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Regulation of synthesis and secretion of LH and FSH in cows and ewes
Abstract
The effect of synthetic progestins to synchronize time of estrus when the corpus luteum is present in cows and heifers was evaluated in experiment 1. Pregnancy rate as a result of artificial insemination was greater in cows and heifers treated with norgestomet with the corpus luteum present during the treatment period. Greater concentrations of $17\beta$-estradiol during the treatment period may contribute to the decreased conception of cows treated with the synthetic progestin in the absence of the corpus luteum. Experiment 2 was designed to study if there were doses at which the synthetic progestin norgestomet which could mimic the function of the corpus luteum in heifers. Heifers received one, two, four, or eight norgestomet implants. The fluctuation in the pattern of LH secretion was dependent upon the relative concentration of progestin. There was an increase in frequency but a decrease in amplitude of the pulses as dose of progestin decreased. Dosage of norgestomet influences frequency of release of LH pulses, rate of ovarian follicle growth, secretion of $17\beta$-estradiol, time to the preovulatory surge of LH after cessation of treatment, and size of the ovulatory follicle. Experiment 3 was designed to determine if synthesis and secretion of LH and FSH were solely dependent on LHRH. Ovariectomized ewes received either a low (10 $\mu$g/kg of body weight) or a high (100 $\mu$g/kg of body weight) dose of an antagonist to LHRH for either 3 or 6 days. Concentrations of LH in serum were suppressed approximately four hours after the first treatment with LHRH antagonist and remained low throughout the treatment period. Concentrations of FSH decreased by approximately 50% of the initial concentrations after 6 days of treatment. Receptors for LHRH were nondetectable in all the ewes treated with the LHRH antagonist. Relative amounts of mRNA for $\alpha$, LH$\beta$, and FHS$\beta$ subunits were lower after 6 days of treatment with LHRH antagonist compared to ewes treated with the LHRH antagonist for 3 days. LHRH was required to maintain steady-state amounts of mRNA for FSH and LH over the 6 days of treatment with antagonist. LHRH was required to maintain pituitary stores of FSH but not LH over the treatment period. These data support the hypothesis that differential regulation of LH and FSH secretion occurs in ewes. Synthesis and secretion of LH are dependent on LHRH; however, synthesis but not secretion of FSH appears to be dependent on LHRH.
Subject Area
Anatomy & physiology|Animals|Veterinary services
Recommended Citation
Sanchez-Torres Esqueda, Teresa, "Regulation of synthesis and secretion of LH and FSH in cows and ewes" (1993). ETD collection for University of Nebraska-Lincoln. AAI9415993.
https://digitalcommons.unl.edu/dissertations/AAI9415993