Aging progressively decreases the densities and alters the diurnal rhythms of α₁-adrenergic receptors in selected hypothalamic regions

Associated with the decline in reproductive function that occurs with age in female rats are a diminished ability to secrete LH in response to ovariectomy as well as alterations in the preovulatory LH surge mechanisms. The noradrenergic system, an important regulator of LH release, exhibits age-related alterations in the pattern of neurotransmitter release. In addition, the density of α₁-receptors changes in intact old rats. To determine whether age-related changes in the pulsatile pattern of LH secretion are associated with declines in the densities and/or a loss of diurnal rhythm of α₁-receptors, we measured the density of α₁-receptors at various times of day in young, middle-aged, and old ovariectomized rats. By middle-age, mean concentrations of α₁-receptors decline in the median eminence and suprachiasmatic nucleus. By old age, mean concentrations of α₁-receptors decline in all regions of the hypothalamus examined but not in the dorsal lateral septum. In addition, the diurnal rhythms in α₁-receptors, which occur in the medial preoptic nucleus and the suprachiasmatic nucleus of young rats, are lost by middle-age. These data indicate that progressive alterations in the mean concentrations and diurnal rhythms of α₁-receptors occur with age in brain regions important for the regulation of reproductive functions and may contribute to the age-associated deficits in LH secretion.