Failure of heart rate response to cardioaccelerator nerve stimulation in Siamese cats.

Heart rate responses during stimulation of the cardioaccelerator nerves were compared using Siamese and non-Siamese cats. The positive chronotropic responses of Siamese cats during activation of the cardioaccelerator nerves were significantly less than that observed for non-Siamese cats. There were no differences between the two cat populations when vasopressor and chronotropic responses to norepinephrine were cmpared. Comparison of atria from Siamese and non-Siamese cats using histochemical fluorescence indciated that there was a decreased norepinephrine content of the sympathetic nerves innervating the atria of Siamese cats.