Newborn Piglet Model Research Articles

Hexokinase binding in ischemic and reperfused piglet brain.

Hexokinase catalyzes the first step in cerebral glucose utilization and is a rate-limiting enzyme in glycolysis. Glucose utilization is tightly coupled to cerebral blood flow so that during ischemia the brain has a decreased supply of glucose, as well as oxygen. We studied hexokinase enzymatic activity in a newborn piglet model of ischemia-reperfusion to determine if any changes in the activity or mitochondrial binding of the enzyme occurred. We observed that mitochondrial binding of cortical HK increased from 55 to 71% with ischemia and returned toward control levels, but did not completely recover, after 2 h of reperfusion.

Bacterial translocation in mesenteric ischemia-reperfusion injury: Is dysfunctional motility the link?

The authors previously reported that mesenteric ischemia and reperfusion ( I R ) in a chronic newborn piglet model creates dysfunctional intestinal motility. Whether this leads to inadequate bacterial clearance and translocation (BT) through the gastrointestinal tract remains unclear. To test this hypothesis the authors used their chronic piglet model (weight, 3.5 ± 0.3 kg; age, 18 ± 4 days; on formula feeding); nonocclusive mesenteric ischemia was induced via reversible pericardial tamponade. Mesenteric flow (SMA Doppler measurement via the retroperitoneal approach) was decreased to 25% ± 5% of baseline for 300 minutes in the ischemia group (n = 7) and followed by 14 hours of reperfusion in the I R group (n = 6). Control subjects had a sham operation (n = 7). Mesenteric lymph nodes (MLN), liver (L), spleen (S), ileum, peritoneum, and blood were harvested for blind quantitative microbial analysis. Subjects in the control group had no cultures positive for growth. Eighty-five percent of animals in the ischemia group had positive MLN cultures only ( P < .05 v control). All piglets in the I R group had positive MLN cultures ( P < .05 v control), and one third of them manifested bacteremia. Histological examination did not show mucosal disruption in any group. The validity of this model is confirmed by the negative cultures in the control group and by the presence of normal ileal flora in all animals. In the ischemia and I R groups, MLN cultures were consistently positive with gram-negative bacilli ( Escherichia coli and/or Klebsiella pneumoniae). When subjects of the I R group had more than 1,000 colonies in the MLN, bacteremia with the translocating organisms was also identified. The overall solid organ (L&S) translocation rate was 17% in the I R group but absent in the ischemia-only group. Variables known to contribute to BT were eliminated in our model. The peritoneal cavity was not violated, subjects were studied without the influence of any drugs or anesthesia, and mesenteric ischemia was accomplished without mechanical manipulation of the SMA or hypovolemic shock. To our knowledge, this is the first report of an infant animal model that demonstrates the occurrence of enteric BT following ischemia and I R injury. We suggest that BT is mediated by the dysfunctional motility induced by I R , an abnormality that may be operant in many critically ill infants.

Nitric oxide reverses acute hypoxic pulmonary hypertension in the newborn piglet.

Inhaled nitric oxide has been reported to act as a specific pulmonary vasodilator. We used the newborn piglet to create acute hypoxic pulmonary hypertension and examined the effect of inhaled nitric oxide in this model. Six newborn piglets were instrumented in order to measure cardiac index, pulmonary arterial pressure, and systemic arterial pressure. Pulmonary hypertension was induced by reducing the fraction of inspired oxygen to 0.12 to 0.14. With hypoxia (arterial oxygen saturation between 35 and 45%), pulmonary arterial pressure increased by 48% (p < 0.01), pulmonary vascular resistance increased by 74% (p < 0.01), and both systemic arterial pressure and systemic vascular resistance decreased by 38 and 31%, respectively (p < 0.01). The animals were then giving varying concentrations of inhaled nitric oxide between 5 and 80 parts per million in random order. All concentrations of nitric oxide were associated with a rapid decrease in pulmonary arterial pressure and pulmonary vascular resistance (p < 0.001). Cardiac index increased (p < 0.001) and systemic vascular resistance significantly decreased (p = 0.01) with all doses of inhaled nitric oxide. The ratio of pulmonary to systemic vascular resistance decreased with all levels of inhaled nitric oxide (p < 0.001). For all of the above observations there was no significant difference noted between the varying doses of nitric oxide. The time course of the pulmonary arterial pressure response to nitric oxide was approximately twice as fast as that seen with the inhalation of 100% oxygen (10, 50, 90% responses of 4.1, 8.8, 88.6 versus 6.7, 51.9, 197 s, respectively; p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption of theophylline from the small and large intestine of the neonatal piglet.

