头端延髓腹外侧区在侧脑室注射新斯的明所致升压中的作用

实验在47只乌拉坦(700m/kg)、氯醛糖(35mg/kg)麻醉,肌肉麻痹,人工呼吸的家兔上进行。结果观察到,侧脑室注射(icv)新斯的明引起血压升高,心率(HR)先减慢后有加快趋势,股动脉血流量(FBF)与股动脉血管通道性(COND)减小,左心室内压(LVP)增大,肾交感神经放电(RND)增加,延髓腹外侧头端(rVLM)微量注射阿托品则引起血压下降,HR减慢,FBF与COND增加,LVP与RND减小,若在icv新斯的明之前,预先向rVLM注入阿托品,可阻断新斯的明的升压效应,上述结果提示,rVLM是icv新斯的明升压效应的重要部位,rVLM区M受体功能完整是这种升压作用的关键因素。     

Central antinociceptive effects of lysine-vasopressin and an analogue

Vasopressin (VP) neurons project to extrahypothalamic sites involved in pain perception, including the substantia gelatinosa of the spinal cord as well as the trigeminal and vagus nerves. Previous studies have reported antinociceptive activity following intracerebroventricular (ICV) or subcutaneous (SC) VP injections (16–100 μg) on the tail-flick test while hyperalgesia has been observed in rats either genetically deficient in VP or treated with antisera to VP. The present study investigated whether nanogram (ng) doses of lysine-vasopressin (LVP) and a VP analogue with prolonged activity increased tail-flick latencies and flinch-jump thresholds following ICV or SC injections. LVP (150 and 500 ng, ICV) significantly increased tail-flick latencies while the analogue 1-deamino-(8-Lys-N^?-(Gly-Gly-Gly))-VP (500 ng, ICV) produced more powerful and prolonged analgesia. In contrast, latencies were not increased by SC injections of LVP (150–1500 ng). Further, flinch-jump thresholds were affected minimally by either ICV or SC LVP injections. These data suggest a role for VP in pain modulation and a central site of this action.     

Pressor, tachycardic and behavioral excitatory responses in conscious rats following ICV administration of ACTH and CRF are blocked by naloxone pretreatment

Experiments were conducted to compare the blood pressure and heart rate responses of conscious rats given intracerebroventricular (ICV) injections of adrenocorticotropin (ACTH 1-24) and corticotropin releasing factor (CRF). Under sodium pentobarbital anaesthesia, rats were implanted with a stainless-steel cannula into the lateral cerebral ventricle and had their right femoral artery and vein cannulated. Upon recovery (24-48 hr later) conscious, unrestrained rats were given ICV injections (total volume 5 microliter by gravity flow) of sterile saline, ACTH (1-24) (0.85 and 1.7 nmoles) or CRF (0.55 and 1.1 nmoles) and blood pressure and heart rate were monitored over the next 2 hr (from the abdominal aorta via the femoral arterial catheter). Both ACTH and CRF caused mean arterial pressure (MAP) to increase, which was paralleled with increases in mean heart rate (MHR). Moreover, these elevations in MAP and MHR were temporally associated with excessive grooming (for ACTH) and locomotor activity (for CRF), which occurred before and lasted as long as MAP and MHR were enhanced. Intravenous (IV) pretreatment whereby naloxone was given 10 min before ICV administration of ACTH (1.7 nmoles) or CRF (1.1 nmoles), showed that naloxone blocked the behavioral, pressor and tachycardic effects of both ACTH and CRF. The results demonstrate that the pressor, tachycardic and locomotor effects evoked in conscious rats by ICV administration of ACTH or CRF are antagonized by naloxone and that their hemodynamic changes may, in part, be mediated by prior behavioral activation.     

