To assess the role of renal innervation in O2-dependent control of erythropoietin (EPO) formation, we have determined EPO mRNA levels in both kidneys of unilaterally denervated rats and sham-operated controls using RNase protection. To investigate whether possible effects of renal nerve input are related to the type of hypoxic stimulus and the degree of stimulation, animals were studied under basal conditions, after exposure to normobaric hypoxia (8% O2, 4 h) or CO (0.1%, 4 h), and after acute hemorrhage (decrease in hematocrit from 40.8 +/- 0.5 to 12.7 +/- 0.5% within 7 h; mean +/- SE, n = 6). Serum EPO levels rose on average 22-, 49-, and 48-fold under the three stimuli and were unaffected by unilateral denervation. Renal EPO mRNA levels in unilaterally denervated animals, when expressed in arbitrary units revealed by comparison with an external standard, were 7.0 +/- 1.5 vs. 6.3 +/- 2.0 (normoxia), 432 +/- 136 vs. 451 +/- 156 (normobaric hypoxia), 971 +/- 93 vs. 930 +/- 120 (CO), and 604 +/- 170 vs. 689 +/- 203 (hemorrhagic anemia) in the intact vs. the denervated kidney (mean +/- SE, n = 3). Furthermore, there was no difference between EPO mRNA levels of either kidney of unilaterally denervated animals and levels in sham-operated controls. We conclude that renal nerve input plays no significant role in the control of the EPO gene under both basal and stimulated conditions.