Age Effects on Luteinizing Hormone, Progesterone and Prolactin in Proestrous and Acyclic C57BL/6J Mice1

The proestrous-estrous profiles of plasma luteinizing hormone (LH), prolactin (PrI) and progesterone (P) were determined in aging C57BL/6J mice. Estrous cycles were more variable and average length was greaterinoldermice: 4-6 month, 4.3 ± 0.6 days per cycle; 12-month, 5.3 ± 1.3 days per cycle. Mice sacrificed at 2-h intervals during the preovulatory surge showed age-related deficits (30-50%) of plasma LH, Prl and P. Although peak LH did not differ between the age groups, the older mice had smaller LH elevations during the ascending and descending portion of the surge. Elevations of P were lower in older mice throughout the surge. LH and P were correlated during the ascending phase of the preovulatory surge at the onset of darkness. This correlation supports the hypothesis that elevations of P at proestrus are driven by increases of LH and that the smaller elevation of P in aging mice resulted mainly from reduced LH. Older mice with regular 4-day cycles or with longer cycles had lower P than younger mice of either cycle length class. Since there was a similar effect of age but not of cycle length on PrI at this time, we conclude that age effects on P and PrI do not result from age associated changes in cycle length. The elevations of PrI during the surge were smaller in older mice; this result argues against the possibility that age-related increases of Prl are a cause of irregular cycles. About 40% of 12-month-old mice were acyclic: 32% were in persistent vaginal cornification (PVC) and 8% were in persistent diestrus (PD). Mice in PVC had low P and LH, but moderately elevated PrI; mice in PD had low LH, but moderately elevated P and PrI. These data suggest that the onset of age-related disturbances in LH regulation does not initially result from elevated PrI and that elevated PrI is consequent to the noncycling status.