EFFECT OF AGING ON ERYTHROPOIETIN SECRETION IN MALE-RATS

The secretion of erythropoietin (EPO) and testosterone in response to hypoxia in old (22-25 months), middle (mid)-aged (15-17 months), adult (6-7 months), and young (3 months) male rats was studied. Bats of dif ferent ages were bled by cardiac puncture before and subsequent to 8 h exposure to 12% O-2. The metabolic clearance rate of EPO was determin ed by a single-injection method. The effects of orchidectomy and repla cement of testosterone propionate on plasma EPO concentrations were al so investigated Analysis of the direct effects of testosterone on EPO release from kidney tissue was carried out in an in vitro study. Both basal and hypoxia-induced EPO levels were lower in old rats than in mi d-aged, adult, and young rats (p < .01). Plasma testosterone levels de creased in response to hypoxia in all rats (p < .01) for young, adult, and mid-aged rats, and p < .05 for old rats). The old rats also had l ower plasma testosterone levels following hypoxia when compared with o ther rats (p < .05). The metabolic clearance rate of EPO was not affec ted by age. Orchidectomy decreased rat plasma EPO concentration (p < . 05). This decrease could be restored to intact levels after testostero ne propionate replacement. Both 10(-10) M (p < .05) and 10(-9) M (p < .01) testosterone stimulate EPO release from kidney tissue in vitro. O ver findings indicate that the basal levels of plasma EPO and testoste rone are decreased, and the hypoxia induced EPO is also diminished wit h aging in male rats. These data suggest that the mechanism of toleran ce to hypoxia and the endocrine function of the kidneys in male rats d uring the aging process are testosterone-dependent.