Effect of skeletal muscle fiber type on the pressor response evoked by static contraction in rabbits

Abstract

The purpose of this study was to determine whether the reflex hemodynamic responses to static contraction of predominately glycolytic muscle are greater than the changes elicited by primarily oxidative muscle. Low-frequency electrical stimulation (continuous 21 days) of the tibial nerve of one hindlimb of adult rabbits converted the metabolic characteristics of the predominately glycolytic gastrocnemius to a muscle that was primarily oxidative. After 21 days of stimulation, the rabbits were decerebrated, and static contraction of the glycolytic muscle (unstimulated gastrocnemius) initially decreased heart rate (HR; -16 +/- 3 beats/min) and mean arterial pressure (MAP; -17 +/- 3 mmHg). Thereafter, MAP increased 13 +/- 3 mmHg above baseline. Static contraction of the oxidative muscle (stimulated gastrocnemius) produced similar decreases in HR and MAP (-12 +/- 4 beats/min and -12 +/- 3 mmHg, respectively). However, the subsequent increase in MAP (8 +/- 3 mmHg; above baseline) was less than that evoked by contraction of the glycolytic muscle. The responses evoked by stretch of each muscle and high-intensity electrical stimulation were the same, indicating that the afferents from the muscle were not destroyed by the chronic-stimulation technique. These results support the hypothesis that metabolic by-products play a role in the pressor response to static contraction of skeletal muscle. In addition, these data confirm that contraction of predominately oxidative muscle can evoke a reflex pressor response, albeit smaller than the change elicited from primarily glycolytic muscle.

Aging and the Exercise Pressor Reflex in Humans

“…Compared with oxidative muscle, glycolytic muscle evokes a larger reflex response. 14 Of note, despite the fact that the older subjects' velocity response to ischemia was not different than that of young subjects, venous oxygen saturation tended to be higher in the older group. Diminished oxygen extraction with age has been shown previously 15,16 and may be related to aging-induced mutations of mitochondrial DNA.…”

Aging alters muscle reflex control of autonomic cardiovascular responses to rhythmic contractions in humans

“…During PECO following rhythmic handgrip exercise in old and young individuals, MAP has been reported to be lower in the old, which led to the conclusion that aging attenuates the exercise pressor reflex (34). However, recognizing the well-documented age-related shift in muscle fiber type toward the fatigue resistant type I phenotype (33, 50), which is associated with a slower metabolite accumulation and consequently a reduced stimulus for metabosensitive muscle afferents (57,58), this conclusion may have been in error. Specifically, the observed difference in blood pressure responses during PECO in old compared with young individuals might actually be a consequence of reduced metaboreceptor stimulation in the old and entirely independent of any functional changes in the muscle reflex arc.…”

“…Indeed, based on a limited number of experiments utilizing handgrip exercise and postexercise circulatory occlusion (PECO), the exercise pressor reflex has been suggested to be attenuated in older individuals (24,34). However, potential age-related differences in metabolite accumulation during PECO and the associated differences in the magnitude of the afferent stimulus in the young compared with the old (57,58) may have masked the real effect of aging on the muscle reflex control of the cardiovascular response to exercise.…”

Role of the Exercise Pressor Reflex in Rats With Dilated Cardiomyopathy

“…10,14,21,22 In addition, other factors, including modifications in muscle metabolism and fiber type composition (eg, reductions in the percentage of oxidative fibers and increases in the percentage of glycolytic fibers), 2,3,25 may facilitate these disease-induced alterations in reflex function. For example, because the EPR-mediated circulatory response to activation of glycolytic muscle has been shown to be greater than the response elicited from oxidative muscle, 36 fiber-type transformations could profoundly effect the physiological expression of the pressor reflex.…”