Chronic vascular constrictions and measurements of renal function in conscious rats

Although a tremendous amount of physiologic information has been gained from experiments on anesthetized animals, there is often the question to what extent anesthesia itself, as well as the losses and replacement of fluid that accompany surgical preparations, might have influenced the function being studied. This possible pitfall may apply especially to studies on the kidney because the renal circulation is so exquisitely sensitive to anesthetic agents and changes in fluid balance. Chronic preparations in dogs have been [1] and continue to be used [2] successfully. But the far lesser expense of rats, as well as their common use in physiologic experiments, points up the desirability of a successful chronic preparation in this species. Renal clearances have been performed previously on unanesthetized rats [3, 4], but the methods have not been generally adopted.We here describe a method that can measure renal clearances and extraction of PAH accurately and repeatedly in the same conscious rat over a period of weeks. For our own purposes [5] we also needed a method for constricting blood vessels. The design and construction of a suitable cuff for this purpose, likewise usable in unanesthetized rats, also form part of this report