Release of endogenous catecholamines in the ischemic myocardium of the rat. Part A: Locally mediated release

The accumulation of endogenous catecholamines within the extracellular space of the ischemic myocardium has been studied in the isolated perfused (Langendorff) heart of the rat subjected to various periods of complete ischemia, with subsequent collection of the reperfusate. Catecholamines and deaminated metabolites were measured by radioenzymatic methods, or high pressure liquid chromatography. Ischemic periods of less than 10 minutes are not associated with an increased overflow of catecholamines or metabolites. Longer periods of ischemia are accompanied by the overflow of noradrenaline and its deaminated metabolite 3,4-dihydroxyphenylglycol. This overflow increases with lengthening of the preceding ischemic period (10 minutes: 2.5 +/- 0.6, 20 minutes: 209.8 +/- 17.2, 60 minutes: 1270.5 +/- 148.1 pmol noradrenaline/g heart). Noradrenaline concentration is highest during the first minute of reperfusion, suggesting that the noradrenaline detected during reperfusion is released into the extracellular space of the myocardium during ischemia and is subsequently eluted. Experiments with variation of extracellular calcium concentration and with neuronal uptake (uptake1) blocking agents suggest that different mechanisms of catecholamine release are acting during the course of ischemia. A calcium-independent carrier-mediated efflux of noradrenaline from the nerve terminals is of major importance, using the same carrier as is normally responsible for transporting noradrenaline from the synaptic clefts into the neuronal varicosities. Thus, various uptake1-blocking agents diminish the noradrenaline overflow following ischemic periods of between 10 and 40 minutes. The noradrenaline overflow following longer periods of ischemia is unaffected by uptake1-blocking agents, and additional noradrenaline release at this time is probably consequent upon dissolution of cell membranes. Overflow of adrenaline and dopamine occurs to a minor degree (less than 5% of the corresponding noradrenaline overflow), and only after ischemic periods of more than 15 minutes.     

Effect of sympathetic nerve stimulation on lung vascular permeability in the rat.

The present study was undertaken to evaluate the role of sympathetic nerves in increasing lung vascular permeability. An isolated rat sympathetic nerve-lung preparation was used. Three minutes after an increase in lung weight was induced by elevating the intravascular pressure, stimulation of sympathetic nerves was performed in the presence of papaverine, which further increased the lung weight in a graded manner. After the nerve stimulation, deposits of carbon were observed in alveolar macrophages and perivascular walls, indicating an increase in vascular permeability. The response of lung weight to the sympathetic nerve stimulation was altered, depending on the magnitude of intravascular pressure change as well as on the voltage and frequency of electrical stimulation. Furthermore, these responses were prevented by tetrodotoxin. Calculation of the relationship between the maximal slope of the graded lung weight gain and the slope obtained just before the nerve stimulation gave a slope ratio at a frequency of 30 cps in normal rats of 4.47 +/- 0.21. Treatment with phentolamine diminished the value to 1.93 +/- 0.15, and with reserpine, to 1.43 +/- 0.14. In reserpinized rats, the slope ratio was restored by an administration of norepinephrine to 2.11 +/- 0.05 at 30 cps, being further increased by propranolol and blocked partially by phentolamine. The capillary filtration coefficient was not affected by either of the agents. In capsaicin-treated rats, sympathetic nerve stimulation did not cause any response in terms of lung weight (slope ratio = 1.0).(ABSTRACT TRUNCATED AT 250 WORDS)     

Release of catecholamines follows suckling or electrical stimulation of mammary nerve in lactating rats

