Regional hemodynamic actions of selective corticotropin-releasing factor type 2 receptor ligands in conscious rats

The corticotropin releasing factor system in the kidney: perspectives for novel therapeutic intervention in nephrology

The adaptation to endogenous and exogenous stress stimuli is crucial for survival but also for the onset of various diseases in humans. Corticotropin releasing factor (CRF) system is the major regulator of stress response and homeostasis. The members of this family of peptides extend their actions also outside CNS to the periphery where they may affect various body systems independently, acting via vagal and/or autocrine/paracrine pathways. In search for peripheral targets, kidney has rarely been studied separately, regarding expression and action of CRF and CRF-related peptides. We reviewed the existing literature concerning expression and action of the CRF system in normal and pathological renal tissue and explored possible clinical implications in nephrology. CRF system components are expressed in the kidney of experimental animals and in humans. The intrarenal distribution is reported to be equally extensive, suggesting a physiological or pathophysiological role in renal function and in the occurrence of renal disease. Urocortins have given multiple interesting observations in experimental models of renal disease and clinical studies, showing robust effects in renal regulation mechanisms. We summarize the relevant data and put them in context, proposing applications with clinical significance in the field of hypertension, diabetic nephropathy, chronic kidney disease, cardiorenal syndrome, and peritoneal dialysis.

Prolonged urocortin 2 administration in experimental heart failure: sustained hemodynamic, endocrine, and renal effects

Although acute administration of urocortin 2 has beneficial actions in heart failure, the integrated hemodynamic, hormonal, and renal effects of sustained urocortin 2 treatment in this disease have not been investigated. In the current study, we administered a 4-day infusion of a vehicle control (0.9% saline; n=6) or urocortin 2 (0.75 μg/kg per hour; n=6) to sheep with pacing-induced heart failure. Compared with time-matched controls, infusion of urocortin 2 produced rapid (30-minute) and persistent (4-day) improvements in cardiac contractility (day 4: control 905±73 versus urocortin 2 1424±158 mm Hg/s; P<0.001) and output (2.6±0.1 versus 3.8±0.3 L/min; P<0.001), together with reductions in left atrial pressure (28±1 versus 12±1 mm Hg; P<0.001) and peripheral resistance (30±2 versus 20±2 mm Hg/L per min; P<0.001). In contrast, urocortin 2-induced falls in mean arterial pressure were not established until the second day (day 4: 74±2 versus 72±2 mm Hg; P<0.05). Prolonged urocortin 2 administration was associated with sustained (days 0 to 4) declines in plasma renin activity (day 4: 1.33±0.27 versus 0.73±0.20 nmol/L per hour; P<0.001), aldosterone (970±383 versus 396±96 pmol/L; P<0.05), vasopressin (2.4±0.8 versus 1.3±0.1 pmol/L; P<0.05), endothelin 1 (7.2±0.7 versus 4.5±0.4 pmol/L; P<0.01), and atrial (269±27 versus 150±19 pmol/L; P<0.001) and B-type (65±9 versus 29±6 pmol/L; P<0.001) natriuretic peptides, as well as an acute transient rise in plasma cortisol (day 1: P<0.001). Chronic urocortin 2 also persistently augmented urinary sodium (day 4: 4-fold increase; P<0.001) and creatinine (1.4-fold; P<0.001) excretion and creatinine clearance (1.5-fold; P<0.01) compared with control. Food consumption was temporarily suppressed (P<0.05). In conclusion, 4-day urocortin 2 administration induces sustained improvements in hemodynamics and renal function, in association with inhibition of multiple vasoconstrictor/volume-retaining systems. These findings support the therapeutic potential for urocortin 2 in heart failure.

