Developmental changes in the contractile system of the mesenteric small artery of rabbit

This study investigated developmental changes in the contractile system of the mesenteric small arteries of the rabbit. Arteries about 1 mm in length and 100-250 microns in internal diameter were dissected out from the mesenteric bed of the fetus (29 d of gestation), newborn (3-5 d old), and adult rabbit. Vascular contraction was induced by high KCl concentration, and contractile force was measured using a tension transducer. The sensitivity of vascular contraction to high KCl was similar in the three age groups. To determine the role of Ca influx across the sarcolemma in vascular contraction, the vasorelaxant effect of diltiazem was studied in the artery precontracted with high KCl concentration. The vasorelaxant effect of diltiazem in the fetus and newborn was less than in the adult. To estimate the size of the intracellular Ca pool, caffeine-induced and noradrenaline-induced contraction were measured in the Ca- and Na-free solution. In the fetus and newborn, both the caffeine-induced contraction and noradrenaline-induced contraction were greater than in the adult. The ultrastructural study showed that the endoplasmic reticulum was abundant in the fetus and newborn, and it was scarce in the adult. These data indicate that the dependency of vascular contraction on Ca influx across the sarcolemma increases and the intracellular Ca store decreases with development in the mesenteric resistance arteries.