PAPAVERINE INJECTION INTO THE HINDLIMB CIRCULATION STIMULATES VENTILATION IN SHEEP

To test the hypothesis, previously suggested by Huszczuk et al. (1993) , that distention of the peripheral microvascular network could, per s e, stimulate ventilation, the ventilatory effects of papaverine-induce d muscular vasodilation were studied in ten anaesthetized sheep. Becau se systemic action of papaverine may involve the arterial baro- and ch emoreceptors, the animals were surgically prepared for a reversible is olation of the hindlimb circulation. Papaverine injection (1-2 mg/kg) into the arterial inflow of the isolated limbs provoked a 13 +/- 6 sec -delayed increase in Vover dotE by 1.8 +/- 0.2 L min(-1) (p < 0.01) wi th a concomitant decrease in peripheral vascular resistance and no dec rease in the systemic arterial blood pressure. Identical control injec tion into a jugular vein prior to the hindlimb circulatory separation yielded an increase of Tie by 4.95 +/- 0.58 L min(-1) with a latency o f 21 +/- 2 sec and a coinciding moderate decrease of the systemic arte rial pressure. The present data suggest that papaverine injection into the hindlimb circulation can stimulate ventilation independently of i ts possible effects on the arterial baro- or chemoreceptors, supportin g the hypothesis that muscular vasodilation could contribute to the co ntrol of breathing through a neural link.