Effects of rosuvastatin on cardiovascular morphology and function in an ApoE-knockout mouse model of atherosclerosis.

This study investigated the effects of rosuvastatin on plaque progression and in vivo coronary artery function in apolipoprotein E-knockout (ApoE-KO) mice, using noninvasive high-resolution ultrasound techniques. Eight-week-old male ApoE-KO mice (n = 20) were fed a high-fat diet with or without rosuvastatin (10 micromol.kg(-1).day(-1)) for 16 wk. When compared with control, rosuvastatin reduced total cholesterol levels (P < 0.05) and caused significant retardation of lesion progression in the brachiocephalic artery, as visualized in vivo using an ultrasound biomicroscope (P < 0.05). Histological analysis confirmed the reduction of brachiocephalic atherosclerosis and also revealed an increase in collagen content in the statin-treated group (P < 0.05). Coronary volumetric flow was measured by simultaneous recording of Doppler velocity signals and left coronary artery morphology before and during adenosine infusion. The hyperemic flow in response to adenosine was significantly greater in left coronary artery following 16 wk of rosuvastatin treatment (P < 0.001), whereas the baseline flow was similar in both groups. In conclusion, rosuvastatin reduced brachiocephalic artery atherosclerotic plaques in ApoE-KO mice. Coronary artery function assessed using recently developed in vivo ultrasound-based protocols, also improved.

Candesartan Causes Long-lasting Antagonism of the Angiotensin II Receptor-mediated Contractile Effects in Isolated Vascular Preparations: a Comparison with Irbesartan, Losartan and its Active Metabolite (EXP-3174).

Candesartan is a new angiotensin II type 1 (AT 1 ) receptor blocker. It displays insurmountable antagonism of angiotensin II responses, binding tightly to and dissociating slowly from the AT 1 -receptor. The purpose of this study was to compare the duration of angiotensin II antagonism by the AT 1 -receptor blockers candesartan, irbesartan, losartan and its active metabolite EXP-3174 in an isolated tissue preparation. The contractile response to angiotensin II was studied in the isolated portal vein of the rat, during incubation with AT1-receptor blockers and after an extensive washout period. The portal vein preparation was pre-stretched to a passive force of 5 mN in an organ bath filled with oxygenated Krebs' buffer at 37°C. The contractile tension developed by the vascular smooth muscles was monitored using a force-displacement transducer. The contractile response to repeated administration of angiotensin II was recorded before, during and following exposure (for 30-180 min) to candesartan, 0.1-1 nmol/l, irbesartan, 1-50 nmol/l, losartan, 30-100 nmol/l, and EXP-3174, 1-10 nmol/l. Drug exposure was followed by washing for up to 2 h. Candesartan produced a long-lasting blockade of the vascular contractile response to angiotensin II, as shown by maintenance of inhibition during the washout period. This effect of candesartan was independent of drug concentration and exposure time prior to washing. Irbesartan, losartan and EXP-3174 also blocked the angiotensin II-mediated contraction. However, in contrast to candesartan, the responses to angiotensin II rapidly returned towards baseline values during the washout period. The relatively short-lasting blockade by irbesartan, losartan and EXP-3174 was also independent of drug concentration and exposure time prior to washout. It is concluded that the AT 1 -receptor blockers differ in their ability to inhibit angiotensin II-mediated vascular contraction, with candesartan producing longer-lasting blockade than irbesartan, losartan and EXP-3174. The mechanism of the persistent inhibitory effect of candesartan is at present unclear. Possible explanations include tight binding and slow dissociation from the AT 1 -receptor, tissue accumulation resulting in 'local( dissociation and reassociation to the AT 1 -receptor, and stimulation of internalization of the AT 1 -receptor.

Mechanistic differences of various AT1-receptor blockers in isolated vessels of different origin.

The functional inhibitory characteristics of the angiotensin II type 1 receptor blockers (ARB) candesartan; irbesartan; and losartan and its active metabolite EXP 3174 (EXP) were studied in rabbit aortic strips and rat portal vein preparations in vitro. Moreover, plasma-protein binding was determined, and the binding was high (>98. 5%) for all ARBs. These values were needed to relate the concentrations of the ARBs used in vitro to the nonprotein bound concentrations in clinical use. In both vascular preparations, candesartan caused a marked decrease in the maximal contractile response of the angiotensin II (Ang II) concentration-response curve. Losartan, EXP, and irbesartan caused a rightward parallel shift without any major effects on the maximal response to Ang II. The inhibitory effect of candesartan developed slowly (maximal effect after >30 minutes) and lasted >2 hours despite repeated washing of the vessels. The effect of losartan, irbesartan, and EXP had a faster onset, and most of the inhibitory effect disappeared after washing. The duration of the inhibitory effects of the ARBs were not related to lipophilicity of the compounds. Cooling of the rat portal vein preparations to 4 degrees C before administration of candesartan prevented the persistent inhibition of Ang II response seen at 37 degrees C. For the other ARBs studied, the magnitude of inhibition and the speed of recovery of the Ang II response were independent of the incubation temperature before washing. In addition, when candesartan was given to conscious rats, the inhibitory effect on Ang II-induced blood pressure responses persisted during the 24-hour period despite nondetectable plasma concentrations of candesartan at 24 hours. It is concluded that functional inhibitory characteristics of candesartan differ from those of the other ARBs tested. At clinically relevant concentrations, candesartan is an insurmountable and long-lasting antagonist of the vascular contractile responses to Ang II.