Kisspeptin synchronizes preovulatory surges in cyclical ewes and causes ovulation in seasonally acyclic ewes.

We determined whether kisspeptin could be used to manipulate the gonadotropin axis and ovulation in sheep. First, a series of experiments was performed to determine the gonadotropic responses to different modes and doses of kisspeptin administration during the anestrous season using estradiol-treated ovariectomized ewes. We found that: 1) injections (iv) of doses as low as 6 nmol human C-terminal Kiss1 decapeptide elevate plasma LH and FSH levels, 2) murine C-terminal Kiss1 decapeptide was equipotent to human C-terminal Kiss1 decapeptide in terms of the release of LH or FSH, and 3) constant iv infusion of kisspeptin induced a sustained release of LH and FSH over a number of hours.

Effect of immunization against the alpha N (alphaN) and alpha C (alphaC) peptides of the alpha43 subunit of inhibin on antral follicular growth and atresia and the patterns of gonadotrophin secretion in ewes.

The aims of this study were to investigate the role of inhibin in the distribution of healthy and atretic antral follicles and the secretion patterns of gonadotrophins. Ewes were actively immunized against either alphaN or alphaC of the inhibin alpha subunit with a primary injection and three booster injections. The control ewes received adjuvant only.

Sex, fat and the tilt of the earth: effects of sex and season on the feeding response to centrally administered leptin in sheep.

Whilst there have been many studies in various species examining the effects of leptin on food intake, there is a paucity of data comparing responsiveness in the two sexes. We have, therefore, addressed this issue in sheep. Because this species shows seasonal variation in voluntary food intake (VFI), we also considered the possibility that there might be seasonal variation in the responsivity to leptin.

Effect of immunization against the amino-terminal peptide (alpha N) of the alpha 43-subunit of inhibin on follicular atresia and expression of tissue inhibitor of matrix metalloproteinase (TIMP-1) in ovarian follicles of sheep.

Ewes actively immunized against alpha N, the N-terminal peptide of inhibin alpha 43 precursor, have lowered fertility associated with ovulation failure, restricted tissue remodelling and reduced matrix metalloproteinase-2 activity in the follicular fluid at the time of expected ovulation. This could be due to altered ratios of matrix metalloproteinase-2 and tissue inhibitor of matrix metalloproteinase (TIMP-1), or to the onset of atresia in antral follicles destined to ovulate. The objectives of the present study were to investigate the effects of immunization against alpha N on the localization of TIMP-1 in ovine follicles, and on follicular growth and atresia in the follicular phase.

Endothelin in the ovine uterus during the oestrous cycle and early pregnancy.

Endothelin, which has potent vasoconstrictor and mitogenic actions, was measured by radioimmunoassay in tissue extracts of sheep endometrium and myometrium and was found to be present in similar amounts in both tissues during the oestrous cycle and in increasing amounts during the first 20 days of pregnancy (250-630 pg g-1 wet weight). Immunoreactive endothelin extracted from endometrium eluted at the same position as standard endothelin-1 on reverse-phase HPLC. Immunohistochemical techniques demonstrated that during the oestrous cycle endothelin immunoreactivity was very low in caruncular and intercaruncular stroma, luminal epithelium, outer and inner glandular epithelium, myometrium and blood vessels until after day 12 (oestrus: day 0).

Pituitary and ovarian function in ewes immunized against the amino-terminal peptide (alpha N) of the inhibin alpha 43-subunit.

Immunization of ewes against the amino-terminal peptide (alpha N) of the pro-alpha-subunit of inhibin has been shown to reduce fertility, thought to be due to disruption of ovulation. The aims of this study were to examine the effects of active immunization of ewes against alpha N on circulating concentrations of FSH, LH and on ovarian inhibin and progesterone, and to relate these observations to number of corpora lutea and oocyte recovery rates. Ewes were immunized against one or both of two recombinant full length bovine-alpha N immunogens (FP1 and FP2).

Effect of active immunization against the amino-terminal peptide (alpha N) of the alpha 43 kDa subunit of inhibin (alpha 43) on fertility of ewes.

