Adverse Effects of Caffeine on Embryonic Cardiac Function During Early Cardiac Morphogenesis.

Caffeine is a naturally occurring product that acts as a mild central nervous system stimulant. In humans the major sources of caffeine are coffee, tea, and soft drinks, as well as cocoa, chocolate, and certain medications. Caffeine is metabolized more slowly in pregnant women and due to the hydrophobic properties of caffeine it can cross the placenta and the brain-blood barrier. Studies in human and animal models have shown that caffeine exposure during pregnancy affects the perinatal cardiovascular system as well as central nervous system and can result in intrauterine growth retardation and stillbirth. Recent studies show that caffeine intake increases risk of first-trimester spontaneous abortion in human. However, the extent and the mechanism by which maternal caffeine intake influences embryonic cardiovascular function during early morphogenesis is not known. We hypothesized that caffeine ingestion during early pregnancy impairs embryonic cardiac function by delaying the onset of heart beat and alters the normal increase in heart rate (HR) resulting in growth delay and first-trimester spontaneous abortion. Eight to 12 week-old pregnant CD-1 mice and 81embryos were studied under an approved IACUC protocol. Caffeine was dissolve in distilled water and administered daily by gavage at a dose of 120mg/kg from gestational days 0.5 to 10.5. We monitored embryonic heart rate (HR) from gestational days 8.5 to 10.5 at 24 hour intervals using a 40MHz ultrasound biomicroscope. At gestational day 10.5, embryos were fixed and somite number and external morphology was assessed. This period of gestational includes the onset of heart beat of the primitive heart tube through the completion of heart looping. Onset of heart beat was significantly delayed in caffeine group at gestational day 8.5 (heart beat was detected in 41% of caffeine treated embryos versus 79% of sham treated embryos). HR increase was higher in caffeine group at gestational days 9.5 (127±4 in caffeine vs. 112±5 in sham, respectively, p<0.05) and 10.5 (150±4 vs. 140±4). At gestational day 10.5, caffeine treated mice had a significantly higher rate of embryo abortion (10% in caffeine vs. less than 2% in sham, p<0.05). Somite number was similar in both groups, however, body size, head size, and upper extremity length was significantly smaller in caffeine group. Thus, our results confirm that intrauterine caffeine exposure alters embryonic cardiac function (onset of heart beat, normal HR increase), embryo growth, and embryo survival during a critical period of early cardiovascular morphogenesis.