Cicletanine (CIC), a furopyridine derivative, lowers blood pressure in hypertensive animals and humans. We have previously identified an NaCl-sensitive substrain of spontaneously hypertensive rat (SHR-S) that displays enhanced sensitivity to the depressor effects of exogenous atrial natriuretic peptide (ANP) when fed a high NaCl diet. The current study tested the hypotheses that CIC has an exaggerated antihypertensive effect in NaCl-supplemented SHR-S and that this effect might be ANP dependent. CIC (40 mg/kg/day) or vehicle was administered by gavage in a single daily dose for three weeks beginning immediately prior to initiation of 1% or 8% NaCl diets in seven-week-old male SHR-S. CIC significantly decreased mean arterial pressure (MAP) and the ratio of left ventricular and septum weight to body weight (LV + S/BW) in both 8% NaCl- and 1% NaCl-fed SHR-S. The depressor effect of CIC was greater in the 8% NaCl group (-26 mmHg) than in the 1% NaCl group (-13 mmHg). CIC was associated with significant reduction in RAP in the 8% NaCl group but not in the 1% NaCl group. Neither CIC treatment nor 8% NaCl significantly altered plasma ANP or cyclic guanosine monophosphate (GMP) levels in plasma, aorta, or kidney. CIC was associated with significant decreases in plasma norepinephrine (NE) levels in the 1% NaCl group but not in the 8% NaCl group. The data demonstrate that the antihypertensive effect of CIC is exaggerated in NaCl-sensitive hypertension. The antihypertensive effect of CIC appears not to be related to ANP or cyclic GMP but may be related to a combination of a sympatholytic and natriuretic/diuretic effects in SHR-S.
