In vivo receptor binding of benidipine and amlodipine in mesenteric arteries and other tissues of spontaneously hypertensive rats

Abstract

The present study was undertaken to characterize the in vivo 1,4-dihydropyridine (DHP) receptor binding of long-acting 1,4-DHP calcium channel antagonists in the mesenteric artery and other tissues of SHR. In vivo specific binding of (+)-[ 3H]PN 200–110 in the SHR mesenteric artery was significantly (36.6–49.7 %) reduced 1–8 h after oral administration of benidipine (1.84 μmol/kg). A greater reduction in (+)-[ 3H]PN 200–110 binding in the mesenteric artery was observed at a higher dose (5.53 μmol/kg) of this drug. This dose of benidipine also reduced significantly the in vivo specific (+)-[ 3H]PN 200–110 binding in the aorta but not in the myocardium and cerebral cortex. Following oral administration of amlodipine (17.6 μmol/kg), a significant (51.7–94.2 %) reduction in (+)-[ 3H]PN 200–110 binding was seen at 1–18 h in the mesenteric artery and at 1–12 h in the aorta. Only a slight reduction in myocardial and cerebral cortical (+)-[ 3H]PN 200–110 binding was seen following amlodipine administration. In contrast, oral administration of nifedipine (28.9 μmol/kg) reduced markedly in vivo (+)-[ 3H]PN 200–110 binding in all the tissues of SHR at 1–6 h, and the degree and time-course of the reduction did not differ significantly among the tissues. The area under the curve (AUC) for the receptor occupancy vs time was calculated from the reduction rate (%) of in vivo specific (+)-[ 3H]PN 200–110 binding. The ratios of the AUCmesenteric artery to AUCaorta or AUCmesenteric artery to AUCmyocardium after oral administration of benidipine and amlodipine were greater than the corresponding value for nifedipine. The degree and time-course of arterial receptor occupancy by benidipine and amlodipine agreed well with those of their hypotensive effects in the conscious SHR. In conclusion, the present study demonstrates that benidipine and amlodipine may occupy, in a more selective and sustained manner, 1,4-DHP receptors in arterial tissues than in other tissues of SHR, and thus, such receptor binding specificity may be responsible for the long-lasting hypotensive effects of these drugs.