Urocortin 2 lowers blood pressure and reduces plasma catecholamine levels in mice with hyperadrenergic activity

Exaggerated adrenergic activity is associated with human hypertension. The peptide urocortin 2 (Ucn 2) inhibits catecholamine synthesis and secretion from adrenal chromaffin cells in vitro and administration to mammals lowers blood pressure (BP). The chromogranin A-null mouse (Chga-/-) manifests systemic hypertension because of excessive catecholamine secretion from the adrenal and decreased catecholamine storage. In the present study, we investigated whether systemic administration of Ucn 2 could reduce BP and adrenal and plasma levels of catecholamines in vivo. Ucn 2 peptide was administered to freely moving, conscious Chga-/- and wild-type control mice. Telemetry and HPLC measured changes in BP and catecholamine levels, respectively. In both groups of mice, Ucn 2 dose-dependently decreased BP, and this effect was mediated by corticotropin factor-receptor type 2. However, in Chga-/- mice, the maximal percentage decrease of systolic BP from basal systolic BP was 37% compared with only a 23% reduction in wild-type mice (P=0.04). In Chga-/- mice only, Ucn 2 decreased adrenal and plasma levels of catecholamines as well as adrenal levels of tyrosine hydroxylase protein and phosphorylation. In vitro mechanistic studies demonstrated that Ucn 2 reduces both catecholamine secretion and tyrosine hydroxylase promoter activity, suggesting that the exaggerated action of Ucn 2 to reduce BP in the Chga-/- mouse is mediated through inhibition of both catecholamine synthesis and secretion. The data suggest that Ucn 2 may be therapeutically useful in regulating the exaggerated sympathoadrenal function of hyperadrenergic hypertension.

Corticotropin-releasing factor receptors and urocortins, links between the brain and the heart

Corticotropin-releasing factor (CRF), a 41 amino acid peptide, was discovered as a key signal in mediating neuroendocrine, autonomic, and behavioral responses to stress. It was revealed later that there exist additional CRF-like peptides, termed urocortins. The CRF receptor subtype 1 (CRF1 receptor) is predominant in the brain whereas subtype 2 (CRF2 receptor) is highly expressed in the brain and the heart. Both centrally and peripherally administered CRF and urocortins produce significant hemodynamic effects via activation of CRF receptors in the brain and the heart. CRF and urocortins are important neural and cardioactive hormones, and are potentially useful therapy for heart failure.

Mechanisms involved in the regional haemodynamic effects of intermedin (adrenomedullin 2) compared with adrenomedullin in conscious rats

BACKGROUND AND PURPOSE

Intermedin (IMD) is a newly identified member of the calcitonin family of peptides that shares structural and functional homology with adrenomedullin (AM). In vivo cardiovascular effects of AM have been described, but relatively little is known of the in vivo actions of IMD. The purpose of this study was to compare the regional haemodynamic effects of IMD with those of AM in conscious rats, and investigate possible underlying mechanisms.

EXPERIMENTAL APPROACH

Measurements of blood pressure, heart rate and renal, mesenteric and hindquarters haemodynamics were made in conscious, chronically-instrumented rats.

KEY RESULTS

IMD caused tachycardia and vasodilatation in all three vascular beds, associated with modest hypotension. At an equimolar dose (1 nmol.kg(-1)), most of the cardiovascular effects of IMD were greater than those of AM. The AM receptor antagonist, AM(22-52), was equally effective in attenuating the renal and mesenteric vasodilator effects of IMD (1 nmol.kg(-1)) and AM (3 nmol.kg(-1)), but inhibition of NO synthase was more effective at reducing the vasodilator effects of IMD than AM. Vascular K(ATP) channel blockade with U-37883A did not inhibit the vasodilator effects of either peptide.

CONCLUSIONS AND IMPLICATIONS

In vivo, the regional haemodynamic profile of IMD resembles that of AM, and some of the vasodilator effects of IMD are mediated by AM receptors and NO, but not by K(ATP) channels. The cardiovascular effects of AM have been implicated in various pathological conditions, but whether or not endogenous IMD fulfils a similar role remains to be determined.

