Responses of exposure to cigarette smoke at three dosage levels on soleus muscle fibers in Wistar-Kyoto and spontaneously hypertensive rats.

Fiber type distributions, cross-sectional areas (CSAs) and succinate dehydrogenase (SDH) activities in the soleus (SOL) muscle in normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats were determined after exposure to cigarette smoke at three different dosage levels using a smoking machine. The rats were exposed to cigarette smoke at a rate of 15 puffs/min, for 20 min/day with 23 cigarettes (low-dosage), 26 cigarettes (medium-dosage) or 30 cigarettes (high-dosage) for 8 weeks. There were no effects on the body weight, SOL weight, fiber type distribution, CSA or SDH activity of WKY after exposure to cigarette smoke, irrespective of the dosage level. In contrast, the body weights of SHR were lower after exposure to cigarette smoke, irrespective of the dosage level. The SOL weights of SHR were lower after exposure to cigarette smoke at the medium- and high-dosage levels. A lower percentage of type I fibers, a higher percentage of type IIA fibers and a smaller CSA of both type I and type IIA fibers were observed in SHR after exposure to cigarette smoke at the high-dosage level, but not at the low- and medium-dosage levels. These results indicate that heavy cigarette smoke causes changes in the enzyme histochemical properties with a reduced CSA of the SOL in SHR, but not in WKY.