| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Biology of Reproduction, Vol 25, 938-944, Copyright © 1981 by Society for the Study of Reproduction
1 Department of Physiology and Biophysics,
Colorado State University,
Fort Collins, Colorado 80523 The effects of estradiol and progesterone on 1) hypophyseal and serum concentrations of
luteinizing hormone (LH) and follicle-stimulating hormone (FSH); 2) hypothalamic content of
gonadotropin releasing hormone (GnRH); and 3) numbers of receptors for GnRH were examined
in ovariectomized ewes. Three days after ovariectomy, ewes were given 16 mg progesterone (n = 5),
0.7 mg estradiol (n = 5) or 16 mg progesterone plus 0.7 mg estradiol (n = 5) s.c. in ethanol twice
daily for 3 weeks prior to slaughter. Ten control ewes were given injections of ethanol according to
the same schedule. Five intact ewes were killed 12 days after an induced ovulation. Blood samples
were collected daily for 4 days prior to slaughter, and the serum was analyzed for concentrations
of progesterone, estradiol, LH, and FSH. Hypothalami were removed after sacrifice and the
amount of GnRH present in the preoptic area, median eminence, and hypothalamus proper was
determined. In addition, the pituitary gland from each animal was removed and the number of
receptors for GnRH and concentrations of LH, FSH, and prolactin were measured. Steroid treatment produced concentrations of estradiol and progesterone similar to those observed during late
pregnancy in ewes. Administration of either progesterone or estradiol, suppressed (P<0.01) serum
concentrations of LH to levels similar to those observed in intact ewes. In contrast, serum concentrations of FSH were suppressed (P<0.01) only in the ewes receiving injections of estradiol (alone
or in combination with progesterone). Although progesterone suppressed serum concentrations of
LH, it had no effect on hypophyseal concentrations of LH or on serum or hypophyseal concentrations of FSH; administration of estradiol suppressed hypophyseal concentrations of LU (P<0.05)
and FSH (P<0.01) and this effect was not antagonized by progesterone. In contrast to serum and
pituitary concentrations of gonadotropins, the number of receptors for GnRH was higher (P<0.01)
in ovariectomized ewes receiving injections of estradiol (or estradiol plus progesterone) than in the
other groups. Contents of GnRH in the three hypothalamic areas examined did not change (P>
0.05) as a result of treatment. Likewise, neither hypophyseal weight nor prolactin content was
affected by steroid treatment, suggesting that the effects of the steroids were limited to the gonadotrophs. These data indicate that estradiol can increase the number of receptors for GnRH,
while the quantity of LH and FSH released into the circulation or contained in the pituitary decreases. Thus, the effects of estradiol appear to be mediated at the level of the pituitary gland. In
contrast, the inhibitory effect of progesterone on secretion of LH is not mediated via receptors
for GnRH or pituitary concentrations of LH, suggesting an influence at higher neural centers.
Accepted on August 17, 1981
This article has been cited by other articles:
|
|
 |
|
  M. L. Looper, J. A. Vizcarra, R. P. Wettemann, J. R. Malayer, T. D. Braden, R. D. Geisert, and G. L. Morgan Influence of estradiol, progesterone, and nutrition on concentrations of gonadotropins and GnRH receptors, and abundance of mRNA for GnRH receptors and gonadotropin subunits in pituitary glands of beef cows J Anim Sci, January 1, 2003; 81(1): 269 - 278. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. M. Turzillo, T. E. Nolan, and T. M. Nett Regulation of Gonadotropin-Releasing Hormone (GnRH) Receptor Gene Expression in Sheep: Interaction of GnRH and Estradiol Endocrinology, December 1, 1998; 139(12): 4890 - 4894. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
