CAPILLARY AND MUSCLE-FIBER TYPE CHANGES IN DOCA-SALT HYPERTENSIVE RATS

Background: Discrepancies concerning the effect of hypertension on cap illaries and muscle fiber types in skeletal muscle have been reported, This study demonstrates the effects of hypertension produced by deoxi corticosterone acetate (DOCA) and salt load on the extensor digitorum longus (EDL) and soleus muscles of the rat. Methods: Hypertension was produced by subcutaneous injections of DOCA and supplemented with drin king 1% NaCl solution, One group was treated for 7 weeks and another f or 14 weeks. Fiber types were classified by ATPase reaction at pH 4.35 , capillaries were counted in alpha-amylase-PAS-stained sections, and ultrastructure was studied by conventional methods of transmission ele ctron microscopy. Results: In the 7-week group, a decrease in the perc entage of IIA, with an increase in IIB and I fiber types, was found in the EDL muscle, Capillary density was not reduced, but endothelial ce lls showed surface infoldings into the lumen. Altered mitochondria and an infiltrate of macrophages was present in pericytes, In the 14-week group, a decrease in capillary to fiber index was found in both soleu s and EDL muscles, EDL fiber type changes were the same as at 7 weeks, The soleus muscle showed an increased percentage of type I fibers, So me capillaries were degenerated, and others showed an increase in the endothelial cell area covered with pericytes, which resembled smooth m uscle cells. Conclusion: Hypertensive rats showed changes in the perce ntage of fiber types in the soleus and EDL muscles, Capillaries adjace nt to muscle fibers were reduced and showed morphological changes that resembled arterioles. (C) 1996 Wiley-Liss, Inc.