Central nervous effects of CRF and angiotensin II on cardiac output in conscious rats

Cardiovascular functions of central corticotropin-releasing factor related peptides system

The corticotropin-releasing factor (CRF) related peptides system has widespread distributions in central nervous system, to perform many physiological and pathophysiological functions, including cardiovascular functions. A complex connection exists between the central CRF related peptides system and cardiovascular system. There are multiple pathways and mechanisms through which the central CRF related peptides system influences cardiovascular functions. A dysfunction in the central CRF related peptides system may lead to a wide range of alterations in cardiovascular functions. Though there are difficulties or limitations in establishing exact modulatory roles of the central CRF related peptides system in cardiovascular functions. The central CRF related peptides system as target to prevent cardiovascular diseases is being pursued with increasing interest. In this review, we summarize recent understanding on cardiovascular functions of the CRF related peptides system in limbic forebrain, hypothalamus and brain stem structures, discuss mechanisms of the central CRF related peptides system in control of cardiovascular functions, and suggest that the central CRF related peptides system may be a potent candidate for prevention of cardiovascular diseases.

Central actions of corticotropin-releasing factor on autonomic nervous activity and cardiovascular functioning

The physiological role of corticotropin-releasing factor (CRF) in mediating stress-induced activation of the pituitary-adrenal axis, together with the neuroanatomical distribution of immunoreactive CRF and CRF receptors, provides a compelling rationale for investigating actions of CRF within the central nervous system (CNS) on autonomic nervous outflow and cardiovascular function. Evidence is reviewed showing that CRF acts within the CNS to elicit stress-like patterns of autonomic nervous outflow and cardiovascular changes in conscious animals. In addition, blockade of CRF-mediated neurotransmission is demonstrated to alter the expression of stress-induced autonomic nervous and cardiovascular responses. Together, the anatomical, pharmacological and physiological data support the hypothesis that the autonomic nervous and cardiovascular responses to selected stressful stimuli may be mediated in part by CRF-containing neuronal pathways.

Urocortin Induces Endothelium-Dependent Vasodilatation and Hyperpolarization of Rat Mesenteric Arteries by Activating Ca2+-Activated K+ Channels

Urocortin, a member of corticotropin releasing factor (CRF) peptide family, has positive chronotropic and inotropic effects on heart and also shows a vasodilatory effect. However, the mechanism underlying its vasodilatory effect has yet to be elucidated. Endothelium-dependent relaxation of resistance arteries is mainly achieved by activation of K+ channels. Therefore, we investigated possible role of K+ channels and hyperpolarization for the vasodilatory effect of urocortin using the isolated perfused rat mesenteric arteries. Urocortin (0.2 nM) produced a slow-onset decrease in the perfusion pressure of the mesenteric vascular bed, which was elevated by an alpha1-adrenoceptor agonist, phenylephrine (2-4 microM). Urocortin also hyperpolarized the main mesenteric artery. Removal of endothelium with saponin treatment considerably inhibited the relaxation and hyperpolarization induced by urocortin. In contrast, the hyperpolarization was not significantly changed by cyclooxygenase inhibitor, indomethacin (1 microM) and/or nitric oxide synthase inhibitor, N(omega)-nitro-L-arginine (100 microM). Urocortin-induced relaxation was not affected by the combination of a guanylyl cyclase inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 1 microM), indomethacin and N(omega)-nitro-L-arginine. However, the relaxation and hyperpolarization were abolished by high extracellular potassium concentration (40 mM) or by a large conductance Ca(2+)-activated K+ channel blocker, charybdotoxin (1 nM). Glibenclamide (1 microM), an ATP-dependent K+ channel inhibitor, did not affect the relaxation and hyperpolarization. These results suggest that urocortin causes endothelium-dependent relaxation and hyperpolarization of rat mesenteric arteries, probably through the activation of charybdotoxin sensitive Ca2+-activated K+ channels. These findings also indicate an essential role of the endothelium for the urocortin-elicited vascular relaxation and hyperpolarization.