Urocortin 2 inhibits furosemide-induced activation of renin and enhances renal function and diuretic responsiveness in experimental heart failure

BACKGROUND

Urocortin 2 (Ucn2), a novel peptide with therapeutic potential in heart failure, and diuretics have opposing effects on renal function and the renin-angiotensin-aldosterone system. Because any prospective new treatment is likely to be used in conjunction with standard diuretic therapy, it is necessary to investigate the combined effects of these agents.

METHODS AND RESULTS

Ucn2 and furosemide were administered for 3 hours, both singly and combined, in 7 sheep with pacing-induced heart failure. Compared with time-matched controls, separate Ucn2 and furosemide administration significantly increased urine output (furosemide>Ucn2), urine sodium (furosemide>Ucn2), potassium (furosemide>Ucn2), and creatinine excretion (Ucn2>furosemide) and creatinine clearance (Ucn2>furosemide). Compared with furosemide treatment alone, Ucn2+furosemide produced a further diuresis (P<0.05), natriuresis (P<0.05), and a sustained increase in creatinine excretion (P<0.05) and clearance (P<0.05), without additional potassium elimination. All active treatments reduced mean arterial pressure (Ucn2+furosemide=furosemide>Ucn2), left atrial pressure (Ucn2+furosemide>Ucn2>furosemide), and peripheral resistance (Ucn2+furosemide=Ucn2>furosemide), whereas only Ucn2, singly and in combination with furosemide, increased cardiac output and dP/dt(max). In contrast to the increase in plasma renin activity elicited by furosemide alone, Ucn2 and Ucn2+furosemide markedly reduced plasma renin activity. All active treatments decreased plasma aldosterone (Ucn2+furosemide=Ucn2>furosemide), whereas only Ucn2 and Ucn2+furosemide reduced vasopressin and natriuretic peptide concentrations.

CONCLUSIONS

Ucn2 cotreatment with furosemide enhanced hemodynamic and renal function and diuretic responsiveness (without additional potassium depletion) in experimental heart failure. Furthermore, Ucn2 reversed furosemide-induced increases in plasma renin activity and induced greater decreases in plasma aldosterone and vasopressin. These data indicate that adjunct Ucn2 therapy with diuretics in heart failure is beneficial.

Urocortin 2 combined with angiotensin-converting enzyme inhibition in experimental heart failure

Ucn2 (urocortin 2) is a recently discovered peptide with therapeutic potential in heart failure. As any new treatment is likely to be used in conjunction with standard ACEI (angiotensin-converting enzyme inhibitor) therapy, it is important that the combined effects of these agents are assessed. In the present study, we investigated the effects of Ucn2 and an ACEI (captopril) administered for 3 h, both separately and together, in eight sheep with pacing-induced heart failure. Ucn2 and captopril alone both increased CO (cardiac output; Ucn2>captopril) and decreased arterial pressure (captopril>Ucn2), left atrial pressure (Ucn2>captopril) and peripheral resistance (Ucn2=captopril) relative to controls. Compared with either treatment alone, combined treatment further improved CO and reduced peripheral resistance and cardiac preload, without inducing further falls in blood pressure. In contrast with the marked increase in plasma renin activity observed with captopril alone, Ucn2 administration reduced renin activity, whereas the combined agents resulted in intermediate renin levels. All active treatments decreased circulating levels of aldosterone (Ucn2+captopril>Ucn2=captopril), endothelin-1 and the natriuretic peptides (Ucn2+captopril=Ucn2>captopril), whereas adrenaline (epinephrine) fell only with Ucn2 (Ucn2+captopril=Ucn2), and vasopressin increased during captopril alone. Ucn2, both separately and in conjunction with captopril, increased urine output, sodium and creatinine excretion and creatinine clearance. Conversely, captopril administered alone adversely affected these renal indices. In conclusion, co-treatment with Ucn2 and an ACEI in heart failure produced significantly greater improvements in haemodynamics, hormonal profile and renal function than achieved by captopril alone. These results indicate that dual treatment with these two agents is beneficial.

