Authors : S. T. Willard , J. A. Carroll , M. A. Lammoglia , C. N. Kemper-Green , Jr. H. Welsh and R. D. Randel
Abstract: An investigation was conducted to determine whether plasma concentrations of growth hormone (GH) and GH secretory profiles (pulse frequency and amplitude) were associated with ovarian follicular growth during the estrous cycle in the Brahman cow. To investigate these relationships, blood plasma was collected and transrectal ultrasonography of the ovaries performed on Brahman cows (n = 9) from d 1 following estrus (d 0) through the mid-luteal phase. Intensive blood sampling (10-min intervals for 6 h) was conducted on d 3 of the estrous cycle, d of the first observed 8 mm follicle and at 48 h after PGF2a injection. PGF2 a was administered at the appearance of the second 8 mm follicle post-estrus. Daily plasma samples were analyzed for progesterone (P4) and estradiol (E2), while samples collected daily and during intensive sampling were analyzed for GH by RIA. Plasma GH did not differ (P > 0.10) during the first 12 d of the estrous cycle, while plasma P4 increased (P < 0.01) and E2 decreased (P < 0.01). Overall GH mean, baseline GH, number of GH peaks and peak height also did not differ (P > 0.10) among intensive sampling periods. However, the amplitude of GH peaks tended (P < 0.08) to be greater at 48 h after PGF2a administration compared to d 3 of the estrous cycle or on the day of the first 8 mm follicle. Moreover, plasma GH on d 4 through d 8 were positively correlated (r-value > 0.73 depending on day; P < 0.02) with numbers of large follicles on d 7 and 8. In summary, while mean daily plasma GH did not differ during the estrous cycle, correlations among GH, ovarian steroids and numbers of large follicles may support a role for GH in mediating ovarian follicular population dynamics, directly or indirectly, in the bovine.
S. T. Willard , J. A. Carroll , M. A. Lammoglia , C. N. Kemper-Green , H. Welsh, Jr. and R. D. Randel , 2003. Plasma Concentrations of Growth Hormone, Growth Hormone Secretory Dynamics and Changes in Follicular Development During the Bovine Estrous Cycle . Journal of Animal and Veterinary Advances, 2: 102-109.