Secretory patterns of LH and FSH during development and hypothalamic and hypophysial characteristics following development of steroid-induced ovarian follicular cysts in dairy cattle

Abstract

Two experiments were conducted to (1) investigate developmental endocrinology of ovarian follicular cysts (cysts) in cattle and (2) evaluate effects of cysts on hypothalamic and hypophysial characteristics. Cysts were induced with oestradiol-17 beta (15 mg) and progesterone (37.5 mg) dissolved in alcohol and injected s.c. twice daily for 7 days. Cysts were defined as the presence of follicular structures (which may or may not have been the same structure) of 2.0 cm in diameter or greater that were present for 10 days without ovulation and corpus luteum development. In Exp. 1,22 non-lactating, non-pregnant Holstein cows were allocated to 3 groups. Beginning on Day 5 (oestrus = Day 0) of the oestrous cycle, 7 cows (Controls) were treated with twice daily s.c. injections of ethanol (2 ml/injection) for 7 days. Luteolysis was then induced with PGF-2 alpha and blood samples were collected daily every 15 min for 6 h from the morning after the PGF-2 alpha injection (Day 13) until oestrus. Steroids to induce cysts were injected as previously described into the remaining cows (N = 15). Three blood samples were collected at 15-min intervals every 12 h throughout the experimental period. Additional blood samples were collected every 15 min for 6 h on a twice weekly basis. After steroid injections, follicular and luteal structures on ovaries were not detected via rectal palpation for a period of 36 +/- 4 days (static phase). Then follicles developed which ovulated within 3-7 days (non-cystic; N = 7) or increased in size with follicular structures present for 10 days (cystic; N = 8). Mean (+/- s.e.m.) concentrations of LH, FSH, oestradiol-17 beta and progesterone in serum remained low and were not different during the static phase between cows that subsequently developed cysts or ovulated. During the follicular phase, mean serum concentration of LH (ng/ml) was higher (P less than 0.1) in cows with cysts (2.9 +/- 0.2) than in cows without cysts (1.1 +/- 0.1) or control cows (1.4 +/- 0.2). In addition, LH pulse frequency (pulses/6 h) and amplitude (ng/ml) were higher (P less than 0.1) in cows with cysts (3.6 +/- 0.3 and 2.2 +/- 0.3, respectively) than in non-cystic (2.3 +/- 0.2 and 1.0 +/- 0.2, respectively) and control (1.8 +/- 0.1 and 1.1 +/- 0.2, respectively) groups during the follicular phase. There were no differences in the FSH, oestradiol-17 beta or progesterone characteristics in cows of any of the 3 groups during the follicular phase.(ABSTRACT TRUNCATED AT 400 WORDS)

Changes in the Peripheral Concentrations of Inhibin, Follicle-Stimulating Hormone, Luteinizing Hormone, Progesterone and Estradiol-17.BETA. During Turnover of Cystic Follicles in Dairy Cows with Spontaneous Follicular Cysts

“…These findings are consistent with the present results showing that the E 2 level increased in parallel with follicular growth until the day when the follicles that became cysts reached 15.2 ± 2.3 mm in diameter. The present results showed that the LH concentration of the peripheral plasma was similar to those of previous reports showing that LH secretion is generally high in cows with cysts [2,[16][17][18]. Both these previous studies and our present study suggest that a high level of LH secretion activates follicular growth and that there is continuous secretion of E 2 in cows with follicular cysts.…”

Follicular cysts occur after a normal estradiol-induced GnRH/LH surge if the corpus hemorrhagicum is removed

“…This would lead to a decrease in E 2 production from the cyst, decreased circulating E 2 and potentially removal of the mechanisms that were downregulating E 2 responsiveness in the hypothalamus. Indeed cystic cows have elevated LH secretion compared with non-cystic cows (Hamilton et al 1995, Cook et al 1991. Additional support for this idea is the finding that cystic cows that 'self-corrected' (similar to TRT-OV in this study) had mean and pulsatile LH levels that were intermediate between cows that remained cystic and normally cycling cows (Hamilton et al 1995).…”

Gonadotropin requirements for dominant follicle selection in GnRH agonist-treated cows

“…Both LH pulse frequency (pulses/4 h) and pulse amplitude (ng/pulse) during the intensive sampling period were determined for individual cows as previously described (Cook et al 1991). The following criteria were used to define an LH pulse: (1) an increase above the preceding nadir greater than or equal to two standard deviations above the mean LH concentration during the intensive sampling period for each individual cow, (2) the ascending portion of the peak could not contain more than one value between the nadir and the peak value, and (3) the peak value must be followed by at least two consecutive declining hormone values.…”