The effect of norepinephrine on cardiac output, arterial blood pressure, and heart rate in dogs treated with chlorothiazide

Multifunctional cardiac microphysiological system based on transparent ITO electrodes for simultaneous optical measurement and electrical signal monitoring

Drug-induced cardiotoxicity is a significant contributor to drug recalls, primarily attributed to limitations in existing drug screening platforms. Traditional heart-on-a-chip platforms often employ metallic electrodes to record cardiomyocyte electrical signals. However, this approach hinders direct cardiomyocyte morphology observation and typically yields limited functionality. Consequently, this limitation may lead to an incomplete understanding of cardiomyocyte characteristics. To address these challenges, we introduce a multifunctional cardiac microphysiological system featuring transparent indium tin oxide electrodes. This innovative design aims to overcome the limitations of conventional heart-on-a-chip systems where metal electrodes interfere with the observation of cells and increase the difficulty of subsequent image processing of cell images. In addition to facilitating optical measurement combined with image processing capabilities, this system integrates a range of electrodes with diverse functionalities. These electrodes can realize cellular electrical stimulation, field potential monitoring, and impedance change tracking, enabling a comprehensive investigation of various cardiomyocyte traits. To demonstrate its versatility, we investigate the effects of four cardiac drugs with distinct pharmacological profiles on cardiomyocytes using this system. This platform provides a means for quantitatively and predictively assessing cardiac toxicity, which could be applied to conduct a comprehensive evaluation during the drug discovery process.

Mechanism of Thiazide Diuretic Arterial Pressure Reduction: The Search Continues

Thiazide diuretic (TZD)-mediated chronic reduction of arterial pressure is thought to occur through decreased total peripheral vascular resistance. Further, the decreased peripheral vascular resistance is accomplished through TZD activation of an extrarenal target, resulting in inhibition of vascular constriction. However, despite greater than five decades of investigation, little progress has been made into the identification of the TZD extrarenal target. Proposed mechanisms range from direct inhibition of constrictor and activation of relaxant signaling pathways in the vascular smooth muscle to indirect inhibition through decreased neurogenic and hormonal regulatory pathways. Surprisingly, particularly in view of this lack of progress, comprehensive reviews of the subject are absent. Moreover, even though it is well recognized that 1) several types of hypertension are insensitive to TZD reduction of arterial pressure and, further, TZD fail to reduce arterial pressure in normotensive subjects and animals, and 2) different mechanisms underlie acute and chronic TZD, findings derived from these models and parameters remain largely undifferentiated. This review 1) comprehensively describes findings associated with TZD reduction of arterial pressure; 2) differentiates between observations in TZD-sensitive and TZD-insensitive hypertension, normotensive subjects/animals, and acute and chronic effects of TZD; 3) critically evaluates proposed TZD extrarenal targets; 4) proposes guiding parameters for relevant investigations into extrarenal TZD target identification; and 5) proposes a working model for TZD chronic reduction of arterial pressure through vascular dilation.

Simultaneous electrical recording of cardiac electrophysiology and contraction on chip

Prevailing commercialized cardiac platforms for in vitro drug development utilize planar microelectrode arrays to map action potentials, or impedance sensing to record contraction in real time, but cannot record both functions on the same chip with high spatial resolution. Here we report a novel cardiac platform that can record cardiac tissue adhesion, electrophysiology, and contractility on the same chip. The platform integrates two independent yet interpenetrating sensor arrays: a microelectrode array for field potential readouts and an interdigitated electrode array for impedance readouts. Together, these arrays provide real-time, non-invasive data acquisition of both cardiac electrophysiology and contractility under physiological conditions and under drug stimuli. Human induced pluripotent stem cell-derived cardiomyocytes were cultured as a model system, and used to validate the platform with an excitation-contraction decoupling chemical. Preliminary data using the platform to investigate the effect of the drug norepinephrine are combined with computational efforts. This platform provides a quantitative and predictive assay system that can potentially be used for comprehensive assessment of cardiac toxicity earlier in the drug discovery process.

