Hypertensive end-organ damage and premature mortality are p38 mitogen-activated protein kinase-dependent in a rat model of cardiac hypertrophy and dysfunction.

BACKGROUND: Numerous pathological mediators of cardiac hypertrophy (eg, neurohormones, cytokines, and stretch) have been shown to activate p38 MAPK. The purpose of the present study was to examine p38 MAPK activation and the effects of its long-term inhibition in a model of hypertensive cardiac hypertrophy/dysfunction and end-organ damage. METHODS AND RESULTS: In spontaneously hypertensive stroke-prone (SP) rats receiving a high-salt/high-fat diet (SFD), myocardial p38 MAPK was activated persistently during the development of cardiac hypertrophy and inactivated during decompensation. Long-term oral treatment of SFD-SP rats with a selective p38 MAPK inhibitor (SB239063) significantly enhanced survival over an 18-week period compared with the untreated group (100% versus 50%). Periodic echocardiographic analysis revealed a significant reduction in LV hypertrophy and dysfunction in the SB239063-treatment groups. Little or no difference in blood pressure was noted in the treatment or vehicle groups. Basal and stimulated (lipopolysaccharide) plasma tumor necrosis factor-alpha concentrations were reduced in the SB239063-treatment groups. In vitro vasoreactivity studies demonstrated a significant preservation of endothelium-dependent relaxation in animals treated with the p38 MAPK inhibitor without effects on contraction or NO-mediated vasorelaxation. Proteinuria and the incidence of stroke (53% versus 7%) were also reduced significantly in the SB239063-treated groups. CONCLUSIONS: These results demonstrate a crucial role for p38 MAPK in hypertensive cardiac hypertrophy and end-organ damage. Interrupting its function with a specific p38 MAPK inhibitor halts clinical deterioration.

Eprosartan reduces cardiac hypertrophy, protects heart and kidney, and prevents early mortality in severely hypertensive stroke-prone rats.

OBJECTIVE: Eprosartan is a selective angiotensin II type I receptor antagonist approved for the treatment of hypertension. In the present studies, eprosartan's ability to provide end-organ protection was evaluated in a model of cardiomyopathy and renal failure in stroke-prone rats (SP). METHODS: SP were fed a high fat (24.5% in food) and high salt (1% in water) diet (SFD). Eprosartan (60 mg/kg/day) or vehicle (saline control) (n = 25/group) was administered by intraperitoneally-implanted minipumps to these SP on the SFD for 12 weeks. Normal diet fed SP and WKY rats (n = 25/group) were also included for comparison (i.e. served as normal controls). Mortality, hemodynamics, and both renal and cardiac function and histopathology were monitored in all treatment groups. RESULTS: Eprosartan decreased the severely elevated arterial pressure (-12%; P < 0.05) produced by SFD but did not affect heart rate. Vehicle-treated SP-SFD control rats exhibited significant weight loss (-13%; P < 0.05) and marked mortality (50% by week 6 and 95% by week 9; P < 0.01). Eprosartan-treated SP-SFD rats maintained normal weight, and exhibited zero mortality at week 12 and beyond. Eprosartan prevented the increased urinary protein excretion (P < 0.05) that was observed in vehicle-treated SP-SFD rats. Echocardiographic (i.e. 2-D guided M-mode) evaluation indicated that SP-SFD vehicle control rats exhibited increased septal (+22.2%) and posterior left ventricular wall (+30.0%) thickness, and decreased left ventricular chamber diameter (-15.9%), chamber volume (-32.7%), stroke volume (-48.7%) and ejection fraction (-22.3%), and a remarkable decrease in cardiac output (-59.3%) compared to controls (all P < 0.05). These same parameters in eprosartan-treated SP-SFD rats were normal and differed markedly and consistently from vehicle-treated SP-SFD rats (i.e. treatment prevented pathology; all P < 0.05). Cardiac-gated MRI data confirmed the ability of eprosartan to prevent cardiac pathology/remodeling (P < 0.05). Histopathological analysis of hearts and kidneys indicated that eprosartan treatment significantly reduced end-organ damage (P < 0.01) and provided corroborative evidence that eprosartan reduced remodeling of these organs. Vehicle-treated SP-SFD rats exhibited a 40% increase in the plasma level of pro-atrial natiuretic factor that was reduced to normal by eprosartan (P < 0.05). CONCLUSION: These data demonstrate that eprosartan, at a clinically relevant dose, provides significant end-organ protection in the severely hypertensive stroke-prone rat. It preserves cardiac and renal structural integrity, reduces cardiac hypertrophy and indices of heart failure, maintains normal function of the heart and kidneys, and eliminates premature mortality due to hypertension-induced end-organ failure.

