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D T Armstrong

Publications and source records attributed to D T Armstrong.

At least 145 records · Page 8Linked to original sources
PubMed1983

Prostanoid content of human milk: relationships to milk fatty acid content.

Analysis of human milk was conducted to determine if transitions in milk lipid composition and thus the changes in fatty acid synthesis that occur during lactogenesis are related to levels of specific prostanoids present in milk lactated. Serial samples representative of a complete expression and reflecting varying concentrations of milk fatty acids were collected over the first 37 days of lactation. Milk from mothers delivering infants at term and mothers delivering premature infants of 28-33 weeks gestational age was compared to examine potential relationships between prostanoid concentration and gestational age effects on milk lipid content. Milk levels of prostaglandin E, prostaglandin F and the metabolite of prostacyclin--6-keto-prostaglandin F1 alpha were determined by radioimmunoassays. Transitions in fatty acid content for all milk lipid classes were determined by quantitative analysis of fatty acids by glass capillary gas liquid chromatography. During lactation the levels of prostaglandin E correlated with milk content of 6-keto prostaglandin F1 alpha. For term mothers, milk content of prostaglandin E, 6-keto prostaglandin F1 alpha, total fatty acids and medium chain fatty acids increased from early lactation when compared with subsequent days sampled. Levels of these milk constituents observed for early milk of preterm mothers were significantly different when compared with term mothers and in addition did not follow the same longitudinal pattern during subsequent days of lactation. Physiologically significant levels of prostaglandins in milk may reflect the balance between hormonal and subcellular controls over lactogenesis. It is also conceivable that the presence of these prostanoids in milk may influence gastrointestinal physiology and nutrient absorption in the neonate.

6-Ketoprostaglandin F1 alpha↗
PubMed1982

PGE2 and dibutyryl-cAMP enhance the response of rat granulosa cells to FSH.

Granulosa cells isolated from immature Sprague-Dawley rat ovaries produce progesterone (31.7 pg/micrograms cell protein) in response to an acute FSH stimulus (5 micrograms/ml NIH-FSH-S11, 2 H). After culture for 48 h in the absence of hormones (control culture), progesterone production by the granulosa cells in response to FSH is significantly reduced (2.9 pg/micrograms cell protein). Cells cultured with prostaglandin E2 (PGE2, 1 microgram/ml) or dibutyryl-cAMP (dbcAMP, 1 mM) exhibited a discernibly greater steroidogenic response to FSH (12.5 and 53.4 pg/microgram cell protein, respectively) than that of control cultures. Therefore the presence of PGE2 or dbcAMP in the culture medium helps to maintain the steroidogenic capacity of granulosa cells in culture. It is probable that this capacity is maintained at a locus distal to the production of cAMP by FSH. Paradoxically, granulosa cells cultured with PGE2 produce less cAMP in response to FSH stimulation than cells in control cultures (15.9 vs. 250.3 fm/micrograms cell protein). This may be due to a suppressive effect of prior exposure to PGE2 on the subsequent activity of adenylate cyclase when the FSH is introduced and a concomitant elevation of phosphodiesterase activity.

1-Methyl-3-isobutylxanthine↗
PubMed1982

Implantation and later fetal development in immature rats given a superovulatory dose of pregnant mare's serum gonadotropin, later neutralized by antiserum.

