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 agerelated 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 arreceptors occur with age in brain regions important for the regulation of reproductive functions and may contribute to the age-associated deficits in LH secretion. (Endocrinology126: 2392–2397, 1990)

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