We demonstrated recently that in mare luteinizing hormone receptors (LHr) are expressed in the dominant follicle starting around the early dominant stage (25 mm). This suggests that such follicles are capable to respond to an LH stimulus in respect of maturation and ovulation. Nevertheless, premature gonadotropin injection is known to induce luteinization without ovulation in various mammals including mare. In order to evaluate the intrafollicular alterations associated with the induced luteinization, mares received 25mg equine pituitary extract (CEG) when the largest growing follicle reached either 33-35 or 28-30mm. Preovulatory follicles, considered healthy (H, with normal ultrasonic morphology) or luteinized (LUT, antrum with echogenic particles) were aspirated 34h after CEG injection. Progesterone (P), estradiol 17
(E) and prostaglandin (PGF2
) concentrations were assayed in follicular fluid, expression of LHr and steroidogenic enzymes (Western blot), and apoptotic rate (3'end labeling of DNA) were measured in granulosa cells, and the oocyte maturation stage was determined by chromatin configuration. In follicular fluid, P levels (8636±3491 vs 1176±112ng/ml, p<0.05) were higher in LUT compared to H, whereas E (1203±353 vs 2556±303ng/ml, p<0.005) and PGF2 levels (2.7±2.2 vs 19.3±4.3ng/ml, p<0.005) were lower in LUT than H. No obvious difference was observed in granusosa cell content of LHr, steroidogenic acute regulatory protein, 3
-hydroxysteroid dehydrogenase or aromatase between the two groups. The level of DNA fragmentation in granulosa cells was negatively correlated to intrafollicular E concentration, but no significant difference in the apoptotic rate was observed between LUT and H. Fewer mature oocytes were present in LUT than H. In conclusion, follicular alterations induced by premature induction of ovulation are not associated with changes in granulosa cell death, LHr content or steroidogenic enzymes expression.
This abstract is being presented on Tuesday, August 3 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.