Biomedical subjects

K M Reber

Publications and source records attributed to K M Reber.

3 recordsLinked to original sources

PubMed2001

Age-dependent changes in the postnatal intestinal microcirculation.

Significant changes occur in intestinal hemodynamics during the transition from fetal to newborn life and then again during the first postnatal month. Most importantly, basal vascular resistance substantially decreases following birth. It then decreases further between postnatal days 1 and 3, plateaus, and then begins a slow, progressive increase between postnatal days 12 and 30. The basal rate of intestinal blood flow mirrors the changes in vascular resistance in an inverse manner. The postnatal changes in vascular resistance appear to be mediated, in large part, by an increase in the constitutive and stimulated production of nitric oxide. Most importantly, the diameter of terminal mesenteric arteries (150-300 microm diameter) in newborn (i.e., 1 day old) swine is determined by three intrinsic vascular control systems: endothelial production of nitric oxide and endothelin, and the inherent myogenic response of vascular smooth muscle. In contrast, these vessels in older subjects (i.e., 35 days old) are primarily passive in nature and fail to demonstrate significant diameter change in response to blockade of endogenous nitric oxide production or endothelin receptors, or applied perturbations of pressure or flow rate. The circulatory physiology of the perinatal and newborn intestine is exceptional when compared to the adult condition inasmuch as several hemodynamic variables change quite dramatically between fetal and neonatal life and during the first postnatal month. The unique hemodynamic conditions that characterize the perinatal and newborn intestine appear to be part of the overall physiological transition that occurs as the fetus, once born, replaces the placenta with his gastrointestinal tract to obtain nutrition. The goal of this review is to describe the circulatory physiology of the perinatal and newborn intestine, with a particular emphasis on those portions of the intestinal microcirculation that have thus far been studied. First, however, it is important to discuss the age-dependent changes that occur within the intestinal circulation during perinatal and early newborn life.

Age Factors↗

PubMed2001

Relationship between flow rate and NO production in postnatal mesenteric arteries.

We studied mesenteric arterial arcades from 3- and 35-day-old swine to determine the relationship between perfusate flow rate and release of nitric oxide (NO) into mesenteric effluent. Mesenteric arterial arcades were perfused under controlled-flow conditions with a peristaltic pump using warm oxygenated Krebs buffer. Basal rates of NO production were 43.6 +/- 4.2 vs. 12.1 +/- 2.5 nmol/min in 3- vs. 35-day-old mesentery during perfusion at in vivo flow rates (9 vs. 20 ml/min, respectively). Rate of NO production was directly related to flow rate over a wide range of flows (5-40 ml/min) in 3- but not 35-day-old mesentery. Both age groups demonstrated a brisk, albeit brief, increase in NO production in response to infusion of NO-dependent vasodilator substance P (10(-8) M/min). Tyrosine kinase inhibitor herbimycin A and L-arginine analog L-NMMA significantly attenuated flow-induced increase in NO production, and phosphatase inhibitor phenylarsine oxide increased magnitude of flow-induced increase in NO production in 3-day-olds. Removal of extracellular Ca(2+) and depletion of intracellular Ca(2+) stores (Ca(2+)-free Krebs with EGTA plus thapsigargin) had no effect on NO production in either group. Thus, basal rate of NO production is greater in mesenteric arterial arcades from 3- than from 35-day old swine, a direct relationship between flow rate and NO production rate is present in mesentery from 3- but not 35-day-olds, and phosphorylation events are necessary for this interaction to occur.

Age Factors↗

PubMed1998

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.

Animals↗