Fractal rigidity by enhanced sympatho-vagal antagonism in heartbeat interval dynamics elicited by central application of corticotropin-releasing factor in mice

The dynamics of heartbeat interval fluctuations were studied in awake unrestrained mice following intracerebroventricular application of the neuropeptide corticotropin-releasing factor (CRF). The cardiac time series derived from telemetric ECG monitoring were analyzed by non-parametric techniques of nonlinear signal processing: delay-vector variance (DVV) analysis, higher-order variability (HOV) analysis, empirical mode decomposition (EMD), multiscale embedding-space decomposition (MESD), multiexponent multifractal (MEMF) analysis. The analyses support the conjecture that cardiac dynamics of normal control mice has both deterministic and stochastic elements, is nonstationary, nonlinear, and exerts multifractal properties. Central application of CRF results in bradycardia and increased variability of the beat-to-beat fluctuations. The altered dynamical properties elicited by CRF reflect a significant loss of intrinsic structural complexity of cardiac control which is due to central neuroautonomic hyperexcitation, i.e., enhanced sympatho-vagal antagonism. The change in dynamical complexity is characterized by an effect referred to as fractal rigidity, leading to a significant impairment of adaptability to extrinsic challenges in a fluctuating environment. The impact of dynamical neurocardiopathy as a major precipiting factor for the propensity of cardiac arrhythmias or sudden cardiac death by unchecked central CRF release in significant acute life events in man is critically discussed.

The role of corticotropin releasing factor and its antagonist, astressin, on micturition in the rat

The purpose of this investigation was to evaluate the role of corticotropin releasing factor (CRF) on micturition. CRF is involved in the endocrine and central nervous system responses to stress and is also expressed in sites responsible for the control of micturition. In this investigation, cystometric experiments were performed in awake and unrestrained Wistar rats and on Spontaneous Hypertensive Rats, which are used as a rodent model of detrusor overactivity and anxiety. In vitro effects of CRF were evaluated using strips of detrusor muscle in an organ bath preparation. CRF (6.0 microg) administered via intrathecal and intraperitoneal routes, but not intracerebroventricularly, lowered the micturition threshold. CRF reduced the intercontraction interval by 28% and 26% after intrathecal or intraperitoneal administration, respectively, and reduced micturition volume by 34.7% and 30.2%, respectively. In Wistar-Kyoto rats, 6.0 microg intrathecal CRF significantly reduced intercontraction interval (423 +/- 79 vs. 669 +/- 59 s) and micturition volume (0.30 +/- 0.04 vs. 0.69 +/- 0.07 ml) compared to controls that received saline vehicle. These effects were blocked by pretreatment with 6.0 mug intrathecal astressin, a potent CRF antagonist, demonstrating that the effects are CRF receptor mediated. In Spontaneous Hypertensive Rats, 6.0 mug intrathecal CRF was found to have minimal stimulatory effects on the bladder, whereas astressin reduced baseline detrusor overactivity. CRF had no direct contractile effects on detrusor muscle strips. These results demonstrate that in the absence of detrusor overactivity, CRF stimulates micturition when administered via the intrathecal or intraperitoneal routes. Further studies are needed to explore the possibility whether CRF antagonists are effective for detrusor overactivity and the overactive bladder syndrome.

Induction of bradycardia in trout by centrally administered corticotropin-releasing-hormone (CRH)