Comparative effects on blood pressure and heart rate of dynorphin A(1–13) in anterior hypothalamic area, posterior hypothalamic area, nucleus tractus solitarius, and lateral cerebral ventricle in the rat

The objective of this study was to explore the effects of the endogenous opioid peptide dynorphin A(1–13) on the CNS regulation of blood pressure and heart rate. Wistar rats, anesthetized with pentobarbital and halothane, received dynorphin A(1–13) microinjected into the anterior hypothalamus area (AHA), the posterior hypothalamic area (PHA), the nucleus tractus solitarius (NTS), or the lateral cerebral ventricle (ICV). Dynorphin A(1–13), 20 (12 nmol) or 30 μg ICV, produced significant (p < 0.05) reductions in blood pressure and heart rate. Naloxone, 50 μg/kg ICV, completely prevented the blood pressure response and significantly (p < 0.05) blunted the heart rate response to the highest dynorphin concentration, 30 μg ICV (18 nmol). Dynorphin A(1–13), 5 μg, in the NTS significantly (p < 0.05) decreased systolic and diastolic blood pressure and heart rate with the response being evident 10 min and persisting for 30 min after injection. In contrast, the same dose of dynorphin A(1–13) in the AHA produced an immediate, marked, and significant (p < 0.05) decrease in systolic and diastolic blood pressure and heart rate that attained its maximum 1–3 min and returned rapidly towards baseline levels. Dynorphin A(1–13), 5 or 10 μg in the posterior hypothalamic area, was not associated with any change in blood pressure or heart rate. Injection of the diluent at any site was not associated with any changes in blood pressure or heart rate. The maximum change in blood pressure with dynorphin was greater in the AHA than NTS, and the maximum change in heart rate was greater in the NTS than AHA. These data indicate a potential role for dynorphin as a modulator of the CNS regulation of blood pressure and cardiac rate, and this is mediated in part through different areas in the brain that maybe localized to the anterior hypothalamic area and nucleus tractus solitarius but not the posterior hypothalamic area.     

Effect of an oral contraceptive on the lysine-8-vasopressin test in the diagnostic evaluation of pituitary function.

A comparative study was performed on the plasma 11-hydroxycorticosteroids (11-OHCS) responses to lysine-8-vasopressin (LVP) before and during ingestion of an oral contraceptive wieh oestrogenic activity. A total of 19 healthy women with a normal menstrual cycle and normal plasma 11-OHCS content in blood samples at 8 a.m. and 4 p.m. were included in the study. The results show that the mean response of plasma 11-OHCS to the administration of LVP was equal in magnitude before and during ingestion of the contraceptive, although the baseline value of 11-OHCS doubled as a result of the treatment. On the other hand, during contraceptive treatment the increase of plasma 11-OHCS concentration after the administration of LVP was somewhat slower, reaching its peak later than before treatment. The noticeable variation in individual responses of plasma 11-OHCS to LVP increased during the treatment. Three subjects showed weak responses to LVP, although the adrenocortical responses to exogenous ACTH were quite normal. The inidvidual responses to LVP before and during ingestion of an oral contraceptive with oestrogenic activity are discussed.     

Systemic site of action for pressor effect of angiotensin II injected into the fourth cerebral ventricle of rats?

