Struktura i aktywność jajników oraz kompetencja mejotyczna oocytów w okresie dojrzewania płciowego klaczy
AbstractSexual maturity is the effect of a complex biological process conditioned by sex, inborn characteristics and the environment. The way in which maturity is reached has a significant influence on fertility of an adult female. In spite of the fact that numerous studies have been carried out on horses, little is known about the mechanisms that control the sexual maturation in this species. The available literature provides only fragmentary information on steroidogencsis in mare ovaries from birth to sexual maturity. So far research has mainly focused on evaluation of estradiol and/or progesterone concentration in peripheral blood serum. Information on the dynamics of follicle development in prepubertal mares and use of their oocytes for biotechnology in horse reproduction is also scarce. In the present study a complex research was carried out to determine morphological changes as well as an attempt to establish hormonal relationship that takes place within the ovaries of mares during sexual maturation in folliculogenesis and reproductive biotechnology aspect was taken up. Studies included: a) histomorphological estimation of filly follicles and analysis of their distribution in ovary cortex; b) evaluation of steroidogenic activity of filly ovaries on the basis of 313-hydroxysteroid dehydrogenase (313-1-IST)) activity visualization, aromatase (P450arom) and androgen receptors (AR) immunoexpression in follicles and corpora lutes; analysis of estradiol (E2.), progesterone (P4) and testosterone (T) concentration in follicular fluid (FF) and estimation of relationship between steroid concentration in FF and follicle physiological state; c) in vivo and postmortem assessment of fillies ovaries; d) comparative morphometric evaluation of oocytes of fillies and mares; e) an attempt to improve in vitro maturation rate of fillies oocytes using BCB (brilliant cresy1 blue) test for oocyte selection, oocytes culture in the presence of EGF and f) an attempt to in vitro fertilization of fillies oocytes. The studies were carried out both on ovaries collected after slaughter from 298 fillies of Bold Type aged from about 6-18 months and in vivo in fillies (n = 9) aged from about 5 months till they reach sexual maturity. The ovaries of 69 mares aged > 5 years were used as a control groups. In the present study, distribution of preantral and antral follicles in the ovary cortex of fillies was shown for the first time. It was found that most (about 79%) of preantral follicles were distributed in groups of 2-34 inside the cortex, while antral follicles were located more superficially in peripheral part of cortex. The tissue adjacent directly to the ovulation fossa contained no preantral follicles. Such distribution of follicles seems to he characteristic for horse ovaries. This information may prove useful for research on isolation and in vitro maturation of preantral horse follicles as well as for investigations on mechanisms which control the development and differentiation of preantral follicles in this species. It was also stated for the first time that ovaries of fillies aged at least 6 months are able to produce steroids, It is provided by the activity of 3P-HSD and expression of P450arom in ovarian follicles cells as well as that of presence of estradiol, progesterone and testosterone in follicular fluid. No relationship was found between the age of fillies and E2, P4 and T concentration in follicular fluid. The level of estradiol in the follicles of fillies that were > 10 mm in diameter was almost twice lower than in those of mares. The level of E2 in follicular fluid increased with the growing of a follicle and was dependent on P45Oarom immunoexpression. Lack of aromatase in atretic follicles decreased E2 concentration in follicular fluid both in fillies and mares. No significant influence of atresia on progesterone and testosterone concentration in FF was found. The current study shows for the first time the presence of androgen receptors in the cells of all compartments of equine ovary. More intensive AR immunoexpression in follicles and ovarian stroma cells of fillies younger than 10 months than in mares allows to assume that atresia proceeds more intensively in follicles of prepubertal females than in those showing regular estrous cycles. It may also indicate greater sensitivity of filly follicles to androgens and a significant influence of these hormones in the development of equine ovary. Activity of 3P-TISD and expression of 13450arom and AR in luteal cells are specific for every protein and depend on the functional state of corpus luteum. On the basis of clinical and ultrasound examination of reproductive tract and ovaries it was found that in horses functional maturity of the ovary and the first ovulation is not accompanied by dilatation of uterine cervix. It means that a mare is not sexually mature yet. Based on pustmotrem evaluation of the ovaries and the presence of corpus luteum it was found that most (57%) fillies of Bold Type gained sexual maturity at the age of about 1.5 year. No influence of the age of fillies and mares on the size of oocytes was found. However, a significant relationship between cumulus oophorus morphology and volume of ouplasm as well as width of oocytes perivitelline space was determined. It seems that the use of BCB test for selection of oocytes of fillies is rather doubtful because of its low efficiency. The addition of EGF to culture medium stimulated fillies oocytes cumulus oophorus expansion more effectively than FSH, but it did not influence significantly their nuclear maturation. The obtained results of ooeytes culture of 6-18 months old fillies proved their ability to mature in vitro. Nevertheless at the present stage of studies it is not possible to state explicitly their usefulness for in vitro production of equine embryos. Further research on in vitro fertilization of filly oocytes with use of both standard and assisted microsurgical techniques are required.
|Other language title versions||Ovarian structure and activity, and meiotic competence of oocytes during sexual maturation in mares|
|Publisher||Uniwersytet Rolniczy im. Hugona Kołłątaja w Krakowie, MNiSW |
|Publishing place (Publisher address)||Kraków|
|Book series /Journal (in case of Journal special issue)||Zeszyty Naukowe Uniwersytetu Rolniczego im. Hugona Kołłątaja w Krakowie. Rozprawy, ISSN 1899-3486, (0 pkt)|
|Publication size in sheets||6.0|
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