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The aim of this study was to investigate the mechanisms of the cardiodepressive action of ionic and non-ionic contrast media currently used in coronary arteriography. Experiments carried out on isolated preparations of cat papillary muscle, treated with increasing concentrations of Telebrix 39, Radioselectan, Hexabrix and Iopamidol 370 and 300, on the one hand and, on the other hand, a pre-determined dose of Telebrix and Iopamidol 300 during hypoxia and subsequent reoxygenation, showed that, at constant Ca2+ concentrations: (1) The cardiodepressive effects of contrast media are correlated with the hyperosmolality that they induce. When osmolality was higher than 400 mOsm, all the products caused a reduction of the peak force (PF: 40.49 +/- 5.15%), the maximum velocity of contraction (Vmax: 39.85 +/- 3.66%) and of the peak velocity of relaxation (Vrelax: 23.30 +/- 2.20%) (P less than 0.01). The time to peak force (TPF), on the other hand, remained constant, whereas the half-relaxation time (THR) was increased. No significant differences were observed between these effects and those induced by control iso-osmolar solutions when the same osmolality was induced. In practice, however, the critical hyperosmolality value of 400 mOsm is never reached when using non-ionic contrast media such as Hexabrix and Iopamidol 300. This could explain the excellent tolerance to these substances. (2) During hypoxia and reoxygenation, the effect of hyperosmolality is more marked. Thus, the non-ionic contrast medium, Iopamidol 300 (340 mOsm), reduces the hypoxic contractility depression (PF: 53.10 +/- 2.60% compared to the control values of 47.60 +/- 5.00%, P less than 0.01), whereas, at the same dose, the ionic medium Telebrix is hyperosmolar (440 mOsm) and induces a more pronounced hypoxic depression of contractility (P less than 0.01). The critical hyperosmolality is never reached during ventriculography (320 mOsm), whatever the medium used, but it can be observed during coronary arteriography. It is, therefore, important to use non-ionic contrast media in the investigation of unstable angina and of acute myocardium infarction.

The purpose of the present study was to investigate the effects of low concentrations of nifedipine on the cat myocardium under normal conditions, and during hypoxia with subsequent reoxygenation, and, thus, to find out whether the protective effect on hypoxic myocardium described by different investigators existed at these levels. Experiments carried out on five series of each 10 papillary muscles showed that: (1) Nifedipine (0.02 μg/ml) exerted a negative ino tropic effect on maximum unloaded velocity of shortening and total force (Vmax: 92.91 ± 2.92%; PF: 92.10 ± 2.60%), whereas depression of peak velocity of relaxation became marked only at 0.2 μg/ml (Vrelax: 88.87 ± 3.91%). This dose-dependent effect is also Ca$ $-dependent. (2) Nifedipine (0.02 μ/ml) protected against the depression of Vmax, PF and Vrelax during hypoxia (PO2 = 25 mm Hg) Vmax: 82.60 ± 3.45% v. 78.45 ± 1.35% control; PF: 54.65 ± 4.41% v. 48.74 ±3.51% and Vrelax: 92.55 ± 4.50% v. 68.47 ± 1.30%). (3) The association of nifedipine (0.02 μ/ml) and nitroglycerin (0.3 μ/ml) accelerated the recovery of the depression of peak velocity of relaxation during reoxygenation (Vrelax: 99.90 ± 5.63% v. 89.96 ± 5.15% nifedipine alone).