Angiotensin II (ANG II) causes a systemic pressor effect when injected into the cerebral ventricles. In the rat fourth ventricle, the effective doses for the ANG II pressor effect are over 100 times larger than in the systemic circulation. Considering the discrepancy of doses, the possibility that ANG II may reach the systemic circulation and promote pressor effects, following injection into the fourth ventricle, was investigated. The effects on blood pressure of different vasoactive peptides that produce pressor responses when injected into the central nervous system were compared. Dose-response curves were obtained for intravenous or fourth cerebroventricular injections of ANG II, lysyl-vasopressin (LVP), bradykinin (BK), or endothelin-1 (ET-1). The ED50 ratios for intracerebroventricular/intraveneous injections were 110 for ANG II, 109 for LVP, 0.01 for BK, and approximately 0.4 for ET-1. In cross-circulation preparations, pressor responses occurred in the donor rat following injection into the fourth cerebral ventricle of the recipient animal, showing that effective doses of ANG II, administered to the fourth cerebral, reach the systemic circulation. The same results were obtained for the microinjection of 4 nmol of LVP into the fourth cerebral ventricle of recipient animals. High-performance reverse-phase liquid chromatography analyses of arterial blood showed that approximately 1% of the [125I]ANG II injected into the fourth cerebral ventricle may be recovered from the systemic circulation a few seconds after the microinjection. The systemic administration of the ANG II receptor antagonist losartan blocked the response to ANG II injected into the fourth ventricle whereas antagonist administration in the same ventricle did not. Angiotensin injections into the lateral ventricle produced pressor responses that were reduced by antagonist administration to the same ventricle but not by systemic administration of the antagonist. The data suggest that the pressor effect resulting from ANG II or LVP injections into the fourth cerebral ventricle may be due to the action of this peptide in the systemic circulation. On the other hand, the pressor effect due to ANG II microinjection into the lateral ventricle apparently results from the direct stimulation of central periventricular structures.     

Diuretic effect of intraventricular and intravenous infusions of noradrenaline in conscious sheep

Infusion of noradrenaline at rates between 32-160 nmol.min-1 for 30 min into one lateral cerebral ventricle of conscious sheep caused a diuresis which was accompanied by negative solute-free water reabsorption and which lasted for 90-120 min. The range of noradrenaline infusion rates used reflects differences between individual animals in the rate of infusion necessry to cause diuresis. Intracerebroventricular (ICV) infusion of noradrenaline at half the diuretic rate caused no significant changes in urine flow. The diuresis induced by ICV noradrenaline infusion was prevented by concurrent ICV administration of the alpha-adrenergic antagonist, phentolamine, but was not prevented by concurrent ICV administration of the beta antagonist, propranolol, or by concurrent intravenous infusion of phentolamine. Intravenous infusion of noradrenaline at rates that were diuretic by ICV infusion caused a diuresis of approximately 30 min duration which coincided with the period of intravenous noradrenaline infusion. This diuresis was prevented by concurrent intravenous infusion of phentolamine. These results were interpreted as indicating that the higher rates of ICV infusion of noradrenaline caused the prolonged water diuresis by acting at a site in the brain and, thereby, inhibiting the release of endogenous vasopressin. ICV infusion of noradrenaline at all rates was followed by a reduction in mean arterial blood pressure and pulse pressure with variable changes in heart rate and by depression of the rates of renal clearance of PAH, potassium and total solute.     

A model of the coronary vascular bed and its verification by a physiological experiment

We analysed the relationship between artery pressure (AP) and coronary flow (F) in the canine coronary bed, using an electrical analog model of the coronary circulation. The model contained a capacitance of epicardial vessels, input and terminal resistances, diode, and the number of e.m.f., simulated the intramyocardial pressure and zero-flow pressure. These e.m.f. are assumed to be a linear functions of left ventricular and aortic pressure. The value of coronary blood flow was calculated from experimental curves of AP and LVP and setting parameters. Good agreement was obtained between theoretical and experimental curves of coronary blood flow.     

A model for the study of the oral administration of peptide hormones.

The intragastric administration of lysine vasopressin (LVP) to rats is used as a model to study the biological activity of orally administered peptide hormones. Using a modification of the antidiuretic assay of Sawyer, LVP given by stomach tube caused a significant antidiuresis that was dose dependent in doses of 300 to 2000 mU. The simultaneous administration of the protease inhibitor, Trasylol, increased the antidiuretic effect of LVP. The synthetic peptide (1-deamino, 4 valine)-8-D-arginine-vasopressin also caused a dose-dependent prolonged and significant antidiuresis. No pressor effect was observed after intragastric administration of LVP in doses up to 40 U/rat. We are now using this model to test other procedures for enhancing the activity of lysine vasopressin administered in the gastrointestinal tract such as encapsulation into liposomes. The information gained with vasopressin will then be applied to insulin with the ultimate goal of making oral administration practical.     

