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Washington State University,,4 Pullman 99163 and Colorado State University,,6 Fort Collins 80521
Abstract
Thirty mature Columbia ewes were divided randomly into six equal treatment groups. Each treatment consisted of a single intramuscular injection during mid anestrus of either oil, 12.5, 25, 50, 100 or 200 µg of 17ß-estradiol (E2). Five ml blood samples were collected via jugular vein puncture immediately preceding E2 treatment and at 3-hr. intervals for 27 hr. after treatment. Serum FSH concentrations were determined by a validated double antibody radioimmunoassay. Laparotomies were performed 60 hr. after E2 treatment to determine ovulation rate. The mean basal concentration of all serum FSH values for the oil treated ewes over the entire time period studied was 308 ± 3.8 ng/ml (NIH-FSH-S4). Peak concentrations of FSH in serum were 429 ± 41, 563 ± 24, 501 ± 28, 475 ± 60 and 412 ± 37 ng/ml for the 12.5 through 200 µg E2 groups, respectively, and were all greater (P < .05) than the mean peak serum FSH concentration in the oil treated ewes (337 ± 13 ng/ml). The mean time interval between E2 treatment and peak levels of serum FSH for all groups was 15.4 hours. Serum FSH reached peak levels at the same time as previously reported for LH in the same serum samples. One ewe in each of the 12.5 µg and the 200 µg E2 groups ovulated during treatment. When data from the 100 and 200 µg E2 groups were pooled, a decrease (P < .05) in serum FSH was detected 3 to 9 hr. after E2 treatment, but no FSH difference (P > .05) was found at these times with the lower E2 doses. It would appear from the present study and previous findings that estrogen induces both FSH and LH release from the pituitary at the same time and thus may control release of both hormones by the same mechanism.
The release of FSH and LH from the pituitary gland into the circulation appears to be under the control of a single releasing hormone as indicated by various studies in man, rat and sheep (Schally et al., 1971; Redding et al., 1972; Reeves et al., 1972; Jonas et al., 1973). It has also been well established that a single injection of estrogen can induce release of LH from the anterior pituitary gland of the anestrous ewe (Goding et al., 1969; Radford, Wallace and Wheatley, 1970; Beck and Reeves, 1973). Recently Jonas et al. (1973) found that infusion of anestrous ewes with 17ß-estradiol induced release of both LH and FSH from the pituitary gland. The purpose of this study was to evaluate serum FSH concentrations at various time intervals in anestrous ewes treated with varying dosages of E2.
1 Scientific Paper 4089, College of Agriculture Research Center, Washington State University. Project 0137.
2 The authors thank G. D. Niswender for providing the facilities and antiovine FSH serum used for conducting the FSH-RIA (Supported in part by the National Institutes of Health, NIH Contract 69-2134); and L. E. Reichert for FSH used for iodination.
3 This study was supported in part by USPHS Grant from National Institute of Child Health and Human Development AM06192.
4 Department of Animal Sciences.
5 Present address: Department of Dairy Science, Michigan State University, East Lansing 48823.
6 Department of Physiology and Biophysics.
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  J. A. Arreguin-Arevalo, T. L. Davis, and T. M. Nett Differential Modulation of Gonadotropin Secretion by Selective Estrogen Receptor 1 and Estrogen Receptor 2 Agonists in Ovariectomized Ewes Biol Reprod, August 1, 2007; 77(2): 320 - 328. [Abstract] [Full Text] [PDF]
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