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Biomedical subjects

D T Armstrong

Publications and source records attributed to D T Armstrong.

At least 199 records · Page 11Linked to original sources
PubMed1976

Site at which FSH regulates estradiol-17beta biosynthesis in Sertoli cell preparations in culture.

Sertoli cells were isolated from testes of 20-day-old rats and were maintained in primary culture. The ability of these cells to synthesise estradiol-17beta from a variety of exogenous substrates, progesterone, testosterone,androstenedione, 19-hydroxyandrostenedione and 19-hydroxytestosterone in the presence and absence of follicle-stimulating hormone (FSH) was examined. In the presence of each of the substrates alone for 24 h the rate of estradiol-17beta synthesis was very low. FSH (NIH-FSH-S11, 5 mug/ml) stimulated estradiol-17beta synthesis 75-fold when added to medium containing testosterone (5 X 10(-7)M) but caused only marginal stimulation when added to medium containing progesterone (5 X 10(-7) M). Both FSH and dibutyryl cyclic AMP (bu2cAMP) stimulated the conversion of each of the substrates, androstenedione, 19-hydroxyandrostenedione and 19-hydroxytestosterone to estradiol-17beta, and the effects were similar to those observed in the presence of testosterone. These data indicate that, under the culture conditions employed, progesterone is not an effective substrate for conversion to estradiol-17beta by Sertoli cells. Estradiol-17beta synthesis was stimulated by FSH in the presence of the C19 steluences the conversion of androgens to estrogens, either directly or indirectly, at the aromatisation step (i.e. the conversion of 19-hydroxylated androgens to estrogens).

Androstenedione↗
PubMed1976

Effects of indomethacin and aminoglutethimide phosphate in vivo on luteinizing-hormone-induced alterations of cyclic adenosine monophosphate, prostaglandin F, and steroid levels in preovulatory rat ovaries.

Changes in levels of cyclic adenosine monophosphate (cAMP), prostaglandin F (PGF), progesterone, testosterone, and estradiol-17beta, in preovulatory rat ovaries induced by exogenous luteinizing hormone (LH) have been measured. Ovarian cAMP reached maximal levels 15 min and 1h after LH administration by intravenous and intraperitoneal routes, respectively, and then declined to pre-LH levels by 8 h. Progesterone levels in ovaries and serum rose approximately in parallel with cAMP, but remained elevated throughout the 8-h sampling period. Ovarian testosterone increased to maximal levels 1 h after LH injection, followed by a rapid decline to below pre-LH levels. Ovarian estradiol-17beat concentrations declined steadily throughout the sampling period, reaching almost undetectable levels 8 h after LH treatment. Elevated ovarian PGF levels were observed only at the 4- and 8-h sampling times. Indomethacin treatment, 1 h before LH, prevented the LH-induced increase in ovarian PGF levels, depressed PGF values considerably in saline-injected controls but produced no significant inhibition of ovarian cAMP and progesterone levels. Aminoglutethimide phosphate depressed ovarian concentrations of all three steroids (progesterone, testosterone, and estradiol-17beta) to essentially undetectable levels, both in control and LH-injected rats, but did not alter the LH-induced changes in ovarian cAMP and PGF levels. These observations support the concept of cAMP as a mediator of the LH-induced alterations of ovarian steroidogenesis in vivo during the preovulatory period, but argue against an obligatory role of PGF in this process.

Aminoglutethimide↗
PubMed1976

Stimulation of aromatization of exogenous and endogenous androgens in ovaries of hypophysectomized rats in vivo by follicle-stimulating hormone.

