Pressure and flow characteristics of terminal mesenteric arteries in postnatal intestine.

The responses of buffer-perfused terminal mesenteric arteries from 3- and 35-day-old swine to manipulation of intravascular pressure and flow rate were determined. Under in vivo conditions, these vessels demonstrated age-dependent differences in resting diameter (182 vs. 301 microns in 3- vs. 35-day-old swine). A proximal-to-distal pressure gradient was present in vessels from both age groups (delta 13 vs. delta 16 mmHg in 3- vs. 35-day-old swine), suggesting their functional role as resistance vessels. Vessels were mounted within an in vitro perfusion apparatus that allowed independent regulation of inflow and outflow pressure. Vessels from both age groups demonstrated the development of active tone in response to an incremental rise in pressure, applied in the absence of flow. However, myogenic vasoconstriction was only observed in younger arterioles. Similarly, both groups demonstrated dilation in response to a flow stimulus generated in the absence of a net change in intravascular pressure, although the magnitude of this response was significantly greater in younger vessels (+27 vs. +7% in 3- vs. 35-day-old swine). The dilatory response to flow was eliminated by NG-monomethyl-L-arginine (10(-4)M) but restored by coadministration of L-arginine (10(-3)M). Myogenic vasoconstriction was overridden by flow-mediated dilation in terminal mesenteric arteries from 3- but not 35-day-old swine after concomitant application of pressure and flow stimuli. We conclude that the hemodynamic characteristics of terminal mesenteric arteries are age dependent in postnatal swine.