The hypothesis that catecholamines may be released by mammary gland stimulation during lactation was tested by measuring, with an HPLC electrochemical method, plasma epinephrine (E) and norepinephrine (NE) concentrations during suckling in conscious rats and during electrical stimulation (pulses: 1 msec duration, 10/sec at 5-30 V) of the central end of a cut abdominal mammary nerve in urethane-anesthetized rats. Plasma E and NE concentrations were significantly elevated in two different strains of rats (Wistar and Holtzman) within 5 min of suckling. The concentration of E and NE did not change in control unsuckled rats during the same time period. As a complementary indication of sympathetic activation, it was observed that piloerection occurred during suckling. Plasma E levels (but not NE levels) increased significantly within 30 sec of a 2-min period of nerve stimulation in lactating rats on either day 7 or day 21 of lactation, as well as in nonlactating rats. The effect was significantly greater in nonlactating rats. The levels of E and NE were not altered after sham stimulation, whereas adrenalectomy abolished the rise in plasma E after mammary nerve stimulation. Blockade of the rise in plasma E also occurred after rapid injection of 100 microliters milk intraductally into each of two thoracic mammary glands, 15 sec before the onset of mammary nerve stimulation. These results show that E and NE can be released in response to suckling, and that activation of ductal mechanoreceptors may inhibit such release. These mechanisms may operate to regulate the rate of milk removal during suckling in the rat.     

Effect of cardiac sympathetic nerve stimulation on acutely ischemic myocardium--a comparison with the response to exogenous noradrenaline

To assess the integrity of an adrenergic nervous function in acute myocardial ischemia, the contractile response of the ischemic region to cardiac sympathetic nervous stimulation (CSNS) was measured in comparison that with to exogenous noradrenaline (NA) infusion. In 13 anesthetized open chest mongrel dogs, haemodynamic changes, segmental wall motion, and the concentration of NA in the efferent coronary vein were measured. CSNS was performed by electrically stimulating the left ansa subclavia. Data concerning baseline values, values during CSNS, and those obtained during NA infusion both before and up to 5 h after coronary occlusion were compared. Regional myocardial blood flow of the ischemic region was also measured using the H+ clearance method. Systolic expansion with coronary occlusion was not changed or augmented by CSNS. However, improvement was observed in all experiments when NA infusion was used. The percent change of systolic shortening, indicating the response of segmental wall motion to CSNS, decreased soon after occlusion, recovered temporarily within 30 min after occlusion, but did not improve throughout the period after 60 min. The decrease of NA overflow into the efferent vein by CSNS showed a biphasic pattern; reduction occurring immediately after occlusion and again 3-5h after occlusion. Throughout these experimental studies it was considered that the preserved responses to the exogenous injected NA represented the contribution of presynaptic factor.     

Dispersion of refractoriness in canine ventricular myocardium. Effects of sympathetic stimulation

In 18 dogs on total cardiopulmonary bypass, the average interval between local activations during artificially induced ventricular fibrillation (VF interval) was measured from extracellular electrograms, simultaneously recorded from up to 32 ventricular sites. VF intervals were used as an index of local refractoriness, based on the assumption that during ventricular fibrillation, cells are reexcited as soon as they have recovered their excitability. In support of this, microelectrode recordings in two hearts during ventricular fibrillation did not show a diastolic interval between successive action potentials. Refractory periods determined at a basic cycle length of 300 msec with the extrastimulus method correlated well with VF intervals measured at the same sites. Thus, this technique allows assessment of spatial dispersion of refractoriness during brief interventions such as sympathetic stimulation. The responses to left, right, and combined stellate ganglion stimulation varied substantially among individual hearts. This was observed both in dogs with an intact (n = 12) and decentralized (n = 6) autonomic nervous system. Individual ventricular sites could show effects of both left and right stellate ganglion stimulation (42% of tested sites) or show effects of left-sided stimulation only (31%) or right-sided stimulation only (14%). In 13% of sites, no effects of stellate stimulation were observed. Apart from these regional effects, the responses could be qualitatively different; that is, within the same heart, the VF interval prolonged at one site but shortened at another in response to the same intervention, although shortening was the general effect and prolongation the exception. Whenever sites responded to stellate ganglion stimulation with a shortening of VF interval, this shortening was approximately 10% for left, right, or combined stimulation, whether the autonomic nervous system was intact or decentralized. In six of 12 hearts in the intact group, there was a distinct regional effect of left stellate ganglion stimulation; in the other six hearts, the effects were distributed homogeneously over the ventricles. In three hearts, the effect of left stellate ganglion stimulation was strongest in the posterior wall, and in the other three hearts, in the anterior wall. The effects of right stellate ganglion stimulation were restricted to the anterior or lateral part of the left ventricle. Dispersion of VF intervals increased after left and combined stellate ganglion stimulation in the intact group and after right stellate ganglion stimulation in the decentralized group, but not significantly in every heart. This points to a marked individual variation with regard to the effects of sympathetic stimulation on electrophysiological properties of the heart.     