The cardiovascular effects of centrally and peripherally administered synthetic salmon corticotropin-releasing-hormone (CRH), a member of a family of stress-related neuropeptides, were investigated in the unanesthetized trout, Oncorhynchus mykiss. In group 1, trout bearing a cannula in the dorsal aorta, neither intracerebroventricular (i.c.v.) nor intra-arterial (i.a.) injections of CRH produced any significant change in mean heart rate (HR) and mean dorsal aortic blood pressure. These results stand in contrast to the previously reported hypertensive effects of i.a. and i.c.v. injections of trout urotensin-I. In group 2, non-cannulated trout bearing two subcutaneous electrocardiographic electrodes, conditions that are considered to be less stressful to the animals, the baseline level of HR was significantly reduced compared to the corresponding value for cannulated trout. In these trout, no significant change occurred in the HR after i.c.v. administration of 1 pmol of CRH. However, i.c.v. injection of 5 pmol of CRH caused a 12% (P<0.01) decrease in HR during the 20-25 min post-injection period. In addition, the heart rate variability (HRV), a marker of vagal input to the heart, was increased by 120%. The CRH antagonist, CRH-(9-41)-peptide alone had no effect on HR or HRV but blocked CRH-induced bradycardia. In the non-cannulated trout, i.c.v. injection of trout urotensin-I (5 pmol) produced no significant change in HR and HRV. In contrast, i.c.v. administration of angiotensin II (5 pmol) elicited a highly significant 33% (P<0.001) increase in the mean HR as well as inducing a marked (64%) reduction in HRV. Our results suggest that picomolar doses of CRH act centrally to evoke a bradycardia by a probable mechanism that involves enhancement of the parasympathetic drive to the heart.

Cardiac dynamics in corticotropin-releasing factor receptor subtype-2 deficient mice

The action of corticotropin-releasing factor (CRF) is mediated by two recently identified receptors, CRFR1 and CRFR2, that differ with respect to their anatomical distribution and pharmacologic ligand-binding properties. Here we show by an analysis of circadian heartbeat interval fluctuations that CRFR2-deficiency in mice does not interfere with the dynamical mechanisms underlying the control of heart rate. Hence, intact CRFR2 would not constitute an indispensable requirement of physiologic cardiac rhythm regulation. However, both CRFR2 knockout (-/-) and wildtype control (+/+) mice showed altered dynamical properties of cardiac interbeat fluctuations in contrast to homogenetic inbred strains of mice (C57BL/6N and C57BL/6J). The results stress the impact of genetic background and support the generalized notion that transgenic 129/Sv-derived knockout mice exhibit altered cardiac dynamics which is interpreted to reflect an attenuation of neuroautonomic sympatho-vagal antagonism.

Fractal dynamics of heart beat interval fluctuations in corticotropin-releasing factor receptor subtype 2 deficient mice

Non-linear fractal analysis of cardiac interbeat time series was performed in corticotropin-releasing factor receptor subtype 2 (CRFR2) deficient mice. Heart rate dynamics in mice constitutes a self-similar, scale-invariant, random fractal process with persistent intrinsic long-range correlations and inverse power-law properties. We hypothesized that the sustained tachycardic response elicited by intraperitoneal (ip) injection of human/rat CRF (h/rCRF) is mediated by CRFR2. In wildtype control animals, heart rate was increased to about maximum levels (approximately 750 bpm) while in CRFR2-deficient animals baseline values were retained (approximately 580 bpm). The tachycardic response elicited by ip-application is mediated by CRFR2 and is interpreted to result from sympathetic stimulation. However, the functional integrity of CRFR2 would not present a prerequisite to maintaining the responsiveness and resiliency of cardiac control to external environmental perturbations experimentally induced by extrinsic ip-application of h/rCRF or under physiological conditions that may be associated with an increased peripheral release of CRF. Under stressful physiological conditions achieved by novelty exposure, CRFR2 is not involved in the cardiodynamic regulation to external short-term stress. While the hypothesis of involvement of CRFR2 in cardiac regulation upon pharmacological stimulation cannot be rejected, the present findings suggest that the mechanism of action is by sympathetic stimulation, but would not unambiguously allow to draw any conclusions as to the physiological role of CRFR2 in the control of cardiac dynamics.

