Biomedical subjects

S Lun

Publications and source records attributed to S Lun.

At least 55 records · Page 3Linked to original sources

PubMed1987

Influence of follicular health on the steroidogenic and morphological characteristics of bovine granulosa cells in vitro.

In 24-h cultures, steroid production by cells from non-atretic follicles increased with increasing follicular diameter. Cells from atretic follicles, of all sizes, produced low amounts of oestradiol-17 beta, but very high amounts of progesterone, relative to cells from non-atretic follicles. Increasing the culture period to 72 h caused little change in daily progesterone and oestradiol-17 beta production by granulosa cells from atretic follicles. In contrast, in cells from non-atretic follicles, daily progesterone production increased and daily oestradiol-17 beta production decreased to the levels observed with cells from atretic follicles. Dibutyryl cyclic AMP (1.0 mM) significantly stimulated progesterone production by cells from atretic, but not from non-atretic, follicles. Testosterone (1 microgram/ml) had no effect on progesterone production by cells from atretic follicles, while oestradiol-17 beta, oestrone, testosterone, androstenedione and 5 alpha-dihydro-testosterone (0-1000 ng/ml) each significantly suppressed progesterone production by cells from non-atretic follicles in a dose-dependent manner. Morphometric analysis revealed few subcellular differences between cells from non-atretic and atretic follicles. Mean cell volume was significantly higher for cells from atretic compared to non-atretic follicles, but the mean volumes of the major subcellular components were not influenced by follicle health. The mean surface area of the plasma and nuclear membrane, and granular endoplasmic reticulum was also significantly higher in cells from atretic compared to non-atretic follicles.

Animals↗

PubMed1987

Differences in gonadotrophin-stimulated cyclic AMP production by granulosa cells from booroola x merino ewes which were homozygous, heterozygous or non-carriers of a fecundity gene influencing their ovulation rate.

Granulosa cells from follicles of different sizes from Booroola x Merino ewes which were homozygous (FF), heterozygous (F+) or non-carriers(++) of a fecundity gene were obtained 0-48 h after cloprostenol injection on Day 10 of the oestrous cycle. The highest mean amounts of cAMP produced by the cells did not differ between the genotypes. However, in the ++ ewes it was attained by cells from follicles greater than or equal to 5 mm in diameter, whereas in F+ and FF ewes it was attained by cells from follicles 3-4.5 mm in diameter. Cells from 1-2.5-mm diameter follicles of FF ewes were more sensitive to FSH and LH than were corresponding cells from F+ or ++ ewes. Granulosa cells from greater than or equal to 5 mm diameter follicles of ++ ewes 12-24 h after injection of cloprostenol had a lower mean response to FSH and LH than did cells obtained 0-6 or 36-48 h after cloprostenol. No such effect of time was evident for cells from any size of follicles obtained from F+ or FF ewes. In 1-2.5-mm diameter follicles, the mean aromatase activity of granulosa cells from ++ and F+ ewes was similar, but significantly lower than that of cells from FF ewes. In 3-4.5 mm diameter follicles, the mean aromatase activity of cells from F+ and FF ewes was similar, and significantly higher than that of cells from ++ ewes. For all 3 genotypes, there was a significant positive relationship between FSH or LH stimulation of granulosa cell cAMP production and cellular aromatase activity.

Animals↗

PubMed1986

Adenosine cyclic 3',5'-monophosphate and steroid production by small ovarian follicles from Booroola ewes with and without a fecundity gene.

