Intrauterine growth restriction induces increased capillary density and accelerated type I fiber maturation in newborn pig skeletal muscles

Abstract

Humans with low birth weight exhibit evidences of vascular dysfunction. Recent findings indicate a microvascular rarefaction in skeletal muscles soon after postnatal development in rats suffered by intrauterine protein restriction. To examine the effects of intrauterine growth restriction on capillary density, muscle fiber distribution and accompanying muscular and systemic circulation immediately after birth, studies were conducted on 1-day-old anesthetized normal weight (n = 7) and intrauterine growth restricted (n = 6) piglets. Cardiac output and hind limb muscle blood flow were measured by colored microspheres. Counting of type I fibers and skeletal capillary numbers was done by immunohistochemical staining. Increased proportion of type I fibers and capillary density was found in the flexor digitalis superficialis and gastrocnemius medialis (P < 0.05) in newborn IUGR piglets. Furthermore, a marked correlation was shown between capillary density and type I fiber fraction for all flexor muscles studied (P < 0.05). Moreover, cardiac output and muscular blood flow were markedly increased in IUGR piglets (P < 0.05). Correspondingly, total peripheral resistance, as well as vascular resistance, of hind limb flexors appeared significantly decreased (P < 0.05). Compromised intrauterine environmental conditions leading to fetal growth restriction provokes coordinated structural and functional adaptation of skeletal muscles.