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Biomedical subjects

D T Armstrong

Publications and source records attributed to D T Armstrong.

At least 163 records · Page 9Linked to original sources
PubMed1980

Steroid biosynthesis by isolated human ovarian follicular cells in vitro.

Cultured thecal preparations from human ovarian follicles obtained from patients during the follicular phase of the menstrual cycle produced large amounts of delta 4-androstenedione and smaller amounts of testosterone and other androgens when stimulated by hCG, (Bu)2cAMP, and prostaglandin E2, but not when stimulated by FSH. Prostaglandin E2 also stimulated thecal cAMP production under the same conditions. By contrast, androgen production by granulosa cells was negligible with or without gonadotropins in the culture medium. Granulosa cells also did not produce 17 beta-estradiol, even when exposed to FSH and hCG, unless supplied with exogenous delta 4-androstenedione. On the other had, thecal, preparations did not produce significant amounts of 17 beta-estradiol even in the presence of FSH, hCG, and relatively large amounts of exogenous delta 4-androstenedione. These observations suggest that delta 4-androstenedione produced by LH or hCG-stimulated thecal cells is the main substrate for the synthesis of 17 beta-estradiol by FSH-stimulated granulosa cells in vivo.

Adult↗
PubMed1980

Concentrations of thromboxane B2 and 6-oxo-prostaglandin F1 alpha in amniotic fluid, decidual tissue, and placenta in the later stages of pregnancy in the rat.

To determine if the levels of TXA2 and PGI2 within the uterus change at parturition in rats, the concentrations of their respective stable products, TXB2 and 6-oxo-PGF1 alpha (6-k-PGF1 alpha) were measured in amniotic fluid, decidual and placental tissues by specific radioimmunoassays which have been verified by gas chromatography-mass spectrometry. Samples were collected on days 15, 20, 21, and 22 of pregnancy and during labor on day 23. In general, levels of TXB2 and 6-k-PGF1 alpha as well as those of PGE and PGF were highest during labor on day 23, although levels of TXB2 and 6-k-PGF1 alpha in amniotic fluid and decidual tissue, respectively, peaked on day 22. The concentrations were generally highest in decidual tissue, and lowest in amniotic fluid. These findings suggest that TXA2 and PGI2 may have a role in parturition in rats.

17-alpha-Hydroxypregnenolone↗
PubMed1979

Effect of danazol on estradiol-17beta and progesterone secretion by porcine ovarian cells in vitro.

The effect of danazol on progesterone (P4) and estradiol-17 beta (E2) secretion by cultured porcine granulosa cells was studied. Danazol markedly inhibited both basal and luteinizing hormone (LH)-stimulated P4 secretion by both granulosa and luteal cells in a dose-dependent manner during 24 hour culture periods. E2 secretion by granulosa cells was low (less than 3 ng/mg of protein) when cultured in the absence of an exogenous aromatizable substrate but was markedly increased when testosterone (T) was added to the media. Danazol inhibited E2 secretion by granulosa cells only when cultured in the presence of testosterone. E2 secretion by luteal cells was low even in the presence of testosterone and was not affected by danazol. These findings support the hypothesis that danazol can directly inhibit ovarian steroidogenesis independently of its inhibitory action on gonadotropin secretion.

Animals↗
PubMed1979

Pre-ovulatory changes in cyclic AMP and prostaglandin concentrations in follicular fluid of gilts.

The concentrations of cyclic adenosine 3', 5'-monophosphate (cyclic AMP) and prostaglandins E and F (PGE and PGF) were determined in follicular fluid collected from follicles of prepubertal gilts at various times after treatment with pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG) to induced ovulation. The concentrations of cyclic AMP, PGE and PGF in the follicular fluid after PMSG treatment but prior to hCG injection were about 1 pmol/ml, 1 ng/ml and 0.2 ng/ml, respectively. After hCG administration, the follicular fluid levels of cyclic AMP increased markedly, reaching a peak (400-fold increase) about 4 h after injection and then declined gradually to pre-hCG levels. A second rise (2.5- to 5-fold increase) occurred about 30 h after hCG with the levels being sustained up to the expected time of ovulation. In contrast, the levels of PGE and PGF remained relatively constant until 28-30 h after hCG treatment. Thereafter, the concentrations of both prostaglandins began to rise with the increases becoming more pronounced and reaching maximal values as the expected time of ovulation approached. These data provide further evidence for a physiological role of follicular prostaglandins in the process of ovulation but do not support an obligatory role for prostaglandins in the acute gonadotropin stimulation of cyclic AMP formation.

Animals↗
PubMed1979

Suppression of follicular cAMP and steroid response to gonadotrophins by pretreatment with gonadotrophin.

This study examines the effect of preincubation of sheep ovarian follicles with hCG or FSH on the ability of isolated theca and granulosa to increase cAMP levels in response to a second incubation with hCG or FSH. Secondly, the effect of preincubation of small follicles with hCG on androstenedione and testosterone production is examined in intact follicles. Preincubation with hCG resulted in a decrease in the ability of theca from large (4--6 mm in diameter) and small (1--3 mm) follicles and granulosa from large follicles to increase cAMP levels in response to a second exposure to hCG. Similarly, preincubation with FSH suppressed the response of isolated granulosa from small and large follicles to a second exposure to FSH. A partial, but significant inhibition of the response to the other hormone was observed after preincubation with both FSH and hCG. Intact small follicles pretreated with hCG were unable to increase testosterone secretion in response to a second exposure to hCG.

Androstenedione↗
PubMed1979

Inhibition by estradiol-17 beta of porcine thecal androgen production in vitro.

Thecal preparations from medium-sized procine ovarian follicles (3.5-5 mm diameter) were incubated for 4 h in a chemically defined medium in the presence or absence of highly purified luteinizing hormone (LH) and/or estradiol-17 beta (estradiol). LH (1 microgram/ml) stimulated the thecal production of testosterone (T) and dihydrotestosterone (DHT) by 2- to 3-fold. Although estradiol (10 microgram/ml) alone had only a slight but non-significant inhibitory effect on basal testosterone production, it significantly inhibited the production of both T and DHT as well as decreasing the DHT/T ratio in a dose-related manner in the presence of LH. Production of cyclic adenosine 3',5'-monophosphate (cAMP) and progesterone by the thecal cells was stimulated 50-to 200-fold and 2.5-fold, respectively, by LH. Estradiol had no significant effect on thecal cAMP and progesterone production in the presence or absence of the gonadotropin. These findings are consistent with the concept that estradiol produced by granulosa cells following hormonal stimulation may serve as a local negative feedback mechanism to control thecal androgen production.

Androgens↗