Intracerebroventricular administration of MK-801 increases food intake through mechanisms independent of gastric emptying

Systemic or hindbrain administration of MK-801, a noncompetitive N-methyl-D-aspartate receptor antagonist, increases meal size. To examine whether MK-801 enhances intake by increasing gastric emptying, we administered MK-801 (2.0 microg/3.0 microl) into the fourth ventricle [intracerebroventricular (ICV)] and measured feeding and gastric emptying of 5-ml NaCl or 15% sucrose loads. In a parallel experiment, we examined food intake and gastric emptying following intraperitoneal (IP) injection of MK-801 (100 microg/kg). MK-801, either IP or ICV, increased 30-min sucrose intake compared with control (12.3 +/- 0.7 vs. 9.8 +/- 0.5 and 16.6 +/- 2.0 vs. 10.7 +/- 0.7 ml, for IP and ICV administration, respectively). Also, IP MK-801 increased 5-min gastric emptying of NaCl (4.13 +/- 0.1 ml emptied) and sucrose (3.11 +/- 0.1 ml emptied) compared with control (3.75 +/- 0.2 and 2.28 +/- 0.1 ml emptied for NaCl and sucrose loads, respectively). In contrast, ICV MK-801 did not alter NaCl emptying (3.82 +/- 0.1 ml emptied) compared with control (3.82 +/- 0.3 ml emptied) and actually reduced gastric emptying of sucrose (2.1 +/- 0.2 and 2.94 +/- 0.1 ml emptied, for MK and vehicle, respectively). These data confirm previous results that systemic as well as hindbrain injection of MK-801 increases food intake. However, because ICV MK-801 failed to increase gastric emptying, these results indicate that MK-801 increases food intake through mechanisms independent of altered gastric emptying.     

Naloxone-like influence of TRH and ACTH-(4-7) on hypothalamic blood flow autoregulation in the rat

The influence of intracerebroventricularly (ICV) administered thyrotropin-releasing hormone pGlu-His-Pro-NH2 (TRH), pGlu-His-Phe-NH2 (TRH analog, (TRHa)), Met-Glu-His-Phe(ACTH-(4-7)) and His-Phe-Arg-Trp-Gly (ACTH-(6-10)) on autoregulation of cerebral blood flow was studied in anesthetized, ventilated rats. Autoregulatory capacity of the cerebrovascular bed was tested by hypothalamic blood flow (HBF) and total cerebral blood volume (CBV) determinations during consecutive stepwise lowering of the systemic mean arterial pressure to 80, 60 and 40 mmHg, by hemorrhage. None of the peptides caused a change in resting HBF or CBV upon ICV administration (5 micrograms/kg). However, the same dose of TRH, TRHa and ACTH-(4-7) resulted in impairment of autoregulation. ACTH-(6-10) was not effective. Thus, the disturbed autoregulation may be due to the presence of the dipeptide Glu-His which is common to TRH, TRHa and ACTH-(4-7).     

Sildenafil acts on the central nervous system increasing sympathetic activity.