Genetic hypertension and increased susceptibility to cerebral ischemia.

A review of the sensitivity of genetically hypertensive rats to cerebral ischemia was presented together with original data describing the systematic comparison of the effects of focal ischemia (permanent and temporary with reperfusion) performed in hypertensive and normotensive rats (i.e., blood pressures verified in conscious instrumented rats). Microsurgical techniques were used to isolate and occlude the middle cerebral artery (MCAO) of spontaneously hypertensive (SHR), Sprague-Dawley (SD) and Wistar Kyoto (WKY) rats at the level of the inferior cerebral vein. Following permanent (24 h) MCAO, persistent and similar decreases in local microvascular perfusion (i.e., to 15.6 +/- 1.7% of pre-MCAO levels) were verified in the primary ischemic zone of the cortex for all strains using Laser-Doppler flowmetry. A contralateral hemiplegia that occurred following MCAO, evidenced by forelimb flexion and muscle weakness, was greater in SHR (neurological grade = 2.0 +/- 0.1) than SD (1.0 +/- 0.4) or WKY (0.7 +/- 0.4) rats (N = 7-9, p less than 0.05). SHR also exhibited sensory motor deficits following MCAO compared to sham-operation, with decreased normal placement response of the hindlimb (% normal = 20 vs. 83, N = 23-30, p decreased rota-rod (41 +/- 7 vs. 126 +/- 19 on rod, N = 10-15, p less than 0.05) and balance beam (25 +/- 5 vs. 116 +/- 29 s on beam, N = 5-7, p less than 0.05) performance. However, an index of general motor activity was not affected by permanent MCAO. Triphenyltetrazolium-stained forebrain tissue analyzed by planimetry revealed a significantly larger and more consistent cortical infarction in SHR (hemispheric infarction = 27.9 +/- 1.5%) compared to SD (15.4 +/- 4.1%) and WKY (4.0 +/- 2.4%) rats (N = 7-9, p less than 0.05), occupying predominantly the frontal and parietal areas. Also, a significant degree of ipsilateral hemispheric swelling (4.6 +/- 0.9%, N = 7-9, p less than 0.05) and increased brain water content (78.4 +/- 0.3% to 80.4 +/- 0.2%, N = 8-9, p less than 0.05) was identified in SHR that was not observed in SD or WKY rats. A novel model of temporary MCAO also was evaluated in the hypertensive and normotensive rat strains. Initially, the effect of increasing MCAO-time followed by 24 h reperfusion in SHR was studied. During temporary MCAO (20 to 300 min), persistent and stable decreases in local microvascular perfusion (i.e., to 15-20% of pre-MCAO levels) were verified in the primary ischemic zones of the cortex.(ABSTRACT TRUNCATED AT 400 WORDS)

The myocardial beta-adrenergic system in spontaneously hypertensive heart failure (SHHF) rats.

