The pituitary-ovarian complex in the aged anoestrous golden hamster

Plasma and pituitary hormones of young (3--5 months of age) dioestrous hamsters with normal cycles and aged (13--17 months of age) anoestrous hamsters were compared. The anoestrous hamsters exhibited lower plasma values of progesterone (P less than 0.001), oestradiol-17 beta (P less than 0.005) and prolactin (P less than 0.001) and higher levels of plasma gonadotrophins (P less than 0.001) than did the dioestrous animals. Pituitary concentrations of LH were higher (P less than 0.005) in anoestrous hamsters, but pituitary FSH and prolactin values did not differ. In another series of experiments three groups of hamsters (3--5- and 13--17-month-old with normal cycles and 13--17-month-old in anoestrus) were ovariectomized. Blood samples were taken by cardiac puncture every 3--4 weeks after receiving s.c. injections of oestradiol-17 beta (1 or 10 micrograms/100 g body wt) for 2 or 9 consecutive days. The markedly lower levels of gonadotrophins in aged anoestrous hamsters indicated that the hypothalamic-hypophysial complex was incapable of responding to the same degree as it did in young and aged cyclic animals. Prolactin values were similarly depressed in all 3 groups. Oestradiol-17 beta treatment caused reduced gonadotrophin and increasing prolactin concentrations in all 3 groups. These results indicate that the ovaries of the senescent anoestrous hamster produce less steroids and suggest that age-related changes in the hypothalamic-hypophysial complex are largely responsible for the cessation of regular oestrous cycles.