Hydrocortisone and exercise effects on articular cartilage in rats

The combined effects of hydrocortisone and running exercise on articular cartilage were assessed in female Sprague-Dawley rats. Animals were divided into three groups: 12 control (C), 12 who received an injection of 0.1 mL hydrocortisone once a week for three weeks (HC), and 12 rats who received three weekly injections of hydrocortisone and ran twice daily for six weeks (HC + run). Previous study revealed that rats that ran on a treadmill for three to 12 months did not have articular cartilage that was different from controls and thus a fourth group of rats, runners only, was not included in this analysis. At sacrifice, both knees were examined, photographed, and subsequently decalcified, then sectioned at 6 mu and stained. HC + run rats had significant more surface degeneration on femoral cartilage than HC or C rats. Eight of 12 HC + run rats displayed fibrotic invasion and/or subchondral bone replacement of degenerated articular cartilage, a feature not seen in HC or C rats. Cross-sections from HC + run rats displayed areas of cell death, and loss of matrix staining. Results suggest that, in rats, running exercise combined with intraarticular injections of hydrocortisone is more detrimental to articular cartilage than hydrocortisone or running alone.