NO INFLUENCE OF AGING ON THE CIRCADIAN-RHYTHM OF ERYTHROPOIETIN IN HEALTHY-SUBJECTS

The diurnal rhythm in the circulating serum levels of erythropoietin ( Epo) was investigated in a group of 20 clinically healthy subjects age d 30-55 years and in a group of 20 healthy subjects aged 55-75 years. Venous blood samples were drawn during the span of a whole day every 4 h, starting from midnight, for the determination of serum Epo levels by radioimmunoassay. Statistical analysis was carried out by means of the 'cosinor' method. Both groups presented a significant (p < 0.05) c ircadian rhythm in serum Epo levels, with maximum in the afternoon. Th e younger subjects had significantly (p < 0.05) higher mean daily leve ls and higher diurnal variations of serum Epo than older subjects; no difference (p > 0.05) was found between the groups regarding the peaks of the rhythms. These data confirm the presence of a circadian rhythm in serum EPO levels and suggest that the aging process does not influ ence the physiological diurnal fluctuations, but modifies the mean dai ly levels and the amplitude of the diurnal variations, such as it occu rs for many other variables. This behavior is an index of aging, but d oes not seem to have clinical implications.