Reduced muscle vascular resistance in intrauterine growth restricted newborn piglets

It has been shown that asymmetrical intrauterine growth restriction is deno ted by disproportional reduction of muscle mass compared to body weight red uction. However, the effects of IUGR on regional vascular resistance and bl ood flow of skeletal muscles and their contractile function have not been s tudied until now. Therefore, muscle blood flow (MBF) and isometric force ou tput of serial stimulated hindlimb plantar flexors was measured in thiopent al -anesthetized normal weight (NW; n = 9) and intrauterine growth restrict ed (IUGR; n = 9) one-day-old piglets. Additionally, muscle vascular resista nce (MVR) and thyroid hormones were estimated. MBF was found to be markedly increased in IUGR piglets by 36% with a concomitant MVR reduction of 37% ( p < 0.05). Isometric force of the plantar flexors was considerably higher i n NW than in IUGR piglets (p < 0.05). However, amount of muscle fatigue was more pronounced in NW piglets (9.1 +/- 2.8%) than was in IUGR piglets (3.7 +/- 2.3%) (p < 0.05). Furthermore, specific tension of NW muscles (18.8 +/ - 0.7N/cm(2)) was significantly lower than for IUGR muscles (21.2 +/- 0.9N/ cm(2)) (P<0.05). IUGR newborn piglets exhibited increased plasma levels of thyroxine (T-4) (p < 0.05), whereas triiodothyronine (T-3) showed similar v alues in both animal groups. These data clearly indicate that muscle hemody namics and contractile function are more developed in newborn IUGR piglets. Furthermore it is suggested that the improved tolerance to fatigue during isometric contractions may indicate an increased oxidative capacity of calf muscles due to intrauterine growth restriction.