Effects of Follicle-Stimulating Hormone With and Without Luteinizing Hormone on Serum Hormone Concentrations, Follicle Growth, and Intrafollicular Estradiol and Aromatase Activity in Gonadotropin-Releasing Hormone-Immunized Heifers

To evaluate the roles of FSH and LH in follicular growth, GnRH-immunized anestrous heifers (n = 17) were randomly assigned (Day 0) to one of three groups (n = 5 or 6). Group 1 received i.m. injections of 1.5 mg porcine FSH (pFSH) 4 times/day for 2 days; group 2 received i.v. injections of 150 μg pLH 6 times/day for 6 days; group 3 received both pFSH and pLH as described for groups 1 and 2. After slaughter on Day 6, measurements were made of follicle number and size, and follicular fluid concentrations of progesterone (P 4 ), estradiol (E 2 ), and aromatase activity. Injection of pFSH increased ( P < 0.01) the serum concentrations of FSH between 12 and 54 h. Infusion of pLH increased ( P < 0.05) mean and basal concentrations of LH and LH pulse frequency. Serum E 2 concentrations were higher ( P < 0.05) for heifers given pFSH + pLH than those given either pFSH or pLH alone. There was no difference ( P ≥ 0.24) between treatments in the number of small follicles (1.0), whereas 18 of 21 large follicles (all in the pFSH + pLH treatment) were E 2 -active; of these, 8 of 18 had aromatase activity. Concentrations of E 2 and E 2 activity in follicular fluid were correlated ( r ≥ 0.57; P < 0.0001) with aromatase activity in heifers given pLH + pFSH. In conclusion, pLH failed to stimulate follicle growth greater than 5 mm; pFSH stimulated growth of medium follicles that were E 2 -inactive at slaughter and failed to increase serum E 2 concentrations; whereas pFSH + pLH stimulated growth of medium follicles and E 2 -active large follicles, and a 10- to 14-fold increase in serum E 2 concentrations.