-Responsiveness to beta-adrenergic stimulation is reduced in the failing human myocardium. This results principally from reduced beta-adrenergic receptor (betaAR) density, elevated beta-adrenergic receptor kinase 1 (betaARK1) levels, and functional uncoupling of remaining receptors. The temporal nature of changes in the human myocardial beta-adrenergic system relative to onset of symptomatic heart failure (HF) has been difficult to discern. A relatively new model of HF, the spontaneously hypertensive heart failure (SHHF) rat spontaneously and reproducibly develops left ventricular hypertrophy (LVH) and progresses to HF, thus enabling longitudinal studies to examine the cellular and molecular bases for hypertension-induced cardiac hypertrophy and subsequent HF. The purpose of this study was to examine age-dependent changes in the betaAR system in this model. Lean male SHHF rats at 3, 7, 14, and 20 months were compared with age-matched Sprague-Dawley (SD) control rats ([C]; 4 animals/group). At all ages the SHHF rats had elevated blood pressures and left ventricular end-diastolic pressure relative to the SD control rats (P<0.05). Compared with age-matched SD control rats, LVH was evident by 3 months in SHHF rats; 20-month-old SHHF rats had significantly greater LVH compared with the other SHHF rat groups. beta-adrenergic responsiveness (maximal heart rate to isoproterenol) was reduced only in 20-month-old SHHF rats. betaARK1 protein levels and activity were elevated at 14 months (162+/-10% and 195+/-20% C, respectively), and betaARK1 protein remained elevated at 20 months (140+/-14% C). In contrast, G protein-coupled receptor kinase 5, a second receptor kinase in the heart, remained unchanged at all ages. betaAR density did not change with age in the SD control rats and was similar in the SHHF rats until 20 months of age when the receptor number was reduced (30+/-1%). These data indicate that cardiac dysfunction is coincident with reduced betaAR density. Importantly, cardiac dysfunction was preceded by elevated betaARK1 levels and activity, thus suggesting that betaARK1 may be a precipitating factor in the transition from hypertension-induced compensatory cardiac hypertrophy to HF. Furthermore, these results indicate that the SHHF rat is a powerful model for use in examination of the mechanisms involved in alterations of beta-adrenergic signaling that occur in human HF.

Mouse strain differences in susceptibility to cerebral ischemia are related to cerebral vascular anatomy.

The consequences of cerebral ischemia were studied in three different strains (BDF, CFW, and BALB/C) of mice. The different strains exhibited significant differences in susceptibility to 24-h focal ischemia. Following middle cerebral artery occlusion (MCAO), infarct volumes (mm3) were 5 +/- 3 in BDF, 15 +/- 5 in CFW, and 23 +/- 3 in BALB/C mice (p < 0.05). MCAO plus ipsilateral common carotid artery occlusion (CCAO) resulted in infarct volumes of 15 +/- 9 in BDF, 38 +/- 10 in CFW, and 72 +/- 12 in BALB/C mice (p < 0.05). In addition, MCAO plus CCAO produced death by 24 h in 42% of CFW and 67% of BALB/C mice, but not in any BDF mice (p < 0.05). CCAO alone produced multifocal hemispheric infarctions in 36% of BALB/C mice but not in the other two strains. Brains of all mouse strains subjected to sham surgery were free of any ischemic injury. Arterial blood pressures, blood gases, and blood cell profiles were relatively similar for the three mouse strains. However, carbon black studies of the cerebrovascular anatomy revealed an incomplete circle of Willis (i.e., a significant decrease in the frequency of patent posterior communicating arteries) for BALB/C compared with BDF mice (p < 0.05), with CFW mice being intermediary. Based on these anatomical data, BALB/C mice also were evaluated following transient global brain ischemia produced by bilateral CCAO. BALB/C mice exhibited a > 85% reduction in cortical microvascular perfusion and EEG power within 1 min of bilateral CCAO. Also, hippocampal neuronal CA1 damage and mortality over 7 days were related to the duration of global brain ischemia (p < 0.05). These data demonstrate a significant difference between mouse strains in their sensitivity to cerebral ischemia that appears to be related, at least in part, to the functional vascular anatomy at the level of the posterior communicating arteries. In particular, we point out the potential usefulness of BALB/C mice as a sensitive and reproducible model of focal and global ischemia.

Identification, characterization, and functional role of phosphodiesterase type IV in cerebral vessels: effects of selective phosphodiesterase inhibitors.

