The mode of GABAB receptor-mediated inhibition of the preovulatory luteinizing hormone surge in female rats.

In estrogen-primed ovariectomized rats, intraventricular injections of baclofen, a selective GABAB receptor agonist, either delayed, eliminated or disrupted the steroid-induced LH surge, depending on the time and the dose of the agonist injected. The delay in the onset of the LH surge was not due to a phase delay in the circadian clock, since the retarded LH surge, when observed, had a short duration, terminating in the evening simultaneously with the termination of the normal LH surge in control animals. Rather, rapid disruption of the ongoing LH surge after baclofen injection during the surge suggested a direct involvement of the GABAB receptor-mediated inhibitory component in the LH surge mechanism.