In this study, the newborn piglet model was used to assess theophylline absorption from various areas of the GI tract. 13 piglets, ages 9-14 days, had their intestines surgically exposed. Four segments of equal length (jejunum, ileum, right colon and left colon) were simultaneously perfused with a saline solution containing [3H]-polyethylene glycol 4000 to measure water shifts and theophylline at a total dose of 5 mg/kg, a typical neonatal dose. Absorption of theophylline, appearance in serum, and the effects of the drug on water and electrolyte movement in the intestinal segments were monitored. Serum concentrations of theophylline after an intravenous and oral dose were also studied in 2 piglets. The data showed excellent absorption of the drug from all intestinal segments studied (jejunum 0.97 +/- 0.16, ileum 0.7 +/- 0.13, right colon 0.7 +/- 0.13, and left colon 0.88 +/- 0.19 micrograms/cm/min), despite a concomitant secretion of sodium chloride and water. No statistical differences in absorptive capacity were seen among segments. The results suggest that as little as 100 cm of residual intestine could, theoretically, absorb a 5 mg dose of theophylline if presented slowly. These findings have ramifications for neonates who may receive theophylline orally or rectally.

The role of the eae gene of enterohemorrhagic Escherichia coli in intimate attachment in vitro and in a porcine model.

The eaeA gene of enteropathogenic Escherichia coli (EPEC) is necessary for intimate attachment to epithelial cells in vitro. Enterohemorrhagic E. coli (EHEC) strains also possess an eae gene and are capable of intimate attachment and microvillus effacement in vitro and in animal models. To assess the role of the EHEC eae gene in intimate attachment, we constructed an eae deletion/insertion mutation in wild-type EHEC O157:H7 strain 86-24 by using linear electroporation of a recombinant allele. The mutant obtained was deficient in inducing f-actin accumulation in HEp-2 cells and was incapable of attaching intimately to colonic epithelial cells in a newborn piglet model of infection. Intimate attachment in vivo was restored when the EHEC eae gene or the eaeA gene of EPEC was introduced into the mutant on a plasmid. These results indicate that the eae gene is necessary for intimate attachment of EHEC in vivo. In addition, the complementation achieved by the EPEC locus indicates that the eae gene of EHEC and the eaeA gene of EPEC are functionally homologous.

Meconium aspiration syndrome: physiological and inflammatory changes in a newborn piglet model.

In order to evaluate further the physiological and inflammatory changes of meconium aspiration syndrome (MAS), 25 newborn piglets (1-2 days old, 1.5 +/- 0.4 kg) were studied. Piglets were briefly ventilated with 100% oxygen and then received an intratracheal bolus of 3 mL/kg of a 20% suspension of human meconium. They were then further ventilated, keeping PaCO2 at approximately 40 torr and PaCO2 at 70 torr during 4, 12, 24, and 48 h studies. Pulmonary function studies and tracheal aspirates were obtained at time zero and serially throughout the study. Bronchoalveolar lavage was performed at the end of the study to examine endogenous surfactant function. Control piglets received 3 mL/kg of intratracheal saline and were then ventilated for 48 h at an inspired oxygen concentration and mean airway pressure matched to the meconium treated group (to control for the effects of hyperoxia and barotrauma on the lung). MAS caused acute decreases in gas exchange and dynamic lung compliance, which returned toward baseline by 48 h (P < 0.001, ANOVA). Tracheal aspirate absolute neutrophil count, neutrophil chemotactic activity, albumin, and total protein concentrations also increased significantly over time (P < 0.001). Endogenous surfactant function appeared to be significantly inhibited by the meconium. All variables of lung injury were significantly higher in the meconium group compared to the saline control group over the 48 h study. Newborn piglets provide a clinically relevant model of MAS, demonstrating physiological and inflammatory changes with apparent alterations in endogenous surfactant function. Effective therapies for MAS may require interventions directed at all of these components of lung injury.

Adenosine triphosphate (ATP) treatment of hypoxic pulmonary hypertension (HPH): Comparison of dose dependence in pulmonary and renal circulations