The role of the phosphodiesterase type IV isozyme (PDE IV) in the regulation of cerebrovascular tone was investigated in the canine basilar artery in vitro and in vivo. The PDE isozymes extracted from the canine basilar artery were isolated by diethylaminoethanol (DEAE)-Sepharose affinity chromatography and identified based on sensitivity to isozyme-selective PDE inhibitors. [3H]cAMP hydrolysis was observed in one major and one minor peak of activity. The predominant peak was inhibited by the addition of cGMP (25%), siguazodan (26%), rolipram (39%), and the combination of siguazodan and rolipram (95%). Selective PDE IV inhibitors BRL 61063, rolipram, and denbufylline were equieffective inhibitors of [3H]-ccAMP hydrolysis mediated by PDE IV isolated from the canine basilar artery [concentrations producing 50% inhibition (IC50S) = 0.21 +/- 0.05 microM, 0.67 +/- 0.23 microM, and 0.73 +/- 0.16 microM, respectively]. In precontracted isolated ring segments of the canine basilar artery, selective PDE IV inhibitors produced potent and complete relaxation (IC50S < 150 nM). In contrast, zaprinast (a selective PDE V inhibitor) and siguazodan (a selective PDE III inhibitor) produced only weak relaxation of the basilar artery (IC50S = 4.5 microM and > 10 microM, respectively). Vasorelaxation produced by PDE IV inhibitors was not altered by removing the endothelium, 1-NAME, or adenosine receptor antagonism. In a canine model of acute cerebral vasospasm, all three selective PDE IV inhibitors reversed basilar artery spasm produced by autologous blood without altering mean arterial blood pressure. In contrast, prolonged treatment with BRL 61063 failed to alter the development of basilar spasm in the two hemorrhage canine models of chronic cerebral vasospasm. Denbufylline-induced relaxation in vitro was also significantly impaired in basilar arteries obtained from the model of chronic vasospasm. In conclusion, PDE IV appears to be the predominant isozyme regulating vascular tone mediated by cAMP hydrolysis in cerebral vessels. In addition, vasorelaxation modulated by PDE IV is compromised in chronic cerebral vasospasm associated with subarachnoid hemorrhage.

Peripheral versus central cardiorespiratory effects of morphine.

The administration of morphine sulfate (MS, 2 mg/kg) into the right atrium in decerebrate rats, produced a dramatic bradycardia, apnea, and a slight transient biphasic blood pressure response within 1 sec. The bradycardia was slowly restored to control levels within 8-10 min and was prevented by pretreatment with atropine. Apnea (7.3 +/- 2.2 sec) was followed by a period of rapid shallow breathing. Acute tolerance to these effects developed to subsequent doses of morphine. In paralyzed artificially ventilated animals, morphine produced: (1) cessation of phrenic nerve (PN) activity which was followed by bursts of shortened duration; and (2) concomitant excitation of the recurrent laryngeal nerve (RLN), this activity exhibited a continuous discharge which was asynchronous with that of phrenic nerve. These actions of morphine were qualitatively similar to those observed with phenyldiguanide (PDG) and were found to be reflexogenic, i.e. emanating from the lungs via stimulation of pulmonary C-fibers. Bilaterally vagotomized animals only responded to morphine with respiratory depression, characterized by a severe decrease in respiratory rate and minute ventilation. On the other hand, animals with intact vagi showed stimulation of rate and minute ventilation following a brief period of apnea. They were less sensitive than vagotomized animals to the depressant action during the first 8 min after administration of morphine. All the effects of morphine were blocked by pretreatment with naloxone (50-400 micrograms/kg, i.v.). These results indicate that the initial cardiorespiratory effects of morphine are due to a peripheral reflex action arising from the stimulation of opiate receptors associated with pulmonary C-fibers, e.g. J-fibers.

Hypertensive response following stimulation of opiate receptors in the caudal ventrolateral medulla.

