REINSTATEMENT OF VAGINAL CYCLES IN AGED FEMALE RATS

Abstract

Old constant estrous and young cycling control rats were injected with L-dopa, 200 mg/kg, for a period of 14 days. L-Dopa reinstated vaginal cycling in the old rats and it did not affect the vaginal cycling in young rats. Likewise, 200 mg/kg of L-tyrosine reinstated vaginal cycling. The effect of L-dopa on old rats was blocked by pimozide, by high doses of MK-486 [L-methyldopahydrazine] and Ro 4-4602 [benzyradzine], and by fusaric acid. High doses of phenoxybenzamine or L-propranolol did not alter the L-dopa effect on old rats. A low dose of MK-486 or Ro 4-4602 increased the efficacy of L-dopa in reinstating vaginal cycling. L-Dopa probably reinstates vaginal cycling in old rats by stimulating dopamine receptors. The possibility that a simultaneous stimulation of norepinephrine .alpha. and .beta. receptors and/or a decrease of CNS serotonin is necessary for this effect is discussed.