No abstract

The present study is concerned with the operation by which the kidney, during antidiuresis, conserves water for the body by elaborating a urine osmotically more concentrated than the blood.It is appropriate to emphasize that in the mammals the osmotic pressure of the plasma and the interstitial fluid is one of the most closely guarded of all the homeostatic states, and that the kidney is chiefly responsible for the regulation of this osmotic pressure within narrow limits. Osmotic dilution of the plasma is normally offset by the excretion of a urine osmotically more dilute than the plasma, as in water diuresis, while an increase in osmotic concentration of the plasma is offset by the excretion of urine osmotically more concentrated than the plasma. The present paper is concerned only with the mechanism of the excretion of a hypertonic urine.That no osmotic concentration is achieved in the separation of the glomerular filtrate is established, to the satisfaction of all investigators, by the well known micropuncture studies of Richards and his coworkers in the Amphibia, and Walker, Oliver, and their coworkers in the guinea pig, rat and opossum. These studies have also demonstrated, at least under the recorded experimental conditions, that the urine remains isosmotic with the plasma, ,or nearly so, throughout the length of the proximal segment, at a time when the bladder urine may be concentrated osmotically to a considerable extent.Unfortunately, such icropuncture studies as are

No abstract

Renal structure and function were investigated in two groups of long-term lithium treated patients. Lithium was administered in two different ways either in a one-dose per day schedule where the whole dose of lithium was given between 8 and 10 p.m. or in a schedule where the lithium dose was given, divided into two or three doses, during the day. Kidney biopsy was performed, and structural changes in the kidney tissue were determined together with 24-h urine volume in the individual patients. The functional as well as the structural changes were most pronounced in patients given their lithium in divided doses during the day. Lithium may be more harmful to the kidney when the lithium administration gives a relatively constant serum lithium level than when the administration causes greater variations including peak values and low minimum levels in serum lithium. The reason for this might be that a number of regenerative processes only occur in periods with low lithium concentrations.