CONCENTRATIONS OF INSULIN-LIKE GROWTH FACTOR-I AND STEROIDS IN FOLLICULAR-FLUID OF PREOVULATORY BOVINE OVARIAN FOLLICLES - EFFECT OF DAILY INJECTIONS OF A GROWTH HORMONE-RELEASING FACTOR ANALOG AND(OR) THYROTROPIN-RELEASING-HORMONE

To determine whether long-term administration of growth hormone (GH)-releasing factor (GRF) and(or) thyrotropin-releasing hormone (TRH) alters ovarian follicular fluid (FFL) concentrations of insulin-like growth factor-I (IGF-I), progesterone, and estradiol (E2), and follicular growth, Friesian x Hereford heifers (n = 47; 346 +/- 3 kg) were divided into the following four groups: control (vehicle; n = 11); 1-mu-g GRF (human [Des NH2 Tyr1, D-Ala2, Ala15] GRF [1-29]-NH2).kg-1 BW.d-1 (n = 12); 1-mu-g TRH.kg-1 BW.d-1 (n = 12); or GRF + TRH (n = 12). Daily injections (s.c.) continued for 86 d. On d 89, heifers that had been synchronized were slaughtered and ovaries were removed. Follicles were grouped by magnitude of diameter into the three following sizes: 1 to 3.9 mm (small, n = 55), 4.0 to 7.9 mm (medium, n = 63), and greater-than-or-equal-to 8 mm (large, n = 71). Growth hormone-releasing factor and(or) TRH did not affect (P > .10) IGF-I concentrations in FFL of any follicle size group. Growth hormone-releasing factor increased (P < .06) size (xBAR +/- pooled SE) of large follicles (14.7 vs 13.0 +/- .6 mm). Growth hormone-releasing factor also increased (P < .05) progesterone concentrations 4.4-fold above controls in FFL of medium-sized follicles but had no effect on progesterone in FFL of the small or large follicles. Thyrotropin-releasing hormone did not alter FFL progesterone or E2 concentrations in any follicle size group. We conclude that the GRF and(or) TRH treatments we employed did not affect intra-ovarian IGF-I concentrations, but GRF may alter steroidogenesis of medium-sized follicles and growth of large follicles.