Baroreceptor control of heart rate in chickens (Gallus domesticus)

The baroreceptor control of heart rate was examined in nonanesthetized, nonrestrained, White Leghorn chickens (n = 10) by measuring the heart period response to modest increases in systolic blood pressure induced by IV boluses of phenylephrine (0.04 micrograms/g). In each animal, a sciatic artery and a femoral vein were chronically instrumented for the measurement of blood pressure and heart rate, together with venous access. Sustained and consistent cardiac slowing was seen in all chickens in response to small increases in systolic pressure. The mean slope of the regression equation between heart period and systolic pressure was 13.9 +/- 0.8 s X 10(-4)/mm of Hg. This sensitivity was reduced to 2.1 +/- 1.5 s X 10(-4)/mm of Hg by anesthetizing the chickens with isoflurane (inspired concentrations of 1%).