Sildenafil induces vasodilation and is used for treating erectile dysfunction. Although its influence on resting heart function appears to be minimal, recent studies suggest that sildenafil can increase sympathetic activity. We therefore tested whether sildenafil injected into the central nervous system alters the autonomic control of the cardiovascular system in conscious rats. The effect of sildenafil citrate injected into the lateral cerebral ventricle was evaluated in conscious rats by means of the recording of lumbar sympathetic nerve activity (LSNA), spectral analysis of systolic arterial pressure and heart rate variability, spontaneous baroreflex sensitivity, and baroreflex control of LSNA. Intracerebroventricular (ICV, 100 microg /5 microl) administration of sildenafil caused remarkable tachycardia without significant change in basal arterial pressure and was associated with a conspicuous increase (47 +/- 14%) in LSNA. Spectral analysis demonstrated that systolic arterial pressure oscillations in the low frequency (LF) range were increased (from 6.3 +/- 1.5 to 12.8 +/- 3.8 mmHg(2)), whereas the high frequency (HF) range was not affected by ICV administration of sildenafil. Sildenafil increased pulse interval oscillations at LF and decreased them at HF. The LF-HF ratio increased from 0.04 +/- 0.01 to 0.17 +/- 0.06. Spontaneous baroreflex sensitivity measured by the sequence method and the baroreflex relationship between mean arterial pressure and LSNA were not affected by ICV administration of sildenafil. In conclusion, sildenafil elicited an increase in sympathetic nerve activity that is not baroreflex mediated, suggesting that this drug is able to elicit an autonomic imbalance of central origin. This finding may have implications for understanding the cardiovascular outcomes associated with the clinical use of this drug.     

Vasopressin does not enhance memory processes: a study in human twins

Behavioral effects of lysin-vasopressin (LVP) were investigated applying two paradigms from human experimental psychology. The first task was designed to simulate amnesic symptoms in normals. The second task addressed the emotional value of the items to be processed. Additionally, EEG recordings were used as indicators of the central nervous system effectiveness of LVP. Blood pressure and heart rate measured peripheral arousal. The co-twin control method was employed to increase experimental power. Contrary to the prediction of the vasopressin memory hypothesis none of the specific memory parameters was improved by LVP treatment. Changes in the electrical activity of the brain, but not in blood pressure and heart rate indicated central nervous system actions of LVP. However, interpretation of LVP effects in terms of memory processing seems not to be justified.     

Analgesic and cardiovascular effects of centrally administered substance P

Substance P (SP) injected intracerebroventricularly (ICV) into rabbits caused dose-related thermal analgesia with the maximum effect after 2 micrograms. The analgesia was measured by timing the withdrawal of the rabbit's ear from an infrared beam. Equimolar amounts of the related peptides physalaemin and eledoisin-related peptide also caused analgesia, but the SP N-terminal fragment (1-9) was inactive. This suggests that the analgesic message of SP resides within the C-terminal fragment. The analgesia caused by each peptide developed more rapidly but did not last as long as that after central injection of beta-endorphin. In separate experiments, 2 micrograms SP injected ICV increased blood pressure and decreased heart rate. The analgesic, bradycardic and pressor responses to central administration of SP were opposite to effects of peripherally administered SP, described previously. These results indicate that the effect induced by SP depends upon its specific neuroanatomical site of action.     

Mechanics of left ventricular relaxation, early diastolic lengthening, and suction investigated in a mathematical model

We investigated the determinants of ventricular early diastolic lengthening and mechanics of suction using a mathematical model of the left ventricle (LV). The model was based on a force balance between the force represented by LV pressure (LVP) and active and passive myocardial forces. The predicted lengthening velocity (e') from the model agreed well with measurements from 10 dogs during 5 different interventions (R = 0.69, P < 0.001). The model showed that e' was increased when relaxation rate and systolic shortening increased, when passive stiffness was decreased, and when the rate of fall of LVP during early filling was decreased relative to the rate of fall of active stress. We first defined suction as the work the myocardium performed to pull blood into the ventricle. This occurred when contractile active forces decayed below and became weaker than restoring forces, producing a negative LVP. An alternative definition of suction is filling during falling pressure, commonly believed to be caused by release of restoring forces. However, the model showed that this phenomenon also occurred when there had been no systolic compression below unstressed length and therefore in the absence of restoring forces. In conclusion, relaxation rate, LVP, systolic shortening, and passive stiffness were all independent determinants of e'. The model generated a suction effect seen as lengthening occurring during falling pressure. However, this was not equivalent with the myocardium performing pulling work on the blood, which was performed only when restoring forces were higher than remaining active fiber force, corresponding to a negative transmural pressure.     

