Atrial natriuretic peptide is produced less in the intercaval sinus than in the pectinated right atrium.

To explain the lower atrial natriuretic peptide concentrations after total cavopulmonary connection than after the Fontan procedure, a prospective study was carried out in seven rats to count the specific granules of atrial natriuretic peptide by electronmicroscope. After fasting from water for 12 days, the quantity of specific granules in the right atrial appendage (pectinated part), intercaval sinus (smooth part), and superior vena cava were counted. The number of specific granules present in the pectinated part of right atrium was 97 +/- 19 in 20 cells, while in the intercaval sinus it was 23 +/- 19 (mean +/- SD). The difference was significant statistically (p < 0.0001). No granule was present in the superior vena cava. We conclude that the granularity of atrial natriuretic peptide is less in the intercaval sinus than the pectinated part of the right atrium.