Flow-Mediated Dilation (FMD) Occurs in the Perinatal Mesenteric Microvasculature and is Age Dependent ♦ 1017

The mechanostimulus of flow across endothelial cells activates the constitutive isoform of nitric oxide synthase (NOS); this action increases nitric oxide (NO) production, which in turn relaxes vascular smooth muscle. This response, called FMD is a key determinant of vessel diameter. FMD occurs in the large conduit arteries (ie., dia >3 mm) of the newborn mesenteric circulation; its presence in the mesenteric microcirculation is not known, but would be significant because of the pivotal role of these arterioles is setting vascular resistance across the gut. To this end, terminal mesenteric arterioles (ie., those piercing the gut wall) from 3- and 35-d old swine were mounted between glass microcannulae and buffer-perfused in vitro by means of a servocontrolled pump apparatus which allowed independent manipulation of flow rate and intravascular pressure. Vessel diameter (in μm) was measured at: zero flow (noQ); 100 μl flow (Q100); 100 μl flow after LNMMA, an NOS inhibitor (Q+L); and during perfusion with Ca2+-free buffer to determine maximal diameter (MaxD); intravascular pressure was held constant at 40 mmHg.Table