Gadolinium attenuates exercise pressor reflex in cats

The exercise pressor reflex, which arises from the contraction-induced stim ulation of group III and IV muscle afferents, is widely believed to be evok ed by metabolic stimuli signaling a mismatch between blood/oxygen demand an d supply in the working muscles. Nevertheless, mechanical stimuli may also play a role in evoking the exercise pressor reflex. To determine this role, we examined the effect of gadolinium, which blocks mechanosensitive channe ls, on the exercise pressor reflex in both decerebrate and alpha -chloralos e-anesthetized cats. We found that gadolinium (10 mM; 1 ml) injected into t he femoral artery significantly attenuated the reflex pressor responses to static contraction of the triceps surae muscles and to stretch of the calca neal (Achilles) tendon. In contrast, gadolinium had no effect on the reflex pressor response to femoral arterial injection of capsaicin (5 mug). In ad dition, gadolinium significantly attenuated the responses of group III musc le afferents, many of which are mechanically sensitive, to both static cont raction and to tendon stretch. Gadolinium, however, had no effect on the re sponses of group IV muscle afferents, many of which are metabolically sensi tive, to either static contraction or to capsaicin injection. We conclude t hat mechanical stimuli arising in contracting skeletal muscles contribute t o the elicitation of the exercise pressor reflex.