[Study of combined effects of mixtures of pesticides from various chemical groups on calcium absorption in the rat intestine. I. Dichlorvos and thiram].

Investigation was made of the effect of many-times repeated treatment with single pesticides: tiuram and dichlorfos (administered in a daily dose corresponding to 5% of LD50), and with their mixture, on calcium uptake by rat duodenum sections. Calcium uptake was examined by the method of Papworth and Patrick, as modified by the present authors. The amount of calcium transported by the sections was determined by the liquid scintillation method. Total transport was expressed in microM Ca2+/g tissue/h; subsequently, the participation of active and passive transport in total transport was determined. It was shown that administration of DDVP to rats during 14 days caused disturbances in active absorption of calcium, manifesting themselves by a significant decrease in the constant Jm (maximal transport rate) and in the constant Kt, this pointing to a rise of calcium affinity to the carrier. The effect of DDVP on passive transport was only slight. Under the same experimental conditions tiuram exerted an effect on both active and passive calcium transport. It caused a drop in the constant Jm and Kt (active transport), and to inhibition of passive transport. According to statistical treatment of the results, the effect of both pesticides combined on active transport does not differ from the effect of DDVP itself. Thus, the differences in diffusion probably result from the action of tiuram.