LAUSR

Introduction: The developing heart undergoes changes in metabolic substrates parallel with perinatal developmental stages. The preferred substrates for fetal hearts are carbohydrates, which transitions to a preference for fatty acids postnatally. The underdevelopment of lipid metabolism mechanisms in preterm infants cause imbalances or dysfunction in uptake, cellular processing, and storage of fatty acids; and increase the risks for long term cardiovascular and metabolic diseases. It is unknown whether the heart can process fatty acids before birth, and how it affects cardiomyocyte growth. The aim of this study was to determine the effects of Intralipid infusion on fetal sheep cardiac myocyte growth. We hypothesized that the size of cardiomyocytes would remain unchanged, however we expected an increase in maturity. Methods: Intralipid 20® was infused into instrumented fetal sheep (IL, 0.4 ml/kg/hr for 8 days, n=4F/7M); the contralateral twin received saline at a comparable rate (CON, n=7F/4M). Hearts were collected at 133 days gestational age (dGA; term is 147 dGA), and enzymatically dissociated, then myocytes fixed in paraformaldehyde. The length and width were measured in 100 myocytes using a wet mount, under calibrated light microscopy (40x, Zeiss Axiophot), and analyzed with Image Pro 6.3. Nucleation was determined in 500 cells; percentage binucleation is a surrogate measure of maturation. Data are presented as mean ± standard deviation. Groups were compared by t-test. Results: Body weight (IL, 4.2 ± 0.6 vs. CON, 4.1 ± 0.6kg) and heart weight (IL, 29.9 ± 4.1 vs. CON, 27.2 ± 4.6g) were not different between the lipid and control fetuses. Interim results indicate no differences in length or diameter in cardiomyocytes of the left and right ventricle (IL, N=3-7; CON, N=7-9). We found no differences in cardiomyocyte length in the septum, but Intralipid (N=10) increased the diameter of mononucleated (+12%, P=0.016) and binucleated (+11%, P=0.012) myocytes (vs. CON, N=7). In the septum, Intralipid treatment increased binucleation (P<0.02; 69.2 ± 8.0% vs 60.8 ± 9.7%). In the RV, increased binucleation was only a tendency (P<0.06; 70.7 ± 6.4% vs 60.8 ± 9.9%; IL n=6). Binucleation was unaffected in the LV (67.1 ± 9.9%). Summary/Conclusion: The increase in diameter of fetal cardiomyocytes in the septum could reflect different regional regulation of growth to the infused intralipid. Interestingly, parallels could be made between the septal hypertrophy described in offspring from diabetic mothers. This study is funded by NIH R01HL146997 and R01HL142483. KI is funded by a NIH supplement to R01HL142483. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.