EFFECT OF ACIDOSIS ON CONTRACTION, INTRACELLULAR PH, AND CALCIUM IN THE NEWBORN AND ADULT-RABBIT AORTA

This study investigated the effect of acidosis on intracellular pH (pH (i)), intracellular calcium concen tration ([Ca](i)), and vascular con traction in the aorta of the newborn and adult rabbit. Isometric tensi on, pH(i), and [Ca](i) were measured in an isolated ring preparation. After the vascular contraction was induced with 50 mM KCl, the effect of respiratory acidosis produced by elevation of PCO2 was studied. Res piratory acidosis caused a transient depression followed by a recovery of contractile tension. The decrease in developed tension was greater in the newborn than in the adult. The decrease in pH(i) during acidos is was similar in the two age groups. [Ca](i) increased during acidosi s and the increase was greater in the newborn than in the adult. These data show that the vasorelaxant effect of acidosis in the newborn aor ta is greater than that in the adult aorta. The greater vasodilation i n the newborn cannot be explained by the difference in pH(i) or [Ca](i ).