The impact of aging on luteinizing hormone (LH) and thyroid-stimulating hormone (TSH) in the rat brain.

Immunoreactive and bioactive luteinizing hormone (LH), thyroid-stimulating hormone (TSH) and growth hormone (GH) have been described by this and other laboratories to be present in discrete areas of the rodent and primate brain. In the present studies, LH and TSH concentrations in serum, pituitary, hypothalamus, brainstem, cerebellum, cerebral cortex and hippocampus were measured in male Sprague-Dawley rats at 2.5 months of age, when 11-12 months old and at 24 months of age. There was a significant decrease in hypothalamic TSH concentrations in the 11-12-month-old rats compared to younger animals (672 +/- 127 ng/mg vs 86 +/- 17 ng/mg, P less than 0.001). This was unaccompanied by any changes in TSH levels in serum, anterior pituitary, or in any of the extrahypothalamic brain areas that were examined. In contrast, there was a significant 50% drop in LH concentrations in the anterior pituitary gland of 11-12-month-old animals when compared with young controls (72 +/- 58 micrograms/mg vs 137.2 +/- 27 micrograms/mg, P less than 0.05) without any noted change in serum or brain LH concentrations. Similar decreases in LH concentration were also seen in the anterior pituitary glands of two-year-old animals. These discordant profiles between pituitary and brain LH and TSH provide additional circumstantial evidence that these brain peptides do not represent contaminants from the anterior pituitary. Further, these significant changes in TSH and LH concentrations that develop with aging may implicate these particular peptides in the development of certain features of senescence.