Vagal Tone and Proinflammatory Cytokines Predict Feeding Intolerance and Necrotizing Enterocolitis Risk.

BACKGROUND: Necrotizing enterocolitis (NEC) is the leading cause of death due to gastrointestinal disease in preterm neonates; yet, clinicians lack reliable and noninvasive predictive tools. PURPOSE: We aimed to test that diminished high-frequency heart rate variability (HF-HRV) and elevated levels of proinflammatory cytokines would have utility in NEC prediction. METHODS: In this multisite prospective study, we enrolled 250 preterm (26-34 weeks' postmenstrual age [PMA]) neonates with physiological stability at 72 hours of life. HRV was measured noninvasively using electrocardiograhic data from standardized cardiorespiratory monitors at postnatal week 1 of life and weekly thereafter until 35 weeks' PMA or discharge; blood was collected for cytokines at postnatal weeks 1 and 3. NEC was diagnosed via Modified Bell's Staging Criteria. RESULTS: HF-HRV was decreased at weeks 1 and 2 in neonates (47% females) who developed feeding intolerance or stage 2+ NEC. In addition, these neonates displayed elevated levels of IL-8 at week 1 and increased levels of IL-1ß, IL-6, TNF-α, and IL-8 at week 3 of life. Low HF-HRV was associated with elevated IL-6 or IL-8 levels at weeks 1 and 3 of life. Logistic regression indicated that only HF-HRV was a significant predictor of feeding intolerance or NEC development. IMPLICATIONS FOR PRACTICE AND RESEARCH: HRV is a promising noninvasive modality for NEC risk detection. The association of low HF-HRV with elevated proinflammatory cytokines provides evidence for a putative role of the vagal cholinergic pathway in NEC pathogenesis. Future studies should focus on application of these techniques to test clinical therapeutics.Video Abstract available at https://journals.lww.com/advancesinneonatalcare/Pages/videogallery.aspx?autoPlay=false&videoId=54.

Ghrelin ameliorates the phenotype of newborn rats induced with mild necrotizing enterocolitis.

BACKGROUND: We have shown previously that an attenuated rodent model of mild necrotizing enterocolitis (NEC) increases intestinal histopathological severity grade, prevents typical developmental increases in the high-frequency spectrum of heart rate variability (HF-HRV), alters the nitrergic myenteric phenotype, and increases IL-6 and IL-1ß when combined with anterior subdiaphragmatic vagotomy. The aims of the present study were to test the hypotheses that in mild NEC-induced pups, administration of the orexigenic hormone ghrelin (a) reduces the histopathological score, (b) increases the HF-HRV power, (c) improves the altered myenteric phenotype, and (d) subdiaphragmatic vagotomy prevents the effects of ghrelin. METHODS: Newborn Sprague Dawley rats were subjected to seven days of brief periods of cold stress and hypoxia to induce mild NEC with or without anterior subdiaphragmatic vagotomy. HRV was measured at postnatal days one, five, and ten; intraperitoneal ghrelin (0.05 mg kg-1 ) was administered postnatal days five through ten b.i.d. Pups were sacrificed at day 12, and whole brains, gastrointestinal tissues, and blood were collected for immunohistochemical, corticosterone, and cytokine analysis. KEY RESULTS: Ghrelin treatment reduced the intestinal histopathological score, increased the HF-HRV power, improved the altered intestinal myenteric phenotype, and subdiaphragmatic vagotomy prevented the effects of ghrelin. There were no differences in serum cytokines or corticosterone between groups. CONCLUSIONS AND INFERENCES: Our data suggest that ghrelin administration is able to recover the mild NEC-induced changes to the histology, HF-HRV, and myenteric phenotype in a vagally dependent manner.

Correlation between the motility of the proximal antrum and the high-frequency power of heart rate variability in freely moving rats.

BACKGROUND: Cardiac vagal tone can be monitored non-invasively via electrocardiogram measurements of the high-frequency power spectrum of heart rate variability (HF-HRV). Vagal inputs to the upper GI tract are cumbersome to measure non-invasively. Although cardiac and GI vagal outputs arise from distinct brainstem nuclei, the nucleus ambiguus, and the dorsal motor nucleus of the vagus, respectively, we aim to test the hypotheses that in freely moving rats HF-HRV power is correlated to proximal antral motility and can be altered by high levels of circulating estrogen and vagal-selective treatments known to affect antral motility. METHODS: Male and female Sprague-Dawley rats were implanted with a miniaturized strain gauge on the proximal gastric antrum and ECG electrodes to collect simultaneous antral motility and electrocardiogram. After recovery, male rats underwent baseline recordings before and after administration of saline (N = 8), cholecystokinin (CCK; N = 7), ghrelin (N = 6), or food (N = 6). Female rats (N = 6) underwent twice-daily recordings to determine baseline correlations during estrous cycle stages. KEY RESULTS: There was a significant positive correlation between HF-HRV and proximal antral motility at baseline in males and females with low, but not high, estrogen levels. In male rats, the significant positive correlation was maintained following CCK, but not ghrelin or food administration. CONCLUSIONS AND INFERENCES: Our data suggest that in rodents, HF-HRV positively correlates to proximal antral motility at baseline conditions in males and low-estrogen females or following interventions, such as CCK, known to affect vagal tone. This correlation is not observed when antral motility is influenced by more complex events.

Necrotizing enterocolitis attenuates developmental heart rate variability increases in newborn rats.

BACKGROUND: We have shown previously that a decreased high-frequency spectrum of heart rate variability (HF-HRV), indicative of reduced vagal tone, shows promise in predicting neonates likely to develop necrotizing enterocolitis (NEC) before its clinical onset. We hypothesized that NEC induction in rat pups decreases HF-HRV power; subdiaphragmatic vagotomy worsens the severity of the NEC phenotype, increases levels of pro-inflammatory cytokines, and alters the myenteric phenotype. METHODS: Newborn Sprague-Dawley rats, representative of preterm human neonates, were subjected to 7-8 days of brief periods of cold stress and hypoxia to induce NEC with or without unilateral subdiaphragmatic vagotomy. HRV was measured at postnatal days one and five, pups were sacrificed at day 8/9, and gastrointestinal tissues and blood were collected for immunohistochemical, corticosterone, and cytokine analysis. KEY RESULTS: Compared to control, NEC-induced rats showed the following: (a) typical histological signs of grade 2 NEC, which were more severe in rats that underwent vagotomy; (b) reduced developmental increases in time (RMSSD) and frequency (HF) HRV spectra when combined with the stress of laparotomy/vagotomy; (c) increases in nitric oxide synthase-immunoreactivity in the myenteric plexus of jejunum and ileum; furthermore, compared to mild NEC and controls, vagotomized NEC rats had increased plasma values of pro-inflammatory cytokines IL-1ß and IL-6. CONCLUSIONS AND INFERENCES: Our data suggest that in rodents, similar to neonatal observations, NEC induction attenuated developmental HF-HRV increases, furthermore, subdiaphragmatic vagotomy worsened the histological severity, increased pro-inflammatory cytokines, and altered the nitrergic myenteric phenotype, suggesting a role of the vagus in the development of NEC pathology.