Premature Lambs Exhibit Normal Mitochondrial Respiration after Long-Term Extrauterine Support

Background: in an effort to mitigate the major morbidities and mortality associated with extreme prematurity, we have developed an EXTrauterine Environment for Neonatal Development (EXTEND) designed to provide physiologic support of extremely premature infants. Objectives: we have previously shown that long-term, physiologic support of premature fetal lambs is possible with EXTEND, but in this study, we sought to demonstrate bioenergetic equipoise at the tissue level. Methods: four premature fetal lambs were delivered by hysterotomy at gestational ages (GA) of 105-107 days (term similar to 145 days), cannulated via the umbilical vessels, and transitioned to support on EXTEND for 3-4 weeks. Five control fetuses were age-matched to the GA of experimental fetuses at the time of study end (128-134 days GA) and immediately sacrificed after hysterotomy. Mitochondria were isolated from the heart, liver, kidney, and skeletal muscle of fetuses at the time of sacrifice, and oxygen consumption rates (OCRs) were measured. Results: there were no differences in basal mitochondrial OCR between EXTEND and control fetuses for heart, kidney, or skeletal muscle. For liver, the basal OCR was higher in EXTEND fetuses compared to controls. There were no differences in physiologic maximal OCR or reserve capacity for any tissue analyzed. Conclusions: fetal lambs supported by EXTEND demonstrate physiologic mitochondrial function as evidenced by adequate basal and physiologic maximal cellular respiration as well as preserved reserve capacity.