Theodore Cooper

Histochemical and Chemical Studies of the Localization of Adrenergic and Cholinergic Nerves in Normal and Denervated Cat Hearts

The localization of adrenergic and cholinergic nerves in normal and denervated cat hearts was studied histochemically. The norepinephrine content of atria and ventricles was chemically determined by a spectrofluorometric method. In hearts denervated 9 to 42 days, little or no norepinephrine was detected. Histochemically, many catecholamine-containing fibers were present in the atria and ventricles of normal cats, whereas in denervated cats there were none in one and very few in four. There were many cholinergic nerves in the atria and a small to moderate number in the ventricles. The left atria of denervated hearts showed a marked reduction in cholinergic nerve fibers. It is concluded that cardiac denervation by mediastinal neural ablation is often incomplete. When norepinephrine is not detectable by chemical analysis, individual nerve fibers not sectioned can still be histochemically identified.

Cardiac Norepinephrine Stores and the Contractile State of Heart Muscle

In order to assess the role played by endogenous norepinephrine (NE) stores in the intrinsic contractile state of cardiac muscle, the right ventricular papillary muscles from normal cats and cats with cardiac NE depletion produced by chronic cardiac denervation or reserpine pretreatment were studied. The contractile state of NE-depleted ventricular myocardium was found to be normal. The resting and active length-tension curves, the forcevelocity relations, and the augmentation of isometric tension achieved by paired electrical stimulation and by increasing frequency of contraction were not depressed in either group of NE-depleted muscles. Similarly, no changes in the absolute refractory period and electrical excitability were observed. It is concluded that cardiac stores of NE are not fundamental for maintaining the intrinsic contractile state of the myocardium. Further, release of endogenous NE from cardiac muscle does not appear to play an essential role in the mediation of the positive inotropic effects of increasing frequency of contraction or of sustained postextrasystolic potentiation.

Circulatory Responses to Electrical and Reflex Activation of the Nervous System after Cardiac Denervation

Rigorous testing procedures assessed the extent of extrinsic cardiac denervation in three groups of animals subjected to cardiac extirpation and reimplantation (E&R), mediastinal neural ablation (MNA) or thoracic ganglionectomy (BSTG). After E&R, all dogs were completely denervated. Evidence for vagal reinnervation appeared as early as 26 days and for both vagal and sympathetic reinnervation in 74 days. After one, two and three years, the functional responses to reflex and electrical activation of the nervous system were similar to those in normal dogs. After MNA, only one animal of eight was totally denervated. Seven showed varying degrees of cardiac activation in response to diencephalic stimulation or stimulation of the cardiac sympathetic nerves. Thus MNA, though surgically feasible, cannot be assumed to be successful without rigorous testing. After BSTG, four of eight dogs showed complete separation of sympathetic cardiac outflow from the CNS; in all eight, moderate to large cardio-accelerator responses were elicited from the distal vagosympathetic trunk after atropinization. There is little correlation between the over-all cardiac responses persisting in all operated animals and total cardiac catecholamine content, or between cardio-accelerator responses and right atrial catecholamine content.

Heart Autotransplantation: Effect on Myocardial Catecholamine and Histamine

Complete excision and reimplantation of the canine heart is followed by a fall in myocardial norepinephrine to negligible levels. These decreases are at- tributable to the sympathetic denervation which necessarily accompanies the operative procedure. Myocardial histamine levels in survivors of this operation were not significantly different from those of normal dogs.

Direct Positive Inotropic Effect of Acetylcholine on Myocardium

The effects of acetylcholine and nicotine on isometric tension, in the presence and absence of atropine, hexamethonium, and endogenous norepinephrine stores, were examined in isolated cat atria and papillary muscles. Acetylcholine exerted a negative inotropic effect, competitively inhibited by atropine, in atrial and papillary muscle; in higher concentrations in papillary muscles, it produced a positive inotropic effect that was independent of cardiac norepinephrine stores and that was not blocked by atropine or hexamethonium. Nicotine, in addition to releasing norepinephrine, was found to exert, in higher concentrations, a direct positive inotropic effect, not antagonized by hexamethonium. These data are compatible with the existence of two distinct cholinergic receptors in the myocardium: a muscarinic receptor intimately associated with vagal nerve endings; and a spatially separate receptor, whose stimulation produces responses similar to those produced by nicotine. This hypothesis allows for the reconciliation of much apparently contradictory data concerning acetylcholine and parasympathetic control of the heart; it accounts for the opposite inotropic effects of acetylcholine on atria (negative) and ventricles (positive) and for the opposite effects of vagal nerve stimulation (negative) and exogenous acetylcholine (positive) on ventricular myocardium.