Immunization against the amino-terminal peptide (alpha N) of the alpha 43 subunit of inhibin was shown previously to reduce fertility in ewes. The aim of this study was to examine the effects of active immunization of ewes against alpha N on egg recovery and fertilization rates. Ewes were immunized against alpha N immunogen, and were given 800 I.

Peripheral concentrations of immunoreactive inhibin during pregnancy and parturition in the ewe.

The aim of this study was to measure the peripheral concentrations of immunoreactive inhibin (ir-inhibin) and progesterone (P) during pregnancy and parturition in the ewe and to relate the concentrations of ir-inhibin to P and to the number and sex of the fetuses. P increased across pregnancy with higher levels in ewes with 2 fetuses (n = 5) than in those with 1 fetus (n = 6), and concentrations falling before birth. ir-Inhibin concentrations were relatively stable during the first 40 days of pregnancy for example (Day 20, 34.

Investigation of the mechanism by which insulin-induced hypoglycemia decreases luteinizing hormone secretion in ovariectomized ewes.

Ovariectomized ewes were treated with 100 IU insulin, iv, which caused reductions in blood sugar and plasma LH concentrations. The effect was prevented by the infusion (iv) of glucose, suggesting that neuroglycopenia and not a direct action of insulin was the cause of reduced LH secretion. An iv infusion of naloxone (40 mg/h for 2 h), which commenced 25 min before the insulin injection, blocked the inhibitory effect of insulin on LH secretion, but it did not prevent the decrease in plasma glucose concentrations.

Direct pituitary inhibition of prolactin secretion by dopamine and noradrenaline in sheep.

The effects of dopamine, noradrenaline and 3,4-dihydroxyphenylacetic acid (DOPAC) on the release of prolactin were examined in ovariectomized ewes. Infusion of dopamine (0.5 or 1 microgram/kg per min for 2 h i.

Immunisation against the amino-terminal peptide (alpha N) of the alpha 43 subunit of inhibin impairs fertility in sheep.

Processing of the 58 kDa to the 31 kDa form of inhibin (Inh) involves cleavage of the amino-terminal peptide (alpha N) from the alpha 43-subunit. We show that active immunisation of female sheep against a recombinant bovine alpha N impairs their fertility. In Exp 1, 5 treated (Group 1; 300 micrograms alpha N) and 6 control ewes (Group 2; adjuvant only) were immunized (Day 1) and given boosters on Days 22 and 56.

Effects of immunization against recombinant bovine inhibin alpha subunit on circulating concentrations of gonadotrophins in ewes.

Immunization of ewes against a pure recombinant preparation of the alpha subunit of bovine inhibin (alpha-bI) resulted in a three- to fourfold increase in ovulation rate, associated with antibodies in plasma recognizing pure native 31 kDa inhibin. The aim of this study was to examine the effects of this immunization on basal and GnRH-stimulated plasma concentrations of FSH and LH in ewes during the anoestrous and breeding seasons. The groups were untreated control ewes (n = 5), control ewes treated with keyhole limpet haemocyanin (KLH alone, n = 4), ewes treated with alpha-bI alone (n = 4) and alpha-bI-KLH conjugate-treated ewes (n = 3).

Gonadotropin-releasing hormone associated peptide (GAP) and putative processed GAP peptides do not release luteinizing hormone or follicle-stimulating hormone or inhibit prolactin secretion in the sheep.

A series of experiments was performed to monitor plasma luteinizing hormone (LH), follicle-stimulating hormone (FSH), and prolactin responses to human gonadotropin-releasing hormone (GnRH) associated peptide (GAP) and related peptides. Ovariectomized hypothalamo-pituitary disconnected (HPD) ewes were challenged with injections (1-10 micrograms i.v.

Effects of constant infusion of gonadotrophin-releasing hormone in ovariectomized ewes with hypothalamo-pituitary disconnection: further evidence for differential control of LH and FSH secretion and the lack of a priming effect.

