Autoregulatory escape from vasoconstriction of intestinal circulation in developing swine

Abstract

The capability of the developing intestinal circulation to maintain a vasoconstrictor response during postganglionic adrenergic nerve stimulation or norepinephrine infusion was examined in 34 swine aged 6 h to 2 mo anesthetized with pentobarbital sodium. Aortic and portal venous pressures, electrocardiogram (ECG), and blood flow (F) through the superior mesenteric artery were recorded, and intestinal vascular resistance (MVR) was calculated as mean pressure difference per mean F. Baroreceptor reflex inhibition by bilateral occlusion of the carotid arteries increased MVR, section of the splanchnic nerve and postganglionic fibers decreased MVR, and short-latency F decreases were obtained during mesenteric nerve stimulation (MNS). Latencies for the decreases in F shortened with age and with increasing MNS frequency (5-17 Hz) at any age. Prolonging MNS for 60 s at 10 or 12 Hz led to sustained high MVR in 6-h to 7-day-old animals; however, MVR decreased toward control before the end of the 60-s MNS period in animals 1 to 2 mo old. Intra-arterial infusion of norepinephrine (0.5 microgram X kg-1 X min-1) decreased F and increased MVR in all animals; but by 5 min of infusion, F was returning toward control level in all but the youngest. This demonstration that the least mature intestinal circulation was least capable of autoregulatory escape from vasoconstriction provides further evidence of its functional immaturity.

The role of the intestinal microcirculation in necrotizing enterocolitis

“…31,32 This hypothesis fell out of favor as later studies noted that infants with NEC rarely suffered intrapartum asphyxia, 33 that NEC rarely occurs in the 1 st week of life, 33 and that sustained adrenergic stimulation, a central facet of the diving reflex, does not cause sustained intestinal blood flow reduction, nor does it cause intestinal tissue hypoxia. 34,35 …”

Developmental expression of eNOS in postnatal swine mesenteric artery

“…To this end, realtime PCR was used to quantify eNOS mRNA expression and Western blotting was used to quantify eNOS protein expression in homogenates of mesenteric artery obtained from late gestation fetal subjects and subjects on postnatal days 1,3,10, and 30. These postnatal age groups were selected to reflect the dietary transition from sow's milk to grain that occurs during the first postnatal month in swine.…”

Regional Circulatory Responses to Hindlimb Work in Developing Swine

“…We have reported the absence of vas cular 'escape' from adrenergic stimulation of the kidney [ 10] or small intestine [ 11 ] at this age. Taken together with the data in ta bles 2 and 3, such findings could account for more effective vasoconstriction in these cir culations during any evoked cardiovascular reflex.…”

“…6] in dogs and cats. Such observations would be of particular in terest because of the reported decrease in intestinal blood flow during graded treadmill exercise in adult swine [8,9], Since postgan glionic mesenteric nerve stimulation leads to intestinal vasoconstriction in swine at birth [11], increased intestinal vascular resistance during SNS-induced hindlimb work in dayold animals ( fig. 3b) that are too young to exhibit intestinal blood flow autoregulation (table 2) in the fasting or fed states [1,21] could be due to reflex vasoconstriction.…”

“…Taken together with the data in ta bles 2 and 3, such findings could account for more effective vasoconstriction in these cir culations during any evoked cardiovascular reflex. On the other hand, the autoregulatory capabilities of renal and intestinal vascula ture in month-old swine (table 2, 3) [1,[10][11][12] could prevent reduction of blood flow. The maintenance of intestinal blood flow during induced hindlimb work in 1-and 2-week-olds cannot be so clearly attributed to autoregulation (table 3) [1,11].…”