Vago-sympathetic innervation of the heart of the puff adder,bitis arietans

Abstract 1. 1. The effects of drugs and vagal simulation on the rate of the perfused heart in situ and on the heart rate and arterial blood pressure in vivo were studied in the puff adder. Fluorescent histochemistry of the catecholamines in the different parts of the heart was also performed. 2. 2. The ventricle, atria and sinus venosus are all densely innervated by adrenergic fibres. Adrenergic fibres around coronary vessels were also observed by fluorescent histochemistry. 3. 3. The adrenergic fibres reach the heart together with the vagi, and may join the vagi from the sympathetic chains. No direct sympathetic fibres to the heart were seen. 4. 4. Acetycholine causes bradycardia or cardiac arrest, and also arrythmia, while isoprenaline, adrenaline and noradrenaline increase the heart rate both in situ and in vivo . Vagal stimulation normally causes bradycardia or cardiac arrest, but in some cases a tachycardia was seen. Tachycardia during vagal stimulation was normally seen after pretreatment with atropine in vivo . 5. 5. Reflex bradycardia in response to elevated blood pressure due to injection of noradrenaline or phenylephrine was seen only occasionally.