DEVELOPMENTAL-CHANGES IN THE CONTRACTILE SYSTEM OF THE MESENTERIC SMALL ARTERY OF RABBIT

This study investigated developmental changes in the contractile syste m of the mesenteric small arteries of the rabbit. Arteries about 1 mm in length and 100-250 mu m in internal diameter were dissected out fro m 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 c oncentration, and contractile force was measured using a tension trans ducer. The sensitivity of vascular contraction to high KCl was similar in the three age groups, To determine the role of Ca influx across th e sarcolemma in vascular contraction, the vasorelaxant effect of dilti azem was studied in the artery precontracted with high KCl concentrati on. The vasorelaxant effect of diltiazem in the fetus and newborn was less than in the adult. To estimate the size of the intracellular Ca p ool, caffeine-induced and noradrenaline-induced contraction were measu red in the Ca- and Na-free solution. In the fetus and newborn, both th e caffeine-induced contraction and noradrenaline-induced contraction w ere greater than in the adult. The ultrastructural study showed that t he endoplasmic reticulum was abundant in the fetus and newborn, and it was scarce in the adult. These data indicate that the dependency of v ascular contraction on Ca influx across the sarcolemma increases and t he intracellular Ca store decreases with development in the mesenteric resistance arteries.