Norepinephrine, a known inducer of myocardial hypertrophy, was found to have marked effects on the myocardial adrenergic system, which occurred prior to the development of a significant increase in heart weight. The chronic subhypertensive infusion (1.4 microgram/min) in free-roaming dogs produced a threefold increase in plasma norepinephrine (determined by radioimmunoassay). After 3 mo of infusion, right and left ventricular norepinephrine content (ng/mg protein) decreased significantly by twofold (right, 2.50 +/- 0.24; left, 2.08 +/- 0.36) compared with controls (right, 4.76 +/- 1.48; left, 4.65 +/- 1.49), and beta-receptor density (125I-pindolol) increased (right, 0.122 +/- 0.029; left, 0.153 +/- 0.021) over the controls (right, 0.082 +/- 0.015; left, 0.069 +/- 0.008 pmol/mg protein). Accompanying the beta-receptor changes, isoproterenol-stimulated adenylate cyclase activity also increased significantly [right, 29.2 +/- 2.1; left, 29.5 +/- 1.0 vs. controls, right, 13.8 +/- 1.1; left, 20.2 +/- 2.2 pmol adenosine 3',5'-cyclic monophosphate (cAMP) generated X min-1 X mg protein-1]. Because the above changes occurred in the absence of cardiac hypertrophy, it suggests that alterations in the myocardial adrenergic system are dependent on the stimulus (in this case norepinephrine) invoking the change and not the degree of hypertrophy. It also suggests that changes in the adrenergic system may not directly reflect the mechanism involved in the development of hypertrophy.
Simultaneous measurements of hemodynamics, arterioventricular (AV) conduction, and renal functioner were obtained in conscious dogs. Catheters were implanted for the long-term measurement of central aortic, right ventricular, and pulmonary artery pressure. AV conduction was assessed following surgical implantation of multipolar electrode plaques in the area of the bundle of His, as well as on the epicardium of the right and left atria and ventricles. Renal function was assessed utilizing standard techniques. Following control measurements, lidocaine, 1 mg/kg, or procaine amide, 10 mg/kg, was administered intravenously. Subsequently, serial measurements were obtained for a 90-min period. No significant changes in hemodynamics were observed following either drug. Procaine amide produced a significant increase in heart rate and a minimal increase in QRS duration associated with a decrease in low right atrial to His bundle conduction time. However, no significant changes in cardiac conduction were observed after lidocaine administration. Renal function was unaffected by lidocaine but significantly depressed by procaine amide, as demonstrated by a decrease in GFR and effective renal flow. In summary, acute administration of procaine amide significantly alters renal function in the conscious dog with minimal effects on AV conduction and hemodynamics.
Distension of the main pulmonary artery (MPA) induces pulmonary hypertension, most probably by neurogenic reflex pulmonary vasoconstriction, although constriction of the pulmonary vessels has not actually been demonstrated. In previous studies in dogs with increased pulmonary vascular resistance produced by airway hypoxia, exogenous arachidonic acid has led to the production of pulmonary vasodilator prostaglandins. Hence, in the present study, we investigated the effect of arachidonic acid in seven intact anesthetized dogs after pulmonary vascular resistance was increased by MPA distention. After steady-state pulmonary hypertension was established, arachidonic acid (1.0 mg/min) was infused into the right ventricle for 16 min; 15-20 min later a 16-mg bolus of arachidonic acid was injected. MPA distension was maintained throughout the study. Although the infusion of arachidonic acid significantly lowered the elevated pulmonary vascular resistance induced by MPA distension, the pulmonary vascular resistance returned to control levels only after the bolus injection of arachidonic acid. Notably, the bolus injection caused a biphasic response which first increased the pulmonary vascular resistance transiently before lowering it to control levels. In dogs with resting levels of pulmonary vascular resistance, administration of arachidonic acid in the same manner did not alter the pulmonary vascular resistance. It is concluded that MPA distension does indeed cause reflex pulmonary vasoconstriction which can be reversed by vasodilator metabolites of arachidonic acid. Even though this reflex may help maintain high pulmonary vascular resistance in the fetus, its function in the adult is obscure.
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