Role of corticotropin-releasing factor, vasopressin and the autonomic nervous system in learning and memory

Learning and memory are essential requirements for every living organism in order to cope with environmental demands, which enables it to adapt to changes in the conditions of life. Research on the effects of hormones on memory has focused on hormones such as adrenocorticotropic hormone (ACTH), glucocorticoids, vasopressin, oxytocin, epinephrine, corticotropin-releasing factor (CRF) that are released into the blood and brain following arousing or stressful experiences. Most of the information have been derived from studies on conditioned behavior, in particular, avoidance behavior in rats. In these tasks, an aversive situation was used as a stimulus for learning. Aversive stimuli are associated with the release of stress hormones and neuropeptides. Many factors play a role in different aspects of learning and memory processes. Neuropeptides not only affect attention, motivation, concentration and arousal or vigilance, but also anxiety and fear. In this way, they participate in learning and memory processes. Furthermore, neuropeptides such as CRF and vasopressin modulate the release of stress hormones such as epinephrine. In turn, systemic catecholamines enhance memory consolidation. CRF and vasopressin are colocalized in neurons from the nucleus paraventricularis, which project to nuclei in the brainstem involved in autonomic regulation. The objective of this paper is to discuss the role of CRF, vasopressin, and the autonomic nervous system (ANS) in learning and memory processes. Both CRF and vasopressin have effects in the same direction on behavior, learning and memory processes and stress responses (release of catecholamines and ACTH). These neuropeptides may act synergistically or in a concerted action aimed to learn to adapt to environmental demands.

Cardiovascular actions of centrally and peripherally administered trout urotensin-I in the trout

The cardiovascular effects of centrally and peripherally administered synthetic trout urotensin (U)-I, a member of the corticotropin-releasing hormone family of neuroendocrine peptides, were investigated in unanesthetized rainbow trout Oncorhynchus mykiss. Intracerebroventricular injections of U-I (5.0 and 12.5 pmol) produced a sustained increase in mean dorsal aortic blood pressure (P(DA)) without significant change in heart rate (HR). This elevation in P(DA) was associated with an increase in cardiac output, but systemic vascular resistance did not change. Intra-arterial injection of U-I (12.5-500 pmol) evoked a dose-dependent increase in P(DA), but in contrast to the hemodynamic effects of centrally administered U-I, the hypertensive effect was associated with an increase in systemic vascular resistance and an initial fall in cardiac output. HR did not change or underwent a delayed increase. Pretreatment of trout with prazosin, an alpha-adrenoreceptor antagonist, completely abolished the rise in arterial blood pressure after intra-arterial administration of U-I, which was replaced by a sustained hypotension and tachycardia. Trout U-I produced a dose-dependent (pD(2) = 7.74 +/- 0.08) relaxation of preconstricted rings of isolated trout arterial vascular smooth muscle, suggesting that the primary action of the peptide in the periphery is vasorelaxation that is rapidly reversed by release of catecholamines. Our results suggest that U-I may regulate blood pressure in trout by acting centrally as a neurotransmitter and/or neuromodulator and peripherally as a neurohormone functioning either as a locally acting vasodilator or as a potent secretagogue of catecholamines.

Effects of central leptin administration on blood pressure in normotensive rats

We tested the hypothesis that intracerebroventricular (i.c.v.) administration of leptin would increase mean arterial pressure (MAP) in ad libitum (AL) fed and food deprived (FD) normotensive rats. Male Sprague-Dawley rats were chronically instrumented with a guide cannula directed at the lateral ventricle and a carotid arterial catheter. Following recovery from surgery, the MAP and heart rate (HR) response to i.c.v. administration of vehicle (5 microl saline over 1 min) or leptin (0.3 microg or 3.0 microg in 5 microl saline) were determined in conscious, unrestrained AL fed (n=7-10) and 48-h FD (n=5-10) rats. Food deprivation significantly reduced MAP (AL=116+/-3; FD=104+/-3 mmHg; P < 0.01) without altering HR. In AL rats, high dose leptin (3.0 microg, i.c.v.) produced a significant increase in MAP when maximal responses were evaluated (9+/-2 mmHg; P < 0.05), but did not significantly alter MAP and HR over time during the 90 min measurement period. In FD rats, low dose leptin (0.3 microg, i.c.v.) produced significant elevations in MAP (7+/-3 mmHg) after a latency of 60 min, while high dose leptin (3.0 microg, i.c.v.) produced an increase in MAP within the first 10 min (10+/-3 mmHg) followed by an additional increase 1 h after injection (6+/-2 mmHg). Leptin administration also produced delayed increases in HR in FD rats (0.3 microg, 34+/-5 b.p.m.; 3.0 microg, 57+/-10 b.p.m). These results indicate that leptin may modulate cardiovascular function through central mechanisms and may do so to a greater extent in food deprived animals.

