A comparative analysis of the vasomotor responses and innervation of small arteries in rat locomotor and respiratory muscles

Characteristics of the small arteries (with a diameter of 200-250 μm) feeding the medial gastrocnemius muscle and diaphragm were studied. Recording of the mechanical activity of ring segments under isometric conditions demonstrated that, similar to other arteries feeding the muscles with a high content of slow fibers, the diaphragm arteries are highly sensitive to adrenoceptor agonists and acetylcholine. The differences in the endothelium-dependent relaxation in response to acetylcholine were retained in the presence of L-NAME and diclofenac. The diaphragm and gastrocnemius arteries similarly responded to serotonin. On the other hand, a high innervation density was characteristic of the diaphragm arteries unlike the arteries of other slow muscles. The density of adrenergic nerve plexus in the diaphragm arteries was considerably higher than in the gastrocnemius arteries. The results suggest that the characteristics of small diaphragm arteries are determined not only by the oxidative capacity of diaphragm muscle fibers, but also by the fact that this is a respiratory muscle.