According to the present knowledge in magnesium pathobiochemistry with regard to NIHL a protective effect of magnesium on the noise affected hair cell is probably. In order to prove this effect statistically we estimated the frequency depending permanent threshold shift (PTS) by means of measurement of acoustically evoked brainstem potentials of27 "industrial-noise" exposed guinea pigs, 15 guineapigs received a 300 ppm Mg-diet and 12 animals a 2000 ppm Mg-diet respectively. The quality of noise: 4 weeks exposure 8 hours daily; frequency range from 1,0 kHz to 31,5 kHz; noise peak level 95 dB. The "magnesium-status" of the animals was estimated by means of magnesium analysis (atomabsorption) in serum, erythrozytes and myocardium. The PTS under magnesium-deficiency was highly significant greater in comparison with PTS of normal magnesium-nourished animals (WILCOXON rank sum test). In accordance with the present knowledge we recommend the magnesium-prophylaxis for noise-exposed risk groups.

The influence of nimodipine (Nimotop, CAS 66085-59-4), a selectively cerebrovascularly acting 1,4-dihydropyridine calcium antagonist, on the cochlear blood flow (CBF) was studied in 19 guinea pigs (6 controls). The hydrogen clearance measurements were carried out under alpha-chloralose-ethylurethane anaesthesia, artificial respiration with simultaneous control of electrocardiogram, blood pressure, body temperature and arterial pH (hourly). The indirect measurement of CBF was carried out by means of hydrogen clearance in the perilymphatic space (basal turn) before and after intravenous application of 1 microgram nimodipine/kg/min. The mean arterial blood pressure remained within the +/- 5% range of the initial value during the experiment. Under treatment with nimodipine the CBF showed a non-significant average increase of 4.69% and under placebo (20% ethanol, 17% polyethylenglycol 400, citrate buffer), a non-significant average decrease of 6.16%. The influence of nimodipine on CBF was underlined by the overcompensation of the placebo effect.