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 mug 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 <greater than or equal to> 0.24) between treatments in the number of small follicles (<5 mm). Heifers given pFSH or pFSH + pLH had more (P <less than or equal to> 0.02) medium follicles (5.0-9.5 mm) than those that were given pLH alone (none present). Heifers given pFSH + pLH had more (P = 0.04) large follicles (greater than or equal to 10 mm) than those given either pLH or pFSH alone (none present). Overall, only 1 of 35 small follicles and 2 of 96 medium follicles were E-2-active (i.e., E-2:P-4 >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 greater than or equal to 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.