The tissue contents of adenosine cyclic 3',5'-monophosphate (cAMP) in freshly dissected follicles (0.13-1.00 mm diam.) were significantly higher in Booroola ewes containing a major fecundity gene (FF and F+ ewes) compared to those values in Booroolas with no copy of the gene (++ animals; P less than 0.025). After a 1 h incubation with LH + FSH, the respective proportions of follicles with a diameter of 0.13-0.52 mm (n = 288) and 0.53-1.00 mm (n = 271) that had synthesized greater than or equal to 0.6 pmol cAMP and greater than or equal to 1.0 pmol cAMP were significantly influenced by genotype (Booroola ewes homozygous for the F-gene, FF greater than heterozygous, F+ greater than ++; P less than 0.01 for both follicle size ranges). The contents of progesterone, androstenedione, testosterone and oestradiol-17 beta in minced ethanolic extracts of freshly dissected follicles (n = 188) were undetectable regardless of Booroola genotype. However, when follicles of 0.53-1.00 mm but not 0.13-0.52 mm diameter were cultured for 48 h with LH + FSH under 70 kPa of a 50% O2, 45% N2 and 5% CO2 gas mixture, the proportions that synthesized high levels of progesterone (greater than or equal to 4.0 ng), androstenedione (greater than or equal to 3 ng), and oestradiol (greater than or equal to 0.8 ng) were significantly influenced by genotype (FF greater than F+ greater than or equal to ++; P less than 0.05 for each steroid). No significant genotypic differences were noted for testosterone synthesis. Collectively, these results show that the Booroola F-gene has an influence on the maturation of ovarian follicles from an early stage of growth.

Androstenedione↗

PubMed1986

Use of bovine follicular fluid to increase ovulation rate or prevent ovulation in sheep.

Romney ewes were injected intramuscularly once or twice daily for 3 days with 0, 0.1, 0.5, 1 or 5 ml of bovine follicular fluid (bFF) treated with dextran-coated charcoal, starting immediately after injection of cloprostenol to initiate luteolysis on Day 10 of the oestrous cycle. There was a dose-related suppression of plasma concentrations of FSH, but not LH, during the treatment period. On stopping the bFF treatment, plasma FSH concentrations 'rebounded' to levels up to 3-fold higher than pretreatment values. The mean time to the onset of oestrus was also increased in a dose-related manner by up to 11 days. The mean ovulation rates of ewes receiving 1.0 ml bFF twice daily (1.9 +/- 0.2 ovulations/ewe, mean +/- s.e.m. for N = 34) or 5.0 ml once daily (2.0 +/- 0.2 ovulations/ewe, N = 25) were significantly higher than that of control ewes (1.4 +/- 0.1 ovulations/ewe, N = 35). Comparison of the ovaries of ewes treated with bFF for 24 or 48 h with the ovaries of control ewes revealed no differences in the number or size distribution of antral follicles. However, the large follicles (greater than or equal to 5 mm diam.) of bFF-treated ewes had lower concentrations of oestradiol-17 beta in follicular fluid, contained fewer granulosa cells and the granulosa cells had a reduced capacity to aromatize testosterone to oestradiol-17 beta and produce cyclic AMP when challenged with FSH or LH. No significant effects of bFF treatment were observed in small (1-2.5 mm diam.) or medium (3-4.5 mm diam.) sized follicles. Ewes receiving 5 ml bFF once daily for 27 days, from the onset of luteolysis, were rendered infertile during this treatment period. Oestrus was not observed and ovulation did not occur. Median concentrations of plasma FSH fell to 20% of pretreatment values within 2 days. Thereafter they gradually rose over the next 8 days to reach 60% of pretreatment values where they remained for the rest of the 27-day treatment period. Median concentrations of plasma LH increased during the treatment period to levels up to 6-fold higher than pretreatment values. When bFF treatment was stopped, plasma concentrations of FSH and LH quickly returned to control levels, and oestrus was observed within 2 weeks. The ewes were mated at this first oestrus and each subsequently delivered a single lamb.

Animals↗

PubMed1986

Differences in ovarian activity between booroola X merino ewes which were homozygous, heterozygous and non-carriers of a major gene influencing their ovulation rate.

