Lighting conditions affect the levels of plasma gonadotropins differently in old and young castrated male rats.

ABSTRACT

It has been suggested that the decreased plasma levels of FSH and LH, often found in old male rats, are due to a diminished adenohypophyseal capacity to secrete the hormones and/or by changes in the hypothalamic regulatory system. We studied the effect of varying lighting conditions (12/12 h LD, continuous light and continuous darkness) on the plasma levels of the gonadotropins in castrated young adult and old male rats. We expected the sensitivity of the regulatory system to light to decrease or disappear with aging. The results for FSH supported this hypothesis: the plasma levels of FSH were more stable to changes of lighting conditions in the old rats. In disagreement with our hypothesis, the levels of LH were more sensitive to light changes in old than in young rats. It was concluded that the regulatory systems of the two hormones vary differently with age.