Fiber Type Distribution, Cross-Sectional Area, and Succinate Dehydrogenase Activity of Soleus and Extensor Digitorum Longus Muscles in Spontaneously Hypertensive Rats.

Abstract

Fiber type distributions, cross-sectional areas (CSAs), and succinate dehydrogenase (SDH) activities of the slow soleus (SOL) muscle and the deep (EDLd) and superficial (EDLs) regions of the fast extensor digitorum longus (EDL) muscle were determined in 10- and 20-week-old male spontaneously hypertensive rats (SHR) and compared with those in age-matched normotensive Wistar-Kyoto rats (WKY). There were no differences in the body weight or the SOL and EDL weight between WKY and SHR at 10 weeks of age, while the body weight and the SOL and EDL weight were lower in SHR than in WKY at 20 weeks of age. A higher percentage of type IIA and type IIC fibers and a lower percentage of type I fibers were observed in SOL of SHR at 10 weeks of age. A higher percentage of type IIB fibers and a lower percentage of type IIA fibers were observed in EDLd and EDLs of SHR at 10 weeks of age. In contrast, there were no differences in the fiber type distribution, except a higher percentage of type IIA fibers and a lower percentage of type I fibers in EDLd of SHR, in SOL, EDLd, or EDLs between WKY and SHR at 20 weeks of age. There were no differences in the CSA, except a smaller CSA of type IIC fibers in SOL of SHR, in SOL, EDLd, or EDLs between WKY and SHR at 10 weeks of age. In contrast, a smaller CSA of type I fibers was observed in SOL of SHR at 20 weeks of age. A smaller CSA of all types of fibers in EDLd and of type IIA fibers in EDLs was observed in SHR at 20 weeks of age. There were no differences in the SDH activity of fibers between WKY and SHR, irrespective of the age and fiber type. It is concluded that age-related differences in the fiber type distribution or CSA are observed in the skeletal muscles between SHR and WKY.