Differences in the function and composition of individual ovarian follicles were noted in Booroola Merino ewes which had previously been segregated on at least one ovulation rate record of greater than 5 (FF ewes, N = 15), 3-4 (F+ ewes, N = 18) or less than 3 (++ ewes, N = 18). Follicles in FF and F+ ewes produced oestradiol and reached maturity at a smaller diameter than in ++ ewes. In FF (N = 3), F+ (N = 3) and ++ (N = 3) ewes, the respective mean +/- s.e.m. diameters for the presumptive preovulatory follicles were 3.4 +/- 0.3, 4.1 +/- 0.2 and 6.8 +/- 0.3 mm and in each of these follicles the respective mean +/- s.e.m. numbers of granulosa cells (X 10(6)) were 1.8 +/- 0.3, 2.2 +/- 0.3 and 6.6 +/- 0.3. During a cloprostenol-induced follicular phase, the oestradiol secretion rates from FF ewes with 4.8 +/- 0.4 'oestrogenic' follicles, F+ ewes with 3.2 +/- 0.2 'oestrogenic' follicles and ++ ewes with 1.5 +/- 0.02 'oestrogenic' follicles were not significantly different from one another. Moreover, the mean total numbers of granulosa cells from the 'oestrogenic' follicles from each genotype were identical, namely 5.4 X 10(6) cells. Irrespective of genotype the mean weight of each corpus luteum was inversely correlated to the ovulation rate (R = 0.91, P less than 0.001). Collectively, these findings support the notion that the maturation of greater than or equal to 5 follicles in FF ewes and 3-4 follicles in F+ ewes may each be necessary to provide a follicular-cell mass capable of producing the same quantity of oestradiol as that from 1-2 preovulatory follicles in ++ ewes.

Animals↗

PubMed1986

125I-labelled hCG binding characteristics in theca interna and other tissues from Romney ewes and from Booroola x Romney ewes with and without a major gene influencing their ovulation rate.

Specific receptors for 125I-labelled hCG in ovarian follicle wall were located in the theca interna. No specific binding of 125I-labelled hCG was found in theca externa and/or stromal tissue. The kinetics of 125I-labelled hCG binding to theca interna followed second order kinetics with calculated association rate constants (ka +/- s.d.) of 1.57 +/- 0.16 X 10(6) and 0.57 +/- 0.02 X 10(6) litres mol-1 sec-1 at 37 degrees C and 22 degrees C respectively. Dissociation of specifically bound 125I-labelled hCG from theca interna was minimal at 37 degrees C and 22 degrees C. The binding of 125I-labelled hCG to theca interna could be displaced with PMSG, FSH-P and sheep LH but other sheep pituitary hormones and LH-releasing hormone showed little or no cross-reaction. The calculated binding capacities (Bmax) and equilibrium dissociation constants (Kd) for 125I-labelled hCG binding to theca interna did not differ between Romney ewes and Booroola x Romney ewes with and without the fecundity (F) gene on Day 10 of the oestrous cycle, during anoestrus or at 36 h after an injection of cloprostenol on Day 10 of the oestrous cycle. When the data for Day 10 and anoestrus were pooled, the median (range) Bmax and Kd values in non-atretic follicles (greater than or equal to 3 mm diameter) were 12.0 (5.1-23.5) fmol/mg protein and 0.10 (0.05-0.16) nM respectively. At 36 h after cloprostenol injection the respective median (range) Bmax and Kd values in non-atretic follicles (greater than or equal to 3 mm diam.) increased to 46.9 (28.4-70.3) fmol/mg protein and 0.23 (0.13-0.65) nM respectively. In corpora lutea the hCG binding characteristics were similar in all the above breeds/genotypes. On Day 10 of the cycle, the mean Bmax but not the mean Kd value was significantly higher (P less than 0.01) than the corresponding value at 36 h after cloprostenol injection. In granulosa cells, from follicles of greater than or equal to 5 mm diameter of Romney and Booroola x Romney (++) ewes and from follicles of greater than or equal to 3 mm diameter of Booroola x Romney (F+) ewes, the hCG binding characteristics were similar. In granulosa cells from smaller sized follicles from the above breeds/genotypes, no specific hCG binding was noted.

Animals↗

PubMed1985

Influence of follicular atresia on LH-induced cAMP and steroid synthesis by bovine thecae interna.

