During luteal regression episodic pulses of oxytocin secretion become coupled to the release of prostaglandin F2 alpha (PGF2 alpha) following synthesis of endometrial oxytocin receptors, but in early pregnancy the inhibition of oxytocin receptor formation by the conceptus prevents the development of the pulsatile pattern of PGF2 alpha release needed to achieve luteolysis. Oxytocin receptors are present on the luminal epithelium in ovariectomized and anoestrous ewes, in pregnant animals throughout most of gestation (day 21 to term) and in explants of endometrial tissue cultured in vitro. These receptors can be downregulated for a brief period by progesterone (10-12 days in sheep, 12-14 days in cattle). This period of inhibition can be extended by infusion of interferon tau (IFN-tau) (which probably inhibits oxytocin receptor gene transcription) or of oxytocin into the systemic circulation (which may act further downstream, possibly at the level of translation). Oxytocin receptors also develop on the caruncular stroma and deep glands at oestrus, but these need positive upregulation and appear dependent on an oestrogenic environment. Only epithelial receptors are needed to achieve a maximal PGF2 alpha response to an oxytocin challenge, but the presence of oxytocin receptors does not necessarily confer responsiveness as other factors may influence intracellular coupling mechanisms and precursor availability. The duration of the luteal phase is regulated by the time of the initial post-ovulatory rise in progesterone and the duration of exposure to progesterone.(ABSTRACT TRUNCATED AT 250 WORDS)

/pdf/the-oxytocin-receptor-luteolysis-and-the-maintenance-of-1kz5tgvyh4.pdf

The oxytocin receptor, luteolysis and the maintenance of pregnancy

Maturation processes that culminate in puberty and sexual maturity are initiated before birth, continue through prepuberty (> 50 days before puberty) and peripuberty (50 days before puberty) and are completed early after puberty. The hypothalamus is the primary site of change during transition to sexual maturity. Maturation of the hypothalamus results from decreased negative feedback of oestradiol that leads to increased frequency of release of LH pulses. Increased tonic release of LH pulses during sexual maturation is the primary endocrine factor that regulates the onset of puberty in ewe lambs and heifers. Increased frequency of release of LH pulses enhances development of ovarian follicles which produce enough oestradiol to induce behavioural oestrus and a preovulatory surge of gonadotrophins. In later stages of peripuberty, ovulation or luteinization of follicles results in transient increases in progesterone for shorter periods than is typical for luteal phases of the oestrous cycle of mature ewes and cows. Transient increases in progesterone are not generally preceded by behavioural oestrus. After the demise of the transient luteal structures, puberty is attained with occurrence of the first behavioural oestrus that is accompanied by ovulation and development of a corpus luteum with a typical lifespan. At puberty, all components of the hypothalamic-pituitary-ovarian axis are in place for oestrous cycles to be expressed. Factors that can influence the pubertal rise in release of LH pulses are genotype, gender, season of year when pubertal age is attained, growth or nutritional intake, social cues or treatment with exogenous progestins. Sexual maturation continues after puberty with an enhanced probability of pregnancy occurring from actions of ovarian steroids at the uterus.

/pdf/endocrine-basis-for-puberty-in-heifers-and-ewes-4h9o0jt6i6.pdf

Endocrine basis for puberty in heifers and ewes

Part 1 Molecular genetics: introduction to molecular biology basic techniques in genetic analysis for molecular biology in clinical and reproductive medicine transgenic technology in animal reproductive processes - methods, interpretation and contributions Part 2 Cell biology: polypeptide growth factors and their role in regulating the cell cycle apoptosis and its impact in clinical reproductive medicine molecular carcinogenesis Part 3 Hormone synthesis, action and signal transduction: gonadotropin releasing hormones and the GnRH receptor studies of recombinant gonadotropins - intersection of basic science and therapeutics gonadotropin receptors synthesis of the sex steroid hormones - molecular and structural biology with applications to clinical practice steroid hormone receptors Part 4 Gamete and embryo biology: molecular biology of gamete maturation - female molecular biology of gametogenesis - spermatogenesis fertilization preimplantation embryo development implantation and endometrial function Part 5 Clinical genetics: the role of genetic counseling and infertility genetic counseling in reproductive disorders preimplantation in genetic diagnosis ethics of assisted reproduction - the case of preimplantation genetic diagnosis Part 6 Genetics of adult reproductive dysfunction - genetics of female reproductive dysfunction genetics of male reproductive dysfunction

Molecular biology in reproductive medicine

Physiology and Technology of Reproduction in Female Domestic Animals

This study was conducted to compare the effects of prostaglandins (estroPLAN® and Lutalyse®) and progestagens (CIDR® and FGA-45®) in synchronizing oestrus in Yankasa ewes between January and February 2014. Thirty three (33) Yankasa ewes aged 1.5- 3 years, 21 to 26 kg body weights, with body condition score of 2.5- 3.5 were used in this study. Ewes were randomly allocated into 5 groups, Group 1 (ewes treated with Lutalyse® [YK-LT], n= 7), Group 2 (ewes treated with estroPLAN® [YK-ET], n= 7), Group 3 (ewes treated with EAZI- BREED™ CIDR® [YK-CD], n= 5), Group 4 (ewes treated with Fluorogestone acetate-45® [YK-FG], n= 7) and Group 5 (Control [YK-CT], n= 7). Natural breeding was carried out using sexually active rams for 5 days following progestagen withdrawal and second prostaglandin administration. 100% oestrus response was observed in YK-ET, YK-CD and YK-FG, respectively. Time to onset of oestrus was 68.23 ± 17.28 h in YK-LT, 49.29 ± 4.5 h in YK-ET, 33.48 ± 8.6 in YK-CD, 53.27 ± 12.3 in YK-FG and 39.2 ± 13 in YK-CT. Duration of oestrus was longest in YK-LT (51.35 ± 13.9 h) and shortest in YK-CT (17.2 ± 6.9 h). Mounts per oestrus period was highest in YK-CT (26.9 ± 4.8) and lowest in YK-ET (14.3 ± 4.3). Conception rate was 100% in the YK-LT, YK-ET, YK-CD groups respectively. It is concluded that estroPLAN® and CIDR® offered the best results in synchronizing oestrus in Yankasa ewes and may be used by farmers to enhance productivity.

http://kubanni.abu.edu.ng:80/jspui/bitstream/123456789/9510/1/PROSTAGLANDIN%20VERSUS%20PROGESTAGEN%20PROTOCOLS%20IN%20OESTRUS%20SYNCHRONIZATION%20IN%20THE%20YANKASA%20EWE.pdf

Mohammed A. Younes

Papers

A comparison of ovarian function in juvenile and adult ewes using in vitro culture and proteomics.