Development of preovulatory follicles expected to form short-lived corpora lutea in beef cows

Abstract

Summary. Oestrus, expected to be followed by a short luteal phase, was induced in post-partum cows by weaning their calves at 35 days after parturition. Ovaries containing the first preovulatory follicles (Type F) formed after parturition were collected 3 h after the onset of oestrus. For comparison, preovulatory follicles (Type C) were collected 3 h after the onset of oestrus in normally cycling cows. The number of granulosa cells was determined and the concentrations of receptors for follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in granulosa cells and for LH in theca cells were measured. Concentrations of oestradiol-17\g=b\,testosterone, androstenedione and progesterone in follicular fluid were also measured. Type F follicles contained about twice the number of granulosa cells (based on DNA) as did Type C follicles (45\m=.\8\m=+-\ 1 1 \ m= . \ 3 and 24\m=.\5 \ m=+-\ 3\m=.\9 \g=m\gDNA/follicle, respectively; P < 0\m=.\05) but these cells had fewer receptors for LH (0\m=.\13\ m=+-\0\m=.\02vs 0\m=.\29\ m=+-\ 0\m=.\03fmol/\g=m\g DNA; P < 0\m=.\01) and FSH (0\m=.\61\ m=+-\0\m=.\08vs 1\m=.\3\ m=+-\0\m=.\29fmol/\g=m\gDNA; P < 0\m=.\08) than did those from Type C follicles. Additionally, there were fewer receptors for LH in theca tissue from Type F than from Type C follicles (28\m=.\3 \m=+-\5\m=.\2vs 51\m=.\3\ m=+-\6\m=.\1 fmol/follicle; P < 0\m=.\01). Concentrations of oestradiol-17\g=b\(475\m=.\8\ m=+-\ 85\m=.\6vs 112\m=.\9\ m=+-\ 40\m=.\0 ng/ml; P < 0\m=.\01) and androstenedione (214\m=.\1 \m=+-\48\m=.\7vs 24\m=.\7 \ m=+-\7\m=.\7ng/ml; P < 0\m=.\01) in follicular fluid were higher in Type C than in Type F follicles. There were therefore more granulosa cells in Type F follicles which contained fewer receptors for LH and FSH and accumulated less oestradiol-17\g=b\ in the follicular fluid. We suggest that the characteristics of preovulatory follicles may influence the life-span of the subsequently formed corpus luteum and short luteal phases may de due, in part, to altered follicular development.

Functional and morphological characteristics of the first corpus luteum formed after parturition in ewes

“…Therefore, although preovulatory follicles expected to result in short-lived corpora lutea in cows contained more granulosa cells than subsequently formed preovulatory follicles (Braden et al, 1989), this does not result in a short-lived corpus luteum with an increased proportion of large luteal cells. However, data from preovulatory follicles were obtained from cows (Braden et al, 1989) while the present study was conducted in ewes and so species differences cannot be excluded.…”

“…Therefore, it appears that the luteolytic process may be mediated via large luteal cells which may be derived from granulosa cells of the preovulatory follicle (Donaldson & Hansel, 1965;McClellan et al, 1975;Alila & Hansel, 1984). The first preovulatory follicle formed after parturition in cows contains approximately twice the number of granulosa cells as are in subsequently formed preovulatory follicles (Braden et al, 1989 …”

Detecção imunoistoquímica de receptores de estrógeno e progesterona no endométrio de vacas Nelore (Bos taurus indicus) durante o anestro pós-parto

“…As concentrações plasmáticas de E só se restabelecem por volta do nono dia do puerpério, devido à emergência da primeira onda de desenvolvimento folicular consequente ao restabelecimento da secreção hipofisária de FSH que acontece entre o terceiro e o quinto dia pós-parto (Yavas e Walton, 2000, Crowe, 2008. Porém, a concentração de E é baixa comparada aos valores encontrados no plasma (Garverick et al, 1988) e no fluído folicular (Braden et al, 1989) durante o ciclo estral, principalmente no período preovulatório. Foi observado por Borges et al (2004) uma média de cinco (4-8) ondas foliculares em vacas da raça Gir entre quatro e 50 dias pós-parto, sendo o diâmetro máximo dos folículos dominantes para as diversas ondas, em média, 8,9mm (6,6-12,2mm).…”

“…Durante o anestro puerperal, as concentrações de P 4 são insignificantes e as de E variáveis, na dependência do grau de desenvolvimento folicular. A despeito dos relatos de que os folículos que se desenvolvem durante o anestro têm menor capacidade esteroidogênica (Garverick et al, 1988;Braden et al, 1989), essa produção foi aparentemente suficiente para que a expressão dos receptores nos dois tecidos endometriais alcançassem concentrações semelhantes às observadas durante as fases folicular e luteínica inicial em animais apresentando ciclos estrais regulares. Como não havia disponibilidade plasmática de P 4 , a expressão dos receptores manteve-se sempre elevada.…”

Effects of progesterone pretreatment on the oxytocin receptor concentration and the response to oxytocin during the simulated early luteal phase in the ovariectomized ewe

“…The corpus luteum that develops from the first ovulation following a period of reproductive quiescence (for example seasonal or lactational anoestrus or puberty) is often short¬ lived, and is correlated with a transient increase in circulating progesterone concentrations (Lamming et al, 1981;Braden et al, 1989;Garverick et al, 1992). Anoestrous ewes can be induced to ovulate with GnRH, although without progesterone pretreatment a large proportion of the ewes undergo prema¬ ture luteolysis by the normal luteolytic mechanism (involving prostaglandin F2a (PGF2(1) from the uterus and oxytocin from the corpus luteum; Hunter et al, 1989).…”