HEMORRHAGE EFFECTS AN PLASMA ANP, NH2-TERMINAL PRO-ANP, AND PRESSER HORMONES IN ANESTHETIZED AND CONSCIOUS RATS

We examined the effect of hemorrhage on plasma NH2-terminal pro-atrial natriuretic peptide (NT-pro-ANP) and atrial natriuretic peptide (ANP) in anesthetized and conscious rats. Blood (1.5 ml/time point) was wit hdrawn at 0, 10, 20, and 30 min. In anesthetized rats it caused decrea se in mean arterial pressure and led to bradycardia in 2 min. Right at rial pressure decreased significantly after 12 min. However, plasma AN P did not change, and NT-pro-ANP actually increased from 481 +/- 55 to 609 +/- 73 pmol/l (P < 0.01) at 20 min and to 696 +/- 82 pmol/l (P < 0.01) at 30 min. Also plasma arginine-8-vasopressin (AVP) and epinephr ine increased significantly at 30 min. No significant changes in plasm a endothelin and norepinephrine were found. The increase in NT-pro-ANP after hemorrhage was not blocked by AVP V-1-receptor, alpha- and beta -catecholaminergic receptor, or muscarinic-receptor antagonists. The p lasma I-125-ANP disappearance curve was shifted to the right after hem orrhage in anesthetized rats, suggesting that the elimination of ANP w as decreased. In conscious rats, heart rate and right atrial pressure did not change significantly after hemorrhage, and mean arterial press ure did not decrease until 22 min. NT-pro-ANP decreased from 1,467 +/- 146 to 1,072 +/- 130 pmol/l (P < 0.01) at 20 min and to 941 +/- 41 pm ol/l (P < 0.01) at 30 min. Plasma ANP did not respond to hemorrhage in conscious rats. In conclusion, we found no change in plasma ANP durin g hemorrhage in either anesthetized or conscious rats, but we did find a significant increase in plasma NT-pro-ANP levels in anesthetized ra ts and a significant decrease in conscious rats. We suggest that this divergence may be due to different hemodynamic responses to hemorrhage .