The aim of the present study was to examine the interrelationships between the luteinizing hormone (LH) receptor, the LH-induced changes in adenosine cyclic 3', 5'-monophosphate (cAMP) and steroid synthesis in theca interna tissue of large antral follicles (greater than or equal to 8 mm diameter) from oestrous cycling cows. Three distinct types of theca interna were identified (types I, II and III), all of which contained an LH receptor: type I was capable of secreting increased amounts of cAMP dehydroepiandrosterone, androstenedione and testosterone when exposed to LH; type II was capable of secreting increased amounts of cAMP and progesterone but not the androgens when exposed to LH; type III was incapable of cAMP or steroid synthesis when exposed to LH. Follicles with type I thecae contained: a full complement of granulosa cells; high intrafollicular concentrations of oestradiol; and granulosa cells with a high capacity to metabolise testosterone to oestradiol. These follicles were considered to be non-atretic structures. Follicles with types III thecae contained: fewer granulosa cells; low intrafollicular concentrations of oestradiol; and granulosa cells with a low capacity to metabolise testosterone to oestradiol. Moreover, follicles with type III thecae contained the highest concentrations of progesterone and the lowest concentrations of androstenedione and testosterone. These follicles were considered to be severely atretic structures. Follicles with type II thecae contained granulosa cell populations and progesterone, and androgen concentrations which were intermediate between those with thecae of types I and III. These follicles were considered to be at an intermediate stage of atresia.(ABSTRACT TRUNCATED AT 250 WORDS)

Androstenedione↗

PubMed1985

Ovarian activity in Booroola X Romney ewes which have a major gene influencing their ovulation rate.

A marked difference in both the function and composition of individual ovarian follicles was noted in Booroola X Romney ewes (6-7 years of age) which had previously been segregated on at least one ovulation rate record of 3-4 (F + ewes, N = 21) or less than 3 (++ ewes, N = 21). Follicles in F + ewes produced oestradiol and reached maturity at a smaller diameter than in ++ ewes. In F+ ewes (N = 3), the presumptive preovulatory follicles were 4.4 +/- 0.5 (s.e.m.) mm in diameter and contained 2.1 +/- 0.3 X 10(6) (s.e.m.) granulosa cells, whereas in ++ ewes (N = 3), such follicles were 7.3 +/- 0.3 mm in diameter and contained 6.5 +/- 0.8 X 10(6) cells. During a prostaglandin (PG)-induced follicular phase, the secretion rate of oestradiol from ovaries containing 3 presumptive preovulatory follicles in F + ewes was similar to that from ovaries with only one such follicle in ++ ewes. We suggest that the putative 'gene effect' in F + ewes is manifested during early follicular development and that it may be mediated via an enhanced sensitivity of granulosa cells to pituitary hormones. As a consequence, the development of 3 preovulatory follicles in F + ewes may be necessary to provide a cell mass capable of producing the same quantity of oestradiol as that from one preovulatory follicle in ++ ewes.

Androstenedione↗

PubMed1985

Gonadotrophin-stimulated cyclic AMP production by granulosa cells from Booroola x Romney ewes with and without a fecundity gene.

The influence of follicular size and health on FSH and LH stimulation of cAMP production by granulosa cells in vitro was studied in cells from Booroola X Romney ewes, with (F+) and without (++) a fecundity gene. The granulosa cells were obtained 0-48 h after the initiation of luteolysis on Day 10 of the oestrous cycle by cloprostenol. The highest mean amounts of cAMP produced by granulosa cells challenged with FSH or LH were not significantly different between the genotypes. However, they were achieved using granulosa cells from follicles greater than 3-4 mm in diameter in F+ ewes but from follicles greater than 4 mm in diameter in ++ ewes. Follicles may thus attain ovulatory maturity at a smaller diameter in F+ ewes than in ++ ewes. Granulosa cells from most atretic follicles gave a poor cAMP response to FSH or LH, compared to cells from non-atretic follicles. Granulosa cell responsiveness to FSH was independent of the time the cells were recovered after cloprostenol treatment in F+ ewes, but not in ++ ewes. Cellular responsiveness to LH was independent of time for sheep of both genotypes. There was a significant positive relationship for sheep of both genotypes between the level of aromatase activity in granulosa cells and cellular responsiveness to FSH and LH.

Animals↗

PubMed1985

FSH influences follicle viability, oestradiol biosynthesis and ovulation rate in Romney ewes.