In an earlier experiment, 29-day-old female rats were superovulated with 40 IU pregnant mare's serum gonadotropin (PMSG) and very few blastocysts were recovered from the uterus on Day 5. Administration of a PMSG antiserum (a/s) prior to ovulation resulted in recovery of blastocysts in all rats and the present set of experiments was undertaken to investigate the later development of these blastocysts. Implantation was found to occur in only approximately 50% of superovulated (SOV) a/s-treated animals regardless of whether or not estrogen was given on Day 4. It is suggested that the exposure to high preovulatory estrogen and an imbalance in the progesterone/estrogen ratio during the early preimplantation period are possible causes of the loss of blastocysts. The majority of SOV a/s-treated rats in which implantation occurred carried fetuses to Day 20, although there was a further small loss of pregnancy between Days 8 and 20. On Day 8 steroid concentrations in both serum and ovaries were similar to those observed on Day 5 in earlier experiments. By Day 20 serum and ovarian progesterone concentrations were significantly higher than on Day 8 in all superovulated rats, which may reflect increased production by the larger number of corpora lutea in these animals. The present set of experiments shows that in a significant percentage of SOV a/s animals blastocysts are capable of implanting and continuing to develop into normal fetuses by Day 20. However, at least 50% of SOV a/s-treated rats fail to maintain pregnancy between Days 5 and 8 and this could be a result of a failure in the uterus to provide a suitable environment for implantation or to abnormalities in the blastocysts.

Animals↗
PubMed1982

Estradiol-17 beta and androgen secretion by isolated porcine ovarian follicular cells in vitro.

The cellular sources and gonadotropic regulation of porcine ovarian estrogen and androgen were assessed by culturing isolated granulosa cells and thecal cells from medium size follicles (4-6 mm diameter) separately for 24 h in a chemically defined medium containing gonadotropins and (or) testosterone. At the end of the culture period, estradiol-17 beta (estradiol) and androgens in the media were determined by radioimmunoassays. Production of estradiol by granulosa cells without an exogenous aromatizable androgen was low in the absence or presence of a highly purified preparation of either follicle-stimulating hormone (FSH. 0.25 microgram/mL) or luteinizing hormone (LH. 1 microgram/mL). Addition of testosterone or androstenedione (0.5 microM), but not dihydrotestosterone or pregnenolone, significantly increased estradiol secretion. Additional increases were observed when FSH, LH, prostaglandin E2, or dibutyryl cyclic 3'.5'-adenosine monophosphate was present. Production of estradiol by thecal cells was low in the presence or absence of exogenous testosterone, and was essentially unaffected by the presence of gonadotropins. Thecal cells, however, released large amounts of androstenedione and smaller amounts of testosterone and other androgens during 24-h culture and the production of these androgens was stimulated by LH but not by FSH. Androgen secretion by granulosa cells was negligible when compared with the theca and was unaffected by gonadotropins. It is concluded that the theca is the prime site for follicular androgen biosynthesis by the porcine ovarian follicle, and, upon LH stimulation, may provide androgen precursors for estradiol production by granulosa cells.

Androgens↗
PubMed1981

Modulation of functional capacity of small ovarian follicles in the post-partum cow by prolactin.

This study was undertaken to examine the possibility that the prolonged anovulatory period frequently experienced by the post-partum cow is due to a disruption of function at the ovarian level promoted by the high, suckling-induced, blood prolactin concentrations. Fifteen cows, less than 35 days post partum, were allocated to three groups (1, 3 and 5) and given no hormonal treatment, prostaglandin plus pregnant mare serum gonadotrophin (PMSG) treatment or injected with 2-bromo-alpha-ergocryptine to reduce circulating prolactin levels. Ten synchronized cyclic cows were allocated to two groups (2 and 4) and given prostaglandin or prostaglandin plus PMGS treatment. All cows were ovariectomized 1 or 2 days after treatment of Graafian follicles less than 9 mm in diameter were selected after dissection from the ovaries. The follicles were cultured for 18 h with or without prolactin (1 microgram/ml) and steroid accumulation in the culture medium estimated. The follicles were then separated into theca and granulosa which were incubated for 40 min with LH (1 microgram/ml) or FSH (5 micrograms/ml). Cyclic AMP concentrations were estimated as an indication of tissue responsiveness to gonadotrophins. The secretion of oestradiol-17 beta, progesterone, testosterone or androstenedione during 18 h culture did not differ between follicles isolated from post-partum or cyclic cows. The presence of prolactin in the culture medium had no overall effect on steroid secretion although some specific effects within each group were noticed. Incubation with LH increased cyclic AMP levels in the theca but the granulosa did not respond. Likewise FSH increased cyclic AMP levels in granulosa preparations but not in theca. There were no differences in response between post-partum and cyclic cows, but exposure of the follicles to prolactin in vitro did significantly reduce the LH-induced increase in cyclic AMP levels in isolated theca. We have concluded that endogenous prolactin may modify but does not inhibit the resumption of ovarian function following parturition in the beef cow.