Pulmonary vasodilator responses to catecholamines and sympathetic nerve stimulation in the cat. Evidence that vascular beta-2 adrenoreceptors are innervated

We investigated the effects of catecholamines and sympathetic nerve stimulation in the feline pulmonary vascular bed under conditions of controlled pulmonary blood flow. Norepinephrine and nerve stimulation caused dose- and stimulus frequency-dependent increases in pulmonary vascular resistance. However, when pulmonary vascular tone was enhanced and alpha receptors blocked, norepinephrine and nerve stimulation caused dose- and frequency-dependent decreases in pulmonary vascular resistance. The decreases in pulmonary vascular resistance were blocked with propranolol and were of greater magnitude than were constrictor responses observed under basal conditions. Vasodilator responses to nerve stimulation were not modified by atropine. Epinephrine and isoproterenol had marked vasodilator activity in the pulmonary vascular bed when pulmonary vascular tone was elevated. When alpha receptors were blocked, isoproterenol and epinephrine had similar vasodilator activity, and when beta receptors were blocked, epinephrine and norepinephrine had marked vasoconstrictor activity. Selective beta-1 receptors antagonists had little effect on vasodilator responses to isoproterenol, whereas responses to this substance were blocked by propranolol. These results suggest that presence of alpha-and beta-2 adrenoreceptors in the feline pulmonary vascular bed and that both types of adrenergic receptors are innervated by the sympathetic nervous system.     

Response of blood vessels to sympathetic nerve stimulation.

The frequency response curves (FRC) of isolated blood vessels differ from each other not only in their initial slopes, but in their maxima, and their intercept on the frequency axis. Within the physiological range, there is a linear relation between response and frequency. The FRC of most vessels with junctional innervation are similar, varying only somewhat with innervation density. Other factors found to influence the FRC are: variation in innervation distribution, in the extent of myogenic propragation, and large differences in the sensitivity of the alpha-adrenergic receptor. The effectiveness of the transmitter increases with frequency rise. The maximum effective radius of the transmitter released from one varicosity is only several microns. In vessels with light to moderate innervation density at low frequencies, there is probably little overlap of transmitter effect from adjacent varicosities even at the outermost layers of smooth muscle cells. There is a disparity between neurogenic response and that which might be expected from the direct action of the transmitter. It is proposed that a local limited myogenic extension of excitation may extend the local action of a quantum of transmitter.     

Impaired sympathetic nerve function in the inflamed rat intestine.

The effect of intestinal inflammation on norepinephrine release from the myenteric plexus in the Trichinella spiralis-infected rat was assessed. Longitudinal muscle-myenteric plexus preparations were preincubated with [3H]norepinephrine and release was evoked by electrical field stimulation and KCl administration. Preincubation of preparations with desipramine or pretreatment of rats with 6-hydroxydopamine significantly suppressed the uptake and evoked release of [3H]norepinephrine; electrical field stimulation but not KCl-evoked release of [3H] norepinephrine was sensitive to tetrodotoxin. These results confirm the presence of functioning sympathetic nerves in the preparations. T. spiralis infection was associated with significant suppression of both electrical field stimulation and KCl-evoked release of [3H]norepinephrine on the sixth day postinfection, and the suppression persisted 100 days postinfection. No suppression of [3H]norepinephrine release was seen in the worm-free and noninflamed ileum of infected rats. Suppression of [3H]norepinephrine release from the jejunum of infected rats was attenuated by treatment with betamethasone (3.0 mg/kg SC daily). These results are consistent with the hypothesis that intestinal inflammation suppresses the release of norepinephrine from the myenteric plexus in the Trichinella-infected rat.     

