Presented at the Neonatal Society 2003 Autumn Meeting.
Gnanalingham GM1, Clarke L2, Mostyn A1,2, Symonds ME1, Stephenson TJ1
1 Centre for Reproduction and Early Life, Institute of Clinical Research, University Hospital, Nottingham NG7 2UH
2 Department of Agricultural Science, Imperial College London (Wye Campus), Wye, Kent TN25 5AH
Introduction: Mitochondria are involved in cellular energy metabolism. VDAC is a general diffusion porin present in the outer mitochondrial membrane and is important in cellular energy metabolism and apoptosis. VDAC is highly abundant in lung alveoli, being primarily involved in solute exchange. Cytochrome c (Cyto c) is a highly mobile electron transport protein located in the mitochondrial inter-membrane space and is essential in cellular energy conversion. We have previously shown that delivery temperature is a major factor in brown adipose tissue function in the newborn (1). The extent to which delivery temperature affects the abundance of mitochondrial VDAC and cyto c proteins in the lung has not yet been determined.
Methods: Eight triplet-bearing ewes were entered into the study. Four randomly selected ewes were given a 16mcg dexamethasone (DEX) intramuscular injection at 138 days of gestation, followed by Caesarean section delivery at 140 days gestation (term @ 147 days). The 4 untreated ewes (Controls) were delivered by Caesarean section, but at 146 days. One lamb from each ewe was humanely euthanased as a fetus to enable lung dissection, while the remaining lambs were delivered either into a warm (WD, 30ºC) or cool (CD, 15ºC) ambient temperature, with tissue sampling at 6 hours of life. Mitochondrial fractions were prepared by differential centrifugation and protein abundance determined by immunoblotting. Results (in arbitrary units) are presented as means with their standard errors (SEM). Statistical differences between groups were analysed by one-way ANOVA with post-hoc Bonferroni.
*p<0.01, difference between warm vs. fetal or cold controls or DEX, †p<0.05, cold vs. warm or
fetal controls or DEX, and +p<0.05, warm vs. cold or fetal DEX.
There was no difference in the abundance of VDAC or cyto c between controls and DEX groups. WD resulted in an increased VDAC abundance in the lung and was associated with a lower breathing frequency (Controls: WD 46 breadths/minute ± 4, CD 50 ± 4, NS; DEX: WD 51 ± 6, CD 75 ± 5, p<0.05). Cyto c abundance was increased in both CD groups and in the WD DEX group.
Conclusion: Delivery temperature is a major factor determining VDAC abundance in the neonatal lung. Increased VDAC abundance may promote solute exchange, compensating for the lower breathing frequency as a stimulus for lung liquid absorption after birth.
References
1. Clarke L, Heasman L, Firth K and Symonds ME. Am J Physiol 1997; 272: R1931-39.