Animals↗
PubMed1981

Follicle-stimulating hormone induction of luteinizing hormone receptor in cultured rat granulosa cells: an examination of the need for steroids in the induction process.

The induction of LH receptors by FSH in cultured rat granulosa cells and the effects of ovarian steroids on this process were examined. Granulosa cells were isolated from the ovaries of untreated immature rats (25 days old) and cultured with highly purified FSH (Sairam; 250 ng/ml). After culture (48-96 h in chemically defined media), both the binding of [125I]hCG and the responsiveness (cAMP and progesterone production) to an acute LH stimulus (100 ng/ml; NIH B8) were measured. The appearance of LH/hCG-binding sites and LH responsiveness indicates the presence of functional LH receptors. The induction of LH receptors by FSH requires a lag period of 24-48 h. After 48 h, the concentration of LH receptors in cultured granulosa cells continues to increase with time in culture with FSH; the continuous presence of FSH is required to maintain the induction process. If granulosa cells are cultured without hormone for 24-48 h before FSH is added, no induction of LH receptors occurs. However, if 17 beta-estradiol (5 X 10(-7) M) is added during this initial period, then the cells are responsive to the later addition of FSH. This maintenance of FSH responsiveness is not observed when dihydrotestosterone or progesterone is substituted for 17 beta-estradiol in the initial culture period. The FSH-dependent induction of LH receptors in cultured rat granulosa cells can be blocked if an inhibitor of steroidogenesis, such as aminoglutethimide phosphate (AGP; 1 mM), is added along with FSH at the initiation of the culture. The inclusion of progesterone, dihydrotestosterone, or 17 beta-estradiol (but not 20 alpha-dihydroprogesterone) in the culture together with FSH and AGP will overcome the inhibition by AGP and restore the induction of LH receptors. The results suggest that steroids produced by the developing follicle can modulate the FSH-dependent induction of LH receptors, and this may play a role in the development of follicular responsiveness to LH.

Animals↗
PubMed1981

Hormonal and cellular interactions in follicular steroid biosynthesis by the sheep ovary.

Studies of isolated cell types from sheep follicles revealed several functional changes which occur during follicular maturation. Cyclic AMP production by granulosa cells from the smallest follicles studied (1-3 mm diameter) was stimulated by FSH but not by hCG, suggesting functional FSH receptors at this early stage of differentiation. Medium-sized follicles (4-6 mm) responded to both FSH and hCG. Granulosa cells were unable to synthesize androgens, but readily converted exogenous testosterone to oestradiol-17 beta. This conversion occurred to a limited extent in the cells from the smallest follicles, but was much greater in medium and large (greater than 6 mm) follicles. Oestradiol production by theca preparations from small follicles was barely detectable, but increased markedly with increasing follicle size. Androgen (androstenedione and testosterone) production by theca preparations was stimulated by hCG. This stimulation was short-lived, and levels declined to below control values after 6 h of culture. This decline could not be prevented by addition of cyclic AMP. The presence of granulosa cells with thecal preparations (i.e. follicle wall tissue) enhanced production of androgen by the theca, the effect being more marked for testosterone than for androstenedione. In-vivo studies in which granulosa cells and follicular fluid were removed during the preovulatory period suggested that granulosa cells and/or follicular fluid contributed to the oestradiol secreted into the ovarian vein during this period, but did not exclude a significant contribution by the theca as well.

Androgens↗