Systems behavior, feed-back loops, and high blood pressure research

A major challenge to those investigating the etiology and progress of hypertension, as well as of other diseases, results from the fact that the control and regulation of most bodily functions are comprised of multiple feedback loops involving many bodily "systems." Thus, mechanisms which seem to offer clues as to the etiology of an abnormality, when investigated as an isolated function, fail to explain the etiology when sought in the intact experimental animal or patient.

Examples of simple closed-loop systems are described to illustrate the effects of feed-back. A simplified diagram of several factors known to play a role in the control and regulation of the characteristies of the blood vessel wall is described to illustrate the multiplicity of the feed-back pattern which probably occurs. Furthermore, it is evident that almost none of the factors which constitute the loops have been evaluated sufficiently to permit characterization of the system. It is not surprising that apparently promising clues turn out to be disappointing and to become lost in the system.

The medical investigator must learn to deal with methods of analyzing systems containing multiple factors and functions as well as to characterize the properties and behavior of the parts of the system.

Pharmacological, electrophysiological and toxicity studies of Limacia scanden Lour. (Menispermaceae)

Pharmacological studies showed that Limacia scanden Lour. extracts have sympathomimetic activities similar to noradrenaline (NA). A crude extract of Limacia scanden injected intravenously as a single bolus induced a dose-dependent increase in arterial blood pressure in anaesthetized rats and cats. Pretreatment with a non-specific alpha blocker phentolamine (10(-5) M) blocked this effect, whereas the beta blocker propanolol (10(-5) M) did not. The extract also reduced intestinal motility and this response could be blocked by pretreatment with phentolamine (10(-5) M) and specific alpha1-blocker, prazosin (10(-5) M). In superfused rabbit aorta preparations, it induced an increase in contractions. This effect was blocked by pretreatment with prazosin (10(-5) M), whereas the alpha2-blocker yohimbine (10(-5) M) had only a slight effect. The effects of NA on superfused aorta strip contraction were similar to extract. Toxic symptoms were manifested in less than 5 min when the mice were given 465 mg/kg of extract intraperitoneally. Physiological and behavioural changes observed in dying mice implicated serious malfunctioning of the autonomic nervous system and motor activity. Electrophysiological studies on the tonically autoactive neuron (TAN) of the snail Achantina fulica Férussac revealed that crude extract of Limacia scanden induced excitatory responses which were similar to those of serotonin (5-HT) stimulation. Studies with different ionic compositions of the bathing saline revealed that this excitatory effect of Limacia scanden could be attributed either to release of endogenous serotonin or inhibition of 5-HT reuptake in the CNS. This observation could tentatively be used to provide the framework towards elucidating the mechanism and rationale for the use of this plant in traditional medicine in the treatment of depression and affective disorders.

Effect of diuretics on adrenergic receptors in the rat

Diuretics have been reported to alter arteriolar smooth muscle responses to adrenergic stimulation as well as lymphocyte beta-adrenoceptor density. We have investigated the effect of four days treatment with hydrochlorothiazide or furosemide (10 mg/kg and day) injected subcutaneously in the rat on alpha 1-,alpha 2- and beta-adrenoceptors in different tissues. alpha 1-Adrenoceptor density and affinity in whole kidney and heart ventricle as determined by 3H-prazosin binding (in the absence and presence of 10(-5) M phentolamine) were unaltered by diuretic treatment, as were beta-adrenoceptor density and affinity in whole kidney, heart ventricle and skeletal muscle as determined by 125I-iodocyanopindolol binding (in the absence and presence of 10(-7) M (-)-propranolol). The density of alpha 2-adrenoceptors in particulate fraction from whole kidney homogenate as determined by 3H-rauwolscine binding was 12.8% higher in the hydrochlorothiazide-treated group (P less than 0.05) and 15.0% higher in the furosemide-treated group (P less than 0.01) than in the control group. The receptor affinity was similar in the different groups. Thus diuretic-induced alterations in adrenoceptors reported in previous studies were not observed in this study.