The role of follicle-stimulating hormone (FSH) in the regulation of estrogen biosynthesis in vivo has been investigated in immature hypophysectomized rats, utilizing uterine weight and histologic responses, and ovarian estradiol-17beta concentrations as indicators of estrogen secretion. A highly purified FSH preparation produced only borderline increases in uterine weights and in ovarian estradiol-17beta contents when administered alone at 2.5 mug/day for 3 days. Testosterone or androstenedione (5 mg/day), when administered in the absence of FSH, produced typically androgenic stimulation of uteri, and did not increase ovarian estradiol-17beta concentrations. When administered concomitantly with FSH, the uterine weight-stimulating activity of these aromatizable androgens was substantially increased, accompanied by marked hypertrophy of the endometrial mucosal cells, and ovarian estradiol-17beta concentrations were increased 20- to 200-fold. The administration of the non-aromatizable androgen, 17beta-OH-5alpha-androstan-3-one (DHT) (5 mg/day, by itself produced uterine weight increases similar to those caused by testosterone alone; however, no evidence of increased estrogen secretion resulted from the combined treatment of DHT wtih FSH. A highly purified luteinizing hormone (LH) preparation was equally as effective as exogenous androstenedione in increasing ovarian concentrations of immunoreactive androgen (testosterone + DHT) but evoked none of the above signs of estrogen secretion unless administered together with FSH. The weights of ovaries were not affected by the administration of LH or of any of the androgens by themselves, but were approximately doubled by FSH alone. Ovarian weights were increased still further when FSH was administered concomitantly with LH, testosterone , or androstenedione, but not with DHT. It is concluded that FSH and LH regulate ovarian estrogen secretion in vivo by acting at biochemically distinct sites--LH stimulating the synthesis of C19-steroids, which are then converted to estradiol-17beta under specific stimulation by FSH.

Androgens↗
PubMed1976

Androgens augment FSH-induced progesterone secretion by cultured rat granulosa cells.

Granulosa cells have been isolated from ovaries of estrogen-treated immature intact and hypophysectomized rats, and have been maintained in culture in a chemically-defined medium. Progesterone secretion by these cells was testosterone or 17beta-OH-5alpha-androstan-3-one (DHT), progesterone secretion was low or undetectable. However, the addition of testosterone or DHT together with FSH caused a dramatic 8- to 19-fold increase over that caused by FSH alone. On the other hand, luteinizing hormone (LH) alone had no effect on progesterone secretion, but produced a small stimulation when added together with testosterone. These results demonstrate synergism between androgens and FSH in the control of progesterone secretion by granulosa cells in culture.

Animals↗
PubMed1976

Inhibition of ovarian estradiol-17beta secretion by luteinizing hormone in prepubertal, pregnant mare serum-treated rats.

Serum estradiol-17beta levels, elevated prior to the luteinizing hormone (LH) surge, decline abruptly following the release of endogenous LH or the injection of exogenous LH. To investigate the mechanism of this decline, bovine LH (NIH-LH-B8) was administered to immature rats, in which follicular maturation and estrogen biosynthesis were induced by a non-ovulating dose of pregnant mare serum gonadotropin (PMS). Serum and ovarian estradiol-17beta concentrations fell detectably by 4h, and reached levels around 20% of the controls by 8h after iv injection of 10 mug LH. Concomitant decreases occurred in ovarian androgen concentrations, following an initial rise, and in the in vitro ovarian testosterone aromatizing enzyme activity. The LH-induced inhibition of the aromatase activity was found to be of a non-competitive type. It is proposed that two enzyme systems are inhibited as a result of the LH treatment: the C17,20-lyase and the C19 androgen aromatase, thereby leading to decreased concentrations of estrogens in the ovaries and blood.

Androgens↗
PubMed1975

Preliminary evidence of a role for prostaglandin F in human follicular function.

Animal studies have shown that LH causes an increased synthesis of PGF by ovarian follicles both in vivo and in vitro. In lower animals, there is strong evidence that PGF acts as a mediator of certain LH effects, including maturation and extrusion of the ovum. Ovarian follicular tissue of 12 patients was halved or quartered and maintained in organ culture. Part of each follicle was exposed to gonadotropins throughout the culture period, while controls received no treatment. All tissues continued to synthesize PGF but in 11 cases the amount was greater in the gonadotropin-treated. It is concluded that PGF probably plays a role in human follicular function, including ovulation, and may act as a mediator of certain LH functions.

Adolescent↗
PubMed1975

Synthesis of estradiol-17 beta by Sertoli cells in culture: stimulation by FSH and dibutyryl cyclic AMP.

