Effect of atrial natriuretic factor in rat pregnancy.

Protocols were designed to 1) identify atrial natriuretic factor (ANF) bioactivity in pregnant rats, 2) compare ANF activity in atria from gravid and virgin Sprague-Dawley animals, and 3) assess renal and vascular responsiveness to ANF during gestation. Similar quantities of ANF were extracted from atria of term gravid and age-matched controls (assayed as the natriuretic response in awake virgins). We then purified by high-performance liquid chromatography a peptide identical to the synthetic 23 amino acid atriopeptin II (AP II). With equimolar injections of ANF, gravid rats had a blunted natriuretic response (P less than 0.05). However, when dose was based on estimated extracellular volume, awake virgin and pregnant animals displayed similar highly significant dose-response curves to infused AP II (R's 0.8). When hydropenic rats were assayed, both gravid and virgins required 10 times more ANF to initiate a diuresis; dose-response curves again being similar and highly significant. Decrements in blood pressure were also similar in pregnant and nongravid animals. Thus, despite an increased intravascular volume of 70% during gestation, cardiac content of ANF and the renal and vascular responsiveness to this peptide are similar to those in virgin rats, suggesting resetting of ANF-volume relationships during pregnancy.