Effects of advancing age on hypothalamic neurotransmitter content and on basal and norepinephrine-stimulated LHRH release

-In order to elucidate possible mechanism(s) responsible for the age-related decline in LH secretion basal and norepinephrine (NE)-stimulated LHRH release was measured from median eminence (ME) fragments of 4-,11-,18- and 27-month-old male F344 rats. Serum LH levels declined significantly between 11 and 18 months and were still lower at 27 months of age, while testosterone levels declined continuously between 4 and 27 months. Hypothalamic NE and dopamine (DA) content also declined significantly with age, while serotonin and 5-hydroxy-indoleacetic acid content increased with age. Despite the decline in serum LH levels with age, in vitro basal LHRH r release increased gradually with age as did NE-stimulated LHRH release. These data suggest that the age-related reduction in LH secretion by the male rat is due to a reduction in hypothalamic NE metabolism and not to an inability of the LHRH neuron to respond to NE stimulation.