GROWTH-HORMONE PRIMING AS AN ADJUNCT TREATMENT IN SUPEROVULATORY PROTOCOLS IN THE EWE ALTERS FOLLICLE DEVELOPMENT BUT HAS NO EFFECT ON OVULATION RATE

This study investigated the effect of FSH alone and rGH priming follow ed by FSH treatment on follicle populations, follicular fluid concentr ations of components of the IGF system and steroids, and the ovulation rate in sheep. Estrus was synchronized with progestagen sponges. Ewes (n = 10/group) in Group 1 served as untreated controls, while those i n Groups 2 to 5 received a standard superovulatory treatment of 1.1 mg im oFSH twice daily for 4 d. In addition, ewes in Groups 3 and 5 were administered rGH (15 mg/d, im) for the 7 d prior to FSH treatment. Gr oups 1, 2 and 3 were sacrificed just prior to the LH surge; Groups 4 a nd 5 were allowed to ovulate. Daily plasma samples were collected to m onitor GH, IGF-1 and insulin levels. All follicles greater than or equ al to 1.0 mm from Groups 1, 2 and 3 were counted, and follicular fluid from follicles greater than or equal to 2.5 mm was assayed for estrad iol, testosterone, IGF-1 and IGFBPs. Compared with the control, treatm ent with rGH+FSH but not FSH alone increased (P<0.001) plasma concentr ations of GH, IGF-1 and insulin. The mean number of large-(greater tha n or equal to 4.5 mm) and medium-sized (2.5 to 4.0 mm) follicles was i ncreased (P<0.01), and the mean number of small (less than or equal to 2.0 mm) follicles was decreased (P<0.001) by FSH treatment. The mean number of medium-sized (2.5 to 4.0 mm) follicles was further increased (P<0.05) by rGH priming. Estradiol concentration in medium but not in large estrogenic follicles was increased (P<0.05) by rGH priming, whe reas testosterone concentration in estrogenic follicles was not altere d. Components of the IGF system in medium-sized estrogenic follicles w ere similar in all treatment groups; however, in large estrogenic foll icles rGH increased IGF-1 concentrations (P<0.05) and intensity of the 44-42 kDa IGFBP band (P<0.01). Priming with rGH did not alter superov ulatory responses. These results show that rGH priming, when used as a n adjunct to FSH treatment in ewes, alters components of the IGF syste m in large estrogenic follicles and increases the number and physiolog ical maturity of medium-sized follicles in the ovary; it does not howe ver alter ovulation rate responses. (C) 1998 by Elsevier Science Inc.