Myocardial fibrosis has been investigated in 3-, 16-, and 24-mo-old normal rats and also in 24-mo-old rats subjected to deoxycorticosterone acetate (DOCA)-salt treatment-induced-hypertension. Collagen content was assessed both histologically and by hydroxyproline assay. Type I and III procollagen mRNA levels were quantitated by Slot Blot analyses. Aging is associated with fibrosis as shown both biochemically (hydroxyproline concentration in 3-, 16-, and 24-mo-old rats was 0.70 +/- 0.05, 0.92 +/- 0.07, and 1.57 +/- 0.13 mg/g of left ventricle, respectively, P < 0.05 and P < 0.0001 vs. 3 mo) and histologically. By contrast, type I procollagen mRNA levels decreased during aging (from -63%, P < 0.001 in 16-mo-old rats and -51%, P < 0.01 in 24-mo-old rats vs. 3-mo-old rats) as well as type III procollagen mRNA levels. DOCA-salt treatment in 24-mo-old rats had no effect on either the degree of fibrosis or the mRNA levels. We conclude that nonsynchronous changes in myocardial collagen mRNA and protein occur during aging, indicating translational and/or posttranslational mechanisms in collagen regulation. Hypertension during senescence did not modify collagen deposition at either the protein or mRNA levels.
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