COMPLEMENTARY CHANGES IN PLASMA ATRIAL NATRIURETIC PEPTIDE AND ANTIDIURETIC HORMONE CONCENTRATIONS IN RESPONSE TO VOLUME EXPANSION AND HAEMORRHAGE: STUDIES IN CONSCIOUS NORMOTENSIVE AND SPONTANEOUSLY HYPERTENSIVE RATS

SUMMARY 1. Plasma concentrations of atrial natriuretic peptide (ANP) and antidiuretic hormone (ADH) were measured in conscious stroke‐prone spontaneously hypertensive (SPR), spontaneously hypertensive (SHR) and normotensive Wistar‐Kyoto (WKY) rats before and after acute volume expansion or haemorrhage. 2. Plasma ANP concentration was reduced to one‐third of resting values 30 min after a 1.5% haemorrhage (1.5 ml of blood per 100 g bodyweight). Plasma ADH concentration rose immediately 50‐fold on haemorrhage and remained elevated at 30 min. 3. Plasma ANP concentration increased 2.5‐fold relative to resting values 1 min after infusion of 2.0 ml per 100 g 5% dextrose; after 10 min plasma ANP remained elevated. Plasma ADH concentration tended to fall on volume expansion although no significant decrease was observed. 4. There was no difference in the basal levels of ANP and ADH, or in the changes produced by alterations in blood volume, in hypertensive SPR and SHR compared with normotensive WKY. 5. Thus, plasma ANP concentrations moved in opposite directions in response to two physiological stimuli: volume expansion and haemorrhage. Reciprocal changes were observed in plasma ADH.