A method for exposing the rat renal medulla in vivo: micropuncture of the collecting duct

Abstract

A new method involving partial nephrectomy is described by which the distal portion of the rat renal medulla is made accessible to an investigation by the micropuncture technique. Urinary flow was greater and osmolality less in the partially nephrectomized left kidney than the unoperated right kidney but the urine remained hypertonic. Micropuncture of the collecting duct revealed a rising osmotic gradient toward the papillary tip. Electrical potential differences across the collecting ducts were measured by microelectrode techniques. The lumen was electrically negative with respect to the interstitial fluid (mean - 11 mv). It is clear that medullary hypertonicity persists in the partially nephrectomized left kidney and the collecting ducts retain their ability to reabsorb water and maintain a transtubular potential difference. In these aspects of tubular activity, the exposed rat renal medulla appears to be similar to that of the hamster, but has the advantage of a greater exposure of its length to investigation by micropuncture.