Being led by the facts first that application of severe external cold upon the animal (dog) body such as to cause the body temperature to fall below 30°C. causes clearly an acceleration in the epinephrine output rate from the suprarenal gland, and secondly it produces on the other hand some definite changes in the arterial blood pressure, the pulse rate and the blood sugar concentration, the present investigations were made for elucidating what rôle is played by the augmented epinephrine secretion in the alterations in the circulatory systems and in the carbohydrate metabolism.
(1) Small dog was dipped into a cold bath of about 0.5°C., without fastening it on the board or narcotizing, but gently handled by two assistants, until the anal temperature fell to about 30° or often about 28-25°. The arterial blood pressure was continuously recorded by means of a mercury manometer or a Hürtle's; dipping was interrupted from time to time for taking blood samples and anal temperature measurement.
After the final withdrawal from the icewater bath the body temperature continued further to fall for a while with subsequent gradual recovery. The arterial blood pressure ascended promptly to about 200mms. Hg. or higher, but it began to fall somewhat gradually, in parallel with the body temperature fall, and in a later period it fell under the initial level. The pulse rate increased promptly on dipping, usually over 200 beats per minute, but it soon turned to decrease in parallel with the body temperature fall, and when the body temperature inclined to recover, the pulse rate began to increase and in fact there was some large acceleration, of 20-40 beats per minute and of a duration of some ten minutes in the early stage of the recovery. The blood sugar content increased rather slowly, but it recovered the initial value before the body temperature was restored.
The removal of the suprarenal medulla exaggerated the body temperature fall, the blood pressure fall and the bradycardia, the acceleration of the pulse rate in the recovery period being largely reduced too, and prolonged the hyperglycaemic period.
Introduction of adrenaline hydrochloride-saline solution in the magnitude and time relation corresponding to the epinephrine output causable by severe cooling, abolishes these variations due to the loss of the suprarenal medulla. Otherwise expressed; the augmented secretion of epinephrine from the suprarenal glands on cooling the dog excessively, acts to moderate the fall of the body temperature, that of the arterial blood pressure, and the retardation of the heart beat. The hyperglycaemic period is cut short too; this might be accounted for by the other sequences above referred to.
In connection with the above experiments, the following ones were carried out.
(2) By use of avertin, excitement and struggling on dipping the dog into the cold bath was entirely avoided, but the blood pressure elevation and the tachycardia occurred although much weaker than in the dog non-narcotized. The hyperglycaemia was of similar degree to that in the dog under avertin.
(3) Cold water was introduced into the stomach of the dog directly through the stomach fistula previously prepared in such an amount as to cause a heat debt of about three thousand small calories per kilo of body weight. It resulted in a remarkable tachycardia, such as 20-70 beats per minute and often a hypertension of 20-40 mms. Hg. Latencies were longer in comparison to the dipping experiment above quoted. A slight hyperglycaemia slowly developed too.