In urethane-anesthetized rats, vasodepressor neuron pools were located bilaterally in and adjacent to the A1 area of the ventrolateral medulla by injecting the neuroexcitatory amino acid, L-glutamate. Ventrolateral vasodepressor areas included the caudalateral part of the nucleus reticularis gigantocellularis, the rostrolateral part of the nucleus reticularis ventralis, and the dorsal nucleus reticularis lateralis. In the ventrolateral vasodepressor areas L-glutamate elicited a transient fall in blood pressure (BP) and heart rate (HR). The opiate agonist (D-ala2-met5)-enkephalinamide (DAME) was used to stimulate opiate receptors in vasodepressor sites, identified with L-glutamate. In these sites, bilateral injections (0.1 microliter/site) of DAME caused a dose-related (2.5-500.0 ng) increase in blood pressure and heart rate, as well as exaggeration of the response to occlusion of the carotid. The effects of DAME on blood pressure were completely abolished by alpha-adrenergic blockade (phentolamine, 2 mg/kg, i.v.) and all effects of DAME were reversed by the administration of naloxone HCl (1 mg/kg, i.v.). Naloxone reversal was accompanied by an unexpected "rebound" hypertension. Saline had no significant effects when injected, or administered intravenously, in the absence or presence of DAME. It was concluded that stimulation of opiate receptors in the ventrolateral vasodepressor areas activated sympathetic outflow. An enkephalinergic system in this area of the brain stem may serve to modulate blood pressure, heart rate and cardiovascular reflexes.

Vasopressor and depressor areas in the rat medulla. Identification by microinjection of L-glutamate.

L-Glutamate (in 0.1 microliter of 0.9% NaCl) was injected via multibarrelled glass micropipettes into the ventrolateral medulla of urethane-anesthetized rats. This area, explored stereotaxically, extended from 2.2 mm rostral (near trapezoid bodies) to 0.4 mm caudal, with respect to the obex, 2.4 mm lateral to the mid-line on each side and 2.4 mm deep from the ventral surface of the medulla. Two types of responses were elicited by injection of L-glutamate. One type was a dose-related increase in arterial pressure and heart rate; these responses were elicited from the lateral portion of nucleus reticularis gigantocellularis, the medial aspect of nucleus reticularis parvocellularis and the dorsal-lateral reticular nucleus. The second type of response was a dose-related fall in arterial pressure with no change in heart rate; this response was localized caudal to pressure areas in the caudal ventrolateral part of nucleus reticularis gigantocellularis, ventrolateral nucleus reticularis ventralis, nucleus ambiguous and the A1 region. Glutamic acid diethylester (GDEE), an antagonist of L-glutamate, blocked all the cardiovascular effects of L-glutamate. These results indicate the presence of receptors for glutamate in the pressor and depressor areas. Glutamic acid diethylester caused a fall in blood pressure when injected on its own into pressor sites suggesting the existence of a glutaminergic input to the pressor sites. Inhibition of neuronal activity in pressor sites produced by microinjection of muscimol (a potent neuroinhibitory analogue of GABA) caused a decrease in blood pressure. On the other hand, pressor responses resulted following similar inhibition in the depressor sites. These results indicate that the pressor and depressor sites identified in the ventral medulla of the rat may have an important role to play in central cardiovascular regulation.

Differential vasoconstrictor activity of human urotensin-II in vascular tissue isolated from the rat, mouse, dog, pig, marmoset and cynomolgus monkey.

1. Urotensin-II (U-II) and its G-protein-coupled receptor, GPR14, are expressed within mammalian cardiac and peripheral vascular tissue and, as such, may regulate mammalian cardiovascular function. The present study details the vasoconstrictor profile of this cyclic undecapeptide in different vascular tissues isolated from a diverse range of mammalian species (rats, mice, dogs, pigs, marmosets and cynomolgus monkeys). 2. The vasoconstrictor activity of human U-II was dependent upon the anatomical origin of the vessel studied and the species from which it was isolated. In the rat, constrictor responses were most pronounced in thoracic aortae and carotid arteries: -log[EC(50)]s 9.09+/-0.19 and 8.84+/-0.21, R(max)s 143+/-21 and 67+/-26% 60 mM KCl, respectively (compared, for example, to -log[EC(50)] 7.90+/-0.11 and R(max) 142+/-12% 60 mM KCl for endothelin-1 [ET-1] in thoracic aortae). Responses were, however, absent in mice aortae (-log[EC(50)] <6.50). These findings were further contrasted by the observation that U-II was a 'coronary-selective' spasmogen in the dog (-log[EC(50)] 9.46+/-0.11, R(max) 109+/-23% 60 mM KCl in LCX coronary artery), yet exhibited a broad spectrum of vasoconstrictor activity in arterial tissue from Old World monkeys (-log[EC(50)]s range from 8.96+/-0.15 to 9.92+/-0.13, R(max)s from 43+/-16 to 527+/-135% 60 mM KCl). Interestingly, significant differences in reproducibility and vasoconstrictor efficacy were seen in tissue from pigs and New World primates (vessels which responded to noradrenaline, phenylephrine, KCl or ET-1 consistently). 3. Thus, human U-II is a potent, efficacious vasoconstrictor of a variety of mammalian vascular tissues. Although significant species/anatomical variations exist, the data support the hypothesis that U-II influences the physiological regulation of mammalian cardiovascular function.

