MICROVASCULAR ARCHITECTURE IN RAT SOLEUS AND EXTENSOR DIGITORUM LONGUS MUSCLES

Microvascular architecture was investigated in the slow-twitch soleus (SOL) and fast-twitch extensor digitorum longus (EDL) muscles. Rats (n = 5) were anesthetized and papaverine was infused into a carotid artery cannula to induce vasodilation. Microfil casting compound was then infused at an inflation pressure (caudal artery) of 100 mm Hg. Bilateral SOL and EDL muscles were excised 24-72 hr postcasting, dehydrated in ethanol, and cleared in methyl salicylate. Branch frequencies (BR) and segment lengths (SL) of intramuscular arterioles and venules were quantified along primary (1°), secondary (2°), and tertiary (3°) order microvessels using microscopy. In both muscles, BR decreased with increasing vessel order. Regional differences in network organization were observed within the EDL muscle. SL of 1° arterioles was 47% shorter in the SOL muscle indicating more compact microvascular networks compared to the EDL muscle. These findings provide a structural basis for reported differences in blood flow between the SOL and EDL muscles at rest and during exercise. © 1992.