INSULIN AND HEART RATE AFTER SYMPATHECTOMY AND VAGOTOMY

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Abstract
Insulin (35-6 units per kgm.) produced marked acceleration of the heart rate (due to central sympathico-adrenal impulses) in 2 out of 9 normal cats; in the others the heart rate was either unchanged or slowed (owing to central vagus stimulation or peripheral action). In a cat in which the sympathetic chains were removed, the vagi being left intact, the heart rate was retarded by insulin. While after section of the vagi, sympathetics being left intact, the heart rate was so rapid and variable as to make insulin tests unreliable, in 2 out of 3 cats so treated insulin was followed by considerable acceleration. In 2 out of 3 cats (4 out of 5 observations) in which the sympathetics to the adrenals and liver were cut, the cardiac nerves being left intact, insulin slowed the heart rate. Dworkin concludes, in accordance with findings of Bulatao and Carlson, that, while both divisions of the autonomic nervous system may be stimulated during insulin hypoglycemia, the vagus influence predominates in organs innervated by both sets of nerves. In 6 completely sympathectomized cats with heart dener-vated insulin had a delayed action upon the heart rate, manifested in a prolonged, though not marked slowing. This slowing developed gradually, attaining the maximum long after the lowest blood-sugar level had been reached, and some time after injection of glucose. Injected without previous insulin administration, glucose had no definite effect on heart rate in these animals. The slowing could be promptly abolished by atropine sulphate.

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