In this study we investigated the relationship between pulmonary and renal responses to a low dose infusion of adenosine triphosphate-magnesium chloride (ATP-MgCl 2) in a newborn piglet model of hypoxic pulmonary hypertension (HPH). Three- to five-day-old piglets were cannulated for the measurement of pulmonary and systemic arterial pressure, pulmonary and renal artery flow, and urine output. The animals were then made hypoxic by ventilation with a mixture containing 10% oxygen, 4% CO 2, and balance nitrogen. Serial infusions of ATP-MgCl 2 at 0.01, 0.025, 0.05, 0.1, 0.5, and 1.0 mg/kg/min were compared to preinfusion hypoxia baselines. Hypoxia alone produced a significant elevation in pulmonary artery pressure (73%) and a reduction in pO 2. All dose rates of ATP-MgCl 2 ⩾ 0.05 mg/kg/min produced a significant decrease in mean pulmonary artery pressure. However, as baseline mean pulmonary artery pressure increased there was an increased sensitivity to ATP-induced vasodilation. Pulmonary artery flow did not change during ATP infusion, thus, the change in pulmonary vascular resistance accounted for the decrease in pulmonary artery pressure. In contrast to the response of the pulmonary vasculature, systemic pressure was significantly decreased only during the 1.0 mg/kg/min infusion. Renal blood flow decreased by 46% during hypoxia and decreased further only during the highest dose rate of ATP infused (i.e., 1.0 mg/kg/min). Creatinine clearance (Ccr) and fractional reabsorption of Na (FreNa) also fell during hypoxia, but were not further altered during all but the highest dose of ATP infused. These data suggest that a low dose infusion of ATP-MgCl 2 could decrease the vasoconstriction associated with HPH without concomitant adverse systemic or renal side effects.

The effect of leukotriene D 4 on pulmonary and systemic circulation in conscious newborn puglets

In a conscious newborn piglet model, exogenous leukotriene D 4 was found to be a potent pulmonary and systemic vasoconstrictor with significant left ventricular depressant effect. The pulmonary pressor effect was seen only in the arteriolesand not the veins. In hypoxia the pulmonary response was less. The findings were similar to that in lambs. The role of leukotrienes in hypoxic pulmonary vasoconstriction and the foetal pulmonary circulation needs further elucidation.

The effect of theophylline on regional cerebral blood flow responses to hypoxia in newborn piglets.

Theophylline attenuates cerebral hypoxic hyperemia in several adult models and this is thought to be due to receptor-mediated antagonism of adenosine, a proposed mediator of hypoxic hyperemia. This attenuation of hypoxic hyperemia reduces cerebral oxygen delivery and may thus jeopardize cerebral oxidative metabolism. With these considerations in mind, and because theophylline is widely used in neonatal medicine, the present study was designed to investigate the effect of theophylline on regional cerebral blood flow, cerebral oxygen delivery, and cerebral metabolic rate for oxygen during normoxia and hypoxia in the newborn piglet model. In 16 newborn piglets, regional cerebral blood flow (microspheres) increased 250-350% during hypoxia (PaO2 20-30 torr), while cerebral oxygen delivery and cerebral metabolic rate for oxygen were maintained at normoxic levels. Eight of these piglets were then given 10 mg/kg theophylline ethylenediamine intravenously and studies during normoxia and hypoxia were repeated; the remaining eight piglets served as time controls. Regional cerebral blood flow, cerebral oxygen delivery, and cerebral metabolic rate for oxygen during normoxia and hypoxia were not influenced by theophylline, despite plasma theophylline levels of 55-65 mumol/liter, and cerebrospinal fluid theophylline levels of 30-40 mumol/liter. These negative results are reassuring with respect to hypoxic cerebral blood flow control in theophylline-medicated infants. However, they do not support a role for adenosine as a mediator of cerebral hypoxic hyperemia in this model.

Hemodynamic Effects of Halothane in the Newborn Piglet

In order to better understand the mechanism of hypotension and bradycardia in newborn infants under halothane anesthesia, we studied the changes in the four determinants of cardiac output in newborn piglets given 0.5 and 1% end tidal halothane. Cardiac index (CI) was measured by thermodilution. Preload was estimated from the left ventricular diastolic dimension determined by echocardiography and from the left ventricular end-diastolic pressure. Total peripheral resistance index was calculated to assess afterload. Contractility was estimated from left ventricular peak dP/dT, and from left ventricular shortening fraction and mean rate of circumferential fiber shortening determined by echocardiography. All indices of contractility decreased to approximately 50% of baseline values during administration of 1% halothane, whereas heart rate (HR) was reduced to 74% of baseline. Preload and afterload did not change significantly. Mean arterial pressure (MAP) and CI decreased to 67% and 74% of control values, respectively. Smaller, proportional reductions in all variables occurred when 0.5% halothane was administered. Control values of MAP were the only measurements significantly related to piglet age. When five additional animals underwent atrial pacing at the control HR during 1% halothane anesthesia, MAP and CI decreased to 66 and 71% of control values, respectively. dP/dT/DP40, a dP/dT point measurement independent of preload and afterload changes, decreased to 49% of control during pacing. Therefore, the major effect of halothane in newborn piglets is its potent negative inotropic action, not peripheral vasodilation or bradycardia.