This study investigated whether excision of either the right or left atrial appendage of rats alters their natriuretic response and the release of atrial natriuretic factor during acute blood volume expansion or reduction. These animals were subjected to a thoracotomy and either had their right or left atrial appendages removed or underwent a right or left atrial sham appendectomy for comparative, control purposes. Intrajugular vein, intracarotid artery, and intravesical catheters were installed 3-4 weeks later under sodium pentobarbital anesthesia. Then, when the rats were conscious, blood volume was expanded using blood from donor rats once every 15 minutes in 3 increments of 10% of the calculated total blood volume at a rate of 5 ml/kg/min. Blood and urine samples were collected before volume expansion and at the end of each 15-minute period, with the withdrawn blood being replaced. A maximal fourfold increase in urinary volume, urinary sodium excretion, and plasma atrial natriuretic factor was observed in all but the right-atrial-appendectomized animals. Plasma atrial natriuretic factor, urinary volume, and urinary sodium excretion were correlated in all 4 groups. No significant changes in blood pressure or hematocrit were noted. Plasma vasopressin, measured at the end of volume expansion, was significantly lower in animals subjected to left atrial appendectomy. High-performance liquid chromatography of plasma from the control groups indicated that most of the released ANF during blood volume expansion corresponded to a high molecular weight peptide. Additional rats, processed as above, were subjected to 10% blood volume decrements.(ABSTRACT TRUNCATED AT 250 WORDS)