Injection of steroid-free bovine follicular fluid (bFF; 2 X 5 ml s.c. 12 h apart) into anoestrous ewes lowered plasma FSH concentrations by 70% and after 24 h had significantly (P less than 0.01) reduced the number of non-atretic follicles (greater than or equal to 1 mm diam.) without influencing the total number of follicles (greater than 1 mm diam.) compared to untreated controls. Hourly injections of FSH (10 micrograms i.v. NIH-FSH-S12) for 24 h did not influence the number of non-atretic follicles but did negate the inhibitory effects of bFF on follicular viability. Hourly injections of FSH (50 micrograms i.v., NIH-FSH-S12) + bFF treatment for 24 h significantly increased the total number of non-atretic follicles, and particularly the number of medium to large non-atretic follicles (greater than 3 mm diam.) compared to the untreated controls (both P less than 0.01). The 10 micrograms FSH regimen (without bFF) significantly increased aromatase activity in granulosa cells from large (greater than or equal to 5 mm diam.; P less than 0.01) but not medium (3-4.5 mm diam.) or small (1-2.5 mm diam.) follicles compared to controls. The 10 micrograms FSH + bFF regimen had no effect on granulosa-cell aromatase activity compared to the controls. However, the 50 micrograms FSH plus bFF regimen increased the aromatase activity of granulosa cells from large, medium and small non-atretic follicles 2.6-, 8.3- and greater than or equal to 11-fold respectively compared to that in the control cells. Ewes (N = 11) that ovulated 2 follicles had significantly higher plasma FSH concentrations from 48 to 24 h and 24 to 0 h before the onset of a cloprostenol-induced follicular phase (both P less than 0.01) than in the ewes (N = 12) that subsequently ovulated one follicle. Hourly FSH treatment (1.6 micrograms i.v., NIAMDD-FSH-S15) for 24 h but not for any 6 h intervals between 48 and 24 h or 24 and 0 h before a cloprostenol-induced luteolysis also resulted in significant increases (P less than 0.05) in the number of ewes with 2 ovulations.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1984

[125I]hCG binding to bovine thecal tissue from healthy and atretic antral follicles.

[125I]hCG binding to thecal tissue from healthy bovine follicles was examined and compared to [125I]hCG binding to other bovine ovarian tissues. [125I]hCG bound specifically to theca interna but not to theca externa. Binding to theca interna was a time- and temperature-dependent process, the rate of association obeying second-order kinetics with calculated rate constants of 1.97 +/- 0.13 X 10(5) and 0.85 +/- 0.04 X 10(5) 1 M-1 sec-1 at 37 and 22 degrees C, respectively. The dissociation of [125I]hCG from theca interna was a slow biphasic process with only 40% of specifically bound [125I]hCG being liberated after 8 h at 37 degrees C. Unlabelled hCG and LH, but not FSH, prolactin, GH, TSH or GnRH, inhibited [125I]hCG binding to theca interna. The specific binding of [125I]hCG to theca interna was saturable and equilibrium binding data produced a linear plot when fitted to the Woolf equation. The equilibrium dissociation constant (Kd) and maximum binding capacity (Bmax) calculated from Woolf plots were 0.21 +/- 0.02 nM (mean +/- SEM) and 34 +/- 4 fmoles/mg protein, respectively. Constants for [125I]hCG binding to granulosa cells and luteal tissue, respectively, were 0.29 +/- 0.02 and 0.31 +/- 0.04 nM for the Kd values and 32 +/- 6 and 116 +/- 13 fmoles/mg protein for the Bmax values. [125I]hCG binding constants for small (less than 8 mm dia.) and large (greater than or equal to 8 mm dia.) follicles (healthy or atretic) were not significantly different. In addition, there was no difference in the [125I]hCG binding constants of healthy and atretic follicles (large or small).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1984

Steroidogenesis by bovine theca interna in an in vitro perifusion system.

The aims of these studies were: to examine the steroidogenic responses of perifused bovine theca interna to varying flow rates of media and varying amounts of luteinizing hormone (LH), and to compare the steroidogenic outputs of theca interna from follicles of differing size and health with those of other ovarian tissues. The results showed that the outputs of androstenedione by thecae interna from healthy but not atretic follicles, with or without stimulation by LH, were amplified by the flow rate of media. Steroidogenesis by perifused theca interna was also influenced by the mass and concentration of LH as well as by the duration of exposure to LH. When expressed on a per unit mass basis, the outputs of androstenedione from LH-primed thecae interna from small (2-5.5 mm diameter), medium (6-9.5 mm diameter) and large (greater than or equal to 10 mm diameter) healthy follicles were comparable. But when the above data were expressed per total mass of theca interna, the androstenedione output increased significantly with increasing follicular diameter (P less than 0.01). Under the experimental conditions employed, the fraction of androstenedione produced by thecal tissue as a percentage of the total output of progesterone, androstenedione, testosterone and estradiol was 82%, whereas the progesterone, testosterone and estradiol fractions were 1%, 15% and 2%, respectively. By contrast, the granulosa cell output of progesterone, androstenedione, testosterone and estradiol were 79%, 0%, 0% and 21%, respectively. When this cell type was supplied with saturating amounts of androstenedione, it contributed greater than or equal to 90% of the total quantity of estradiol by the two cell types in isolation.

