Walter J. Meek

Rôle of Thyroid in Cyclopropane-Adrenalin Tachycardia.

Summary Following thyroidectomy the duration of cyclopropane-adrenalin tachycardia was decreased in the dog. In the hyperthyroid state the period of tachycardia was longer than in the control.

Effect of Benzedrine Sulphate on Stomach Activity and Emptying Time.

Benzedrine sulphate is used clinically for the relief of pyloro-spasm and the facilitation of fluoroscopic and roentgenoscopic examination. Meyerson and Ritvo 1 reported that the drug brought about satisfactory disappearance of spastic manifestations in 85% of their cases. On the other hand ephedrine sulphate, a closely related sympatho-mimetic compound, in doses of 65 mg. was reported by Van Liere, Lough, and Sleeth 2 as prolonging the emptying time of the stomach from 72.8 to 118%. We were interested in determining the effect of benzedrine on initial and final emptying intervals and to what factors this action might be attributed. Two series of fluoroscopic studies were carried out on normal dogs. Dogs in series A were selected for long initial opening intervals and were fed an opaque meal of 4.1 gm. of barium sulphate and 12.1 gm. of milk per kilo. The dogs weighing from 8.5 to 10 kilos were given 20 mg. of benzedrine orally; those from 10 to 14 kilos were given 30 mg. Dogs in series B were fed a thicker meal of 4.1 gm. barium sulphate, 5 gm, of powdered dog biscuits, and 12.1 gm. of milk per kilo of body weight. These were litter mates and weighed within 2 kilos of each other. They were all given 30 mg. doses of benzedrine, orally. In both series the interval between the time the drug was given and the opaque meal fed was from 10 to 15 minutes. Table I summarizes the data concerning the effect of benzedrine sulphate on initial emptying of the stomach. In series A benzedrine reduced the average interval between the time the meal was given and its appearance in the intestine to 30.8% of the normal.

Effect of a Previous Distention of the Intestine on Reflex Inhibition of Gastric Motility.

In studying the nerve pathways involved in the reflex inhibition of hunger contractions by distention of a Thiry fistula loop in the dog, 1 it was noticed that a previous long-continued distention of the loop brought about a lower threshold for the reflex. In the experiments here reported, five animals were prepared with Thiry fistulae in the usual manner, the loops being 15-20 cm. long and taken from the upper ileum. After complete recovery the dogs were trained to swallow a stomach tube and to lie quietly on the table without any restraint. Gastric movements were recorded by the customary balloon-tambour method. The intestinal loops were distended by air inflation of a thin-walled balloon which was over-size relative to the lumen of the gut. The balloon was tied over a glass rod so that the expansion would be entirely lateral and the pressure readings would closely approximate the pressure actually applied to the intestinal wall. All records were made after a fasting period of 18-24 hours. In testing for inhibition of gastric motility the intestinal loops were inflated for a short period, usually 10-30 seconds. In sensitizing or reinforcing the reflex, the loops were subjected to a continuous pressure of 75 mm. Hg. for 24 hours, following which tests were again made. The essential results may be seen in Table I and Fig. 1. In the control experiments pressures in the loops of 75 to 120 mm. Hg. produced inhibition of gastric movement in 25 out of 55 tests. Each dog responded about half the time, the percentage of responses increasing somewhat with the higher pressures. It was noted that hunger contractions of type 2 were most easily affected. Often there was a marked lowering of tonus with the presence of smaller contractions at this lower level.

Relationship of Chemical Structure of Sympathomimetic Amines to Ventricular Tachycardia during Cyclopropane Anesthesia

Fifteen additional sympathomimetic amines have been tested for their ability to produce ventricular tachycardia in the dog during cyclopropane anesthesia. In a dosage producing a blood pressure rise equal to that caused by 0.01 mgm. of adrenalin per kilogram, the six primary and secondary amines with a catechol nucleus consistently elicited ventricular tachycardia. Tertiary amines with a catechol nucleus and the other amines used did not cause this irregularity.

The origin of the cardiac impulse in the turtle's heart

Recent work has emphasized the sinoauricular node as the seat of origin of the cardiac impulse in the normal heart. This structure must be considered anatomically as forming a connection or junction between remains of the primitive sinus, which has disappeared as a separate chamber in the mammalia, and the auricle. Since indications of the presence of a sinoauricular junction, composed of tissue differentiated histologically from the ordinary cardiac muscle, is found not only in those hearts in which the sinus has disappeared as a separate chamber, but also in the amphibia and reptiles, where a separate sinus venosus is present, it becomes of essential importance to determine whether or not in these animals the heart beat arises as it does in the mammalian heart, that is in the sinoauricular junction. This problem may be attacked by determining that region which shows initial electric negativity when connected with the string galvanometer. We have had this problem in mind for some time, but have been unable to proceed with it because of the difficulty in securing material with sufficiently large hearts to test this point satisfactorily. Recently we have been able to secure one large turtle in which the heart was of sufficient size. In this the right half of the sinus was 35 millimeters long and 20 millimeters wide at its junction with the left half. We compared the onset of negativity at the sinoauricular junction with the right and left halves of the sinus, and found the junction to precede in negativity. It must be borne in mind, however, that in the exposed heart, automaticity and conductivity may sometimes be abnormal, and a fairly long series of observations will be necessary in order to determine without question, the normal origin of the impulse.