Distribution of 14C-gentamicin in vascular smooth muscle

Evaluation of contraction time and recovery period as a parameter in the calcium antagonistic action on the K(+)-depolarized rat duodenum

Verapamil, nifedipine, phentolamine, tolazoline, gentamicin and neomycin inhibited calcium-induced contractions of K(+)-depolarized duodenum of rat by shifting the concentration-response curves to the right. Non-competitive inhibitions were observed with trifluoperazine, lidoflazine, procaine and tetracaine. Lanthanum behaved as a partial agonist in this preparation, while nitroprusside was ineffective. Contraction times in the presence of the antagonists and recovery time of the Ca2+ responses after the removal of the antagonists from the bathing medium were evaluated. From the findings, it is suggested that the contraction time and the time required for tissue recovery after removal of a Ca2+ antagonist are parameters making K(+)-depolarized rat duodenum a potential tool for the evaluation of the pharmacological effects of Ca2+ antagonists.

Reduction of experimental gentamicin nephrotoxicity in rats by dietary calcium loading

Since gentamicin accumulates in the renal cortex before renal failure and calcium reduces gentamicin binding to cell membranes, we examined the effect of dietary calcium loading on gentamicin toxicity in male F344 rats. Rats were fed either a normal (0.5%)- or a high (4%)-calcium-content chow. Calcium loading did not alter inulin clearance, urinary excretion of sodium or total osmoles, or serum ionized calcium. However, calcium loading caused elevation of urinary calcium excretion and lowered urinary cyclic AMP levels. The data suggest that calcium loading may have slowed the accumulation of gentamicin (40 mg/kg per day) by the renal cortex. Histological and functional evidence of nephrotoxicity was delayed in onset and attenuated in magnitude. The results indicate that dietary calcium loading reduces experimental gentamicin nephrotoxicity. Protection may be associated with slower renal cortical accumulation of gentamicin. Calcium-dependent membrane or intracellular events may mediate this effect.

A comparison of the influence of La3+, D600 and gentamicin on frequency-force relationships in isolated myocardium

The capability of heart muscle to respond mechanically to changes in frequency of stimulation was studied in the absence and in the presence of La3+, D600 and gentamicin using left atrial preparations of guniea pigs. L3+ (0.5 x 10(-3) M) and gentamicin (1 x 10(-3) M) depressed the basal contractile state at 1.0 Hz by about 90% (EC90), and inhibited the positive inotropic response to increased driving rate throughout the frequency range that was studied (0.1--2.2 Hz). In contrast, a comparable concentration of D600 (1.05 x 10(-6) M) reduced inotropic responses to high rates of stimulation (> 1.4 Hz) more than responses to low rates (< 0.8 Hz). Muscles exposed briefly (20 min) to an EC90 of La3+ or D600 failed to regain 50% of basal inotropy after one h rinse in normal medium; whereas, muscle exposed to gentamicin recovered 50% inotropy in approximately 5 min. Effects of D600 and La3+ on the frequency-force relationship were not abolished after 1.5--2 h recovery of the muscles in normal solution, but the effects of gentamicin were easily removed by the same recovery procedures. These data indicate that: (1) the cardiodepressant actions of La3+ and D600 were poorly reversible after in vitro treatment, and these actions were manifested at cellular loci essential for normal contractile responses to changes in heart rate, and (2) the cardiac actions of gentamicin were reversible and could be differentiated from the more complex actions of both D600 and La3+.