Administration of nerve growth factor-β to heifers with a pre-ovulatory follicle enhanced luteal formation and function and promoted LH release

Abstract

The objective of this study was to determine the effects of bovine nerve growth factor-β (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 (100 μg IM). The CIDR was removed 5 d later, and heifers were given dinoprost (25 mg IM) at CIDR removal and 24 h later, followed by a second dose of GnRH agonist 48 h later. Heifers were randomly assigned to treatments using a cross-over design. For example, heifers assigned to NGF (250 μg reconstituted in 12 mL PBS IM) in replicate 1 were assigned to control (12 mL PBS IM) in replicate 2. Transrectal ultrasonography was performed before treatment and repeated every 4 h up to 32 h 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 2 d 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.

Keywords: Luteinizing hormone; NGF; Ovulation; Progesterone.