title: Effects of the angiotensin II receptor antagonist losartan on 24-hour blood pressure profiles of primary and secondary hypertensive rats.
abstract: Primary and secondary hypertension differ with regard to circadian blood pressure (BP) profiles. To evaluate the contribution of the renin-angiotensin system (RAS) to circadian BP regulation, we studied cardiovascular effects of the angiotensin II (AII) receptor antagonist losartan and the angiotensin-converting enzyme (ACE) inhibitor enalapril in animal models of primary and secondary hypertension after morning and evening dosing. Systolic/diastolic BP (SBP/DBP) and heart rate (HR) were measured telemetrically in spontaneously hypertensive rats (SHR) and transgenic hypertensive rats (TGR[mRen-2]27). Losartan (0.3 to 30 mg/kg) or enalapril maleate (10 mg/kg) were injected intraperitoneally (i.p.) either at 0700 or 1900 h. Baseline SBP/DBP and HR showed significant circadian rhythmicity in both strains. The 24-h means in SBP/DBP were 190/127 mm Hg in SHR and 200/139 mm Hg in TGR. TGR showed a reversed circadian profile in BP, with peaks occurring during the daily resting period, whereas HR peaked at night. Losartan reduced BP dose dependently; reductions in TGR were significantly greater and obtained at 30-fold lower doses than in SHR. Maximum decreases induced by losartan were similar to those induced with enalapril 10 mg/kg. Both drugs reduced BP in TGR more effectively when applied at 0700 than at 1900 h, resulting in a normalized circadian BP profile. Our results demonstrate that the RAS is involved in both the pathomechanism of hypertension and in the inverse circadian BP pressure pattern in TGR.
mesh_terms: D000804:Angiotensin II / Q000037:antagonists & inhibitors*; D057911:Angiotensin Receptor Antagonists; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology*; D001713:Biphenyl Compounds / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects*; D002940:Circadian Rhythm; D004305:Dose-Response Relationship, Drug; D004656:Enalapril / Q000494:pharmacology; D006973:Hypertension / Q000188:drug therapy / Q000503:physiopathology*; D007093:Imidazoles / Q000494:pharmacology*; D019808:Losartan; D008297:Male; D051381:Rats; D011918:Rats, Inbred SHR; D012084:Renin-Angiotensin System / Q000502:physiology; D013777:Tetrazoles / Q000494:pharmacology*
chemical_list: D057911:Angiotensin Receptor Antagonists; D000959:Antihypertensive Agents; D001713:Biphenyl Compounds; D007093:Imidazoles; D013777:Tetrazoles; D000804:Angiotensin II; D004656:Enalapril; D019808:Losartan