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Biology of Reproduction, Vol 22, 205-210, Copyright © 1980 by Society for the Study of Reproduction
1 Department of Physiology and Biophysics,
Colorado State University,
Fort Collins, Colorado 80523 To study the events associated with down-regulation of receptors for luteinizing hormone (LH)
in the ovine corpus luteum, normally cycling ewes were injected i.v. with 1 mg LH on Day 10 of
the estrous cycle. Changes in concentrations of LH and progesterone in serum, luteal concentrations of progesterone and numbers of luteal receptors for LH were measured up to 72 h after
LH injection. Serum levels of LH increased more than 1000-fold (P<0.01) from a control level of
298 ± 23 pg/ml (mean ± SEM) to 327 ± 22 ng/ml at 10 min, then returned to control levels by
24 h. Progesterone concentrations in serum increased (P<0.05) from 2.63 ± 0.29 (least squares
mean ± SEM) to 4.09 ± 0.29 ng/ml within 10 min after administration of LH, remained elevated
for 2 h, decreased to control levels within 4 h, but never decreased below control levels. Progesterone content of the corpus luteum was correlated (r = 0.78, P<0.05) with progesterone concentrations in serum. The number of unoccupied receptors decreased (P<0.05) by 66% from control
levels of 2.63 ± 0.48 x 10-12 mol/corpus luteum to 0.90 ± 0.48 x 10-12 mol/corpus luteum by
12 h. Recovery to control levels had occurred between 24-48 h. Within 10 min the total number
of receptors for LH increased 260% while the number of occupied receptors increased 13-fold
from control levels of 0.41 ± 0.66 x 10-12 mol/corpus luteum to 5.43 ± 0.73 x 10-12 mol/corpus
luteum. The number of receptors occupied by LH decreased rapidly until 6 h and had returned to
control values by 24 h. Serum concentrations of progesterone were correlated (r = 0.80, P<0.05)
with the number of occupied receptors during the first 24 h after LH injection. In addition, there
was good correlation between the number of receptors occupied by LH at 10 min (5.43 x l0-12
mol/corpus luteum) and the number of total receptors lost from 10 min to 24 h (6.75 x 10-12
mol/corpus luteum) after LH injection. These data suggest that down-regulation of ovine luteal
receptors for LH involves the loss of occupied receptors, perhaps via internalization of hormone-receptor complexes. In addition, a mechanism for the replacement of receptors is proposed.
Note:
ACKNOWLEDGMENTS
The authors wish to express their appreciation to
Dr. Robert Canfield for his gift of highly purified
hCG. Also, the expert technical assistance of Keith
Gressman and Vaughn Cook is gratefully acknowledged.
This article has been cited by other articles:
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Y.-J. Chen, Q. Feng, and Y.-X. Liu Expression of the Steroidogenic Acute Regulatory Protein and Luteinizing Hormone Receptor and Their Regulation by Tumor Necrosis Factor {alpha} in Rat Corpora Lutea Biol Reprod, February 1, 1999; 60(2): 419 - 427. [Abstract] [Full Text] [PDF]
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