Spontaneous Pressure Diuresis in Conscious Rats

Pressure diuresis is thought to be a long-term mechanism that is essential for regulation of blood volume and arterial pressure (AP). We recently found that experimentally-induced changes in AP result in changes in urine flow (UF) within 6 seconds in anesthetized rats. To test our hypothesis that the long-term nature of pressure diuresis is the result of the cumulative sum of many short-term changes in UF occurring in response to spontaneous changes in AP, AP (via an aortic catheter) and UF (via a gravimetric method) were measured over 2 hours in 8 conscious, free-moving, chronically instrumented rats. A total of 24 2-hour recordings was obtained at a frequency of 0.1 Hz. For all trials, mean AP averaged 130.0 ± 4.1 mm Hg and mean UF averaged 25.2 ± 10.1 lllfmin. A significant, positive linear relationship between UF and AP was observed in 16 (67%) ofthe trials, and a significant negative relationship was observed in 2 of the trials. Our results 1) demonstrate that a positive relationship between UF and AP can be observed in conscious, freemoving rats; and 2) suggest that short-term changes in UF occur in response to spontaneous changes in AP.