Ovine fetal cardiovascular, renal, and fluid balance responses to 3 days of high arginine vasopressin levels

To determine the effects of sustained high levels of arginine vasopressin (AVP) on the fetus and whether these effects were the same as those found during acute infusion of AVP, chronically catheterized fetal sheep aged 121-136 days were infused for 3 days with either AVP (45 mU.kg(-1).h(-1)) or saline. The bradycardia, acidemia, and failure of glomerulotubular balance that occurred with acute AVP infusion were reversed by day 3 of AVP (P < 0.005) and the acute rise in arterial pressure was attenuated (P < 0.005). By contrast, the rise in the glomerular filtration rate was sustained (P < 0.005) and urinary osmolality increased further to 426 +/- 30 mosmol/kg (P < 0.01). Although placental blood flow did not change acutely with AVP, it had fallen by day 3 (P < 0.01). In addition, with AVP but not saline extracellular volume fell from 588 +/- 28 to 493 +/- 29 ml/kg (P < 0.002) and the plasma/interstitial volume ratio rose from 0.18 +/- 0.01 to 0.21 +/- 0.01 (P = 0.001). These findings suggest that although release of ANP may be beneficial in acute stress in utero, sustained high levels may be detrimental to fetal health and sodium balance.