Influence of antidiuretic hormone on peritoneal membrane area and permeability.

The present study was carried out to determine if antidiuretic hormone (ADH) altered the solute handling characteristics of the peritoneal membrane. Lightly anesthetized dogs primed with urea-(14)C (60 mol wt) and inulin (5200 mol wt) were volume expanded with hypotonic saline solution to suppress endogenous ADH as assessed by urine/plasma osmolality. With ADH suppressed, two to three control peritoneal dialysis exchanges were carried out. A constant infusion of ADH in a physiologic dose of 150 mU/hr in saline was begun and the urine/plasma osmolality followed until it was significantly greater than one. Two to three experimental dialysis exchanges were then carried out. Dialysance across the peritoneal membrane was calculated for inulin (D(I)) and urea (D(U)). In 16 such studies D(U) fell in all but three (the mean value for the fall was 2.8 +/-2.6 ml/min; P < 0.001). D(I) varied randomly and showed no significant change. In all 16 studies D(I)/D(U) rose (D(I)/D(U) = 0.054 +/- 0.054; P < 0.005). Seven dogs were studied with an identical protocol but saline was infused without ADH. D(U) and the dialysance ratio varied randomly. D(U) fell in one and did not change or rose in four and D(I)/D(U) rose in two and fell in three. The data are interpreted to show a fall in area but an increase in mean pore radius of the "peritoneal membrane" in response to physiologic amounts of intravenous ADH. The fall in area is consistent with a decreasing splanchnic blood flow.