E.J. Schiffrin

Prevention of necrotizing enterocolitis in the rat with prenatal cortisone

Cortisone acetate is known to accelerate maturation of the immature intestine. The effect of prenatal administration of cortisone acetate on the morbidity and mortality of necrotizing enterocolitis was examined in a rat pup model. Pregnant rats were administered cortisone acetate, 20 mg/100 g of body weight, or normal saline by daily IP injection from day 18-21 of gestation. Rat pups were taken from the mothers before suckling was initiated, fed a simulated rat milk formula, and subjected to daily ischemic insults to produce an animal model of necrotizing enterocolitis. Both morbidity and the mortality rates were significantly improved with prenatal cortisone treatment. Maturation of the intestinal mucosal barrier was accelerated with the cortisone treatment as measured by decreased serum concentrations of a fed antigen, ovalbumin. Aerobic bacterial colonization of the small intestine and translocation of bacteria to the liver were decreased in the pups pretreated with steroids. These changes observed in a rat model of necrotizing enterocolitis may explain the decreased incidence of necrotizing enterocolitis in human infants born to mothers who received corticosteroids late in gestation.

Influence of the polyamine, spermidine, on intestinal maturation and dietary antigen uptake in the neonatal rat.

Summary Polyamines appear to have an important role in postnatal growth of the rat intestine. In the present study, we examined the effect of spermidine on the maturation of the intestine and on its ability to exclude macromolecules. Two litters of Sprague-Dawley rat pups were assigned to one of four experimental groups. These groups received, on Days 7, 8, and 9, either (a) saline by gavage; (b) spermidine, 0.9 mg (6 μmol) by gavage; (c) cortisone acetate, 3.5 mg i.p.; or (d) saline i.p. On Day 10, animals were fed by gavage with a mixture of bovine serum albumin (BSA; 2 mg/g) and the γ-globulin fraction of mouse antiovalbumin (anti-OVA) antiserum (1 mg/g) and were bled 4 h later. Intestinal tissues were processed for histologic examination, sucrase determination, and identification of neonatal intestinal Fc receptor (FcRn) by Western blot. Serum immunoreactive BSA (iBSA) and mouse IgG1 and IgG2a anti-OVA antibodies were estimated by enzyme-linked immunosorbent assay. Sucrase activity was elevated in cortisone- and spermidine-treated compared to control rats. iBSA and anti-OVA were significantly reduced in cortisone-treated compared to control rats but were not diminished significantly in the spermidine-treated animals. A decrease in the neonatal intestinal Fc receptor was apparent in the spermidine-fed group; cortisone produced a large reduction in FcRn. Spermidine-fed animals showed morphologic evidence of maturation, with loss of giant vacuoles in the distal intestine; cortisone did not produce significant changes in morphology. Thus, while spermidine, like cortisone, enhanced the appearance of the disaccharidase sucrase, it did not significantly reduce the uptake of BSA or IgG, which is usually observed in mature compared to immature animals. The reason for this dichotomy is not known.

Influence of prenatal corticosteroids on bacterial colonization in the newborn rat

The interactions between bacteria and the hosts intestinal barrier appear to be important regulators of bacterial colonization. In this study we investigated the effect of prenatal corticosteroids, known to accelerate the intestinal maturation of newborn rats, on bacterial colonization in the rat pup. Pregnant rats were treated with either cortisone acetate or normal saline on days 18-21 of gestation and were allowed to deliver spontaneously. The pups, after normal delivery, were sacrificed at different times during the first 10 days of life. The entire small intestine was removed, and each lumen was flushed to exclude nonadherent, transient organisms and homogenized. Tenfold dilutions were plated on horse-blood agar (total bacteria) and MacConkeys medium (gram-negatives). Quantitation and bacterial typification was determined after 24 h of incubation at 37 degrees C. Total bacteria and gram-negatives found in association with the mucosa were significantly lower in pups prenatally treated with steroids. These changes were not related to any changes in motility or intraluminal digestion. This suggests that the developmental condition of the hosts intestinal barrier may be an important regulator of the bacterial microenvironment of the newborn small intestinal mucosa.

Effect of acute burn trauma on phagocytic activity of the reticuloendothelial system in rats.

The effect of acute burn trauma on phagocytic activity of the reticuloendothelial system measured in vivo with technetium 99m sulfur colloid was examined in rats subjected to acute burn trauma. After the scald injuries (10-second, full-thickness burns) were induced, a reduction in phagocytic activity by the spleen took place with an accompanying increase in the uptake of colloid material by the lungs. Uptake of colloid material by the liver was essentially unchanged. These uptake changes, observed within hours after the inducement of acute burn trauma and apparently continuing for 7 days after burn injury, may explain, in part, the development of septicemia in patients with burns because altered phagocytic activity of the reticuloendothelial system can result in subsequent overabundance of microorganisms and bacteria in the blood.

