Atrial natriuretic factor: the effects of pregnancy and a high-salt diet on atrial levels.

The chronic and relatively acute changes in blood volume that occur during pregnancy and post partum may be associated with alterations in the content of atrial natriuretic factor in the atria. We measured the concentration of atrial natriuretic factor in the right and left atria of virgin, pregnant, and postpartum Sprague-Dawley rats by radioimmunoassay as well as the concentration of atrial natriuretic factor in the atria and plasma of term pregnant rats on a high-salt diet. Neither right nor left atrial concentrations of atrial natriuretic factor were elevated during pregnancy in animals on a normal diet, but both were increased during the first 2 days after delivery. Term pregnant rats on a high-salt diet showed a small increase in atrial natriuretic factor levels in the left atria only, without any change in plasma atrial natriuretic factor levels. We conclude that relatively acute changes in fluid and electrolyte balance are more likely than chronic ones to be associated with alterations in atrial natriuretic factor concentrations in the atria.