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In order to determine the effects of varying doses of disodiumphosphate on the electrical activity of heart, a series of experiments were performed on 1 40 frogs (bufo bufo) during two summers and winters, (weighing Ca, 45-65 gin.)
Before each injection which was performed once in every 24 hours, an electrocardiogram (ECG) recording was obtained from each animal, Then 0.5 ml increasing concentration of disodiumphosphate (Na2 HPO4, 2H20) was injected subcutaneously in the dorsal region of the frogs. Thus each animal received 2.5, 3.75, 5.0, 7.5 and 10 mg of phosphate respectively.
In general, alterations in the pattern of ECG due to increasing dosages of phosphate, being essentially similar in all the animals, were as follows:
After the injection of the 2.5 mg dose, the P wave became shorter and less distinct. The height of QRS complex decreased and that of T wave increased. Thereis also a decrease in the heart beat. 24 hours after the injection, the P and T waves became more distinct, with the T wave occasionally showing positive polarity. Also, the height of QRS seemed to have increased relative to control animal and the
* This paper is published in detail in Persian, in this Journal, pp. 66-78.
recording from the previous day. The S—T distance and the cardiac rhythm approached the control condition with occasional tachycardia.
The observed alterations after the 3.75 mg dose were the same as those for 2.5 mg; but the intensity of alterations increased by increasing dosage. The toxic dose gave similar results but the response time was considerably faster.
Interestingly, when the experiments were done during the winter and early spring, the animals were able to endure repeated injections. Also 40 minutes after receiving the dose of 5 and 7.5 mg, tetanic contractions were often observed which could be eliminated by injection of 5 mg of CaC12.
Second series of experiments were performed on spinal frogs. The doses and other methods were the same as those used in the first series. Compared to the first series some differences in the results were observed. Often the height of QRS complex decreased after each injection; the S—T distance increased but the heart beat decreased. However, by 24 hours after the injection significant changes in the QRS complex and the heart beat were noticeable.
The spinal animals showed higher resistance to the increasing doses of phosphate, but in these animals the tetanic contractions were similarly observed.
It was also observed that spinal animals receiving phosphate lived longer than normal animals.
In general, it can be concluded that disodium phosphate can affect the electrical activites of the heart and that the nature of the effect is partly related to the influence of higher neural centers.