Ontogenic development of vascular reactivity in east and slow muscles of the neonatal rat hindlimb.

During the first three weeks of postnatal development the pattern of vascular reactivity typical of fast and slow muscle differentiates. In adult rat fast musclarteriolar smooth muscle cells are more sensitive to norepinephrine by several orders of magnitude than are those of slow muscle. In the early postnatal period there are no differences in the two types of muscle as far as vascular reactivity is concerned. At the time of weaning the vascular beds show almost the same reactivity patternas is found in the adult.