ACUTE EFFECT OF PHYSIOLOGICAL CONCENTRATIONS OF VASOPRESSIN ON RAT RENAL-FUNCTION

1. The antidiuretic, pressor and electrolyte transport effects of argi nine vasopressin (AVP) were simultaneously evaluated in the anaestheti zed water diuretic rat. Increasing concentrations of AVP (7.5, 75 and 750 ng/ kg bolus and per h), were used to produce plasma levels which approximate the physiological range (4.8 +/- 2.4, 3 5.7 +/- 12.5, 85.2 +/- 16. 1 pg/mL respectively). 2. Administration of a minimally effec tive antidiuretic dose (7.5 ng) increased mean urine osmolality (from 101 +/- 7 to 312 +/- 89 mosmol kg) without altering mean arterial pres sure (MAP), renal plasma flow (RPF) or glomerular filtration rate (GFR ). A maximal antidiuretic dose of AVP (75 ng) increased mean urine osm olality to 2002 +/- 109 mosmol/ kg and was associated with significant mean increases in MAP (9 mmHg), RPF and GFR (25%) by 30-60 min. A fur ther ten-fold increase in AVP (750 ng) produced a greater increase in MAP (116 +/- 6 to 134 +/- 7 mmHg; P<0.01) as well as increasing RPF an d GFR by 35.5 and 38.9% respectively. 3. Increasing concentrations of AVP also progressively increased the fractional excretion of sodium, p otassium and phosphate. However, fractional calcium and magnesium excr etion was significantly decreased with maximal and supramaximal concen trations. 4. These studies support evidence that AVP is a pressor horm one in physiological concentrations in baroreceptor intact animals. It s role in renal electrolyte transport is unclear. Measured increases i n RPF and GFR with the maximal and supramaximal AVP concentrations app ear to be correlated with the increase in MAP.