Osmolality of enteral formula and severity of experimental necrotizing enterocolitis

Administration of hyperosmolar formula is regarded as a risk factor for the development of necrotizing enterocolitis (NEC). However, there are limited number of reports about the relationship between formula osmolality and NEC. The aim of this study is to evaluate the effects of formula concentration in an experimental model of NEC. We studied experimental NEC in C57BL/6 mice. NEC was induced by giving hypoxia, gavage administration of lipopolysaccharide and gavage formula feeding from postnatal day 5-9. We used two types of formula: (1) hyperosmolar formula (HF): 15 g Similac + 75 ml Esbilac (849 mOsm/kg); (2) diluted formula (DF): dilute hyperosmolar formula with an equal amount of water (325 mOsm/kg). Controls were fed by the mother. On postnatal day 9, the ileum was harvested and evaluated for severity of mucosal injury (hematoxylin/eosin staining) and inflammation (PCR for IL6 and TNF alpha mRNA expression). The incidence of NEC was same in both HF and DF (80%). The intestinal inflammatory response was similar between HF and DF (IL6: p = 0.26, TNF alpha: p = 0.69). This study indicates the osmolality of enteral formula does not affect incidence of experimental NEC. This experimental study provides new insights into the relationship between formula feeding and NEC.