Neuroendocrine axes function in healthy aging: Evaluation of predictive and manipulable blood serum indexes

Aging is characterized by alteration of neuroendocrine axes function. We evaluated possible predictive and manipulable blood serum indexes of function of these axes in healthy elderly. The study was carried out on 15 healthy young-middle aged subjects (age range 36-55 years) and 15 healthy old-aged subjects (age range 67-79 years). Melatonin, cortisol, TRH, TSH, FT4, GH and IGF1 serum levels were measured on blood samples collected every four hours for 24 hours. The presence of circadian rhythmicity, the differences in MESOR, amplitude and acrophases, the differences in the mean of 06:00-10:00-14:00 h values and the mean of 18:00-22:00-02:00 h values hormone serum levels and ratios (melatonin/cortisol ratio, TRH/TSH ratio and GH/IGF1 ratio) between the two groups were evaluated. A normal circadian rhythmicity was recognizable for melatonin, cortisol, TRH, TSH and GH secretion in young-middle aged subjects and for melatonin, cortisol TSH and GH in old-aged subjects, that showed higher cortisol MESOR value (P = 0.001) and lower TSH MESOR value (P = 0.002). Old-aged subjects presented higher GH/IGF1 ratio in the photoperiod (P = 0.02), and higher TRH/TSH ratio in the scotoperiod (P = 0.001). There was no statistically significant difference in melatonin/cortisol ratio between young-middle aged and old-aged subjects. Aging is associated with alteration of some neuroendocrine axes function, but melatonin/cortisol ratio is a valuable predictive and manipulable blood serum index of normal function in healthy aging.