Androstenedione↗

PubMed1984

Changes in gonadotrophin secretion and ovarian antral follicular activity in seasonally breeding sheep throughout the year.

Overall, significantly more antral follicles greater than or equal to 1 mm diameter were present in Romney ewes during anoestrus than in the breeding season (anoestrus, 35 +/- 3 (mean +/- s.e.m.) follicles per ewe, 23 sheep; Day 9-10 of oestrous cycle, 24 +/- 1 follicles per ewe, 22 sheep; P less than 0.01), although the mean numbers of preovulatory-sized follicles (greater than or equal to 5 mm diam.) were similar (anoestrus, 1.3 +/- 0.2 per ewe; oestrous cycle, 1.0 +/- 0.1 per ewe). The ability of ovarian follicles to synthesize oestradiol did not differ between anoestrus and the breeding season as assessed from the levels of extant aromatase enzyme activity in granulosa cells and steroid concentrations in follicular fluid. Although the mean plasma concentration of LH did not differ between anoestrus and the luteal phase of the breeding season, the pattern of LH secretion differed markedly; on Day 9-10 of the oestrous cycle there were significantly more (P less than 0.001) high-amplitude LH peaks (i.e. greater than or equal to 1 ng/ml) in plasma and significantly fewer (P less than 0.001) low amplitude peaks (less than 1 ng/ml) than in anoestrous ewes. Moreover, the mean concentrations of FSH and prolactin were significantly lower during the luteal phase of the cycle than during anoestrus (FSH, P less than 0.05, prolactin, P less than 0.001). It is concluded that, in Romney ewes, the levels of antral follicular activity change throughout the year in synchrony with the circannual patterns of prolactin and day-length. Also, these data support the notion that anovulation during seasonal anoestrus is due to a reduced frequency of high-amplitude LH discharges from the pituitary gland.

Anestrus↗

PubMed1984

Some aspects of thecal and granulosa cell function during follicular development in the bovine ovary.

The patterns of ovarian follicular development and the steroidogenic properties of individual follicles (greater than or equal to 2 mm diam.) were assessed in Angus cows from Day - 5 until Day + 1 of the oestrous cycle (oestrus = Day 0). Individual follicles were judged to be healthy or atretic using a new classification system incorporating assessments of thecal vascularity and colour, the number of granulosa cells, the presence or absence of debris in follicular fluid and the status of the oocyte. The results suggest that the theca interna of small antral follicles (less than 5 mm diam.) responds to LH and synthesizes androstenedione before the granulosa cells develop an appreciable ability to metabolize androgen to oestrogen. Regardless of follicle size, the output of thecal androstenedione per unit mass of tissue remained unchanged in healthy but not in atretic follicles. On a per cell basis, aromatase activity increased in granulosa cells from healthy but not from atretic follicles with increasing follicle size. Peak levels of aromatizing activity were consistently observed in dominant oestrogen-enriched follicles on Day 0 although similar activity was also observed in some healthy follicles (greater than or equal to 8 mm diam.) on other days of the cycle. Early atresia in bovine follicles was characterized by an absence or lowering of aromatase activity in granulosa cells which always preceded any reduction in the thecal steroidogenic response to LH. It was estimated that between 20 and 60 antral follicles (greater than or equal to 2 mm diam.) per cow may respond to LH by synthesizing androgen whereas only 1-3 follicles (greater than 5 mm diam.) have granulosa cells capable of metabolizing androstenedione or testosterone to oestradiol.

Androstenedione↗

PubMed1984

Seasonal differences in ovarian activity in cows.

