Action of sympathomimetic drugs on the isolated junction of the bile duct and duodenum

The actions of adrenaline, noradrenaline and phenylephrine were studied both on the terminal tract of bile duct (prepared as spiral strips or intact) and on the adjacent duodenum taken from the calf and the cat. These amines contract the terminal bile duct and relax the duodenum. Furthermore, on the basis of the action of some adrenaline antagonists, the hypothesis is advanced that there are alpha-receptors which mediate contraction of muscle in the sphincterial zone of the bile duct.

DRUG ACTION ON PULMONARY CIRCULATION OF UNANESTHETIZED DOGS

A preparation is described which overcomes most of the difficulties previously encountered in the assessment of vasomotor responses of the pulmonary vessels to pharmacologic agents. The use of electromagnetic flow transducers on the main and left pulmonary arteries allows for the observation of immediate local effects following unilateral drug administration before general systemic effects occur. The opposite lung serves as a control, since it is subjected to the same changes of left artrial pressure, pulmonary arterial pressure, and pulmonary blood flow as the test lung. Our studies have demonstrated a direct pulmonary vasoconstrictor response to 5-hydroxytryptamine and acetylcholine in both the conscious and anesthetized dog. Epinephrine was also shown to have a direct pulmonary vasoconstrictor activity, but this could be elicited in only three of the eight dogs studied. Isoproterenol, methoxamine, aminophylline, phenylephrine, γ-amino butyric acid and pentobarbital had no apparent direct pulmonary vasomotor effect.

PHOTOSENSITIVITY OF THE FROG IRIS

The absorption of quanta by rhodopsin leads to the contraction of frog iris muscle. The contractions reach a maximum after about 8 sec. in the light. When the light is turned off the irises relax exponentially with a half-time of about 6 sec. Membrane polarization is not necessary for the response but calcium movement and membrane permeability changes probably are. The response is not mediated by acetylcholine or epinephrine. The curves of log It vs. log t for constant response amplitude bend progressively upward away from a unit slope line at short times as larger response criteria are used because (a) light influences tension development over longer times and (b) the higher intensity, shorter duration flashes are less effective.

ACTIONS OF SYMPATHOMIMETIC DRUGS ON THE SMOOTH MUSCLE AT THE JUNCTION OF THE BILE DUCT AND DUODENUM STUDIED IN SITU

The actions of adrenaline, noradrenaline, phenylephrine and isoprenaline have been examined on flow through the terminal bile duct and on the tone of the duodenum in the vicinity of the terminal bile duct. These drugs were injected intravenously, or intra-arterially into the blood supply of the junction of the bile duct and duodenum. The effects of the antagonistic drugs, dibenamine and dichloroisoprenaline, were also tested. Isoprenaline always relaxed the duodenum and increased the flow through the bile duct. Adrenaline, noradrenaline and phenylephrine relaxed the duodenum, but had variable effects on the flow through the bile duct. It is concluded that adrenaline acts directly on the smooth muscle of the bile duct to contract it, but the influence of the neighbouring duodenal muscle may nevertheless result in an increase in flow through the duct.

RELATIVE ROLES OF THE SYMPATHETIC AND PARASYMPATHETIC NERVOUS SYSTEMS IN THE REFLEX CONTROL OF HEART RATE

This study was designed to define the relative roles of the sympathetic and parasympathetic nervous systems in the reflex alterations of heart rate consequent to changes in arterial pressure. In 23 experiments carried out on 22 anesthetized dogs and in studies performed on four trained, unanesthetized dogs, acute changes in arterial pressure were produced by administering drugs acting on the peripheral vascular bed. The effects of acutely elevating systemic pressure were also investigated in four intact unanesthetized human subjects. Augmenting arterial pressure above control levels with graded doses of phenylephrine always slowed heart rate strikingly. Although complete sympathetic blockade with guanethidine or pronethalol did not significantly alter the degree of slowing, parasympathetic blockade with atropine or vagotomy essentially abolished this response. Conversely, lowering pressure with intravenous injections of nitroglycerin always raised heart rate in the control state, a response abolished by sympathetic blockade with guanethidine or nethalide, but not by parasympathetic blockade with vagotomy or atropine. Thus, when arterial pressure rises above control, the decrease in heart rate is mediated by the parasympathetic nervous system, withdrawal of sympathetic activity playing no detectable role; when pressure falls below control levels, the elevation of heart rate is mediated primarily by the sympathetic nervous system. These findings are not consonant with the traditional concept of control of heart rate which predicates simultaneous reciprocal changes in activity occurring in the two components of the autonomic nervous system.

HEMODYNAMIC DETERMINANTS OF THE AMPLITUDE OF THE FIRST HEART SOUND

The relationships between the amplitude of the first heart sound and various hemodynamic parameters and their analog functions were systematically investigated in 51 dogs under morphine and pentobarbital anesthesia. Simultaneous hemodynamic and phonocardiographic tracings were obtained by cardiac catheterization, high speed recording, and analog computers. Changes in cardiodynamics were induced by: l -epinephrine, levarterenol, phenylephrine, isoproterenol, methoxamine, veratrine, vasopressin, histamine, atropine, saline infusion, mechanical obstruction of the aorta, pulmonary artery, or both venae cavae, embolization of the coronary arteries with plastic microspheres, mechanical rupture of aortic valve leaflets, or hemorrhage. In this way, the relationships were examined over a wide range of pressures, volumes, and cardiodynamics. The results showed that the amplitude of the first sound is not directly related to stroke output, P-R interval, heart rate, end diastolic, or systolic ventricular or aortic pressures. Only the peak rate of rise of left ventricular systolic pressure (first derivative maximum) had a consistent relationship to first sound amplitude. The right ventricle seems to contribute very little to the external first sound. These observations suggest that the amplitude of the first sound is related to left ventricular contractility.