Effects of spaceflight on postnatal development of arterial baroreceptor reflex in rats

Aim: It has been reported that spaceflight attenuates the arterial baroreceptor reflex. As this reflex function changes dramatically during postnatal development, we hypothesized that space flight depresses the developmental changes of the reflex system. To test this hypothesis, we evaluated the baroreceptor reflex function in rats, which were exposed to a microgravity environment on a space shuttle 9–25 days after birth. Methods: Baroreceptor reflex sensitivity and the afferent sensitivity were evaluated by measuring heart rate (HR) and aortic nerve activity (ANA) changes in response to an increase in mean arterial pressure (MBP) derived by phenylephrine injection (20–50 μg kg−1) under urethane‐anaesthesia. Results: Baroreceptor reflex sensitivity (% change of HR/% change of MBP) was lower in the flight group (FLT: −0.19 ± 0.04, n = 4) than either the asynchronous ground control group (AGC: −0.47 ± 0.06, n = 6, P