A comparison of grooming behavior potencies of neurohypophyseal nonapeptides

We have previously demonstrated that intracerebroventricular (ICV) administration of oxytocin (OXY) enhanced grooming behaviors in male and female rats at a 1 microgram dose. In the present study female rats were injected ICV with 1 microgram OXY or equimolar doses of other peptides. At this dose arginine-vasopressin (AVP), arginine-vasotocin (AVT) and lysine-vasopressin (LVP), as well as alpha-MSH, were as effective as OXY in increasing grooming behavior. At equimolar doses, ACTH1-10, tocinoic acid (the ring structure of OXY) and Pro-Leu-Gly-NH2 (the tail structure of OXY) had no significant effect on grooming behavior. The potency of AVP and AVT was determined across a 0.05-5 microgram dose range. Grooming scores increased in an apparent linear manner across a similar OXY dose range. Both AVP and AVT, however, manifested an inverted U grooming response curve. Maximum grooming scores resulted from a 0.1 microgram dose of AVT or a 0.5 microgram AVP dose. Analyses of the aspects of grooming separately found that nonapeptides OXY, AVP and AVT all elevated body grooming, washing, and scratching. Because AVT and AVP administration resulted in grooming scores significantly higher than OXY at lower doses, we concluded that the CNS is more sensitive to the effects of AVT and AVP on grooming behavior than OXY.     

Effect of D-Ala-2-Me-Phe-4-Gly-ol-5 enkephalin on epinephrine-induced arrhythmias in the rat and the interrelationship to the parasympathetic nervous system

The purpose of this study was to evaluate the effects of the millimicrons opioid agonist D-Ala-2-Me-Phe-4-Gly-ol enkephalin (DAGO) on catecholamine-induced arrhythmias. Arrhythmias were produced, in the rat, by continuous infusion of epinephrine until the development of fatal arrhythmias that were usually ventricular fibrillation. Intracerebroventricular (ICV) administration of DAGO, 3 nmol, significantly (p less than 0.05) shifted to the right the relationship between epinephrine and both the onset of ventricular arrhythmias and the development of fatal arrhythmias. Naloxone, 1 mg/kg i.v., prevented these effects of DAGO. Atropine, 1 mg/kg i.v. or 20 micrograms/kg ICV, prevented the shift in these dose response relationships. Antagonism of DAGO's effects on arrhythmias could not be explained by an alteration of the blood pressure response to epinephrine. However, DAGO significantly increased blood pressure and decreased heart rate in separate experiments in animals that did not receive epinephrine and atropine prevent the heart rate and blood pressure effects of DAGO. These data show that 1) the millimicrons opioid receptor agonist DAGO suppresses epinephrine-induced arrhythmias, 2) the site of action can be within the CNS, 3) there is a role for the central parasympathetic nervous system to mediate the effect of DAGO and 4) endogenous opioids could modulate catecholamine-induced cardiac arrhythmias.     

Role of AT2 receptor in the brain in regulation of blood pressure and water intake

The effects of intracerebroventricular (ICV) injection of angiotensin II (ANG II) on blood pressure and water intake were examined with the use of ANG II receptor-deficient mice. ICV injection of ANG II increased systolic blood pressure in a dose-dependent manner in wild-type (WT) mice and ANG type 2 AT(2) receptor null (knockout) (AT(2)KO) mice; however, this increase was significantly greater in AT(2)KO mice than in WT mice. The pressor response to a central injection of ANG II in WT mice was inhibited by ICV preinjection of the selective AT(1) receptor blocker valsartan but exaggerated by the AT(2) receptor blocker PD-123319. ICV injection of ANG II also increased water intake. It was partly but significantly suppressed both in AT(2)KO and AT(1)aKO mice. Water intake in AT(2)/AT(1)aKO mice did not respond to ICV injection of ANG II. Both valsartan and PD-123319 partly inhibited water intake in WT mice. These results indicate an antagonistic action between central AT(1)a and AT(2) receptors in the regulation of blood pressure, but they act synergistically in the regulation of water intake induced by ANG II.     