Neural Responses Following Autotransplantation of the Canine Heart

Orthotopic autotransplantation of the canine heart is followed by loss of direct sympathetic and parasympathetic neural regulation. Stimulation of the vagus nerve or stellate ganglion fails to alter cardiac rate.Myocardial catecholamines are depleted and[see figure in the PDF file]hypersensitivity to exogenous l-norepinephrine is present for months.One year after the operation, there is evidence of cardiac reinnervation and return of normal responses to catecholamines.

Studies on Digitalis XIV: Influence of Cardiac Norepinephrine Stores on the Response of Isolated Heart Muscle to Digitalis

On the basis of studies on cardiac tissue removed from animals treated with antiadrenergic drugs, a number of investigators have suggested that the positive inotropic response to digitalis requires norepinephrine in the cardiac muscle. In the present study the action of strophanthidin was studied in isolated papillary muscles obtained from normal cat hearts, from chronic, totally cardiac-denervated, norepinephrine-depleted hearts, and from reserpine-treated, norepinephrine-depleted cats. Complete force-velocity and length-tension curves were recorded. Following the addition of strophanthidin (1.0μg/ml) to the bath, maximum isometric tension rose by averages of 2.17 ± 0.32 g/mm2 in the normal muscles and 2.65 ± 0.50 g/mm2 in the muscles from the denervated cats, but increased significantly less (P < 0.05) in the muscles from the reserpine-treated animals (1.09 ± 0.36 g/mm2). In addition to these changes in isometric tension, strophanthidin increased the maximum velocity of contraction (Vmax) to a comparable extent in normal and denervated muscles, with a smaller elevation of Vmax in reserpine-treated muscles. Strophanthidin reduced the absolute refractory period to an equal extent in all three groups of muscles. From a comparison of the inotropic responses of the muscles from normal and cardiac-denervated cats it is concluded that cardiac norepinephrine stores and neural integrity are not essential for the positive inotropic effect of strophanthidin or for its effects on the duration of the absolute refractory period. However, it appears that prior reserpine treatment may interfere with the inotropic response to digitalis by a mechanism other than norepinephrine depletion.

Work Capacity and Efficiency of the Autotransplanted Heart

Total extrinsic denervation of the heart was accomplished in six animals by cardiac autotransplantation. The work capacity and efficiency were studied in the postoperative period, when there was depletion of catecholamine stores. The left ventricular oxygen consumption (VO2) of these six cardiac autotransplants (average body weight, 13.6±0.6 kg) and six normal dogs (average body weight, 14.0±0.4 kg) were compared with a right-heart bypass at similar heart rates, mean arterial blood pressures, and systemic flows. The two groups of animals achieved comparable levels of stroke work (17.3 g-m) over the same range of filling pressures. Average maximum rates of left ventricular pressure development were also similar (autotransplants 2455±278 mm Hg/sec, versus 2267±209 mm Hg/sec for normal dogs). At VO2/100 g left ventricle, autotransplants averaged 9.54±0.97 cc/min and normal dogs 9.62±0.76 cc/min. However, left ventricular weights in the autotransplant group were significantly greater (110.9±6.2 g) than in the normal dogs (96.7±3.4 g), and represented a significantly greater percentage of body weight (8.2±0.5% versus sus 6.6±0.3%). Total left ventricular VO2 was greater in autotransplants during performance of comparable levels of external work and at comparable degrees of contractility. No systematic difference in handling of glucose, lactate, or pyruvate was noted between the groups. Respiratory quotients were 1.0 or greater. The normal dogs showed no net change in circulating catecholamines across the coronary bed, whereas autotransplants always showed a net uptake of catecholamines. Myocardial mitochondria were enlarged in electron micrographs of the ventricular myocardium of the autotransplants.The totally extrinsically denervated cardiac autotransplant can achieve a level of performance similar to that of a normal heart, but is less efficient in doing so. Alterations in utilization of circulating catecholamines may aid the hemodynamic adaptation to the cardiac denervation.

Thermodilution method for measuring cardiac output of rats by using a transistor bridge.

Featuring an interlocking bridge amplifier, our new method measures cardiac output in animals from man to the rat, and one can perform many multiple assays with safety in the same animal with accuracy and reliability as reported, using room-temperature saline, whether the animal is in the normal or hyperthermic condition.

Biochemical Studies of Myocardium and Blood During Extracorporeal Circulation in Man

We have studied samples of myocardium from 40 patients with congenital heart disease for catecholamine, histamine, and glycogen content. Blood samples obtained before, during, and after cardiopulmonary bypass in 53 patients were assayed for total protein, osmolality, catecholamines, histamine, lactic acid dehydrogenase activity, and cholinesterase activity. The data show that (1) adequate cardiopulmonary bypass is accompanied by increased sympathetic activity, (2) myocardial damage, indicated by elevated plasma lactic acid dehydrogenase activity, may occur during operation, and (3) depletion of myocardial catecholamine content may be a concomitant of heart disease with chronic congestive failure.