To study the effect of atrial natriuretic peptide (ANP) on vascular permeation 
of albumin in the fetus, ANP (167-600 ng/min) was infused into eight ovine 
fetuses and saline vehicle was infused into eight twin controls (gestational age 
127 +/- 3 d) over a 50-min period. Using two different radiolabeled albumin 
markers, we determined the tissue to blood isotope ratio (TBIR), an index of 
albumin permeation, and the albumin clearance. Although ANP had no hemodynamic 
effect, a marked increase in the hematocrit was observed in ANP-infused fetuses 
compared with initial values (0.37 +/- 0.04 vs 0.42 +/- 0.04, p < 0.005) but was 
unchanged in the twin fetuses receiving saline vehicle (0.35 +/- 0.03 versus 
0.35 +/- 0.02). TBIR and albumin permeation were increased in combined tissues 
of ANP-infused fetuses compared with saline controls (TBIR: 1.49 +/- 0.58 versus 
1.29 +/- 0.3, p < 0.001; albumin clearance: 1091 +/- 1279 versus 827 +/- 1464 
nL/g/min, p < 0.01). In individual tissues, TBIR was significantly increased in 
skin (2.88 +/- 0.67 versus 1.55 +/- 0.35, p < 0.02), muscle (1.6 +/- 0.27 versus 
1.24 +/- 0.26, p < 0.02), adrenal (1.33 +/- 0.10 versus 1.13 +/- 0.15, p < 
0.02), bone (1.67 +/- 0.45 versus 1.20 +/- 0.40, p < 0.02), kidney (1.52 +/- 
0.25 versus 1.24 +/- 0.26, p < 0.03), and gut (1.69 +/- 0.20 versus 1.39 +/- 
0.34, p < 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)