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  • Title: Divergent renal vasodilator action of L- and T-type calcium antagonists in vivo.
    Author: Honda M, Hayashi K, Matsuda H, Kubota E, Tokuyama H, Okubo K, Takamatsu I, Ozawa Y, Saruta T.
    Journal: J Hypertens; 2001 Nov; 19(11):2031-7. PubMed ID: 11677369.
    Abstract:
    OBJECTIVE: To assess the in-vivo action on the renal microvasculature of the calcium antagonists nifedipine (L-type blocker), efonidipine (L/T-type blocker), and mibefradil (predominant T-type blocker). DESIGN: An intravital needle-type charge-coupled device (CCD) camera videomicroscope was introduced to visualize the renal microcirculation directly in vivo. METHODS: In anesthetized mongrel dogs, nifedipine (0.01-1 mg/kg per min), efonidipine (0.033-0.33 mg/kg per min), or mibefradil (0.01-1 mg/kg per min) was infused intravenously after the insertion of a CCD probe into the kidney. Renal microvascular responses to calcium antagonists were directly evaluated, with concomitant observation of renal clearance. RESULTS: Each calcium antagonist caused modest vasodepressor action without affecting heart rate. Nifedipine (1 mg/kg per min, n = 9) increased renal plasma flow (RPF) (14 +/- 4%, P < 0.05) and glomerular filtration rate (GFR) (19 +/- 5%, P < 0.05), and tended to increase the filtration fraction (5 +/- 2% increment, P = 0.07). Efonidipine (0.33 mg/kg per min, n = 9), however, had no effect on filtration fraction, with 14 +/- 6% increments in RPF (P < 0.05) and 14 +/- 7% increments in GFR (P = 0.08). Rather, mibefradil (1 mg/kg per min, n = 9) elicited 6 +/- 2% decreases in filtration fraction (P < 0.05), with slight increments in RPF (6 +/- 3%) and no changes in GFR. In direct in-vivo microvasculature observations, nifedipine caused predominant (22 +/- 2%) dilatation of afferent arterioles (from 15.5 +/- 0.4 to 18.9 +/- 0.4 microm, n = 5), compared with that of efferent arterioles (10 +/- 2%; from 11.0 +/- 0.4 to 12.1 +/- 0.3 microm). In contrast, efonidipine caused a similar magnitude of vasodilatation (16 +/- 4%) compared with 18 +/- 2%; n = 6), and mibefradil caused greater dilatation of efferent arterioles (20 +/- 4%, n = 7) than that of afferent arterioles (13 +/- 4%). CONCLUSIONS: There exists marked heterogeneity in action of nifedipine, efonidipine and mibefradil on the renal microvascular in canine kidneys in vivo. Furthermore, our current observations suggest an important contribution of T-type calcium channel activity to efferent arteriolar tone in vivo.
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