Extreme physiological plasticity in a hibernating basoendothermic mammal, Tenrec ecaudatus.

Physiological plasticity allows organisms to respond to diverse conditions. However, can being too plastic actually be detrimental? Malagasy common tenrecs, Tenrec ecaudatus, have many plesiomorphic traits and may represent a basal placental mammal. We established a laboratory population of T. ecaudatus and found extreme plasticity in thermoregulation and metabolism, a novel hibernation form, variable annual timing, and remarkable growth and reproductive biology. For instance, tenrec body temperature (Tb) may approximate ambient temperature to as low as 12°C even when tenrecs are fully active. Conversely, tenrecs can hibernate with Tb of 28°C. During the active season, oxygen consumption may vary 25-fold with little or no change in Tb During the austral winter, tenrecs are consistently torpid but the depth of torpor may vary. A righting assay revealed that Tb contributes to but does not dictate activity status. Homeostatic processes are not always linked, e.g. a hibernating tenrec experienced a ∼34% decrease in heart rate while maintaining constant body temperature and oxygen consumption rates. Tenrec growth rates vary but young may grow ∼40-fold in the 5 weeks until weaning and may possess indeterminate growth as adults. Despite all of this profound plasticity, tenrecs are surprisingly intolerant of extremes in ambient temperature (<8 or >34°C). We contend that while plasticity may confer numerous energetic advantages in consistently moderate environments, environmental extremes may have limited the success and distribution of plastic basal mammals.

Impact of prematurity and nutrition on the developing gut microbiome and preterm infant growth.

BACKGROUND: Identification of factors that influence the neonatal gut microbiome is urgently needed to guide clinical practices that support growth of healthy preterm infants. Here, we examined the influence of nutrition and common practices on the gut microbiota and growth in a cohort of preterm infants. RESULTS: With weekly gut microbiota samples spanning postmenstrual age (PMA) 24 to 46 weeks, we developed two models to test associations between the microbiota, nutrition and growth: a categorical model with three successive microbiota phases (P1, P2, and P3) and a model with two periods (early and late PMA) defined by microbiota composition and PMA, respectively. The more significant associations with phase led us to use a phase-based framework for the majority of our analyses. Phase transitions were characterized by rapid shifts in the microbiota, with transition out of P1 occurring nearly simultaneously with the change from meconium to normal stool. The rate of phase progression was positively associated with gestational age at birth, and delayed transition to a P3 microbiota was associated with growth failure. We found distinct bacterial metabolic functions in P1-3 and significant associations between nutrition, microbiota phase, and infant growth. CONCLUSION: The phase-dependent impact of nutrition on infant growth along with phase-specific metabolic functions suggests a pioneering potential for improving growth outcomes by tailoring nutrient intake to microbiota phase.

Pre-discharge iron status and its determinants in premature infants.

OBJECTIVE: To evaluate pre-discharge iron status and identify its determinants in infants' ≤ 32 weeks gestational age (GA). METHODS: In a prospective observational study, 24-32 weeks GA infants who did not meet exclusion criteria: congenital viral infections, chromosomal disorders, or cranio-facial anomalies were eligible. Iron status was evaluated by measuring serum ferritin (SF) at 35 weeks post-menstrual age (PMA). Infants with infection or elevated C-reactive protein within 10 days prior to evaluation of iron status were excluded. RESULTS: Of 131 infants studied, 23% had latent iron deficiency (SF < 76 ng/ml), 58% had normal iron status (75-400 ng/ml), and 19% had iron overload (SF > 400 ng/ml). On bivariate analysis, preeclampsia, GA, birth weight, patent ductus arteriosus, prior erythrocyte transfusion, phlebotomy loss, and chronic lung disease were associated with iron status. On ordered logistic regression, prior erythrocyte transfusion (frequency [OR 1.41, 95% CI:1.2-1.6] or cumulative amount [OR 1.03, 95% CI:1.02-1.04]) or net erythrocyte balance (amount of erythrocyte transfusion minus phlebotomy loss; OR 1.04, 95% CI:1.02-1.05) was significantly associated with iron status. Among infants who received > three erythrocyte transfusions, 50% developed iron overload. CONCLUSIONS: Iron status at 35 weeks PMA is extremely variable and is predicted by prior erythrocyte transfusions or net erythrocyte balance in premature infants.

Intravenous lipid and bilirubin-albumin binding variables in premature infants.

BACKGROUND: The lipid intake at which a significant bilirubin-displacing effect occurs as a function of gestational age (GA) is unclear. OBJECTIVE: To determine the effect of gradual increase in IL intake from 1.5 to 3 g/kg per day on bilirubin-albumin binding variables as a function of GA in premature infants with indirect hyperbilirubinemia. METHODS: Infants of 24 to 33 weeks' gestation at birth who received IL (20% Intralipid [Fresenius Kabi, Uppsala, Sweden]) doses of 1.5, 2, 2.5, and 3 g/kg per day over 4 consecutive days were prospectively evaluated. The blood samples were drawn twice at least 8 hours apart on each IL intake to measure total serum bilirubin and free bilirubin by the peroxidase test. The highest free bilirubin on each IL intake, the corresponding total serum bilirubin, and serum albumin were used to calculate the bilirubin/albumin binding constant or binding affinity. RESULTS: Sixty-two infants (median GA: 28 weeks) were studied during the first 10 days of life. None of the subjects had culture-proven sepsis, had triglyceride levels of >2.05 mmol/L, or were receiving steroids. Infants were grouped in 2-week GA intervals. The cumulative frequency of elevated free bilirubin concentration (>or=90th percentile or B(f) >or= 32 nmol/L) as a function of IL intake was inversely related to GA and was significantly different among 2-week GA groups. There was significant decrease in binding affinity and increase in free bilirubin concentration with higher IL intake for 28 week GA groups. CONCLUSIONS: The IL intake may be associated with a significant fall in the binding affinity of bilirubin for plasma protein and a concomitant increase in free bilirubin concentration in premature infants. The lipid intake at which this occurs depends on GA.