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

1. The antidiuretic, pressor and electrolyte transport effects of arginine vasopressin (AVP) were simultaneously evaluated in the anaesthetized 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 effective antidiuretic dose (7.5 ng) increased mean urine osmolality (from 101 +/- 7 to 312 +/- 89 mosmol kg) without altering mean arterial pressure (MAP), renal plasma flow (RPF) or glomerular filtration rate (GFR). A maximal antidiuretic dose of AVP (75 ng) increased mean urine osmolality 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 further 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 and GFR by 35.5 and 38.9% respectively. 3. Increasing concentrations of AVP also progressively increased the fractional excretion of sodium, potassium and phosphate. However, fractional calcium and magnesium excretion was significantly decreased with maximal and supramaximal concentrations. 4. These studies support evidence that AVP is a pressor hormone in physiological concentrations in baroreceptor intact animals. Its role in renal electrolyte transport is unclear. Measured increases in RPF and GFR with the maximal and supramaximal AVP concentrations appear to be correlated with the increase in MAP.