Interactions of NSAIDs with diuretics and beta-blockers mechanisms and clinical implications

Indomethacin attenuates the antihypertensive effect of both thiazide diuretics and beta-adrenoceptor blocking drugs. The mechanisms of these interactions are poorly understood but sodium and water retention, suppression of plasma renin activity, alterations in adrenoceptor sensitivity and impaired synthesis of vasodilator prostaglandins may all contribute to this effect. Other non-steroidal anti-inflammatory drugs (NSAIDs) may share this property of indomethacin but sulindac, which is a selective inhibitor of extrarenal prostaglandin synthesis, appears not to. This may have important clinical and theoretical implications. Clinicians must beware of this potential interaction in any patient receiving treatment for hypertension. NSAIDs may also inhibit the natriuretic response to diuretics with resultant adverse effects in patients with heart failure and other forms of oedema. NSAIDs may also have adverse nephrotoxic effects which may be exacerbated by diuretic therapy.

Factors contributing to blood pressure elevation during norepinephrine and phenylephrine infusions in dogs

To examine the factors contributing to the rise in systemic blood pressure during alpha- and beta-adrenergic stimulation, phenylephrine, an alpha-adrenergic agonist, and norepinephrine, an alpha- and beta-adrenergic agonist, were infused intravenously to anesthetized dogs until mean aortic blood pressure was raised equally by 40-60 mmHg. Changes in preload were estimated by changes in left ventricular end-diastolic pressure or segment length recorded by an ultrasonic technique. By obstructing the inferior vena cava (IVC), the increase in preload could be reduced to control level during phenylephrine and norepinephrine infusions without altering peripheral resistance (mean aortic blood pressure/cardiac output). Normalization of preload reduced the pressure response by 2/3 during phenylephrine infusion and by 1/4 during norepinephrine infusion. However, after beta-adrenergic blockade by propranolol, normalization of preload reduced the pressure response by 2/3 during both phenylephrine and norepinephrine infusions. Thus, during alpha-adrenergic stimulation, the increase in preload is a more important factor than the increase in peripheral resistance. Norepinephrine raised stroke volume by 24 +/- 5%. When the increase in stroke volume was prevented by IVC obstruction, the pressure response to norepinephrine was halved. Thus, during norepinephrine infusion the rise in stroke volume caused by beta-adrenergic stimulation is as important as alpha-adrenergic stimulation for the pressure response.

Responses of the cardiovascular system of the rat to noradrenaline infusions and their modification by adrenoceptor blocking agents

1 The effects of noradrenaline upon the cardiovascular system of the rat, anaesthetized with pentobarbitone, have been investigated.2 Noradrenaline produces a dose-dependent increase in mean arterial blood pressure (MABP) which is due entirely to an increase in cardiac output; total peripheral vascular resistance (TPR) remains unchanged.3 Following beta-adrenoceptor blockade the pressor response to infused noradrenaline is enhanced and is now due mainly to an increase in TPR; the increment in cardiac output is reduced.4 After alpha-adrenoceptor blockade the pressor response is greatly reduced; the residual increase in MABP is due solely to an increase in cardiac output.5 After ganglion blockade resting cardiac output and TPR both fall, resulting in a reduction in MABP. The pressor response to noradrenaline is enhanced and is now due to increases in both TPR and in cardiac output.6 The cardiovascular response of the anaesthetized rat to noradrenaline can be explained in terms of classical alpha- and beta-adrenoceptor stimulation by the amine; the unusual form of the response may be due to an effective predominance of beta-adrenoceptor-mediated effects in this species.7 It is suggested that the failure of exogenous noradrenaline to produce a rise in TPR results from a balance between the alpha-adrenoceptor-mediated increase and beta-adrenoceptor-mediated decrease in this variable. However, this proposed balance is lost if resting vasoconstrictor tone is reduced by ganglion blockade.

Proceedings: Renal control of kidney growth

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