Plasma atrial natriuretic peptide and blood pressure during chronic salt loading in spontaneously hypertensive rats with right atrial appendectomy.

Spontaneously hypertensive rats (SHR) were subjected to right atrial appendectomy (ATRX) or sham operated. Five days after this procedure the rats were put on tap water or 1.5% NaCl as drinking water for 1 week. The blood pressure (carotid artery), 24 hours urinary sodium and kalium excretion, plasma levels of immunoreactive atrial natriuretic peptide (ir-ANP) and the rise in plasma ir-ANP concentrations after an acute volume expansion by homologous whole blood (10%) were evaluated after 1 week on the different diets. At the start of the dietary period the rise in plasma ir-ANP values was blunted in ATRX rats. After 1 week the salt loaded animals excreted tenfold more sodium than control rats. At this time basal ir-ANP values in plasma were not significantly influenced by the ATRX and/or the high salt diet but the rise in plasma ir-ANP concentrations to acute volume expansion was blunted in the salt loaded rats. However, the basal blood pressure was not influenced by the salt diet and/or the ATRX. These data do not support the notion that an alleged deficiency in ANP release mechanisms in the SHR is a major determinant for the blood pressure development in this rat strain.