MRI and echocardiographic assessment of the diastolic dysfunction of normal aging: altered LV pressure decline or load?

Changes in diastolic indexes during normal aging, including reduced early filling velocity (E), lengthened E deceleration time (DT), augmented late filling (A), and prolonged isovolumic relaxation time (IVRT), have been attributed to slower left ventricular (LV) pressure (LVP) decay. Indeed, this constellation of findings is often referred to as the "abnormal relaxation" pattern. However, LV filling is determined by the atrioventricular pressure gradient, which depends on both LVP decline and left atrial (LA) pressure (LAP). To assess the relative influence of LVP decline and LAP, we studied 122 normal subjects aged 21-92 yr by Doppler echocardiography and MRI. LVP decline was assessed by color M-mode (V(p)) and the LV untwisting rate. Early diastolic LAP was evaluated using pulmonary vein flow systolic fraction, pulmonary vein flow diastolic DT, color M-mode (E/V(p)), and tissue Doppler (E/E(m)). Linear regression showed the expected reduction of E, increase in A, and prolongation of IVRT and DT with advancing age. There was no relation of age to parameters reflecting the rate of LVP decline. However, older age was associated with reduced E/V(p) (P = 0.008) and increased pulmonary vein systolic fraction (P < 0.001), pulmonary vein DT (P = 0.0026), and E/E(m) (P < 0.0001), all suggesting reduced early LAP. Therefore, reduced early filling in older adults may be more closely related to a reduced early diastolic LAP than to slower LVP decline. This effect also explains the prolonged IVRT. We postulate that changes in LA active or passive properties may contribute to development of the abnormal relaxation pattern during the aging process.     

Cardiac actions of central but not peripheral urotensin II are prevented by beta-adrenoceptor blockade

Urotensin II (UII) is a highly conserved peptide that has potent cardiovascular actions following central and systemic administration. To determine whether the cardiovascular actions of UII are mediated via beta-adrenoceptors, we examined the effect of intravenous (IV) propranolol on the responses to intracerebroventricular (ICV) and IV administration of UII in conscious sheep. Sheep were surgically instrumented with ICV guide tubes and flow probes or cardiac sympathetic nerve recording electrodes. ICV UII (0.2 nmol/kg over 1 h) caused prolonged increases in heart rate (HR; 33 +/- 11 beats/min; P < 0.01), dF/dt (581 +/- 83 L/min/s; P < 0.001) and cardiac output (2.3 +/- 0.4 L/min; P < 0.001), accompanied by increases in coronary (19.8 +/- 5.4 mL/min; P < 0.01), mesenteric (211 +/- 50 mL/min; P < 0.05) and iliac (162 +/- 31 mL/min; P < 0.001) blood flows and plasma glucose (7.0 +/- 2.6 mmol/L; P < 0.05). Propranolol (30 mg bolus followed by 0.5 mg/kg/h IV) prevented the cardiac responses to ICV UII and inhibited the mesenteric vasodilatation. At 2 h after ICV UII, when HR and mean arterial pressure (MAP) were increased, cardiac sympathetic nerve activity (CSNA) was unchanged and the relation between CSNA and diastolic pressure was shifted to the right (P < 0.05). The hyperglycemia following ICV UII was abolished by ganglion blockade but not propranolol. IV UII (20 nmol/kg) caused a transient increase in HR and fall in stroke volume; these effects were not blocked by propranolol. These results demonstrate that the cardiac actions of central UII depend on beta-adrenoreceptor stimulation, secondary to increased CSNA and epinephrine release, whereas the cardiac actions of systemic UII are not mediated by beta-adrenoreceptors and probably depend on a direct action of UII on the heart.