The effect of urocortin II administration on the coronary circulation and cardiac function in the anaesthetized pig is nitric-oxide-dependent

We planned to determine the primary effects and mechanisms of urocortin II, a member of the corticotrophin-releasing factor (CRF) family highly expressed in the cardiovascular system, on coronary blood flow and myocardial function in vivo. Urocortin II was infused into the left anterior descending coronary artery in 25 anaesthetized pigs whilst measuring haemodynamic variables, coronary blood flow, ventricular dP/dt(max) cardiac output and percentage of segmental shortening. This infusion was repeated after blockade of the autonomic nervous system, nitric-oxide synthase (NOS) or subtype 2 of the CRF receptors. In all experiments changes in heart rate and aortic blood pressure were prevented. Intra-coronary urocortin II increased, within 60 s, coronary blood flow (15+/-3.2%, P<0.05), dP/dt(max) (12.7+/-2.6%, P<0.05), cardiac output (16+/-2.3%, P<0.05) and percentage of segmental shortening (19.8+/-3.8%, P<0.05). Blockade of NOS abolished only the coronary effects whereas blockade of subtype 2 of the CRF receptors abolished all cardiac and coronary effects. It was shown for the first time that urocortin II administration primarily increases coronary blood flow and myocardial function through the release of nitric oxide and activation of subtype 2 of the CRF receptors in the anaesthetized pig. This provides a mechanism through which a local increase of urocortin II levels can help improve a compromised cardiovascular function.

Physiology, pharmacology, and therapeutic relevance of urocortins in mammals: ancient CRF paralogs

Urocortins, three paralogs of the stress-related peptide corticotropin-releasing factor (CRF) found in bony fish, amphibians, birds, and mammals, have unique phylogenies, pharmacologies, and tissue distributions. As a result and despite a structural family resemblance, the natural functions of urocortins and CRF in mammalian homeostatic responses differ substantially. Endogenous urocortins are neither simply counterpoints nor mimics of endogenous CRF action. In their own right, urocortins may be clinically relevant molecules in the pathogenesis or management of many conditions, including congestive heart failure, hypertension, gastrointestinal and inflammatory disorders (irritable bowel syndrome, active gastritis, gastroparesis, and rheumatoid arthritis), atopic/allergic disorders (dermatitis, urticaria, and asthma), pregnancy and parturition (preeclampsia, spontaneous abortion, onset, and maintenance of effective labor), major depression and obesity. Safety trials for intravenous urocortin treatment have already begun for the treatment of congestive heart failure. Further understanding the unique functions of urocortin 1, urocortin 2, and urocortin 3 action may uncover other therapeutic opportunities.

A Comparison between the Cardiovascular Actions of Urocortin 1 and Urocortin 2 (Stresscopin-Related Peptide) in Conscious Rats

The aims of the study were, in conscious Sprague-Dawley rats, to compare the effects of stresscopin-related peptide (SRP) and urocortin (UCN) 1 on blood pressure, heart rate, and regional hemodynamics; to determine whether or not there were residual tachycardic effects of SRP or UCN1 after cardiac autonomic blockade; and to investigate a possible involvement of corticotropin releasing factor type 1 (CRF1) receptor-mediated histamine release in the vasodilator actions of UCN1. SRP and UCN1 (both at 3 nmol/kg i.v.) caused hypotension, tachycardia, and mesenteric and hindquarters vasodilatation, but the magnitude and/or duration of the effects of UCN1 were generally greater than those of SRP. Pretreatment with atropine plus propranolol abolished the tachycardic effects of SRP and UCN1, and, under those conditions, the hypotensive effect of SRP, but not that of UCN1, was enhanced, probably because the hindquarters vasodilator effect of the latter was also reduced. Pretreatment with mepyramine plus cimetidine had no effect on the hemodynamic actions of either SRP or UCN1. It is concluded that, in conscious rats, the tachycardic effects of SRP and UCN1 are due to autonomic nervous activation mainly through baroreflex mechanisms. There is no evidence for an involvement of CRF1 receptor-mediated histamine release in the vasodilator actions of UCN1, but a propranolol-sensitive hindquarters vasodilator action of UCN, but not of SRP, was identified.

