AJP - Endocrinology and Metabolism, Vol 254, Issue 1 E99-103, Copyright © 1988 by American Physiological Society
LH subunit mRNA concentrations during LH surge in ovariectomized estradiol-replaced rats
D. J. Haisenleder, A. L. Barkan, S. Papavasiliou, S. M. Zmeili, C. Dee, M. L. Jameel, G. A. Ortolano, M. R. el-Gewely and J. C. Marshall
Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor 48109.
In cycling rats, pituitary concentrations of luteinizing hormone (LH)
beta-subunit mRNA increase two- to threefold before the afternoon proestrus
LH surge without a corresponding increase in alpha-subunit mRNA. Estradiol
(E2) treatment is known to allow expression of daily LH surges in
ovariectomized (OVX) rats, and the timing, magnitude, and duration of LH
secretion is similar to the LH surge on proestrus. The present study was
conducted to examine whether the regulation of LH subunit mRNAs during the
LH surge in OVX-E2-treated rats is similar to that present on proestrus.
Female Holtzman rats were OVX and Silastic implants containing E2 were
inserted subcutaneously under ether anesthesia. Some animals received
bromocriptine (0.6 mg sc, twice/day beginning 1 h before surgery). On the
2nd day after surgery, groups of animals (n = 4-10/group) were decapitated
at intervals between 1000 and 2100. LH and prolactin (PRL) levels were
measured in trunk blood. LH subunit mRNA concentrations in the pituitaries
were measured by dot-blot hybridization assay. In OVX-E2 rats the LH surge
occurred at 1830 and was accompanied by a selective twofold increase in
alpha-subunit mRNA (from 266 +/- 18 to 459 +/- 61 pg cDNA bound/100
micrograms pituitary DNA) and maximum values were present at 1730. LH
beta-subunit mRNA (m = 29 +/- 1 pg cDNA bound/100 micrograms pituitary DNA)
was unchanged throughout the day. Bromocriptine treatment resulted in the
suppression of serum PRL (m = 23 +/- 2 ng/ml) and the LH surge was delayed
by 1-1.5 h and somewhat blunted.(ABSTRACT TRUNCATED AT 250 WORDS)