Differentiated hemodynamic responses to central versus peripheral administration of corticotropin-releasing factor in conscious rats

Corticotropin-releasing factor (CRF) modifies cardiovascular function and hemodynamic status after administration into the central nervous system and into the peripheral circulation. The mechanisms by which CRF alters arterial pressure and heart rate have been examined in detail whereas little information exists regarding the processes mediating CRF-induced changes in regional blood flow. Therefore, studies were performed in conscious, unrestrained Sprague-Dawley rats to examine potential mechanisms underlying the regional hemodynamic effects of intracerebroventricular versus intravenous administration of CRF. Intracerebroventricular administration of CRF increased arterial pressure, heart rate, and mesenteric vascular resistance while decreasing iliac vascular resistance. Intravenous pretreatment with the CRF receptor antagonist, alpha-helical CRF9-41, did not alter the cardiovascular and hemodynamic responses to central administration of CRF. In contrast, prior ganglionic blockade prevented CRF-induced responses except for the reduction in iliac vascular resistance. Intravenous administration of CRF reduced arterial pressure and mesenteric vascular resistance, elevated heart rate, and transiently increased iliac vascular resistance. Intravenous pretreatment with alpha-helical CRF9-41 completely abolished the cardiovascular and hemodynamic responses to peripheral administration of CRF. Ganglionic blockade prior to intravenous administration of CRF augmented the reductions in arterial blood pressure and mesenteric vascular resistance, prevented the increase in heart rate, and unmasked a decrease in iliac vascular resistance. The divergent actions and mechanisms of action of CRF on regional hemodynamics when administered peripherally, as opposed to centrally, indicate that this peptide produces different hemodynamic effects that are specific to its site of action.

Effects of exercise training on responses to central injection of CRF and noise stress

The purpose of this study was to test the hypothesis that the cardiovascular and sympathoadrenal responses to acute environmental stress are attenuated by exercise training. Furthermore, we tested the hypothesis that the cardiovascular and sympathoadrenal responses to intracerebroventricular (ICV) administration of corticotropin-releasing factor (CRF) would be attenuated by training. Conscious, unrestrained, male Sprague-Dawley rats assigned to either a treadmill trained (16-26 m/min, 30-60 min/day, 5 days/week) or nontrained (16-26 m/min, 10 min/day, 1 day/week) group were studied. After 8-10 weeks of training, maximal oxygen uptake was significantly higher in the trained (108 +/- 3 ml/kg/min) vs. the nontrained (94 +/- 4 ml/min/kg) group. There were no significant differences in baseline mean arterial pressure, heart rate and plasma catecholamine levels associated with training. Trained rats exhibited significantly attenuated elevations in arterial pressure (20 +/- 3 vs. 36 +/- 2 mmHg for nontrained) and heart rate (-3 +/- 3 vs. 12 +/- 5 beats/min for nontrained) in response to acute noise stress. Twenty minutes after ICV administration of CRF, blood pressure (trained = 119 +/- 2 mmHg, nontrained = 127 +/- 2 mmHg), heart rate (trained = 408 +/- 8 beats/min, nontrained = 424 +/- 10 beats/min), plasma norepinephrine levels (trained = 757 +/- 54 pg/ml, nontrained = 775 +/- 100 pg/ml) and plasma epinephrine levels (trained = 266 +/- 29 pg/ml, nontrained = 225 +/- 42 pg/ml) were significantly elevated in both trained and nontrained groups. CRF-induced elevations of blood pressure, but not heart rate or plasma catecholamine levels, were significantly attenuated in the trained group.(ABSTRACT TRUNCATED AT 250 WORDS)