Interdependence of rostral and caudal ventrolateral medullary areas in the control of blood pressure.

Pharmacologic experiments were carried out to test the degree of interdependence of rostral vasopressor and caudal vasodepressor neuron pools in the ventrolateral medulla (VLPA and VLDA, respectively). In two groups of urethane-anesthetized rats, the gamma-aminobutyric acid (GABA) agonist muscimol (10 ng/site) was bilaterally microinjected into both the VLPA and VLDA to inhibit neuronal activity at these sites. In one group of experiments, muscimol was microinjected first into the VLPA and then into the VLDA. Following muscimol microinjection in the VLPA the mean arterial pressure (MAP) and heart rate (HR) decreased to 40 +/- 6 mm Hg and 310 +/- 21 beats/min (bpm) from a control level of 90 +/- 3 mm Hg and 403 +/- 23 bpm. Subsequent microinjection of muscimol in the VLDA had no significant effect on BP or HR. This lack of response was not due to severe fall in BP caused by microinjection of muscimol into the VLPA. In the second group of experiments muscimol was first injected into the VLDA followed by muscimol microinjection into the VLPA. In the VLDA muscimol significantly increased MAP and HR to 139 +/- 4 mm Hg and 427 +/- 4 bpm from a control level of 87 +/- 2 mm Hg and 356 +/- 23 bmp. The aortic depressor nerve response (-37 +/- 1 mm Hg and -47 +/- 4 bpm) was converted to an aortic 'pressor' response (+20 +/- 1 mm Hg and -13 +/- 6 bpm). Subsequent microinjection of muscimol into the VLPA caused MAP and HR to fall to 43 +/- 5 mm Hg and 338 +/- 17 bpm. The aortic 'pressor' response was also abolished (2 +/- 2 mm Hg). These results indicate that neuronal activity in the rostral VLPA is an important determinant for changes in BP and its reflex regulation mediated by the VLDA. However, BP changes mediated by the rostral VLPA are independent of the level of neuronal activity in the VLDA. Sites of VLPA and VLDA interaction are discussed.

Medullary pressor area: site of action of intravenous physostigmine.

Physostigmine, a choline-esterase inhibitor, is known to elevate endogenous levels of acetylcholine. Intravenously administered physostigmine causes a rise in blood pressure via its action in the central nervous system. Exact site of this action of physostigmine is not known. In this paper, it was demonstrated that microinjections of tetrodotoxin (a fast sodium channel blocker), lidocaine (a local anesthetic) and scopolamine (a cholinergic muscarinic receptor blocker) into the rostral ventrolateral medullary pressor area abolished the pressor action of intravenously administered physostigmine. These results demonstrate that the rostral ventrolateral medulla is the site of action of intravenously administered physostigmine and this action is mediated via cholinergic muscarinic receptors.

A comparison of (+)SK&F 10047 and MK-801 on cortical spreading depression.

MK-801 and (+)SK&F 10047 produced a dose-related inhibition of the EEG suppression and cortical hyperemia associated with cortical spreading depression (CSD) and reduced the CSD propagation rate; ED50 = 1 mg/kg, i.v. and 15 mg/kg, i.v., respectively. MK-801 had a delayed onset of action (inversely related to dose) and a prolonged duration of action at all doses (> 2 h). In contrast, (+)SK&F 10047 had a rapid onset of action (< 30 min) and a predictable dose-related duration of action. These results suggests that an efficacious compound acting with moderate affinity as a non-competitive antagonist at the NMDA-receptor channel may possess a preferable time-course and toxicity profile when compared to agents acting similarly, but with high affinity.

Pulmonary opiate receptor activation evokes a cardiorespiratory reflex.

