ATTENUATED RESPONSE OF RENAL MECHANORECEPTORS TO VOLUME EXPANSION IN CHRONICALLY HYPOXIC RATS

Multifiber renal afferent nerve activity responds to volume expansion in sea level rats but not in chronically hypoxic (high altitude) rats, We performed single-unit recordings of renal efferent nerve activity to characterize renal sensory receptors and their responses to volume expansion in these animals. Hypoxia was induced by placing Wistar rats in an altitude chamber (380 Torr, 5,500 m) for 4 wk. Spontaneously fi ring renal R2 chemoreceptor and arterial, ureteropelvic, and venous me chanoreceptors were identified. The basal activity of each receptor ma s similar among these rats. In response to specific stimulus, the incr easing impulse of R2 chemoreceptor was similar between two groups of r ats, but the increasing activity of each mechanoreceptor was less in h ypoxic rats. When challenged with saline load, R2 chemoreceptor activi ty decreased, but. all mechanoreceptors activated in all rats. Despite similar increases of arterial, renal ureteropelvic, and venous pressu re during saline load, the increasing activity of each mechanoreceptor was significantly less in hypoxic rats. These results indicated chron ic hypoxia attenuates the sensitivity of renal mechanoreceptors in res ponse to the stimulation of saline load.