CONTROL OF ATRIAL-NATRIURETIC-FACTOR BY RIGHT AND LEFT ATRIAL DISTENSION IN PREGNANT SHEEP

Previous studies of the atrial stretch-atrial natriuretic factor (ANF) relationship during pregnancy have employed volume expansion and meas ured only right atrial pressure (RAP). Consequently, we studied nonpre gnant (n = 7) and 115- to 125-day pregnant (n = 7) sheep and assessed the ANF response to changes of RAP and left atrial pressure (LAP) indu ced by graded balloon inflation. Ewes prepared with vascular catheters and atrial balloons were studied after recovery from preparatory surg ical procedures. The basal levels of mean arterial pressure (MAP, 83 /- 3 mmHg), RAP (2.1 +/- 0.7 mmHg), LAP (4.7 +/- 0.9 mmHg), and heart rate (HR, 102 +/- 6 beats/min) were similar in nonpregnant and pregnan t sheep. Pregnancy also resulted in elevation of ANF concentration fro m 25 +/- 6 to 57 +/- 4 fmol/ml. With right atrial distension, the RAP- ANF relationships were similar in both nonpregnant and pregnant sheep, with a 10-mmHg increase in RAP increasing ANF by an average of 95 +/- 9 fmol/ml. In nonpregnant sheep, the LAP-ANF relationship was more re sponsive than RAP-ANF because a 10-mmHg increase in LAP resulted in a 193 +/- 10 fmol/ml increase in ANF. Moreover, during pregnancy, the LA P-ANF relationship was significantly more sensitive because a 10-mmHg increase in LAP resulted in a 433 +/- 15 fmol/ml elevation of ANF. The se data demonstrate that plasma ANF levels are more responsive to dist ension of the left atria than to the right. More importantly, the ANF response to left, but not right, atrial distension is enhanced by preg nancy.