The administration of [D-Ala2,Met5]enkephalinamide (D-AME) and [D-Ala2,Leu5]enkephalinamide (D-ALE) into the right atrium of decerebrate rats caused bradycardia, a slight transient biphasic blood pressure response and apnea within 1-2 sec. Apnea was followed by rapid shallow breathing. These effects were dose related (1-1000 micrograms/kg) and blocked by pretreatment with naloxone. Atropine blocked the bradycardia. Sectioning the vagi at the level of the diaphragm did not affect the responses, whereas bivagotomy below the cardiac branches abolished all responses. The triad of responses was attributed to a reflex action arising from vagal afferents within the lung. These results were confirmed in paralyzed , artificially ventilated animals. In these animals, the enkephalin analogues produced a cessation of phrenic nerve (PN) activity followed by a decrease in the duration of bursts. The recurrent laryngeal nerve (RLN) was concomitantly excited in a continuous decremental fashion. This excitation was independent of PN inhibition. Recordings of single and near single pulmonary vagal afferents demonstrated no effect of D-AME or D-ALE on stretch and irritant receptors. However, type J-receptors were stimulated.

Local cutaneous hemodynamic effects of carvedilol and labetalol in the anesthetized rat.

The effects of labetalol and carvedilol and local cutaneous microvascular perfusion and calculated local cutaneous microvascular resistance were investigated in anesthetized rats at submaximal doses that produced equivalent reductions in blood pressure and heart rate. Labetalol decreased cutaneous perfusion (-25 +/- 3%) without significantly affecting cutaneous vascular resistance (-6 +/- 3%). In marked contrast, carvedilol dramatically increased cutaneous perfusion (+64 +/- 9%) and significantly reduced cutaneous vascular resistance (-57 +/- 3%). These results suggest that carvedilol and labetalol possess differences in the mechanisms by which they produce vasodilation in vivo.

Opioids increase laryngeal resistance and motoneuron activity in the recurrent laryngeal nerve.

[D-Ala2,Met5]enkephalinamide (DAME), [D-Ala2,Leu5]enkephalinamide (DALE) and morphine sulfate (MS) increase activity in the recurrent laryngeal nerve (RLN) within 1 s subsequent to right atrial administration. The activation of the RLN was correlated with a large increase in the resistance to airflow in the in situ isolated larynx. Single unit recurrent laryngeal motoneuron recordings showed that the increase in laryngeal resistance was caused by the continuous activation and recruitment of expiratory motoneurons. Results obtained with opioids mimicked those of phenyldiguanide (20-40 micrograms/kg RA), an agent known to stimulate pulmonary J-receptors. Opioid-induced increases in laryngeal resistance were blocked by bilateral section of the RLN and pretreatment with naloxone (100 micrograms/kg RA). Naloxone had no effect on PDG responses. During the initial period of laryngeal motoneuron activation, the phrenic nerve (PN) was inhibited, however, the activation of the RLN was not dependent upon PN inhibition. It was concluded that stimulation of pulmonary opiate receptors, which may be associated with vagal afferents, elicit a reflex activation of expiratory recurrent laryngeal motoneurons resulting in an increase in laryngeal resistance.

Pulmonary resistance and compliance changes evoked by pulmonary opiate receptor stimulation.

The administration of [D-Ala2,Met5]enkephalinamide (DAME, 10-250 micrograms/kg) or morphine sulfate (MS, 2 mg/kg) into the right atrium (RA) of spontaneously breathing decerebrate rats caused an increase in lung resistance (RL) and a decrease in dynamic compliance (Cdyn). The maximal percentage increase in RL for DAME (250 micrograms/kg) and MS (2 mg/kg) was 120 +/- 21 and 160 +/- 40%, respectively, occurring during the first 30 s following an initial period of apnea, and subsiding within 1.5-2.0 min. The fall in Cdyn (DAME = -31 +/- 8%; MS = -35 +/- 4%) followed a more prolonged time course returning to control within 4-5 min. These responses were completely abolished by pretreatment with naloxone HCl (100 micrograms/kg i.v.), as well as bilateral cervical vagotomy. Pretreatment with antihistaminic, antiserotinergic, and antimuscarinic agents had no effect on the opioid induced changes in RL and Cdyn. Further studies carried out in ventilated animals showed blockade of the mechanical responses following the administration of neuromuscular blockers, C7 spinal cord transection, and ventral midline opening and retraction of the chest. Electromyograms obtained from intercostal muscles showed excitation of expiratory motor units and inhibition of inspiratory motor units following the administration of opioids. Similar results were obtained with phenyldiguanide (PDG), a known stimulant of pulmonary J-receptors. However, PDG effects were not blocked by naloxone. It was concluded that changes in RL resulted from a decrease in thoracic volume and resultant decrease in the radial traction of the airways. Changes in Cdyn were caused by spasm of expiratory muscles of the chest wall.

