PARENT SESSION

(W396) EFFECTS OF ABOLISHING LH PULSATILITY BY SUPRA-PHYSIOLOGICAL CONCENTRATIONS OF ESTRADIOL-17 ON OVARIAN ANTRAL FOLLICULAR GROWTH IN ANESTROUS EWES.

Barrett, David¹, Ewen, Kirk¹, Duggavathi, Rajesha², Cook, Susan¹, Davies, Kate¹, Pattullo, Kim¹, Bagu, Edward¹, Rawlings, Norman¹, ¹ University of Saskatchewan, Western College of Veterinary Medicine, Saskatoon, SK, Canada² Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch CEDEX, France

ABSTRACT- One to 3 antral follicles emerge in a wave, from a relatively constant pool of follicles ≤3 mm in diameter, every 4 to 5 d in the ewe. In a previous study we demonstrated that a 10 d treatment, which resulted in supra-physiological serum concentrations of estradiol during the luteal phase of a cycle, suppressed the peaks of serum concentrations of FSH that precede wave emergence and blocked wave emergence without altering the pulsatile secretory pattern of LH. In anestrous ewes, follicle waves continue, preceded by peaks in serum concentrations of FSH, but mean serum concentrations of LH and FSH are lower than during the breeding season. The objective of the present study was to clarify the LH and FSH requirements for wave emergence in the anestrous ewe. Ten ewes received silastic rubber implants containing 10% estradiol-17 (s.c.; Day 0= day of implant insertion); 5 ewes received large implants (10 cm) and 5 ewes received small implants (5 cm). Implants were left in place for 10 d. Five Sham operated control ewes received no implants. Daily transrectal ovarian ultrasonography and blood sampling was done from 4 d before to 20 d after Day 0. Blood samples were taken every 12 min for 6 h on Days 5 and 9. During treatment, serum concentrations of estradiol were significantly higher in ewes with large (11.8±1.6 pg/mL) and small (9.8±1.6 pg/mL) implants compared to controls (3.7±1.6 pg/mL; P<0.01). The number, amplitude, and height of FSH peaks and mean serum concentrations of FSH, were unaffected by the implants. Mean serum concentrations of LH and LH pulse frequency and amplitude were significantly suppressed in ewes with implants compared to controls (P<0.001). Basal serum concentrations of LH were unaffected by the implants. The implants halted follicle wave emergence between Days 2 and 11. During the experiment, daily maximum follicle diameter was significantly smaller in ewes with large (3.5±0.2 mm) and small (4.1±0.2 mm) implants compared to controls (5.4±0.2 mm; P<0.001). We concluded that supra-physiological serum concentrations of estradiol blocked wave emergence and selectively abolished LH pulses without affecting basal serum concentrations of LH or FSH secretory characteristics. Pulsatile LH secretion appears to be essential for antral follicle growth in anestrous ewes.

KEY WORDS: gonadotropins, estradiol-17, antral follicles, anestrous ewes