Effect of Caffeine on Cardiovascular Function in the Stage 24 Chick Embryo

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Abstract
Caffeine is consumed by an estimated 95% of pregnant women. Yet, it is not known if caffeine alters embryonic cardiovascular function. We measured the effect of caffeine on mean and phasic dorsal aortic blood flow and mean vitelline artery pressure with a 20-MHz pulse Doppler velocity meter and a servo-null pressure system, respectively. We calculated vascular resistance, stroke volume index, and heart rate. We injected 5-μl aliquots of anhydrous caffeine dissolved in chick Ringer’s lactate into a vitelline vein in doses from 1.2 x 10^-5 mg (0.15 mg/kg) to 1.2 x 10^-2 mg (150 mg/kg). Control embryos received 5 μl chick Ringer’s lactate. The hemodynamic measurements were continuously recorded from 1 min prior through 5 min after injection. 9 stage 24 chick embryos were studied at each dose. The data were analyzed by one-way analysis of variance and Tukey’s HSD test. Caffeine had no effect on heart rate, but a direct dose-related effect on mean dorsal aortic blood flow, stroke volume index, mean pressure, and vascular resistance. The effect of caffeine on stroke volume index at 5 min was a linear log-dose relationship [y = 0.155 + 0.02 In (dose), p < 0.001]. In the chick, caffeine acutely affects cardiovascular function by increasing myocardial contractility and dilating resistance vessels. We speculate this action is mediated through direct cellular effects: increase in free Ca^++ and cyclic adenosine monophosphate.

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