Human laminin produces human platelet aggregation in vitro.

The effects of laminin isoforms on platelet aggregation were compared and characterized in platelet rich plasma (PRP) obtained from 26 healthy human volunteers. In approximately 38% of the individuals tested, human laminin produced a biphasic platelet aggregation response. Human laminin produced only a primary phase in the remaining "non-responsive" individuals. Mouse laminin, rat laminin and human merosin did not cause platelet aggregation in any of the volunteers. The biphasic platelet aggregation response caused by human laminin was concentration-dependent (0.3-30 nM) and was consistently observed upon repeated testing of "responsive" individuals. The secondary phase of aggregation produced by human laminin in "responsive" individuals was abolished by aspirin, SQ 29,548, a selective thromboxane antagonist, and SK&F 106760, an RGD-derived platelet fibrinogen receptor (GPIIb/IIIa) antagonist. Also, the secondary phase of aggregation was not observed in washed platelets. Both the primary and secondary platelet responses produced by human laminin were abolished by a VLA-6 (alpha 6 beta 1) monoclonal antibody, but not by the YIGSR pentapeptide. In conclusion, human laminin causes thromboxane-dependent platelet aggregation, in vitro, in a significant population of human volunteers. The aggregation response was dependent upon the interaction of human laminin with platelet VLA-6 (alpha 6 beta 1). These novel results suggest that in some individuals laminin may play an important role in hemostasis and thrombogenesis.

Transient forebrain ischemia alters acutely endothelin receptor density and immunoreactivity in gerbil brain.

Pharmacologic studies suggest that endothelin (ET) plays an important role in the pathophysiology of hemorrhagic and ischemic stroke. In the gerbil, transient forebrain ischemia (10 min) resulted in profound motor deficits and a 15% reduction in ET receptor density in the hippocampus at 60 min post-reperfusion. A significant 2-fold increase in forebrain immunoreactive ET accompanied the maximum post-ischemic decrease in ET receptor density. These results suggest that the synthesis and availability of ET are increased acutely in the forebrain following transient cerebral ischemia.

Therapeutic effects of endothelin receptor antagonists in stroke.

The presence of the endothelin isopeptides and endothelin receptors on neurons, glial cells and brain capillary endothelium suggests that endothelins may play a significant role in neuromodulation, astrocytic function and in regulation of cerebral blood flow. Furthermore, endothelins may play a significant role in the central regulation of neuroendocrine and autonomic nervous system functions (i.e., plasma volume, cardiovascular and respiratory control). Endothelin has potent cerebrovascular and proliferative effects suggesting a pathogenic role in cerebrovascular diseases. Endothelin receptors may represent important therapeutic targets for the treatment of both hemorrhagic and ischemic stroke. A review of the available data on endothelin levels and the effects of endothelin antagonists in cerebrovascular diseases is provided in the present report. Most notably is evidence in support of increased brain endothelin levels in hemorrhagic and ischemic stroke both in animal models and in humans. Also, endothelin receptor antagonists exert significant efficacy in animal models of cerebrovascular disease. For example, SB 209670, a rationally designed, potent, nonpeptide endothelin receptor antagonist, exerts therapeutic efficacy in reducing vasospasm following subarachnoid hemorrhage and neuroprotection following ischemic stroke. Certainly the available data warrants further evaluation of novel, selective endothelin receptor antagonists or endothelin converting enzyme inhibitors in cerebrovascular diseases.