Leptin Stabilizes Breathing but does not affect CO2 Chemosensitivity in Newborn Rat Pups

Abstract

Premature infants have periodic breathing (PB) and chronic intermittent hypoxia (CIH) that increases during the 2nd week of life. Leptin (LEP) is a hormone produced by adipocytes and increases central CO2 chemoreceptors sensitivity. LEP is also produced by the placenta, and in newborn infants LEP levels are highest at birth and then rapidly fall. We hypothesis that the fall in LEP after birth is associated with the increase frequency of PB and apnea leading to CIH during the 2nd week of life in premature infants.ObjectiveTo determine the effect of exogenous LEP on breathing stability and CO2 sensitivity during the first week of postnatal life, using whole body flow‐through plethysmograph in freely behaving newborn rats.MethodsSprague Dawley (SD) rat pups remained with the nursing dam until the time of the experiment. On postnatal day (PD) 7, rat pups were injected intraperitoneally with either vehicle (saline/n=5), LEP6 (6 μg/gr/n=4) and LEP9 (9 μg/gr/n=5). After injection the pup was returned to nursing dam and litter mates for 30 mins followed by 30 mins in the plethysmograph prior to recording. Respiratory tracings were captured using PowerLab 8 data acquisition system (ADInstruments) and analyzed using LabChart. Ventilatory parameters; frequency, VT and Ve were compared during 21% O2, 40% O2/0% CO2, 40%O2/5%CO2 and return to 40%O2/0%CO2, and the coefficient of variation (CV) for Ve was calculated for each condition in the 3 treatment groups (SAL, LEP6, LEP9).ResultsSimilar to Stunden et al. in rat pups at PD 7–8 (Stunden et al,, Respir Physiol, 2001), frequency, VT and Ve did not significantly changed in response to hypercapnia (P=0.511), and LEP6 or LEP9 did not alter this response. However, LEP exposure did stabilize breathing with a reduction in the CV during 21%O2, 40%O2/0%CO2 and 40%O2/5%CO2 (Figure 1).ConclusionOur preliminary findings are consistent with that of Stunden et al, who reported no change in Ve in response to hypercapnia at PD 6–8 in SD rats. At this age, the hypothalamus is insensitive to the effect of leptin on feeding and metabolism (MacKay H et al., Mol Metab. 2014). Here we show that leptin does not induce nor augment CO2 chemosensitivity in newborn rats at PD7, but does at PD 18 (Gauda et al, unpublished data), and adults (Isono S et al., Anesthesiology, 2009). However our data does show that leptin stabilizes breathing during the first week of life in newborn rat pups. We speculate that unstable breathing that occurs in premature infants may be associated with the precipitous fall in leptin levels after birth.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.