Sertoli cells isolated from the testes of 18 to 20-day old rats synthesize estradiol-17 beta when grown in primary culture in the presence of testosterone (5 X 10(-7) M). After an initial lag phase of about 2 hours, follicle-stimulating hormone (FSH) stimulates synthesis of estradiol up to 50-fold, synthesis being approximately linear for 24 hours when medium is changed every 2-6 hours. Luteinizing hormone (LH) causes only a marginal stimulation, at concentrations consistent with contamination with FSH. Dibutyryl cyclic 3',5'-adenosine monophosphate (dbcAMP) (10(-4)M) mimicks the effect of FSH. No significant synthesis occurs in the absence of steroid substrate or in the presence of pregnenolone (5 X 10(-7) M). When cells are pre-incubated for 24 hours with FSH in the absence of testosterone, addition of testosterone results in an immediated increase in estradiol synthesis without a lag phase, suggesting that FSH or dbcAMP are capable of inducing the conditions necessary for stimulation in the absence of testosterone. These observations provide the first direct evidence of estradiol-17 beta synthesis by Sertoli cells from normal animals, and offer evidence that synthesis of this steroid is regulated at the level of the aromatizing enzyme system by FSH and cyclic AMP.

Animals↗
PubMed1975

Pre-ovulatory changes in follicular fluid prostaglandin F levels in swine.

The concentration of prostaglandin F (PGF) has been measured by radioimmunoassay in follicular fluid collected from follicles at various time intervals after treatment of prepuberal gilts with pregnant mare serum gonadotropin and human chorionic gonadotropin to induce ovulation. A high proportion of animals will ovulate 116 +/- 8 hr after treatment. Pre-ovulatory follicles can be identified on the basis of gross morphological apperance 10-12 hr before the predicted time of ovulation. The concentration of PGF in fluid from follicles judged not to be pre-ovulatory was relatively constant at about 0.45 ng per g and appeared to be independent of the time of sampling. An increase in the concentration of PGF was observed in fluid collected from follicles classified as destined to ovulate. This increase became more pronounced as the time of ovulation approached and reached a maximum at or about the time of follicle rupture. These data provide evidence in support of a role for prostaglandins in the ovulatory process in the pib.

Animals↗
PubMed1975

Pre-ovulatory elevation of rat ovarian prostaglandins F, and its blockade by indomethacin.

Prostaglandins of the F series have been measured, by radioimmunoassay, in ovaries of prepubertal rats in which first estrus was synchronized by injection of pregnant mare serum gonadotropin. Marked elevations, up to 20-fold, were observed approximately in parallel with the endogenous luteinizing hormone surge which occurs on the evening of proestrus, and within 4 h after injection of exogenous luteinizing hormone on the morning of proestrus. Injection of indomethacin, 0.8 mg per rat, at 14:45 on proestrus, prevented the increase in ovarian prostaglandins F without significantly reducing the proestrous elevation of serum luteinizing hormone. These observations support elevation of serum luteinizing hormone. These observations support a physiologic role of prostaglandins F in rat ovarian responses to luteinizing hormone.

Animals↗
PubMed1975

Follicle-stimulating hormone stimulates estradiol-17beta synthesis in cultured Sertoli cells.

Sertoli cells isolated from testes of 20-day-old rats and maintained in primary culture synthesized estradiol-17beta [1,3,5(10)-estratriene-3,17beta-diol] (measured by specific radioimmunoassay) when testosterone (17beta-hydroxy-4-androsten-3-one) 0.5 muM, was added to the culture medium. No detectable estradiol synthesis occurred when cells were incubated in medium containing pregnenolone (3beta-hydroxypregn-5-en-20-one), 0.5 muM, or containing no added steroid substrate. Follicle-stimulating hormone (FSH) (NIH-FSH-S10, 5 mug/ml) stimulated estradiol synthesis 12- to 80-fold when added to medium containing testosterone, but not when added to medium containing pregnenolone or no exogenous steroid substrate. A highly purified FSH preparation, with FSH potency 50 times that of the NIH-FSH, caused a similar stimulation at a concentration of 0.25 mug/ml of medium, whereas luteinizing hormone (NIH-LH-S18, 5 MUG/ML) Caused only marginal stimulation. Dibutyryl-adenosine 3':5' cyclic monophosphate, 0.1 mM, caused a 30-fold increase in estradiol synthesis by Sertoli cells cultured in medium containing testosterone. These studies provide direct demonstration of estradiol-17beta production by Seroli cells from normal animals, and offer evidence that the synthesis of this steroid is regulated at the level of the aromatizing enzyme system by FSH and adenosine 3':5' cyclic monophosphate.

