Search Results

You are looking at 1 - 6 of 6 items for

  • Author: R. C. Fry x
Clear All Modify Search
Free access

M. A. Driancourt, R. Webb and R. C. Fry

Summary. The process by which a single follicle is selected to ovulate while others regress is unknown in ewes. If the dominant follicle secretes substances that directly inhibit the growth of other follicles, the superovulatory response to the administration of exogenous gonadotrophins may be blunted. Administration of 1250 iu pregnant mares' serum gonadotrophin (PMSG) before or after the emergence of the dominant follicle in the follicular phase, or 1000 iu PMSG in the presence or absence of a large healthy or atretic follicle during the luteal phase did not affect the induced ovulatory response. Comparisons between the ovary with or without the dominant follicle did not reveal any differences in ovulatory response to PMSG. The in-vitro features (i.e. mitotic index, oestradiol and testosterone production) of follicles ipsilateral or contralateral to the dominant follicle during the early and late follicular phases were also similar.

If the dominant follicle secretes substances detrimental to the other follicles, this could be mimicked in vitro. Co-culture of small follicles with the largest follicles in a closed system did not reduce their incorporation of 3H thymidine in granulosa cells, compared with small follicles cultured alone.

These data suggest that dominance is probably not operative in sheep. The administration of 500 iu of PMSG during the midfollicular phase increased ovulation rate in Merino ewes, indicating that dominance is essentially passive in ewes and can easily be overcome by raising gonadotrophin concentration.

Keywords: follicle; ovulation; gonadotrophin; paracrine regulation; sheep

Free access

R. C. Fry, I. J. Clarke and L. P. Cahill

Summary. Ewes were unilaterally ovariectomized and/or hypophysectomized and treated with PMSG and hCG. For a given gonadotrophin treatment the ovulation rate per ewe was maintained, i.e. the ovulation rate of the remaining ovary was significantly increased (P < 0·05), after the removal of one ovary in hypophysectomized and in pituitary-intact ewes. It is concluded that compensation of ovulation rate in the remaining ovary after unilateral ovariectomy in the sheep may be independent of feedback from the ovary and the release of gonadotrophins from the pituitary gland.

Free access

D. Vogiagis, R. C. Fry, R. M. Sandeman and L. A. Salamonsen

Leukaemia inhibitory factor (LIF), a pleiotropic cytokine, is essential for blastocyst implantation in mice and maintains the development of ovine embryos in culture. The expression of LIF was examined by northern blot analysis in endometrial tissue from cyclic (days 4–16) and pregnant (days 4–20) ewes, and the corresponding protein was immunolocalized. Expression of mRNA encoding LIF remained relatively constant throughout the oestrous cycle and was present during early pregnancy. A decrease in mRNA encoding LIF was observed during early pregnancy (on days 12–14) and expression was highest on days 16–20. Immunoreactive LIF was present in the cellular compartments of the endometrium throughout the oestrous cycle and early pregnancy, with maximal immunostaining in the caruncular and intercaruncular luminal epithelium, and moderate staining in the glandular epithelium and intercaruncular stroma. Immunoreactive LIF was also detected in the trophoblast cells of day 17 blastocysts. Separately cultured endometrial epithelial and stromal cells from pregnant animals both expressed mRNA encoding LIF. Ovariectomized steroid-treated ewes were studied to establish whether steroid hormones had a role in regulating endometrial LIF. Ewes treated with oestradiol alone showed lower concentrations of immunoreactive LIF in the endometrium in comparison to ovariectomized, control animals, while treatment of ovariectomized animals with both oestradiol and progesterone had a greater inhibitory effect on LIF immunolocalization. These studies demonstrate the presence of mRNA encoding LIF and protein throughout the oestrous cycle and early pregnancy and suggest that steroid hormones may be involved in their regulation.

Free access

M. A. Driancourt, R. C. Fry, I. J. Clarke and L. P. Cahill

Summary. Ewes were hypophysectomized on Day 0 and ovariectomized 1, 2, 4 or 8 days later. There was no effect of hypophysectomy on the overall population of follicles > 0·8 mm in diameter during the time studied. However, the growth of healthy follicles >2 mm in diameter was prevented by Day 2. Turnover of follicles was very active in the ovaries of hypophysectomized ewes as shown by peaks in the proportion of follicles in early atresia at Day 4 and in advanced atresia at Days 1 and 8. By Day 8, most of the measures of the population of follicles 0·8 to 2 mm in diameter were back to the values of Day 0 ewes. The mitotic index of the granulosa cells of the healthy follicles exhibited a similar pattern with a nadir at Day 2 followed by a return at Days 4 and 8 to values similar to Day 0 ewes.

Ink-marked preovulatory follicles underwent a steady decrease in their histological size after hypophysectomy and this was associated with time-related changes in the health status of these follicles. By Day 1, 4 out of 7 follicles were still healthy while at Days 2, 4 and 8, all follicles were in advanced, late and collapsing atresia respectively. There was no evidence of an ability of PMSG (1000 i.u.) to rescue large follicles in advanced atresia (48 h after hypophysectomy). Furthermore, at 24 h after hypophysectomy, only 2 out of 5 follicles were maintained. However, PMSG partly overcame the depressing effects of hypophysectomy on the population of follicles 0·8 to 2 mm in diameter.

It is concluded that (1) active follicular turnover can occur in the absence of gonadotrophins; (2) it takes about 8 days for a large follicle to disappear in the ovarian stroma; and (3) it is unlikely that rescue of atretic follicles massively contributes to the ovulatory response after PMSG.

Free access

R. C. Fry, I. J. Clarke, J. T. Cummins, B. M. Bindon, L. R. Piper and L. P. Cahill

Summary. Booroola Merino ewes, with (F+; N = 17) and without (++; N = 13) a copy of the fecundity gene were hypophysectomized and 6 weeks later were given an i.m. injection of PMSG (high, medium or low dose) followed by hCG. The induced ovulation rates were observed laparoscopically. Ovulation rates were significantly higher (P < 0·01) in Booroola F+ ewes than in ++ ewes (8·00 ± 1·66 s.e.m. vs 3·62 ± 1·10 respectively). This suggests that the high fecundity of the Booroola ewe may be due primarily to ovarian rather than pituitary factors.

Keywords: Booroola; hypophysectomy; PMSG; hCG; ovulation rate

Free access

R. C. Fry, L. P. Cahill, J. T. Cummins, B. M. Bindon, L. R. Piper and I. J. Clarke

Summary. To determine whether the high ovulation rate of the Booroola Merino ewe could be explained by FSH metabolism we have tested the proposition that FSH may have a longer half-life in the plasma of Booroola Merino ewes than in control ewes. The half-life of plasma FSH was determined by removal of the pituitary gland, to abolish FSH secretion into the peripheral circulation, and monitoring by repeated blood sampling the subsequent decline in plasma FSH concentrations. The half-life of FSH was similar in Booroola (103 ± 14 (s.e.m.) min, N = 8) and control (116 ± 8 min, N = 9) ewes. However, when ewes that had been ovariectomized at least 6 months earlier were hypophysectomized, the half-life of FSH was increased from 110 + 8 min in ovary-intact ewes (N = 11) to 1101 ± 49 min (N = 6) (P < 0·001) with no difference between the two Merino strains. We conclude that changes in the circulating half-life of FSH do not account for the high fecundity of the Booroola but that ovariectomy can alter the half-life of FSH secreted by the pituitary gland.