Experiments were conducted in ovariectomized ewes after hypothalamo-pituitary disconnection (HPD) to examine LH and FSH secretion during constant infusion of gonadotrophin-releasing hormone (GnRH) or physiological saline and to determine whether or not a constant GnRH background enhances or diminishes pituitary responsiveness to GnRH pulses. Whereas pulsatile GnRH infusions maintained LH and FSH secretion, constant infusions (125 or 250 ng/h) led to the complete cessation of LH secretion and reduced FSH secretion. The rate of decline of plasma FSH concentrations was significantly (P less than 0.

The effects of the preimplantation blastocyst in vivo and in vitro on protein synthesis and secretion by cultured epithelial cells from sheep endometrium.

Epithelial endometrial cells were isolated on day 13 from nonpregnant (NPr) and pregnant (Pr) ewes and cultured in the presence or absence of conditioned media from 15-day blastocysts (BM) under optimized conditions in the presence of [35S]methionine (S-met). The incorporation of S-met into secreted protein was analyzed, and individual proteins were identified by autoradiography of two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis. Incorporation of S-met into secreted protein was higher (P less than 0.

The effects of estrogen and progesterone in vivo on protein synthesis and secretion by cultured epithelial cells from sheep endometrium.

Ovariectomized ewes were treated with either nothing or implants of estrogen (E), progesterone (P), or E + P. Epithelial and stromal cells from caruncular and intercaruncular regions of sheep endometrium were dispersed by collagenase digestion and enriched by Ficoll gradient separation. Verification of cell types was by electron microscopy, keratin staining (epithelial cells), cell size, and appearance in culture.

Influence of season and sex on the inhibitory effect of ovine follicular fluid on plasma gonadotrophins in gonadectomized sheep.

The inhibitory effects of follicular fluid on FSH secretion were similar in gonadectomized male and female sheep, and in the anoestrous and breeding seasons. Significant suppression of LH was variable and was observed only at the highest dose of follicular fluid when suppression rarely exceeded 50% of pretreatment values. Basal plasma FSH and LH concentrations were higher in castrated males than in ovariectomized females in both seasons.

Effects on plasma luteinizing hormone and follicle-stimulating hormone of varying the frequency and amplitude of gonadotropin-releasing hormone pulses in ovariectomized ewes with hypothalamo-pituitary disconnection.

The effects on luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion of various regimens of pulsatile gonadotropin-releasing hormone (GnRH) replacement were examined in ovariectomized (OVX) ewes after hypothalamo-pituitary disconnection (HPD). Hourly pulses of 500 ng GnRH restored gonadotropin secretion in OVX-HPD sheep. Replacement beginning 2 days after HPD gave consistent responses of LH and FSH within a week.

Prostaglandin F and 13,14-dihydro-15-keto prostaglandin F in the endometrium and uterine flushings of sheep before implantation.

The concentrations of prostaglandin F (PGF) and its major metabolite, 13,14-dihydro-15-keto prostaglandin F-2 alpha (PGFM), were measured in caruncular and intercaruncular endometrium of pregnant and non-pregnant ewes on Days 9, 11, 13 and 15 after mating (Day 0) and related to the content of PGF and PGFM in the uterine flushings. The tissue concentrations of PGF and PGFM increased with time after mating particularly on Days 13 and 15 and to a greater extent in pregnancy. However, the ratio of PGF to PGFM remained constant at 0.

Effect of various anaesthetics on resting plasma concentrations of luteinizing hormone, follicle-stimulating hormone and prolactin in ovariectomized ewes.

Effects of various anaesthetics on plasma LH, FSH and prolactin levels were studied in ovariectomized ewes. In the first experimental series, conducted between June and November (late breeding season, early anoestrous season), the following treatments were given: saline (i.v.

Oestrogen receptors and protein synthesis in caruncular and intercaruncular endometrium of sheep before implantation.

The rate of protein synthesis was higher in caruncular (P less than 0.05) and intercaruncular endometrium (P less than 0.01) of pregnant compared to non-pregnant ewes on Day 11 (Day 0 = day of oestrus), but not on Days 9, 13 and 15.