Effects of ovariectomy and estrogen on ischemia-reperfusion injury in hindlimbs of female rats

The effects of estrogen and ovariectomy on indexes of muscle damage after 2 h of complete hindlimb ischemia and 2 h of reperfusion were investigated i n female Sprague-Dawley rats. The rats were assigned to one of three experi mental groups: ovariectomized with a 17 beta -estradiol pellet implant (OE) , ovariectomized with a placebo pellet implant (OP), or control with intact ovaries (R). It was hypothesized that following ischemia-reperfusion (I/R) , muscle damage indexes [serum creatine kinase (CK) activity, calpain-like activity, inflammatory cell infiltration, and markers of lipid peroxidation (thiobarbituric-reactive substances)] would be lower in the OE and R rats compared with the OP rats due to the protective effects of estrogen. Serum CK activity following I/R was greater (P < 0.01) in the R rats vs. OP rats and similar in the OP and OE rats. Calpain-like activity was greatest in th e R rats (P < 0.01) and similar in the OP and OE rats. Neutrophil infiltrat ion was assessed using the myeloperoxidase (MPO) assay and immunohistochemi cal staining for CD43-positive (CD43+) cells. MPO activity was lower (P < 0 .05) in the OE rats compared with any other group and similar in the OP and R rats. The number of CD43+ cells was greater (P < 0.01) in the OP rats co mpared with the OE and R rats and similar in the OE and R rats. The OE rats had lower (P < 0.05) thiobarbituric-reactive substance content following I /R compared with the R and OP rats. Indexes of muscle damage were consisten tly attenuated in the OE rats but not in the R rats. A 10-fold difference i n serum estrogen content may mediate this. Surprisingly, serum CK activity and muscle calpain-like activity were lower (P < 0.05) in the OP rats compa red with the R rats. Increases in serum insulin-like growth factor-1 conten t (P < 0.05) due to ovariectomy were hypothesized to account for this findi ng. Thus both ovariectomy and estrogen supplementation have differential ef fects on indexes of I/R muscle damage.