Effects of aging on erythropoietin secretion in female rats

The secretion of erythropoietin (EPO) in old (22 25 months), middle (mid)-aged (15-17 months), adult (6-7 months), and young (3 months) female rats was studied. Rats of different ages were bled by cardiac puncture for measuring plasma EPO, estradiol, and progesterone levels. The metabolic clearance rate of EPO was determined by a single-injection method. The effects of ovariectomy and replacement of estradiol (E) and/or progesterone (P) on plasma EPO concentration were also investigated. Analysis of direct effects of E and/or P on EPO from kidney tissues was carried out in an in vitro study. Plasma EPO levels were higher in both mid-aged and old rats than in young rats (P < 0.01). The metabolic clearance rate of EPO was also greater in adult, mid-aged and old rats than in young rats (P < 0.01). Ovariectomy increased rat plasma EPO concentration which might be inhibited by E (P < 0.01), P (P < 0.01), or E and P (P < 0.05) replacement. Neither E (10(-10) or 10(-9) M) nor P (10(-8) or 10(-7) M) alone altered EPO release from kidney tissue in vitro. Combination of E (10(-10) M) and P (10(-8) x or 10(-7) M) stimulated the EPO release from kidney tissue (P < 0.01). These data suggest that the mechanism of the secretion of EPO by kidneys in female rats during aging is ovarian steroid hormones independent.