Altered Neuroendocrine Status of Middle-Aged Rats Prior to the Onset of Senescent Anovulation

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Abstract
The incidence of senescent anovulation (constant estrus) in female rats increases sharply in the age interval 10-14 months. We have compared the neuroendocrine status of 12-month-old rats, which were still cycling, with that of 6-month-old rats in the reproductive prime. Norepinephrine content in the median eminence of the hypothalamus and circulating levels of FSH and androstenedione were significantly higher in middle-aged rats (12 months old) than in young controls (6 months old). These increases were selective, in that ten other neuroendocrine parameters measured were unchanged. These results indicate that changes occur at multiple levels of the neuroendocrine system during the transitional phase prior to the onset of senescent anovulation.