EFFECTS OF HEAT THERAPY ON RENAL HEMODYNAMICS, COMPENSATORY HYPERTROPHY AND GLOMERULONEPHRITIS IN RATS

To investigate whether back heating (BH) affects renal function, we applied an electric heating pad on the back skin overlying the kidneys in rats. In the acute experiment on saline-expanded, normal conscious rats, BH up to 42 +/- 1-degrees-C for 15 min induced diuresis, natriuresis, kalliuresis, increased urinary kallikrein excretion as well as an increase in renal blood and plasma flow and glomerular filtration rate (GFR). When the rats were uninephrectomized and subjected to either BH twice a day for 1 week or a sham procedure, the study group showed a higher GFR per gram kidney weight and a higher increase in kidney/body weight ratio. When the rats were injected daily with cationic bovine serum albumin for 30 days and then subjected to either BH twice a day for 26 days or a sham procedure, the BH group showed a higher degree of proteinuria during the recovery period and a higher kidney/body weight ratio on the 27th day. Acute BH for 15 min in anesthetized rats increased body temperature, perirenal temperature, heart rate, stroke volume, cardiac output and cardiac index. Taken together, these results suggest that BH may affect the kidneys in normal and pathologic states. These effects may be at least partly related to a change in systemic hemodynamics.