Calcium-channel blockers are widely used in the treatment of systemic sclerosis (SSc), but their in vivo influence on microcirculation is not fully elucidated. We evaluated the acute effect of nifedipine on the cold-induced changes of microvascular dynamics in SSc. Eleven SSc patients and seven healthy volunteers were studied. Dynamic aspects of the nailfold microcirculation (appearance time at the nailfold, transcapillary diffusion, interstitial distribution and interstitial clearance of sodium fluorescein given i.v.) were quantitatively assessed by a computer-aided fluorescence videomicroscope. Fluorescent light intensities (FLIs) at predefinite pericapillary and interstitial sites were measured under three experimental conditions: (1) baseline; (2) after cold test; (3) after single oral administration of 10 mg of nifedipine 5 min before cold exposure. The interval between the intravenous injection of sodium fluorescein and the first appearance of the dye at the nailfold significantly increased after cold exposure in the SSc patients (224.1 +/- 182.3 s vs 27.5 +/- 25.1 s at baseline) (P = 0.0026), but not in the controls (28.0 +/- 13.3 s vs 29.6 +/- 12.4 s at baseline). The effect of cold exposure on the appearance of the dye was not significantly antagonized by nifedipine (112.7 +/- 91.8 s) in the SSc patients (P = 0.07). Cold exposure significantly decreased transcapillary diffusion and interstitial distribution of sodium fluorescein in the SSc patients (P < 0.016), but not in the controls. The cold-induced changes of FLI values were antagonized by nifedipine in the SSc patients (P < 0.016), but not in the controls.(ABSTRACT TRUNCATED AT 250 WORDS)