Regulação da foliculogênese antral, ovulação e luteinização em fêmeas bovinas

Abstract

The knowledge about the endocrine and local control of folliculogenesis, ovulation and luteinization is crucial for understanding physiological and pathological processes, for improving control of the estrous cycle and developing technologies aimed at increasing the ovulatory rate, or contraception, in distinct species. In this context, the objective of this thesis was to advance the understanding of the local control of ovarian function and to investigate an alternative to improve ovulation control and luteal function in cattle. The first study reviewed and discussed the main advances in understanding the local factors involved in folliculogenesis and ovulation, with emphasis on members of the superfamily of transforming growth factors beta (TGF-β), bone morphogenetic protein 15 (BMP15) and growth and differentiation factor 9 (GDF9). In the second study, the effect of two intramuscular administrations of the non-steroidal antiinflammatory drug (NSAID) flunixin meglumine (FM) on ovulation, induced by gonadotropin-releasing hormone (GnRH) was assessed. Parenteral administration of FM (1.1 mg/kg) performed 16h and 26h after ovulation induction with GnRH did not affect ovulation. In a third study, we sought to determine the curve of serum β-hCG concentration over time 0 h (D0), 24 h (D1), 96 h (D4) and 168 h (D7) after administration of 1000 IU of human chorionic gonadotropin (hCG) intramuscularly; to evaluate the effect of 1000 IU of hCG, combined or not with GnRH, on luteal function (P4 production), blood perfusion, CL diameter, area and circumference; and to measure the effect of 1000 IU of hCG on intrafollicular concentrations of estradiol (E2) and P4 24h after ovulation induction. A peak of β-hCG concentration was demonstrated 24 hours after hCG administration, which seven days later returned to levels similar to 0 h. The association of two ovulation inducers (GnRH + hCG) improved the steroidogenic capacity of CL, without altering its structural characteristics (blood perfusion, diameter, area and circumference). When only hCG (1000 IU) was used, an increase in CL size (diameter, area and circumference) was observed, without affecting the concentration of progesterone and blood perfusion. Furthermore, there was no difference in intrafollicular concentrations of E2 and P4, 24h after ovulation induction, between cows in the GnRH and hCG groups. Based on the studies described, oocyte factors (BMP15 and GDF9) are essential in the regulation of follicular differentiation, determination of ovulatory rate and ovulation occurrence. The administration of two doses of FM, in a therapeutic dose, in the final phase of the ovulatory process did not block ovulation and, therefore, does not represent an appropriate model for the study of prostaglandins in the ovulatory process. The administration of 1000 IU of hCG as an ovulation inducer caused mild changes in theluteal function and structure of cyclic cows; however, future research should investigate its use in cows with LH deficiency.