Depressor Effects and Release of Atrial Natriuretic Peptide during Norepinephrine or Angiotensin II Infusion in Man*

Abstract

Alpha-human atrial natriuretic peptide (alpha hANP) is the major circulating form of ANP in man. The potential of synthetic alpha hANP to antagonize the pressor action of norepinephrine (NE) or angiotensin II (AII) and a possible influence of NE or AII pressor infusions on circulating immunoreactive ANP (irANP) were investigated in 14 normal young subjects. After titration of doses to increase mean blood pressure by about 20 mm Hg, NE or AII was infused at a constant rate for 110 min. Mean blood pressure (BP) was similar during NE and AII infusions [109 +/- 4 (+/- SEM) and 108 +/- 3 mm Hg, respectively]. However, synthetic alpha hANP injected in stepwise increasing doses of 10, 40, and 75 micrograms caused significantly greater (P less than 0.001) BP reductions during NE infusion. alpha hANP lowered BP progressively from 147/91 +/- 5/3 to 136/70 +/- 5/3 mm Hg during NE infusion (P less than 0.001) and only minimally from 133/96 +/- 3/3 to 132/89 +/- 4/4 during AII infusion. Heart rate was elevated more (P less than 0.01) after alpha hANP injection during NE infusion. Endogenous plasma irANP increased significantly after 20 min of NE or AII pressor infusion (P less than 0.01 and P less than 0.05, respectively); this rise was more pronounced (P less than 0.05) during NE (from 25 +/- 2 to 80 +/- 20 pg/ml) than during AII (from 21 +/- 3 to 31 +/- 3 pg/ml) infusion. These findings suggest that alpha hANP interacted preferentially with noradrenergic as compared to angiotensinergic BP control. Conversely, for a given rise in BP, NE elicited a greater rise in circulating irANP.