A little while ago I made a note to myself to look up the effects of atrial natriuretic peptide. We’re having an air conditioning / server issue so I took care of this while waiting. Wikipedia, as usual, had the answer:

Atrial natriuretic peptide – Wikipedia, the free encyclopedia

The overall effects of ANP release are a reduction in blood volume and therefore central venous pressure, cardiac output, and arterial blood pressure. It also increases renal sodium secretion and excretion. The overall effect of which is to counter the blood pressure-raising effects of the renin-angiotensin system.