In order to determine the changes in the expression of LHβ messenger ribonucleic acid (mRNA) during GnRH agonist (GnRHa) treatment (0.94mg/28 days), the concentration of the mRNA of LHβ was assessed together with the serum LH concentration, pituitary LH content and LH response to GnRH at various times during long-acting GnRHa treatment in immature female rats.
The serum LH concentration was increased at hour 1, gradually decreased starting at approximately hour 3 and had returned to the control level on day 28. Pituitary LH began to decrease at hour 3. The concentrations of LHβ mRNA were not significantly different from those in the control group from hour 1 to hour 18, but were lower from day 3 to day 28. Serum LH response to native GnRH (1μg) began to be inhibited on day 7.
These results indicate that the short term treatment with GnRHa stimulates the release of preformed LH rather than synthesis of LHβ mRNA and that the long term treatment inhibited the expression of LHβ mRNA in a time dependent manner.