Steady-state Concentrations of MRNA Encoding the Receptor for Luteinizing Hormone During the Estrous Cycle and Following Prostaglandin F(2α) Treatment of Ewes

A partial cDNA was used to measure steady-state concentrations of mRNA encoding the receptor for luteinizing hormone (LH) in ovine corpora lutea. In experiment 1, luteal tissue and purified preparations of small and large steroidogenic luteal cells (n=4 per day) were obtained on days 3 (tissue only), 6, 9, 12 and 15 of the estrous cycle (estrus=day 0). Steady-state concentrations (fmoles receptor mRNA/μg poly(A)(+) RNA) and total quantities of mRNA (fmoles/corpus luteum) encoding the receptor for LH in luteal tissue increased (P<0.05) from day 3 to days 9 and 12 of the cycle; values on days 6 and 15 were intermediate. Small luteal cells contained at least four-fold greater (P<0.001) concentrations of mRNA encoding the receptor for LH than large luteal cells on days 6, 9, 12 and 15 of the cycle. In experiment 2, ewes on days 11 or 12 of the cycle received an infusion of either 1 μmol prostaglandin F(2α) (PGF(2α)) or saline into the ovarian artery. Luteal tissue was collected 1 (n=6), 4 (n=5), 12 (n=5) or 24 (n=5) h following PGF(2α) infusion, and 0 (no infusion;n=3), 12 (n=3) or 24 (n=4) h following saline administration. Concentrations of progesterone in sera decreased (P<0.05) within 12 h and remained low, whereas luteal weight and concentrations of progesterone in luteal tissue did not decrease (P<0.05) until 24 h after PGF(2α) treatment. Steady-state concentrations of mRNA encoding the receptor for LH were reduced (P<0.05) within 4 h of PGF(2α) infusion, and continued to decrease at 12 and 24 h post treatment. Calculated amounts of mRNA encoding the receptor for LH per corpus luteum were reduced (P<0.05) at 12 h after the PGF(2α) treatment and were 10% (P<0.05) of the values in saline-treated ewes at 24 h post-treatment. The increase during the estrous cycle in steady-state concentrations of mRNA encoding the receptor for LH appears to occur prior to the previously observed increase in number of receptors for LH. Following PGF(2α)-induced luteal regression, concentrations of mRNA encoding LH receptor decreased prior to the previously reported decrease in LH binding. Thus, changes in the number of receptors for LH in ovine luteal tissue during luteal development and luteolysis appears to be preceded by corresponding changes in mRNA encoding this receptor.