The effect of long-term administration of alpha 1-blocker prazosin on capillary density in cardiac and skeletal muscle.

The effect of prazosin on heart and muscle blood flow and capillary density was studied in rats. In acute experiments, alpha 1-blocker prazosin almost trebled blood flow in fast skeletal muscles [tibialis anterior (TA) and extensor digitorum longus (EDL)], but did not affect coronary flow when infused i.v. at a dose of 0.5 microgram.ml-1.min-1 for 30 min. Prazosin in an equivalent dose was then given orally over a period of 5 weeks to investigate its effect on capillarisation in heart and skeletal muscle. Capillary density (CD, capillaries.mm-2), estimated in frozen sections stained for alkaline phosphatase, was similar in the hearts of prazosin-treated and control rats. Capillary/fibre ratio in skeletal muscles increased from 1.52 +/- 0.019 in control EDL to 1.69 +/- 0.01 (P less than 0.001) and from 1.56 +/- 0.04 in control TA to 2.16 +/- 0.04 (P less than 0.001). In TA, the increase was greater than in EDL both in the glycolytic periphery (from 1.30 +/- 0.13 to 1.75 +/- 0.11, P less than 0.025) and the oxidative core of the muscle (from 1.837 +/- 0.14 to 2.51 +/- 0.12, P less than 0.005). Unilateral crush of the lateral peroneal nerve and subsequent reinnervation over the next 7 weeks resulted in redistribution of fibre types from a typical mosaic pattern into groups composed of fibres of similar oxidative capacity. Capillary density as well as capillary/fibre ratio in purely glycolytic areas was lower when compared to supply of glycolytic fibres in normal muscles.(ABSTRACT TRUNCATED AT 250 WORDS)