Effects of aging on LH and prolactin after LHRL L-dopa, methyl-dopa, and stress in male rat.

Hypothalamic-pituitary control of prolactin and LH secretion was tested in young (4-6 months) and aged (22-30 months) male Long-Evans rats given L-dopa, methyl dopa, LHRH, or stress treatments. Pretreatment serum LH levels were consistently higher in young than in the aged groups. The increase in serum LH after LHRH injection was only about half as much in aged as compared to young control males. Although acute stress caused a prompt increase in serum LH in young male rats, this treatment was without effect in the aged group. Methyl dopa treatment stimulated serum prolactin secretion in both young and old rats. Although L-dopa treatment caused a reduction in serum prolactin in both age groups, the sensitivity, magnitude, and duration of the reduction was smaller in the aged rats.