Role of skin in the burn-induced reduction of reticuloendothelial phagocytic activity in rats

Acute burn trauma has been demonstrated to depress reticuloendothelial system (RES) phagocytic activity, which could partially explain the development of septicaemia in burn patients. In the present study we have attempted to determine the role that skin plays in the depression of the RES. One group of Lewis rats was subjected to a 100 degrees C scald burn for 10 s. Eschar was then removed and implanted onto the backs of a second group of normal controls. A third group of Lewis rats were subjected to sham treatment; the eschar of these animals was removed and implanted onto the back of a fourth group of normal rats. The excision sites of the donor animals were immediately covered with Biobrane. Twenty-four hours later the technetium-99m sulphur colloid [( 99mTS]SC) method described earlier (Trop et al., 1989) was used to determine phagocytosis in these four groups of animals. Acute burn trauma produced a marked reduction in colloid uptake by the spleen and a marked increase in the uptake of colloid material by the lung, although no effect was observed on liver or kidney uptake. Implantation of the burn eschar into normal control rats had no statistically significant effect upon colloid uptake. These data suggest that alterations in phagocytic activity of the spleen and lung occur within minutes after burn injury and may be unrelated to the presence of the burn eschar itself.

Role of neutrophils in the intestinal alterations associated with thermal injury

We have examined the role of neutrophils in the alterations observed in the intestines of rats subjected to 40 per cent surface area scald injury. Histologically, there was no evidence of neutrophilia in the intestinal tissue, and myeloperoxidase activity in mucosal scrapings was not elevated. The distribution of labelled human neutrophils injected into the burned rats showed no enhancement of uptake in the intestines, although there was increased uptake by the lung. The present data suggest that neutrophil migration may not play a role in the alterations in small intestinal function and morphology seen in burn trauma in the rat, but may be a factor in lung damage associated with thermal injury.

Platelet-activating factor induces intestinal necrosis, but not septic shock, in germ-free and specific- pathogen-free rodents

Platelet-activating factor (PAF) was injected into conventional mice, endotoxin-resistant mice (C3H/HEJ), conventional rats, germ-free rats and specific-pathogen-free (SPF) mice. The PAF resulted in significant necrosis and damage to the small intestines of all the animals tested. In general, the frequency and severity of the lesions were similar in all groups. All the conventional rats and mice, as well as the endotoxin-resistant HEJ mice, were dead 18 h after the injection of the PAF, while all the germ-free rats and the SPF mice survived. These data demonstrate that development of massive intestinal lesions, in the absence of aerobic bacteria, is not sufficient to cause the death of the host from septic shock and endotoxaemia.

Arterial blood pressure immediately after thermal injury: The role of anesthesia

Mean arterial blood pressure was measured in anesthetized rats. The duration that the rats were under anesthesia with ether or methohexital was brief, and the animals were allowed to awaken early after injury. Three hemodynamic measurements were compared: (1) lowest mean arterial blood pressure, (2) duration at lowest mean arterial blood pressure, and (3) time to recover initial mean arterial blood pressure. In these studies the anesthetic agents reduced mean arterial blood pressure by 36%, recovering to normal pressures within 24 to 39 minutes. During the hemodynamic observation period, no significant additional hemodynamic effects as a result of the thermal injury were seen. Administration of resuscitation fluid did not significantly affect hemodynamics during the observation period in this study. These studies demonstrate that anesthesia dominates the short-term cardiovascular effects of thermal injury, and therefore caution is required in the interpretation of acute cardiovascular effects immediately after thermal injuries with patients under general anesthesia.

Effect of acute and chronic lipopolysaccharide (LPS) administration on reticuloendothelial system (RES) phagocytic activity in vivo

The effect of injection or chronic infusion of lipopolysaccharide (LPS) into unanaesthetized rats on the distribution of [99Tcm-]SC has been determined. At a dose of 2.5 mg/kg, LPS injection caused a marked alteration in the distribution of the radiolabelled material, with more uptake being achieved in the lung while less was taken up by the spleen. Kidney and liver uptake were also changed. Chronic infusion of LPS at a similar dose (3 mg/kg in 24 h) caused a marked increase in the uptake of the radioactive material by the lung only. These data are consistent with a working hypothesis that the alterations in RES phagocytic activity of the lung observed in rats subjected to burn trauma could be related in part to LPS, either coming as a bolus, or being continuously presented.

Effect of heta-starch colloidal solutions on reticuloendothelial phagocytic system (RES) function in burned and infected rats

The biodistribution of the plasma expander colloidal solution, heta-starch (HES), has been examined in rats, subjected to thermal injury or sepsis. The ability of these solutions to alter RES phagocytic function of [99mTc]-sulphur colloid ([99mTc]SC) uptake in vivo has been examined. The biodistribution of radiolabelled HES has been determined in normal rats. The HES colloidal solution has no deleterious effect upon RES function in vivo in the thermally injured animals or the septic animals as compared to sham controls. In addition, the HES colloidal solution seemed to be distributed primarily within the liver, spleen and kidney, with a small amount residing in the lung. Thermal injury did not increase the uptake of this material by the lung. These results suggest that the use of HES in thermally injured and septic individuals has no deleterious effects on RES function, nor does it accumulate in the lungs, and hence, should be advocated for use in these situations.