SERUM HORMONES, FOLLICULAR-FLUID STEROIDS, INSULIN-LIKE GROWTH-FACTORS AND THEIR BINDING-PROTEINS, AND OVARIAN IGF MESSENGER-RNA IN SHEEP WITH DIFFERENT OVULATION RATES

Ovulation rate, serum hormone concentrations, follicular fluid (FFL) c oncentrations of steroids and IGF, IGF binding protein (IGFBP) activit y in FFL, and follicular ICE-I and -II mRNA were compared during the f ollicular phase among five genotypes of ewes: Finn (F), Composite III (C), 1/2 Booroola Merino (B) x 1/2 F (BxF), 1/2 F x 1/2 C (FxC), 1/2 B x 1/2 C (BxC). Composite III ewes were a Columbia x Suffolk x Hampshi re crossbred. Ovulation rates for F (n = 7), C (n = 5), BxF (n = 6), F xC (n = 3), and BxC (n = 8) ewes were 3.1, 1.6, 3.8, 2.9, and 2.9 (Poo led SEM = .5), respectively. Concentrations of IGF-I in FFL were 53% g reater (P < .05) in large (greater than or equal to 4.1 mm) than in sm all (< 4.1 mm) follicles but did not differ (P > .10) among genotypes. In contrast, FFL IGF-II concentrations were greater(P < .05) in BxC a nd BxF ewes than in C or FxC ewes but did not differ between small and large follicles. Ligand blotting revealed that IGFBP activity of thre e species (34, 27 to 29, and 24 kDa) were lower (P < .05) in FFL of la rge than in FFL of small follicles but did not differ (P > .10) among genotypes. Follicular wall IGF-I mRNA and IGF-II mRNA was detected in 5 and 32% of the samples from preovulatory follicles, respectively, us ing reverse transcriptase-PCR and ethidium-bromide staining. Ovarian I GF-I mRNA levels, assessed by Northern analysis, in BxF and BxC ewes w ere greater (P < .05) than those in C ewes; ovarian IGF-I mRNA levels in F and FxC ewes were intermediate and did not differ (P > .10) from those in C ewes. Small follicles from BxC and BxF ewes had severalfold greater (P < .05) estradiol concentrations than those from F or C ewe s, whereas large follicles from BxF ewes had twice (P < .05) the estra diol concentrations of follicles from F or C ewes. Progesterone in FFL did not differ among genotypes. Serum LH, FSH, inhibin, IGF-I, and pr ogesterone did not differ (P > .10) among genotypes. In conclusion, hi gher ovulation rates in B-cross ewes (i.e., BxF and BxC vs C) were ass ociated with greater levels of FFL IGF-II, FFL estradiol, and ovarian IGF-I mRNA but were not associated with differences in FFL progesteron e, IGF-I, or IGFBP.