Atrial natriuretic peptide in pregnant and lactating goats

Plasma concentrations of atrial natriuretic peptide (ANP) were measured in 6 goats during pregnancy, lactation and a nonpregnant, nonlactating (= control) period before and during a rapid iv load of 0.9% NaCl. The volume of the load was 20% of blood volume. The infusions increased central venous pressure by 7 +/- 1 mmHg during pregnancy and 8 +/- 1 mmHg during lactation. Before infusions plasma ANP concentrations were 5.7 +/- 0.7 pmol/l (control period), 10.8 +/- 1.8 pmol/l (pregnancy; P less than 0.05), and 6.5 +/- 1.5 pmol/l (lactation; NS). ANP increased significantly in all periods. Maximal values were 12.5 +/- 1.5 (control period), 25.5 +/- 2.3 (pregnancy; P less than 0.01 vs control period, P less than 0.05 vs lactation), and 13.0 +/- 1.6 (lactation; NS). Renal Na excretion increased similarly during pregnancy and control period, but slightly more during lactation. In 4 of the goats iv infusions of ANP (1 microgram/min, 60 min) were given. The infusions caused natriuresis during the control period, but not during pregnancy and lactation, despite more than 10-fold increases of plasma ANP levels. In conclusion, our results indicate that although plasma ANP concentration rose to high levels during acute NaCl loading in pregnant goats, this effect was not important for the natriuresis. Instead, the natriuretic response to ANP appears attenuated during pregnancy, and also during lactation.