of pregnancy, was a significant decline in serum progesterone concentrations associated with an increase in serum 20 alpha-OH-P concentrations (50 +/- 15 ng/ml at 0800 h and 128.5 +/- 15 ng/ml at 1400 h on day 22). Thus the decline in progesterone concentration late in pregnancy can be explained only partially by conversion of progesterone to 20 alpha-OH-P. Further, a dissociation between changes in enzyme activity and in serum concentrations of 20 alpha-OH-P was also observed. A marked increase in serum levels of 20 alpha-OH-P on day 22 preceded any increase in enzyme activity by at least 10 h, and continued increases in enzyme activity on day 23 were not associated with any steady increase in peripheral 20 alpha-OH-P levels. We conclude from these observations that luteal regression is a more complex phenomenon than the regulation of a single enzyme, 20 alpha-hydroxysteroid dehydrogenase, and may involve regulation of both the synthesis and degradation of progesterone.

20-alpha-Dihydroprogesterone↗
PubMed1976

Ovarian follicular development in the rat: hormone receptor regulation by estradiol, follicle stimulating hormone and luteinizing hormone.

The effects of estradiol, FSH and LH on ovarian follicular development and granulosa cell differentiation were examined in the immature rat hypophysectomized on day 24 of age. Administration of estradiol to hypophysectomized rats for 4 days stimulated the growth of large preantral follicles with a concomitant 1.5-fold increase in FSH receptor content and a 4-fold decrease in LH receptor content in the granulosa cells. When highly purified hFSH was administered alone, receptor content for FSH increased progressively for 4 days while receptor for LH remained essentially unchanged. However, when rats were pretreated with estradiol, the response of follicles to FSH was markedly enhanced as indicated by the appearance of large, antral follicles and elevated receptor content for both FSH and LH. Receptor content for FSH increased markedly in response to hFSH following only one day of estradiol pretreatment, while receptor content for LH increased most rapidly in response to hFSH after 3 days of estradiol pretreatment. LH administered to rats possessing large preovulatory follicles caused luteinization of granulosa cells and a marked decline in receptor content for both gonadotropins within 24 h. Receptor content remained low even 48 h after LH administration when granulosa cells were fully luteinized. These results indicated that follicular development and granulosa cell differentiation are dependent on steroid-protein hormone regulation of hormone specific receptors.

Animals↗
PubMed1975

A specific, non-chromatographic radioimmunoassay for human plasma cortisol.

A radioimmunoassay technique has been developed for the measurement of cortisol in a single methylene chloride extract of human plasma without chromatography. The antiserum, obtained by immunizing rabbits with cortisol-3-carboxymethyl-oxime conjugated to bovine serum albumin, had a high affinity (KA = 1.8 X 10(9) 1/mole) and capacity (2.3 X 10(-6) moles/L undiluted serum) for cortisol. The minimum detectable amount determined at the lower 95% confidence limit of the buffer control tubes was 8.3 +/- 4.7 pg/tube and a log dose - logit response standard curve was linear between 20 pg and 20 ng/tube. The antiserum was highly specific for cortisol with only corticosterone, cortisone, 11-deoxycortisol and 21-deoxycortisol showing significant cross-reaction (12.4, 6.6, 3.8 and 3.7%, respectively). The cross-reaction for the other tested naturally occurring and synthetic steroids did not exceed 1%. Regression analysis of cortisol concentration estimates obtained on 20 samples before and after Sephadex LH-20 column chromatography gave a coefficient of correlation (r) of 0.995 and a regression coefficient (b) of 1.04. Recovery of cortisol added to plasma samples was quantitative. The intra-assay error was 8.5% and the inter-assay error averaged 5.7%. The method is simple requiring a single solvent extraction of plasma, therefore permitting large numbers of samples to be handled efficiently by a single technician.

Cross Reactions↗