The plasma concentrations of LH and prolactin and various parameters of ovarian function were examined in cows on known days of the oestrous cycle during May and June (autumn and winter) and during October (spring). Luteinizing hormone peak frequency and plasma prolactin concentrations were significantly higher in October than during the May-June period (LH, P less than 0.05; prolactin, P less than 0.01). The mean diameters of large healthy follicles (greater than or equal to 8 mm diameter) and the dominant oestrogen-secreting follicles were significantly larger (P less than 0.01 for both follicle types) and each follicle contained more granulosa cells (both P less than 0.01) in May-June than in October. The LH responsiveness of theca interna with respect to androstenedione production and the levels of aromatase activity in granulosa cells did not differ with time of year. The corpora lutea were heavier (P less than 0.05) and secreted more progesterone (P less than 0.01) in May-June than in October. It is concluded that seasonal differences in ovarian activity exist in cows and that these differences are probably the consequence of seasonal differences in gonadotrophin secretion.

Androstenedione↗

PubMed1983

Lack of direct effect of dopamine on aldosterone secretion in vivo.

Previous work suggests that aldosterone is modulated by dopamine, which exerts an inhibitory effect at the level of the adrenal cortex. This study reports the effect of dopamine on aldosterone secretion in conscious sheep with cervical adrenal transplants in whom endogenous ACTH secretion was suppressed by dexamethasone. In control experiments (n = 7) local adrenal infusions of angiotensin II (AII) (1.6 ng/min for 120 min) increased aldosterone secretion to peak levels (47.8 +/- 6.8 ng/min. mean +/- SEM) at 20 min, after which secretion fell to stable levels (20-28 ng/min) at 60-120 min. On separate days, sheep were restudied (n = 5) during systemic dopamine infusions (4 microgram/kg . min for 90 min), commencing 30 min before AII stimulation. There was no significant difference, either in the pattern or the sensitivity of the aldosterone response to AII, with dopamine infusions. Large intraadrenal infusions of dopamine (10 microgram/min) also failed to alter the aldosterone response to AII. The possibility that aldosterone was already under maximum tonic inhibition by dopamine was studied in four additional experiments using the dopamine blocking drug, metoclopramide. Although the systemic (iv) administration of metoclopramide increased aldosterone in both intact and transplanted sheep, local infusions of metoclopramide (0.5-15 microgram/min intraarterially) had no consistent effect on the aldosterone response to AII, and the addition of dopamine during metoclopramide infusions also had no effect. These results indicate that local (adrenal) dopaminergic mechanisms play little or no part in the regulation of aldosterone secretion in the sheep. The mechanism whereby aldosterone secretion is increased by systemic metoclopramide remains to be explained.

Adrenal Glands↗

PubMed1983

Adrenal hormone responses to cerebroventricular angiotensin II in the sheep.

The effects of intracerebroventricular angiotensin II on plasma aldosterone levels were studied in conscious and anesthetized sheep. Infusion of angiotensin II at 20 ng/min into the lateral cerebral ventricle raised plasma aldosterone levels. Since plasma cortisol increased in parallel with aldosterone, and as the response of both corticosteroids was obliterated by dexamethasone pretreatment, ACTH appeared to mediate the adrenal-stimulating action of angiotensin II. Central infusion of angiotensin II, was without effect on the peripheral renin-angiotensin system or the sympathetic nervous system as gauged by the lack of change in plasma levels of angiotensin II, norepinephrine, and epinephrine.

Adrenal Cortex↗

PubMed1983

A direct radioimmunoassay for aldosterone in plasma.

This rapid radioimmunoassay for aldosterone is performed directly on 100 microL of unprocessed plasma, with 125I-labeled aldosterone as the labeled antigen. Our use of steroid-free plasma in preparing the standard curve resulted in an overestimate of aldosterone; this problem was overcome by adding to such plasma a mixture of other steroids to provide a constant steroid/aldosterone ratio. Over a wide range of aldosterone concentrations, results agreed well between the present assay and a routine method involving solvent extraction and paper chromatography (r = 0.85), and sensitivity (20 ng/L) and inter- (10.4%) and intra- (3.9%) assay CVs were better with the present assay. Our assay is especially useful for multiple samples and (or) when only small-volume samples are available.

Aldosterone↗