Glomerular filtration and renal plasma flow during hyperthermia

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Abstract
The purpose of this study was to investigate the factors that determine the direction and magnitude of the alteration in GFR (glomerular filtration rate) and RPF (renal plasma flow) in hyperthermia. The investigation was conducted on anesthetized dogs. Creatinine clearance was used as a measure of GFR and para-aminohippuric acid clearance was used as a measure of RPF. The GFR in 12 mildly dehydrated dogs went from a control value of 68.4 ± 4.5 ml/min. at RT (rectal temperature) of 38.9°C to a GFR of 25.1 ± 8.5 ml/min. at a RT of 42.1°C at the end of 5 hours of exposure to heat. Final dehydration averaged –2.0% body weight. The fall in GFR and RPF was not due to dehydration for in a group of six hydrated dogs (+4% body wt. at end) similar results were obtained. No decrease in GFR or RPF occurred in either hydrated or dehydrated dogs until severe hyperthermia (> 41.2°C) was present. Though there was a decline in blood pressure towards the end of each experiment, in both groups, the decrease in GFR and RPF preceded any marked fall in pressure. Both groups showed an increase in hematocrit and a decrease in plasma volume (measured by T-1824 dilution) which became marked at the end of 5 hours of exposure to heat. The decrease in GFR and RPF appears directly related to the hyperthermia for upon rapid cooling GFR and RPF increases towards normal in spite of the persisting decreased blood pressure and plasma volume and increased hematocrit.

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