Effect of vagal stimulation on the overflow of norepinephrine into the coronary sinus during cardiac sympathetic nerve stimulation in the dog.

In anesthetized dogs with the chest open, supramaximal stimulation of the left cardiac sympathetic nerves at 2 and 4 Hz produced an increase of 40-50% in ventricular contractile force (CF) and of 40-65% in coronary sinus blood flow. At these frequencies of stimulation, norepinephrine (NE) overflow into the coronary sinus was 29.8 +/- 5.1 (SE) and 54.9 +/- 13.2 ng/min, respectively. Concurrent, supramaximal vagal stimulation, at a frequency of 15 Hz, had no significant effect on coronary sinus blood flow, but caused a 25% reduction in CF and a 30% decrease in NE overflow. The changes in CF and NE overflow evoked by vagal stimulation were prevented by atropine. These results are consistent with the hypothesis that there are muscarinic receptors on the postganglionic sympathetic terminals in the walls of the ventricles. Acetylcholine released during vagal stimulation combines with these receptors, causes a reduction in the liberation of NE, and thereby attenuates the positive inotropic response.     

交感神经和肌间神经丛在胃电刺激调控胃慢波中的作用

目的研究胃交感神经及肌间神经丛在电刺激调控胃慢波活动中的作用,确定胃电起博的神经机制和作用环节,为今后起搏器的深入研究打下基础。方法10只雄性wistar大鼠随机分为对照组和电刺激组,各5只。全部大鼠植入浆膜电极,电刺激组大鼠行胃电刺激至胃慢波被完全控制。植入电极组不行电刺激。采用免疫组化S P法检测并比较两组大鼠胃窦肌间神经丛和脊髓后角C fos蛋白表达。结果电刺激组大鼠胃慢波全部被完全控制,所需能量为2 70±80 .6ms ,2mA。2组大鼠脊髓中间内侧核,中间外侧核均未见C fos阳性神经元,而后角浅层均见散在C fos表达,比较无显著性差异(P >0 .0 5 )。植入电极组胃窦肌间神经丛未见C fos阳性神经元,电刺激组胃窦肌间神经丛可见C fos阳性神经元。结论适宜参数的胃电刺激可完全控制大鼠胃慢波。肌间神经丛参与胃电刺激调控胃慢波,而交感神经则无明显作用。     

Changes in the ischemic myocardium in experimental paired stimulation of the heart

In dog experiments the dynamics of electrophysiological and morphological indices of the ischemic myocardium in sinus tachycardia was compared with that in deceleration of cardiac contraction under the effect of paired stimulation. Intensification of the damaging effect of a 40-minute occlusion of the coronary artery complicated by destructive changes of the cardiomyocytes was revealed after deceleration of the rhythm; in reperfusion of the ischemic area the effect of electrogram restoration was diminished, which was attended with deeper focal damage to the heart muscle.     

Ontogeny of insulin-induced hypoglycemia stimulation of adrenocorticotropin secretion in the rat: role of catecholamines.

