Abstract
We previously reported that the 16 days spaceflight (FLT) reduced the sensitivity of the aortic baroreflex in rat neonates and showed fewer unmyelinated fibers in its afferent (UMFa) as compared to the ground controls, which might be related with the lower baroreflex response, and that the dams housed for nursing the neonates also showed fewer UMFa. In the post-flight examination, these adult rats were principally served for the histological analysis, however, we tried the baroreflex test (phenylephrine 50 g/kg bolus injection) under anesthesia (urethane 1.0-1.8 g/kg) in two dams of the FLT groups. The indices of the decrease in heart rate in response to the maximal increase in mean arterial pressure (delta-HR bpm/delta-MAP mmHg) were -1.40 and -2.65 in the two FLT animals, and -3.20 and -4.69 in the two ground animals. The results suggest the possibility of a failing of baroreflex sensitivity during and after the spaceflight even in adult rats, relating the fewer UMFa. [J Physiol Sci. 2006;56 Suppl:S237]
