Renal parameter estimates in unrestrained dogs

A mathematical formulation has been developed to describe the haemodynamic parameters of a conceptualised kidney model. The model was developed by considering regional pressure drops and regional storage capacities within the renal vasculature. Estimation of renal artery compliance; pre- and postglomerular resistance and glomerular filtration pressure is feasible by considering mean levels and time derivatives of abdominal aortic pressure and renal artery flow. If the level of flow is not greatly altered during an experimental sequence, it may also be feasible to estimate changes in glomerular filtration rate. Changes in the smooth muscle tone of the renal vessels induced by exogenous angiotensin amide, acetylcholine and by the anaesthetic agent halothane were estimated by use of the model. By employing totally implanted telemetry, the technique was applied on unrestrained dogs to measure renal resistive and compliant parameters while the dogs were being subjected to obedience training, to avoidance reaction and to unrestrained caging. An increase in vasoconstrictor tone in the renal artery and in the afferent arterioles in response to an increasing level of stimulation was demonstrated using this model.