ROLE OF ENDOGENOUS ATRIAL-NATRIURETIC-PEPTIDE IN DOCA-SALT HYPERTENSIVE RATS - EFFECTS OF A NOVEL NONPEPTIDE ANTAGONIST FOR ATRIAL-NATRIURETIC-PEPTIDE RECEPTOR

Background. To explore roles of endogenous atrial natriuretic peptide (ANP) in blood pressure and volume regulation, we examined the effects of a newly developed ANP antagonist, HS-142-1 (HS) in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Methods and Results. We examined 1) the effects of HS on ANP- or brain natriuretic peptide (BNP)-induced reductions in renal vascular resistance (RVR) of rat isolated perfused kidneys, 2) the effects of HS on cyclic GMP (cGMP) production in rat cultured vascular smooth muscle cells pretreated with ANP or BNP, and 3) the renal and systemic effects of HS in DOCA-salt-treated rats and control rats. We found that 1) HS dose-dependently reversed ANP- or BNP-induced decreases in RVR; 2) ANP or BNP at 100 nM caused an eightfold increase in cGMP production. These increases in cGMP were inhibited by HS in a dose-dependent fashion, and 300 mug/ml HS decreased cGMP to the control level. HS alone did not influence RVR or cGMP production; and 3) DOCA-salt rats showed higher plasma concentrations of ANP (198 versus 75 pg/ml) and BNP (23.7 versus 2.7 pg/ml, each p<0.01) than the control rats. Bolus administration of 8 mg/kg HS elevated blood pressure by 8% (p<0.01). This rise in blood pressure was attributed to an increase in systemic vascular resistance (+14%, p<0.05). Conversely, urinary excretion of sodium (-41%), glomerular filtration rate (-27%), and plasma (-77%) and urinary cGMP (-69%, each p<0.01) were decreased by administration of 8 mg/kg HS. These effects were dose dependent in DOCA-salt rats but slight or negligible in the control rats. Conclusions. These results suggest that endogenous ANP and BNP may be involved in the regulation of blood pressure and body fluid volume in DOCA-salt rats in which ANP and BNP secretion is augmented.