[Fluorescence microscopic study of capillary density in the rat skeletal muscle during and after contraction].

Fluorescein isothiocyanate-albumin conjugate was intravenously injected into the rat. The biceps femoris muscles were fixed by snap freezing with isopentane cooled to -150 degrees C. In histological sections infused capillaries were visualized under fluorescence microscopy. Perfused capillary density and number of capillaries per muscle fiber were determined at rest, during and after contraction of the muscle. Capillaries per muscle fiber ratios were 0.73 +/- 0.03 (mean +/- SE) at rest, 0.84 +/- 0.03 during weak contraction, 0.85 +/- 0.02 during strong contraction, and 0.85 +/- 0.02 in postcontraction hyperemia. During strong contraction, muscle blood flow measured by heated thermocouple technique showed a decrease and was not proportional to the increased capillary density. From these results it was assumed that additional factors such as increased velocity of the flow might play an important part in the increase in muscle blood flow during and after contraction.