Frequency of Luteinizing Hormone Pulses in Cattle Influences Duration of Persistence of Dominant Ovarian Follicles, Follicular Fluid Concentrations of Steroids, and Activity of Insulin-Like Growth Factor Binding Proteins

The objectives of the present study were to determine how varying frequency of LH pulses as controlled by varying treatments with progesterone (P 4) in cattle would affect: (1) concentration of steroid hormones and activity of insulin-like growth factor binding proteins (IGFBPs) in the ovarian follicular fluid and blood plasma, and (2) duration of persistence of largest ovarian follicles. There Published as paper no. 12594, Journal Ser. Nebraska Agr. Res. Div. ; Research supported by USDA NRI 90-37240-5714. The mention of trade names is necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable. ∗ Corresponding author. Present address: Department of Animal Sciences, The Ohio State University, 110 Animal Science Building, 2029 Fyffe Rd., Columbus, OH 43210-1095, USA. Tel. : +1-614-292-3232; fax: +1-614-292-2929. E-mail address:kinder.15@osu.edu (J.E. Kinder). 1 Department of Animal Sciences, University of Missouri, Columbia, MO 65211, USA. 2 American Society of Animal Science, 1111 N. Dunlap Ave. Savoy, IL 61874, USA. 3 Rocky Mountain Reproductive Services Inc., P.O. Box 299, Manhattan, MT 59741, USA. 4 Department of Animal Sciences, The Ohio State University, Columbus, OH 43210-1095, USA. 5 Departmento de Zootecnia, Universidad Autonoma Chapingo, Chapingo Edo 56320, Mexico. 6 Programa de Ganaderia, Colegio de Postgraduados, Montecillos Edo 56320, Mexico. 7 International Marketing, T.C. Jacoby, St. Louis, MO 63127, USA. 0378-4320/03/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0378-4320(03)00038-1 188 F.N. Kojima et al. / Animal Reproduction Science 77 (2003) 187–211 were four treatment groups ( n = 7 per group) and a control group ( n = 5) of mature, non-lactating beef cows. Treatments were: (1) two progesterone releasing intravaginal devices (PRIDs) for 16 days (2PRID); (2) a half PRID for 16 days (0.5PRID); (3) two PRIDs for 8 days, then a half PRID for 8 days (2-0.5PRID); or (4) a half PRID for 8 days, then two PRIDs for 8 days (0.5-2PRID). Treatment was initiated on the fifth day of the estrous cycle, which was designated as Day 0, and continued for 16 days. All P4-treated females were administered prostaglandin F 2 on Day 0 and 1 to regress their corpora lutea. Frequency of LH pulses was greater during treatment with the smaller dose of P4 compared with treatment with the larger dose of P 4 and the control group. Ovarian follicles were classified into five categories based on ultrasonographic observations: growing (G); atretic (A); growing dominant (GD); growing persistent (GP); or atretic persistent (AP). At ovariectomy on Day 16, the largest and second largest follicles collected were re-classified into five categories based on follicular concentration of steroids. Classification of the largest follicle collected on Day 16 was influenced by treatment ( P < 0.005), with the 2PRID group having A follicles, the 2-0.5PRID group GP follicles, the 0.5-2PRID group AP follicles, and the 0.5PRID group GD and GP follicles. Concentrations of 17 -estradiol (E2) were greatest in GD and GP follicles ( P < 0.05). There was less (P < 0.05) activity of IGFBP-2 in GD follicles and less ( P < 0.05) activity of IGFBP-3 in GD and GP follicles than other follicles. Activity of IGFBP-4 and -5 was greater ( P < 0.05) in A and AP follicles than G, GD, and GP follicles. Maintenance of a frequent release of LH pulses over a 16-day period did not result in maintenance of persistent follicles throughout this period indicating that duration of dominance of these follicles is finite even when there is frequent release of LH pulses. Follicular atresia is associated with greater activity of IGFBP-2, -4, -5, and greater concentrations of P 4 in follicles, whereas growing dominant and persistent follicles contained greater concentrations of E 2, androstenedione (A 4), and less IGFBP-2 activity than follicles of other classes. Follicle classifications based on ultrasonography or follicular concentration of steroids did differ (P < 0.05) for the largest follicles from the 2PRID group. Two follicles in this group appeared as GD follicles by ultrasonography, but these were atretic based on follicular steroid contents. Objective 1 of the present study yielded the conclusion that concentrations of steroid hormones in follicular fluid and blood plasma could be predictably controlled by regulating the frequency of LH pulses with varying doses of P 4. Objective 2 yielded the conclusion that maintain frequent release of LH pulses over a 16-day period could not maintain persistent follicles throughout this period, indicating that duration of dominance of these follicles is finite even when there is frequent release of LH pulses. Follicular atresia in the present study was associated with increased follicular fluid activity of IGFBP-2, -4, -5, and P 4, whereas growing dominant and persistent follicles contained greater concentrations of E 2, A4, and less IGFBP-2 activity than follicles of other classes. © 2003 Elsevier Science B.V. All rights reserved.