Cardiac Norepinephrine Stores and the Contractile State of Heart Muscle

Abstract

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.

Role of Circadian Rhythmicity in the Heart Rate Variability Preceding Non-Sustained Ventricular Tachycardia

“…3,4 The 24-h cycle of HRV (which is defined as a circadian rhythm) may be an important factor because high sympathetic activity that persists throughout a 24-h period may acceleratereceptor down-regulation 19 and promote a reduction of catecholamine stores in the heart. 20,21 Thus, the patients with reduced circadian rhythmicity of HRV may have impaired autonomic nervous function such as diabetic neuropathy, 12 prior myocardial infarction 13,14 or congestive heart failure. 15,16 Previous studies demonstrated that patients with NSVT also have reduced circadian variation of HRV; 7,10 however, we noted that some patients with NSVT have a preserved circadian rhythm.…”

Influence of the Thyroid State on the Intrinsic Contractile Properties and Energy Stores of the Myocardium*

“…Accordingly, the aim of the present investigation was to determine the effects of hyper-and hypothyroidism on: (a) the intrinsic contractile properties of the myocardium in the presence and absence of intact norepinephrine stores; (b) the contractile responses of the myocardium to various inotropic stimuli; and (c) the high energy phosphate stores in the myocardium. The recent development of methods for detailed and quantitative analysis of mechanical characteristics of isolated cat papillary muscle (8), removed from the nervous, humoral, and metabolic influences that exist in vivo, and the ability to compare the function of muscles obtained from different groups of animals (9), permit critical examination of these problems. In addition, although interpretation of many previous studies of myocardial high energy phosphate stores in altered thyroid states (10)(11)(12)(13)(14) was limited by the extreme lability of these energy stores, recent modifications of biopsy and analytic techniques have made possible the accurate assessment of these stores in vivo (15,16).…”

The effect of sustained stellate ganglion stimulation on left ventricular contractility in the dog.

“…Several studies using isolated heart muscle have demonstrated no significant differences in the resting contractile state of the myocardium between normal and norepinephrine depleted specimens (Cairoli et al 1962;Spann et al 1966). Spann et al suggested that norepinephrine deple tion itself would not change the intrinsic contractile state of the myocardium (Spann et al 1966).…”

“…Spann et al suggested that norepinephrine deple tion itself would not change the intrinsic contractile state of the myocardium (Spann et al 1966). However, another report describes a positive relationship between myocardial norepinephrine depletion and defective myocardial contractility ).…”