Developmental hemodynamic changes in rat embryos at 11 to 15 days of gestation: normal data of blood pressure and the effect of caffeine compared to data from chick embryo.

We attempted to measure arterial blood pressure of the rat embryo. The embryo was excised within the uterus and immersed in Hanks' solution at 37 degrees C. The uterus wall and yolk sac were opened to expose the umbilical vessels. The umbilical artery was punctured with a glass micro-pipette, and blood pressure was measured by using a servo-null micro-pressure system. The mean blood pressure was 0.27 +/- 0.05 mm Hg in the embryo at the 11th day of gestation (n = 7), 0.48 +/- 0.03 mm Hg in the 12-day embryos (n = 19), 1.3 +/- 0.08 mm Hg in the 13-day (n = 11), and 2.6 +/- 0.1 mm Hg in the 15-day embryos (n = 10). Heart rate was 84 +/- 11 in 11-day, 122 +/- 3 in 12-day, 192 +/- 7 in 13-day, and 198 +/- 5 in 15-day embryos. These parameters were stable within 10 min after the excision. A comparison of the data with those of the chick embryo of comparable developmental stages revealed that the blood pressure was lower in 11- and 12-day rat embryos than in the chick embryo of Hamburger-Hamilton stages 18 and 21, but this was reversed in the later stages. In the stage 21 chick embryo, intravenous administration of caffeine (60 +/- 9 mg/kg embryo weight) induced an increase in blood pressure by 11 +/- 3% (n = 8), but did not result in a significant increase in dorsal aortic blood flow (6 +/- 6%, n = 9) or in heart rate. In contrast, caffeine (62 +/- 3 mg/kg) increased the heart rate by 8 +/- 2% (n = 10) without changing the blood pressure in the rat embryo of day 12. The velocity of blood flow in the truncus was measured by a pulsed Doppler flowmeter. Caffeine injection increased the mean velocity by 21 +/- 8%). Herein we indicate that measurement of blood pressure in the rat embryo is feasible, but with some limitations, and that there may be qualitative hemodynamic differences between the rat and chick embryos.