The effects of naloxone on the cardiovascular and respiratory effects of centrally administered corticotrophin releasing factor in conscious rabbits

Cardiovascular effects of long-term central and peripheral administration of urocortin, corticotropin-releasing factor, and adrenocorticotropin in sheep

The neuroendocrine hormones ACTH and corticotropin- releasing factor (CRF), which are involved in the stress response, have acute effects on arterial pressure. New evidence indicates that urocortin (UCN), the putative agonist for the CRF type 2 receptor, has selective cardiovascular actions. The responses to long-term infusions of these hormones, both peripherally and centrally, in conscious animals have not been studied. Knowledge of the long-term effects is important because they may differ considerably from their acute actions, and stress is frequently a chronic stimulus. The present experiments investigated the cardiovascular effects of CRF, UCN, and ACTH in conscious sheep. Infusions were made either into the lateral cerebral ventricles (i.c.v.) or i.v. over 4 d at 5 microg/h. UCN infused i.c.v. or i.v. caused a prolonged increase in heart rate (HR) (P < 0.01) and a small increase in mean arterial pressure (MAP) (P < 0.05). CRF infused i.c.v. or i.v. progressively increased MAP (P < 0.05) but had no effect on HR. Central administration of ACTH had no effect, whereas systemic infusion increased MAP and HR (P < 0.001). In conclusion, long-term administration of these three peptides associated with the stress response had prolonged, selective cardiovascular actions. The striking finding was the large and sustained increase in HR with i.c.v. and i.v. infusions of UCN. These responses are probably mediated by CRF type 2 receptors because they were not reproduced by infusions of CRF.

CRF1-receptor antagonist CP-154526 reduces alerting-related cutaneous vasoconstriction in conscious rabbits

Cutaneous vasoconstrictor responses elicited by salient stimuli in conscious rabbits may be a sensitive physiological index of emotional arousal/anxiety. Ear-pinna blood flow was measured by preimplanted laser Doppler probes, and animals were exposed to situations involving different types of potentially salient stimuli before and after i.v. administration of CP-154526 (15 mg/kg) or diazepam (4 mg/kg). At rest, ear-pinna blood flow was stable (coefficient of varition=11+/-2) and remained at high level 93+/-13% of test time. Exposure to novel environment elicited flow fluctuations (coefficient of variation=79+/-8) and reduced amount of time spent at high level to 25+/-6%. Defined unconditioned stimuli caused rapid falls in ear-pinna flow, with nociceptive stimulation producing more vigorous and consistent effects (flow response index 0.66+/-0.02) compared with non-nociceptive (flow response index 0.49+/-0.04). CP-154526 slightly raised mean arterial pressure (from 81+/-2 to 93+/-3 mmHg), increased heart rate (from 198+/-1 to 220+/-4 beats/min) and produced a mild vasoconstriction in the ear-pinna bed (flow fell from 46+/-10 to 25+/-6 cm/s). CP-154526 substantially reduced cutaneous vasoconstrictor responses elicited by the exposure to novel environment and by defined non-nociceptive stimuli, with flow-response index fall from 0.53+/-0.10 to 0.17+/-0.09 and from 0.47+/-0.04 to 0.24+/-0.04, respectively, without affecting responses to nociceptive stimuli. Diazepam reduced only vasoconstrictor responses elicited by the exposure to novel environment, with flow-response index fall from 0.40+/-0.12 to 0.27+/-0.07. Sensitivity of rapid changes in rabbit ear-pinna blood flow to anxiolytic drugs supports the idea that increased cutaneous vascular tone reflects enhanced arousal in rabbits.

Urocortin promotes hemodynamic and bioenergetic recovery and improves cell survival in the isolated rat heart exposed to ischemia/reperfusion

OBJECTIVES

This study evaluates the hemodynamic, bioenergetic and cytoprotective effects of urocortin (Ucn) in the isolated rat heart exposed to ischemia (I)/reperfusion (R).

BACKGROUND

We have previously demonstrated that administration of exogenous Ucn reduces infarct size in ischemic-reperfused rat hearts.

METHODS

Urocortin 10(-8)M was added to the perfusate before I, before I and during R, and during R alone in the isolated pulsed rat heart exposed to 35 min I followed by 60 min R.

RESULTS

Partial to complete recovery of diastolic pressure and developed pressure was seen irrespective of when Ucn was perfused. In particular, beneficial effects are observed when Ucn is only given during R. Urocortin given only before I, and before I and over R, although not during R alone, also produces significant recovery of high-energy phosphate pools. In each group, improvement in ventricular function is associated with reduction both in myocardial damage, assessed by creatine phosphokinase release, and in endothelial cell and cardiomyocyte apoptosis, assessed by caspase 3 activity and fluorescent-based terminal deoxynucleotidyl transferase mediated nick end labelling enhanced with counterstains. These improvements in ventricular performance, bioenergetics and cell survival are not secondary to any inotropic effects of Ucn.

