Differences in the response pattern of aged female rats to treatment with lergotrile mesylate

Old female rats exhibiting either the constant vaginal estrous (CE) or the prolonged diestrous (PD) state were given lergotrile mesylate (LM). Treatment with 4.5 mg/kg daily significantly reduced prolactin (PRL) levels in both groups. The basal luteinizing hormone (LH) levels were not altered. In the CE group, LM treatment produced a single prolonged cycle, with the reemergence of the CE state. However, in the PD group, the rats exhibited several regular cycles during the treatment period. Several of these rats also showed evidence of having an LH surge during the reinduced cycle. These results suggest that high PRL levels may be a causative factor with respect to acyclicity in the PD rats, but PRL does not seem to be a major contributor to acyclicity in the aged CE rat.