Administration of nerve growth factor- to heifers with a pre-ovulatory follicle enhanced luteal formation and function and promoted LH release.
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The objective of this study was to determine the effects of bovine nerve growth factor- (NGF) on pre-ovulatory follicle vascular area, LH release, ovulation, and luteal function when administered systemically to heifers. Post-pubertal Holstein heifers (n=12) received an intravaginal progesterone-releasing device (CIDR) and GnRH agonist (100g IM). The CIDR was removed 5d later, and heifers were given dinoprost (25mg IM) at CIDR removal and 24h later, followed by a second dose of GnRH agonist 48h later. Heifers were randomly assigned to treatments using a cross-over design. For example, heifers assigned to NGF (250g reconstituted in 12mL PBS IM) in replicate 1 were assigned to control (12mL PBS IM) in replicate 2. Transrectal ultrasonography was performed before treatment and repeated every 4h up to 32h to determine the pre-ovulatory follicle diameter, vascular area, and ovulation. Serum samples were obtained to assess LH concentrations during the periovulatory period and every 2d post-ovulation for measuring progesterone concentrations. A subset of heifers had luteal biopsies performed on days 9 (n=6 per treatment) and 14 (n=6 per treatment) post-ovulation to count luteal cell numbers and measure relative mRNA abundance for steroidogenic and angiogenic enzymes and LH receptor. Treatment with NGF increased pre-ovulatory follicle diameter (P=0.02) and serum LH concentrations (P=0.03) but did not affect time to ovulation (P=0.42). Heifers treated with NGF had increased serum progesterone concentrations in the subsequent luteal phase (P=0.03), but no change in vascular area of the follicle (P=0.16) or CL (P=0.20). Heifers treated with NGF had a greater number of small luteal cells (P<0.01) and a tendency for increased LH receptor (LHR) mRNA abundance in the CL (P=0.10). There was also increased steroidogenic acute regulatory protein (STAR; P=0.05) and a tendency for increased cytochrome P450 family 11 (CYP11A1; P=0.10) mRNA abundance in the CL of NGF-treated heifers. There was decreased prostaglandin E2 synthase (PGES; P=0.03) and its receptor (PGER; P=0.05) mRNA abundance and a tendency for decreased cytochrome P450 family 17 subfamily A member 1 (CYP17A1; P=0.08) and hydroxysteroid 17-beta dehydrogenase (HSD17B; P=0.06) mRNA abundance in the CL of NGF-treated heifers. Administration of NGF improved CL function in heifers potentially as a result of increased LH release.