CONCLUSIONS

This is the first report to show enhanced cardiac function induced by Ucn during I/R. Because the cytoprotective and functional benefits are still produced when Ucn is given only at R, these data suggest that Ucn may be useful clinically in the management of myocardial infarction.

Cardiovascular actions of CRH and urocortin: an update

Urocortin is a potent regulator of cardiac function, with actions that are prolonged in experimental animals. These changes are mediated via binding to CRH receptors found in peripheral tissues. The diversity of actions of urocortin on behaviour, appetite, inflammation and the cardiovascular system suggest that this peptide may be an endogenous factor mediating actions previously attributed to CRH. The present review will focus on the recent understanding of mechanisms mediating the cardiovascular actions of urocortin and CRH reported to date.

Effect of ICV infusion of CRF on blood pressure and adrenal steroids in rabbits

The effect of prolonged, 22 h long, intracerebroventricular (i.c.v.) infusion of corticotropin-releasing hormone (CRF) on plasma cortisol, corticosterone and electrolyte concentrations, mean arterial blood pressure (MAP) and heart rate (HR) were investigated in conscious rabbits. During i.c.v. infusion of CRF, 1 and 3 micrograms/h, at a rate of 17 microliters/h, plasma cortisol and corticosterone concentrations rose to the level noted after ACTH stimulation in rabbits. Plasma [Na] did not change, but plasma [K] was reduced and plasma osmolality increased during the infusion of CRF, 3 micrograms/h. MAP and HR, recorded continuously during i.c.v. infusion of CRF, changed only with the higher dose of CRF: MAP was elevated during the first 5 h of infusion, and then returned to the control level. HR was lower than control at the end of the first hour of infusion and again between 9 and 15 h of infusion. The prolonged rise of CRF concentration in the brain induced a sustained rise in circulating adrenal steroid hormones. MAP did not increase to the level noted after bolus i.c.v. injection of CRF and the rise in MAP was not sustained.

Comparison of hCRF and oCRF effects on cardiovascular responses after central, peripheral, and in vitro application

Three assays have been used to show that the neuropeptides human corticotropin-releasing factor (hCRF) and the ovine analogue oCRF produced substantial dose-dependent cardiovascular responses. The assays included intracerebroventricular (ICV) and intravenous (IV) administration in conscious rats, and also in vitro experiments with resistance arteries. Central administration of the peptides (0.1-10 micrograms, ICV) caused an increase in blood pressure and heart rate, whereas peripheral administration (0.75-750 micrograms/kg, IV) produced a decrease in blood pressure and tachycardia. Isometric ring preparations of mesenteric resistance arteries (diameter 200 microns) relaxed in response to both peptides (1-100 nM). In all cases, the effects were more pronounced for hCRF compared to compared to oCRF. Furthermore, all effects were inhibited by the CRF analogue alpha-helical CRF(9-41), the effect of the analogue being most potent against oCRF. The results of all three assays indicate that the difference in structure between hCRF and oCRF produces differences in biological activity.

Ultrastructural localization and afferent sources of corticotropin-releasing factor in the rat rostral ventrolateral medulla: implications for central cardiovascular regulation

We investigated the ultrastructural localization, afferent sources, and arterial pressure effects of corticotropin-releasing factor (CRF) in the nucleus reticularis rostroventrolateralis (RVL), a region of the ventrolateral medulla containing C1 adrenergic neurons and sympatho-excitatory reticulospinal afferents to sympathetic preganglionic neurons. A polyclonal antibody to CRF was localized in acrolein-fixed sections through the rat RVL by the peroxidase-antiperoxidase (PAP) method. Light microscopy showed that 1-7 perikarya/30 micron section and numerous varicose processes contained CRF-like immunoreactivity (CRF-LI). By electron microscopy, CRF-LI was most intensely localized to large (80-100 nm) dense-core vesicles within numerous terminals and a few perikarya and large dendrites. Approximately half of the terminals containing CRF-LI were in direct contact with unlabeled perikarya or dendrites; the remainder were in apposition to either unlabeled terminals or astrocytes. Most synaptic specializations were asymmetric synapses on small, unlabeled dendrites. To examine potential extrinsic sources of CRF-containing terminals in the C1 area of the RVL, PAP immunocytochemical localization of CRF was combined with retrograde transport of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP). In all cases examined, a number of dually labeled neurons were found in the paraventricular nucleus (PVN) of the hypothalamus and a few dually labeled neurons were observed in the nuclei of the solitary tract; these labeled neurons were ipsilateral to the unilateral injection of WGA-HRP into the C1 area. Fewer dually labeled perikarya were detected in the lateral hypothalamic area and the lateral parabrachial nuclei, ipsilateral to the WGA-HRP injection. Additional physiological studies showed that bilateral microinjections of CRF into the C1 area of the RVL of urethane-anesthetized rats elicited a dose-related increase in arterial pressure. The results suggest that within the C1 area of the RVL, CRF released from terminals, arising predominantly from the PVN of the hypothalamus and probably from local neurons as well, may excite sympathoexcitatory reticulospinal neurons.