We previously reported that insulin-induced hypoglycemia (IIH) induces a large increase in plasma ACTH and corticosterone levels in the developing rat during the stress hyporesponsive period and that this effect is mediated, at least partially, by arginine vasopressin (AVP), but not corticotropin-releasing factor. Nevertheless, ACTH secretion in response to IIH in rats immunoneutralized against AVP was still stimulated, suggesting that other regulatory factors participate in the stimulation of ACTH secretion during IIH. It has been suggested that, in the adult rat, during profound hypoglycemia, epinephrine may act at the pituitary level through beta 2-adrenergic receptors to stimulate ACTH secretion. In this report, we studied the effect of the blockade of beta-adrenergic receptors on the pituitary-adrenal axis response to IIH. Rats (20 or 8 day old) were pretreated with saline or 2.5 mg/kg propranolol (a beta-adrenergic receptors antagonist) and subsequently injected with 3 IU/kg insulin. In 20-day-old rats, insulin injection induced a large increase of plasma ACTH concentrations that were unaffected by propranolol pretreatment. In 8-day-old rats, the IIH-induced increase of plasma ACTH levels was significantly reduced by propranolol pretreatment. Pretreatment of 8-day-old rats with 5 mg/kg CGP 20712A (a selective beta 1-adrenergic receptor antagonist) did not change the plasma ACTH response to insulin injection, while pretreatment with 2.5 mg/kg ICI 118551 (a selective beta 2-adrenergic receptor antagonist) resulted in a significant decrease of the IIH-induced stimulation of ACTH secretion. We next studied the effect of the blockade of circulating AVP and/or beta-adrenergic receptors on the pituitary response to IIH. Pretreatment of 8-day-old rats with antiserum anti-AVP or propranolol was followed by a significant reduction of IIH-induced increase of plasma ACTH concentrations. No additive effect was found after pretreatment with both antiserum anti-AVP and propranolol, suggesting that the stimulatory effect of catecholamines during IIH in 8-day-old rats is mediated through a modulation of hypothalamic AVP secretion.     

交感神经刺激对大鼠缺血性室性心律失常的影响及其机制的探讨

目的 探讨大鼠急性心肌缺血时交感神经刺激对室性心律失常的影响及其潜在的机制.方法 结扎大鼠冠状动脉前降支制备急性心肌缺血模型后随机分组作为心肌缺血组(MI组,n=25)、缺血+交感神经刺激组(MI-SS组,n=25)、交感神经刺激+酚妥拉明+缺血组(MI-SS-Phen组,n=15)、交感神经刺激+普萘洛尔+缺血组(MI-SS-Prop组,n=15)和假手术组(SO组,n=20).心电图监测室性心律失常的发生.蛋白免疫印记法(Western blot)检测缝隙连接蛋白43(Cx43)的磷酸化蛋白及总量表达变化.逆转录聚合酶链反应(PCR)分析Cx43 mRNA的表达变化.免疫荧光观察Cx43表达分布情况.结果 结扎冠状动脉30 min内MI、MI-SS和MI-SS-Phen组分别有1、3和2只大鼠死于心室颤动(室颤);MI-SS组室性心动过速(室速)/室颤发生率(80.0%,20/25)较MI组(52.0%,13/25)明显增加(P＜0.05);与MI-SS组相比,普萘洛尔明显阻断了交感神经刺激促室速/室颤发生的作用(13.3%,2/15,P＜0.05).冠状动脉结扎30 min后,MI组磷酸化Cx43的比例较SO组显著降低(P＜0.05),但其总量并未减少(P＞0.05).与MI组相比,MI-SS组磷酸化Cx43的比例明显增加(P＜0.05),同时其蛋白总量的表达显著降低(P＜0.05);普萘洛尔显著抑制了交感神经刺激导致的Cx43蛋白降解的作用,同时抑制了缺血引起的Cx43脱磷酸化(P＜0.05).MI和MI-SS组Cx43mRNA表达均较SO组显著减少(P＜0.05).免疫荧光结果 显示,与SO组相比,MI组Cx43由端-端连接转化为侧-侧连接,而MI-SS组Cx43分布明显紊乱,不能分辨出Cx43的分布模式.结论 交感神经刺激能够促进室性心律失常的发生,可能主要与β肾上腺素受体的激活从而促进了Cx43的降解有关.     

Electrical stimulation of preganglionic nerve increases tyrosine hydroxylase activity in sympathetic ganglia.

The effect of synaptic stimulation on tyrosine hydroxylase [tyrosine 3-monooxygenase: L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2] activity in the rat superior cervical ganglion was studied. The preganglionic cervical sympathetic trunk was stimulated unilaterally at 10 Hz for 30 min. Forty-eight hours later tyrosine hydroxylase activity was 33% higher on the stimulated than on the control side. The enzyme activity restimulated than on the control side. The enzyme activity remained elevated in the stimulated ganglia for 2 days. No change was observed in total ganglion protein. Comparable increases in tyrosine hydroxylase activity were observed in anesthetized and conscious animals.