Animals↗
PubMed1975

Stimulatory action of follice-stimulating hormone on estradiol-17 beta secretion by hypophysectomized rat ovaries in organ culture.

Ovaries of rats explanted in organ culture 2-3 days after hypophysectomy at 26 days of age synthesize ans secrete estradiol-17beta into the culture medium at approximately linear rates for 48 h. Addition of testosterone (5 times 10- minus 7M) to the culture medium occasionally caused small increases of up to 50 percent in rate of estradiol production. Significant increases (60-200 percent) in estradiol secretion resulted from addition of two different FSH preparations, in concentrations as low as 0.25 mug/ml in the absence of testosterone. In the presence of testosterone, the same FSH preparation caused much more marked increases in estradiol secretion of up to 900 percent. In the absence of testosterone, two different luteinizing hormone preparations failed to increase estradiol secretion significantly, although in the presence of testosterone, small increases were sometimes observed. It is concluded that FSH regulates estradiol biosynthesis in the hypophysectomized rat ovary by a specific stimulatory action on the aromatizing enzyme system.

Animals↗
PubMed1975

Estradiol-17beta biosynthesis in cultured granulosa cells from hypophysectomized immature rats; stimulation by follicle-stimulating hormone.

Granulosa cells isolated from the ovaries of hypophysectomized immature rats synthesize and secrete estradiol-17beta and estrone when grown for 2 days in monolayer culture in a synthetic medium containing testosterone (0.5 muM) and a highly purified follicle-stimulating hormone (FSH) preparation (0.25 mug/ml). Secretion is negligible in the absence of either testosterone or FSH, and a highly purified luteinizing hormone (LH) preparation (0.25 mug/ml) was without significant stimulatory effect. It is concluded that FSH regulates estrogen biosynthesis in granulosa cells of hypophysectomized rats by a specific stimulation of the aromatizing enzyme system.

Animals↗
PubMed1975

Loss of uterine luminal fluid in the rat: relative importance of changing peripheral levels of estrogen and progesterone.

Experiments were conducted to determine the relative importance of the decline in circulating estrogen levels, as opposed to the increase in progesterone levels, in the hormonal control of the loss of luminal fluid from the uterus of the rat, an event which usually occurs early on the morning of estrus. Silastic capsules containing crystalline estradiol-17beta (E2) were implanted subcutaneously in ovariectomized immature rats. Approximately 64 h later, the capsules were either removed (E2 withdrawal) to mimic the fall in peripheral estrogen levels occurring at proestrus, or left in place (continuous E2), and, at the same time, progesterone or oil was administered. Fifteen hours later, irrespective of whether E2 was withdrawn or not, 2 mg progesterone reduced uterine luminal fluid accumulation to levels usually seen in intact animals on the morning of estrus; however, the loss of fluid occurred slightly sooner if E2 was withdrawn when progesterone was administered. By itself, E2 withdrawal resulted in only a small decrease in uterine luminal fluid by 15 h, even though serum E2 levels had fallen to less than 1.5 pg/ml by this time. This loss was brought about by escape of the fluid through the cervix rather than by its reabsorption from the lumen. The dose-response relationships between progesterone and uterine luminal fluid accumulation indicated that when E2 was withdrawn, a smaller amount of progesterone brought about the loss of uterine luminal fluid accumulation than when E2 was continuous. These results suggest that increased progesterone secretion on the afternoon of proestrus is essential for the loss of uterine luminal fluid, and that the decline in estrogen secretion at this time may be of importance by allowing the progesterone to be more effective.

Animals↗