ULTRASTRUCTURE OF BOVINE OVARIAN FOLLICLES INDUCED TO EXTENDED GROWTHBY PERIOESTROUS SUPRABASAL PROGESTERONE LEVELS

The present study was undertaken to determine if a short-term prolonge d growth of the ovulatory follicle (12 to 18 h after expected time of ovulation), induced by progesterone implants, would cause ultrastructu ral changes in the follicular wan. Oestrous behaviour, follicular grow th, follicular and blood plasma levels of oestradiol-17 beta, progeste rone and plasma luteinizing hormone (LH) were monitored in heifers oop horectomized at 9 to 12 h (controls) or 36 h after the onset of oestru s, in order to sample the prl-ovulatory follicle present. The suprabas al plasma progesterone concentrations (approximately 1.2 nmol L(-1)) a llowed expression of oestrus at the expected time, but ovulation was d elayed owing to the absence of a LH-surge. The resulting prolongation of follicle growth was associated with mild degenerative changes in th e follicle wall, i.e. both granulosa and thecal cells presented increa sed electron density, higher amounts of secondary lysosomes and lipid droplets, increased intercellular spaces with presence of debris. No s igns of luteinization were seen.