Endothelial pores in the rat soleus muscle capillaries after experimental limb immobilization

Capillary facilitation of skeletal muscle function in health and disease

Skeletal muscle is highly vascularized, with perfusion being tightly regulated to meet wide-ranging metabolic demands. For decades, the capillary supply has been explored mainly in terms of evaluating the capillary numbers and their function in the supply of oxygen and substrates and the removal of metabolic byproducts. This review will focus on recent discoveries concerning the role played by capillaries in facilitating other aspects of cell regulation and maintenance, in health and disease, as well as alterations during the aging process.

Novelty Capillaries play a central role in the coordination of the vascular response that controls blood flow during contraction and the cellular responses to which they feed into. Nitric oxide is an important regulatory compound within the cardiovascular system, and a significant contributor to skeletal muscle capillary angiogenesis and vasodilatory response to agonists. The microvascular network between muscle fibres may play a critical role in the distribution of signalling factors necessary for optimal muscle satellite cell function.

Electron microscopic study of capillary network remodeling in the extensor digitorum longus muscle of normal adult rat

Capillary networks demonstrate structural changes during maturation, aging, vascular disease, and cancer. Their morphological structure and function have an important influence on each other. Understanding the process of morphological vascular changes in the capillary network with advancing age may help overcome fatal vascular diseases. Aging-related structural changes of the capillary segments may accompany degeneration and regeneration of muscle fibers and serve to remodel the capillary network as a means of adapting to the changing environment. However, difficulty in obtaining human samples has hampered clarification of these microstructural changes. Herein, we examined serial ultrathin sections of capillary segments in the extensor digitorum longus muscle of normal mature (12 months old) rats in an attempt to analyze their structural changes. After bifurcation, a minimum of one capillary segment was filled with erythrocytes and was found to have fenestrations and plural endothelial disruptions, or pores, at the fenestrated portions. Some of the stagnated erythrocytes demonstrated extended protrusions, and their processes appeared to penetrate the basal lamina through the pores. These findings can also show that capillary segments are involved in partial remodeling of the capillary network. A better understanding of age-related structural changes of the capillary networks will help in fine-tuning novel vascular therapy for not only several fatal vascular diseases but also malignant tumors.

Suppressed cutaneous endothelial vascular control and hemodynamic changes in paretic extremities with edema in the extremities of patients with hemiplegia

OBJECTIVE

To investigate peripheral circulatory function and its underlying mechanisms in the paretic upper extremity after a stroke.

DESIGN

Case-control study.

SETTING

A department of physical medicine and rehabilitation in Taiwan.

PARTICIPANTS

A total of 53 hemiplegic patients (28 men, 25 women; mean age +/- standard deviation; 58.2+/-3.8y) were studied. Subjects were divided into edema and nonedema groups. The edema group included 29 hemiplegic patients with edematous paretic upper extremities. Twenty-four hemiplegic patients in the nonedema group did not suffer from limb edema in the paretic upper extremity.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Cutaneous microvascular perfusion responses to 3 grade levels of iontophoretically applied 1% acetylcholine (ACh), 1% ACh plus 1% N(G)-monomethyl-L-arginine (L-NMMA), and 1% sodium nitroprusside (SNP) in the skin of subjects' forearms were determined by laser Doppler perfusion measurements. Moreover, hemodynamic characteristics in the arterial and venous vessels were measured by impedance plethysmography.

RESULTS

Resting arterial inflow and venous capacity, tone, and outflow in paretic extremities did not significantly differ from nonparetic extremities, but the hyperemic arterial inflow was lower in paretic extremities than in nonparetic extremities, and paretic extremities were associated with lower ACh- and ACh plus L-NMMA-induced cutaneous perfusions than nonparetic extremities. ACh-induced cutaneous perfusions also decreased much more significantly in edematous paretic extremities than in nonedematous paretic extremities, and skin vascular responses to SNP do not differ significantly between paretic and nonparetic extremities.

CONCLUSION

Cutaneous microcirculatory function in the paretic upper extremity after stroke may be impaired. The impairment may occur because of decreased endothelium-dependent dilation in skin vasculature. Dysfunction in cutaneous microcirculation tends to be more pronounced in the edematous than in the nonedematous extremities.

Capillary changes with fenestrations in the contralateral soleus muscle of the rat following unilateral limb immobilization

Using electron microscopy, we examined structural changes in the capillaries of the immobilized and contralateral soleus muscles in the rat after the unilateral limb had been immobilized for 4 weeks. Individual contralateral muscle fibers showed a normal structure, compared with the structure in the immobilized muscle fibers. Most capillaries in the contralateral muscle were of the continuous type. However, about 5% of the examined capillaries in these muscles in each rat had fenestrations. The non-nuclear portions of the endothelial cells in these capillaries were extremely thin and were perforated by several fenestrations that were bridged by a single-layered diaphragm. The fenestration of capillaries in the contralateral muscle may have been caused by some the unilateral limb immobilization.

Capillaries with fenestrations around regenerating muscle fibers in the soleus muscle of the dystrophic (dy) mouse

To investigate the morphological changes in capillaries around regenerating muscle fibers in the dystrophic (dy) mouse, we examined capillaries in the soleus muscles of 30-day-old control and dy mice by electron microscopy. In the control mice, the intramuscular capillaries were continuous. In the dystrophic mice, the muscles contained degenerative muscle fibers and many small muscle fibers regenerating after necrosis; these fibers had centrally located nuclei. The capillaries in the dy mice were mostly continuous, but some had a narrow vascular lumen around regenerating muscle fibers, possibly indicating newly formed capillaries. Moreover, about 20% of the capillaries with a narrow vascular lumen had a small number (less than five) of fenestrae bridged by a single-layered diaphragm. These findings suggest that capillary networks around muscle fibers regenerating after necrosis are remodeled by newly formed capillaries, and some of these capillaries have fenestrae in the endothelium to increase the supply of nutrients and oxygen to the regenerating muscle fibers.