Urocortin 2 infusion in healthy humans: hemodynamic, neurohormonal, and renal responses

OBJECTIVES

We sought to examine the effects of urocortin (UCN) 2 infusion on hemodynamic status, cardiovascular hormones, and renal function in healthy humans.

BACKGROUND

Urocortin 2 is a vasoactive and cardioprotective peptide belonging to the corticotrophin-releasing factor peptide family. Recent reports indicate the urocortins exert important effects beyond the hypothalamo-pituitary-adrenal axis upon cardiovascular and vasohumoral function in health and cardiac disease.

METHODS

We studied 8 healthy unmedicated men on 3 separate occasions 2 to 5 weeks apart. Subjects received placebo, 25-microg low-dose (LD), and 100-microg high-dose (HD) of UCN 2 intravenously over the course of 1 h in a single-blind, placebo-controlled, dose-escalation design. Noninvasive hemodynamic indexes, neurohormones, and renal function were measured.

RESULTS

The administration of UCN 2 dose-dependently increased cardiac output (mean peak increments +/- SEM) (placebo 0.5 +/- 0.2 l/min; LD 2.1 +/- 0.6 l/min; HD 5.0 +/- 0.8 l/min; p < 0.001), heart rate (placebo 3.3 +/- 1.0 beats/min; LD 8.8 +/- 1.8 beats/min; HD 17.8 +/- 2.1 beats/min; p < 0.001), and left ventricular ejection fraction (placebo 0.6 +/- 1.4%; LD 6.6 +/- 1.5%; HD 14.1 +/- 0.8%; p < 0.001) while decreasing systemic vascular resistance (placebo -128 +/- 50 dynes x s/cm(5); LD -407 +/- 49 dynes x s/cm(5); HD -774 +/- 133 dynes.s/cm(5); p < 0.001). Activation of plasma renin activity (p = 0.002), angiotensin II (p = 0.001), and norepinephrine (p < 0.001) occurred only with the higher 100-mug dose. Subtle decreases in urine volume (p = 0.012) and natriuresis (p = 0.001) were observed.

CONCLUSIONS

Brief intravenous infusions of UCN 2 in healthy humans induced pronounced dose-related increases in cardiac output, heart rate, and left ventricular ejection fraction while decreasing systemic vascular resistance. Subtle renal effects and activation of plasma renin, angiotensin II, and norepinephrine (at high-dose only) were observed. These findings warrant further investigation of the role of UCN 2 in circulatory regulation and its potential therapeutic application in heart disease.

Vasodilation of Retinal Arteriole Mediated by Corticotropin-Releasing Factor Receptor is Impaired in Streptozotocin-Induced Diabetic Rats

We investigated the vasodilator responses of retinal arterioles induced by stimulating corticotropin-releasing factor receptors in non-diabetic and diabetic rats. Male Wistar rats were treated with streptozotocin (65 mg/kg, i.v.) and experiments were performed 6-8 weeks later. Rats were treated with tetrodotoxin (50 mug/kg, i.v.) to eliminate any nerve activity and prevent movement of the eye and infused with a mixture of norepinephrine and epinephrine to maintain adequate systemic circulation under artificial ventilation. Fundus images were captured with an original high-resolution digital fundus camera system. The vasodilator responses of retinal arterioles were assessed by measuring changes in diameters of retinal arterioles in response to urocortin and urocortin 2. Both urocortin (0.03-1.0 micromol/kg, i.v.) and urocortin 2 (0.1-3.0 micromol/kg, i.v.) increased diameters of retinal arterioles and decreased systemic blood pressure in a dose-dependent manner. The responses to urocortins were reduced in diabetic rats. These results suggest that urocortin and urocortin 2 play as vasodilators in retinal and peripheral resistance arterioles. The impairment of vasodilation mediated by the corticotropin-releasing factor receptors may contribute to the alteration of retinal and systemic circulation in the diabetic state.

