SALT, HYPERTENSION AND RENAL-DISEASE - COMPARATIVE MEDICINE, MODELS AND REAL DISEASES

Dogs are well established as experimental animals for the study of bot h renal disease and hypertension, but most work is based on surgical o r pharmacological models and relatively little on spontaneous diseases . This review argues for the latter as an underexploited aspect of com parative medicine. The most important feature of canine hypertension m ay not be the ease with which models can be produced but the fact that dogs are actually rather resistant to hypertension, and perhaps to it s effects, even when they have chronic renal failure. The importance o f natural models of chronic renal failure is strengthened by the evide nce that self-sustaining progression is a consequence of extreme nephr on loss, that is, a late event, rather than the dominant feature of th e course of the disease. The role of salt in hypertension is discussed and emphasis given to the importance of understanding the physiologic al basis of nutritional requirement and recognizing that it is unlikel y to exceed 0.6 mmol/kg/day for most healthy adult mammals except duri ng pregnancy or lactation. Such a perspective is essential to the eval uation of experiments, whether in animals or humans, in order to avoid arbitrary definitions of 'high' or 'low' sodium intake, and the serio us misinterpretations of data which result. An age-related rise in art erial pressure may well be a warning of excess salt intake, rather tha n a normal occurrence. Problems of defining hypertension in the face o f variability of arterial pressure are also discussed.