Abstract
To study the microvascular circulation, we examined the proportion of open and functioning capillaries in the leg muscles, pancreas and small intestine of anesthetized rats. Fluorescein isothiocyanate (FITC)-labeled Lycopersicon esculentum lectin was injected into the heart and allowed to circulate for 3 min to label open and functioning capillaries. Specimens were removed, frozen, sectioned and double-immunostained. Using one section, open and functioning capillaries were detected by immunostaining for this lectin bound to endothelial cells, while all capillaries were visualized by immunostaining for platelet endothelial cell adhesion molecule-1 (PECAM-1 or CD31). These capillaries were semi-automatically detected and counted by fluorescence microscopy. The percentages of open and functioning capillaries were as follows: the soleus muscle, 93.0 ± 5.5%; superficial zone of the gastrocnemius muscle, 90.8 ± 6.2%; deep zone of the gastrocnemius muscle, 95.6 ± 4.0%; the plantaris muscle, 94.1 ± 2.7%; the pancreas, 86.3 ± 11.7%; and the small intestine, 91.1 ± 4.9% (n = 8, each). There was no significant difference among these data by the Kruskal–Wallis test. This study clearly demonstrated that the proportions of open and functioning capillaries are high and similar among the leg muscles, pancreas and small intestine in spite of their structural and functional differences. This finding agrees with previous studies and supports the notion that the microvascular circulation is mainly controlled by changing of the blood flow in each capillary rather than changing the proportion of open and functioning capillaries.
Highlights
The blood supply is vitally important for the transport of essential materials and metabolic waste
Blood flow of skeletal muscles is low at rest, but drastically increases upon exercise (Nilsson and Ingvar 1967; Terjung and Engbretson 1988; Musch and Terrell 1992; Hawker and Egginton 1999; Kindig et al 2002; Richardson et al 2003) and local warming
Our finding seems to support the notion that microvascular blood flow in various tissues and organs is mainly controlled by regulating the blood flow of each capillary, while the proportion of open and functioning capillaries remains relatively constant (Kindig et al 2002; Maeda et al 2014)
Summary
The blood supply is vitally important for the transport of essential materials and metabolic waste. Capillaries are densely distributed throughout most tissues and organs. Blood flow in various tissues and organs is significantly different. The blood flow of rat per unit time and weight is reported as follows (Musch and Terrell 1992): the soleus muscle, 140 ± 18; superficial zone of the gastrocnemius muscle (gastrocnemius, white), 10 ± 2; deep zone of the gastrocnemius muscle (gastrocnemius, red), 60 ± 12; the plantaris muscle, 15 ± 3; the pancreas, 148 ± 22; and the small intestine, 247 ± 29 ml min−1 100 g−1 (mean ± SE). The regulation mechanism of blood flow in the capillary bed is not fully understood
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