Blockade of volume expansion-induced release of atrial natriuretic peptide by median eminence lesions in the rat.

Since stimulation of the anteroventral third ventricle region (AV3V) induced a rapid elevation of plasma atrial natriuretic peptide (ANP) associated with rapid changes in brain and pituitary content of ANP, whereas lesions of the AV3V were followed by a marked decline in plasma, brain and pituitary content of the peptide, we hypothesized that release of ANP from the median eminence (ME) might be an important pathway to control plasma ANP. Consequently, electrolytic lesions were placed in the ME and the response to hypertonic-volume expansion was determined in conscious rats. In sham-operated controls volume expansion produced a 3.5-fold increase in plasma ANP concentrations within 5 min. Values rapidly declined to near initial levels at 15 and 30 min. Median eminence lesions almost completely blocked the response to volume expansion at 24 and 120 h post-lesion and initial ANP concentrations were lower than those of the sham-operated controls. The results indicate that increased release of ANP from the neurohypophysis may play an important role in the increased plasma ANP concentrations which follow volume expansion.