Myophosphorylase Knock Out Prevents the Exaggerated Exercise Pressor Reflex in Rats With Simulated Peripheral Artery...

Controversy exists on which metabolites determine the exaggerated exercise pressor reflex (EPR) in peripheral artery disease (PAD). In decerebrated rats, we investigated the role played by lactate and hydrogen ions in a model of PAD, which was simulated by ligating the femoral artery for 72 h before the start of the experiment.

Production of lactate and hydrogen ions by the contracting hindlimb muscles was manipulated by knocking out the myophosphorylase gene (pygm). In both knockout (pygm^-/-; n = 13; 6-females) and wild-type rats (pygm^+/+; n = 14; 7-females), the EPR was evoked by statically contracting the triceps-surae muscles. Blood pressure, tension, and renal sympathetic nerve activity were measured. Responsiveness of the metabolic component of the EPR was evaluated by intra-arterial injections of lactic acid and diprotonated phosphate solutions. Responsiveness of the mechanical component of the EPR was evaluated by stretching the calcaneal tendon. In each rat, the pressor responses evoked from the freely perfused triceps-surae muscles were compared to those evoked from the contralateral ischemic triceps-surae muscles.

In pygm^+/+ rats whose femoral artery was ligated, static contraction, lactic-acid injection and diprotonated phosphate injection evoked pressor responses that were 88%, 22%, and 58% greater than those evoked from muscles whose femoral arteries were freely perfused. In pygm^-/- rats, ligation of the femoral artery for 72 h had no effect. In both groups, 72 h of femoral artery ligation exacerbated the pressor response to passive stretch.

Lactate and hydrogen-ions accumulation in contracting myocytes plays a key role in exaggerating the metabolic component of the EPR evoked from hindlimb muscles with chronically-ligated femoral arteries.