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.

Facilitation of cardiac vagal activity by CRF-R1 antagonists during swim stress in rats

Exposure to stressors that elicit fear and feelings of hopelessness can cause severe vagal activation leading to bradycardia, syncope, and sudden death. These phenomena though documented, are difficult to diagnose, treat clinically, and prevent. Therefore, an animal model incorporating these cardiovascular conditions could be useful. The present study examined 'sinking' during a 2-h swim stress, a phenomenon that occurs in 50% of rats during 25 degrees C water exposure. Concurrent measurements of body temperature, immobility, heart rate (HR), and PR interval (a measure of vagal activity) were made. Neither decreases in immobility nor variations in hypothermia during swim were correlated with sinking. Bradycardia was more severe in sinking rats (average minimum HR+/-SEM; 143+/-13 vs 247+/-14; p<0.01), and PR interval was elevated (p<0.0001). To examine potential modulation of vagal activity during stress, corticotropin-relasing factor (CRF) receptor antagonists (antalarmin, R121919 and astressin B), a glucocorticoid receptor antagonist (RU486), and a peripherally acting cholinergic antagonist (methylatropine nitrate) were administered. The centrally acting CRF antagonist, antalarmin (32 mg/kg), produced elongation of the PR interval (p<0.0001), robust bradycardia (135+/-18; p<0.001), and increased sinking (92%; p<0.05), and methylatropine nitrate (3.2 mg/kg) blocked these effects. Corroborating these data, two different CRF antagonists, R121919 (30 mg/kg) and astressin B (intracerebroventricular (i.c.v.), 0.03 mug/rat) increased sinking to 100%. RU486 (20 mg/kg) blocked HPA axis negative feedback and decreased percent sinking to 25%. From these studies, we concluded that sinking during a 2-h water exposure was a result of extreme vagal hyperactivity. Furthermore, stress-induced CRF release may serve to protect against elevated cardiac vagal activity.

Effect of urocortin 1 infusion in humans with stable congestive cardiac failure

In sheep with HF (heart failure), Ucn1 (urocortin 1) decreases total peripheral resistance and left atrial pressure, and increases cardiac output in association with attenuation of vasopressor hormone systems and enhancement of renal function. In a previous study, we demonstrated in the first human studies that infusion of Ucn1 elevates corticotropin (‘ACTH’), cortisol and ANP (atrial natriuretic peptide), and suppresses the hunger-inducing hormone ghrelin in normal subjects. In the present study, we examined the effects of Ucn1 on pituitary, adrenal and cardiovascular systems in the first Ucn1 infusion study in human HF. In human HF, it is proposed that Ucn1 would augment corticotropin and cortisol release, suppress ghrelin and reproduce the cardiorenal effects seen in animals with HF. On day 3 of a controlled metabolic diet, we studied eight male volunteers with stable HF (ejection fraction <40%; New York Heart Association Class II–III) on two occasions, 2 weeks apart, receiving 50 μg of Ucn1 or placebo intravenously over 1 h in a randomized time-matched cross-over design. Neurohormones, haemodynamics and urine indices were recorded. Ucn1 infusion increased plasma Ucn1, corticotropin (baseline, 5.9±0.9 pmol/l; and peak, 7.2±1.0 pmol/l) and cortisol (baseline, 285±42 pmol/l; and peak, 310±41 pmol/l) compared with controls (P<0.001, 0.008 and 0.047 respectively). The plasma Ucn1 half-life was 54±3 min. ANP and ghrelin were unchanged, and no haemodynamic or renal effects were seen. In conclusion, a brief intravenous infusion of 50 μg of Ucn1 stimulates corticotropin and cortisol in male volunteers with stable HF.