HP-228, a novel synthetic peptide, inhibits the induction of nitric oxide synthase in vivo but not in vitro.

alpha-Melanocyte stimulating hormone has been shown to prevent endotoxin shock. A heptapeptide analog (HP-228) has recently been synthesized and shown to be an even more potent protective agent. Because the hypotensive and toxic actions of lipopolysaccharide (LPS) appear to involve the induction of type II nitric oxide synthase (iNOS), we have examined the actions of HP-228 on nitric oxide production using an endotoxemia model in conscious rats given E. coli LPS (5 mg/kg i.v.) and monitored for 6 h. A group of rats received HP-228 (30 micrograms/kg) 30 min before LPS. Using nitro L-arginine methyl ester-sensitive cGMP production as an estimate of nitric oxide synthase activity in aortic segments, ex vivo, we determined that LPS increases iNOS activity and that HP-228 pretreatment markedly reduces this response. Additionally, the rate of conversion of 3[H]-arginine to 3[H]-citrulline was significantly reduced in lung homogenates from HP-228-treated rats. HP-228 did not alter the activity of the constitutive nitric oxide synthase in aortic rings or in cerebella. In isolated rat aortic smooth muscle cells, LPS or interleukin-1 beta caused prominent rises in nitric oxide generated by iNOS. HP-228 did not antagonize the effect of these inducing agents. However, in these cells, plasma obtained from rats 1 h after administration of HP-228 prevented the induction of iNOS by both LPS and interleukin-1 beta. In conclusion, HP-228 prevents the in vivo induction of nitric oxide synthase by LPS.(ABSTRACT TRUNCATED AT 250 WORDS)

Effectiveness of a cytokine restraining agent (CRA (TM)) in attenuating disuse deconditioning induced by hindlimb unloading in rats.

Spaceflight alters many immune responses and among the regulatory components of an organisms response system that have been to be affected by spaceflight is the cytokine network. Spaceflight, as well as ground-based model systems of spaceflight, have been shown to affect the production and activation of various cytokines including interleukins (IL) and tumor necrosis factor (TNF). Levels of urinary IL-2 are elevated on the first day of spaceflight and again after returning from space. Most results from ground-based studies in rodents indicate either no alterations in cytokines or decreased levels. Results from this experiment indicate that HP 228, a potent cytokine restraining agent (CRA (TM)) was effective in attentuating many of the disuse deconditioning changes induced by the ground-based hindlimb suspension model that simulates weightlessness in rats. HP 228 is a novel heptapeptide with unnatural amino acids and can effectively restrain lipopolysaccharide (LPS)-induced increased levels of several key cytokines, including plasma TNF alpha, IL-1 beta and IL-6. HP 228 has also been shown to be effective in several rodent models of pain, inflammation and LPS-induced lethality, as well as in reducing inducible nitric oxide synthase.

Effects of S-dobutamine on ischemic myocardium caused by coronary artery narrowing.

Cardiovascular effects of S-dobutamine were compared with effects of vehicle and other catecholamines in dogs during and after 3 days of approximately 90% ligation of the left anterior descending coronary artery (LAD). Twenty-four hours after LAD ligation, dogs infused with S-dobutamine (2.5 micrograms/kg/min intravenously, i.v.) maintained systolic blood pressure (SBP 149 +/- 6 mm Hg), diastolic blood pressure (DBP 100 +/- 6 mm Hg), and aortic dP/dt60 (2.8 +/- 0.2 s-1), with no significant changes from preligation values. In comparison, saline-treated dogs showed decreases in arterial BP and contractility: SBP 121 +/- 4 mm Hg; DBP 85 +/- 3 mm Hg; and aortic dP/dt60 was 1.9 +/- 0.1 s-1. S-Dobutamine-infused dogs had a heart rate (HR) of 148 +/- 5 beats/min with 44 +/- 14 beats/min premature ventricular contractions (PVCs), whereas dogs infused with saline, R-dobutamine, dopamine, norepinephrine (NE), or isoproterenol (ISO) all displayed a significantly greater number of PVCs at 24 h. Myocardial necrosis was limited by S-dobutamine treatment (2.5 micrograms/kg/min i.v. for 54 h). As demonstrated by histologic examination, S-dobutamine ameliorated the effects of ischemia as compared with vehicle, R-dobutamine, dopamine, hexamethonium, NE, or ISO. Myocardial tissue electrolytes, quantified 72 h after LAD ligation, were maintained by S-dobutamine-infused dogs in all sections of left ventricle (LV); but in saline-treated dogs, Ca2+ increased eightfold, Na+ increased twofold, and both K+ and Mg2+ decreased 50% in tissue "at risk" as compared with tissues "not at risk." Coronary nutrient blood flow (CNBF) to myocardial capillary vessels was calculated by radiolabeled microspheres 2 h after LAD ligation. As compared with CNBF in untreated hearts, endocardial CNBF in hearts receiving S-dobutamine (5 micrograms/kg/min i.v.) increased from 26 +/- 8 to 49 +/- 15 ml/min/100 g in tissue at risk, from 102 +/- 26 to 217 +/- 50 in "border zone," and from 133 +/- 13 to 215 +/- 41 in tissue not at risk. CNBF values in animals receiving vehicle infusion were not significantly different from CNBF values measured after ligation only. The S-enantiomer of dobutamine, infused in dogs for 54 h after coronary artery ligation, maintained cardiac performance, electrolyte balance, and myocardial cellular viability and reduced incidences of arrhythmias through its ability to increase CNBF without increasing HR.

Integrative cardiovascular actions of a novel catecholamine, GP-2-128.

Systematic modification in the chemical structure of dobutamine resulted in production of a long-acting, highly potent catecholamine, GP-2-128 [(1-(3,4-dihydroxyphenyl)-2-[3-(4-carbamyl phenyl)-1-methylpropylamino] ethanol)]. The cardiovascular actions of GP-2-128 were compared with those of isoproterenol (ISO) and dobutamine (DOB) in anesthetized dogs. GP-2-128 significantly increased left ventricular pressure (LVdP/dtmax), cardiac output (CO), and heart rate (HR). It also reduced total peripheral vascular resistance (TPVR). For a given increase in contractility, changes in HR were greater after ISO than after GP-2-128 administration. DOB did not change HR significantly. Both GP-2-128 and DOB reduced TPVR, but ISO was more effective than GP-2-128 and DOB in reducing TPVR. GP-2-128 was 18,000 and 52 times more potent than DOB and ISO, respectively, in increasing LVdP/dtmax. For a given increase in contractility, the cardiovascular actions of GP-2-128 lasted significantly longer than those of DOB or ISO. A 50% mixture of the RR and RS distereoisomer forms of GP-2-128 (GP-2-114) have the same pharmacologic profile as the pure RR distereoisomer. Both GP-2-128 and GP-2-114 produced current-dependent cardiovascular actions when administered by transdermal iontophoresis. The inotropic and chronotropic effects of GP-2-128 are both largely due to stimulation of beta-adrenoceptors, as shown by receptor blockade with propranolol. GP-2-128 is a very potent, long-acting catecholamine that can be administered by other than intravenous (i.v.) route.

Interactions of a novel catecholamine, GP-2-128, with adrenoceptors.

GP-2-128 is a novel catecholamine designed for transdermal iontophoretic delivery in patients with limited mobility to prevent deconditioning and muscular wasting. We characterized the interactions of this agent with alpha- and beta-adrenoceptors in vitro. In electrically stimulated rat left atria, GP-2-128 produced a concentration-dependent increase in contractile force. pD2 values for GP-2-128, isoproterenol (ISO), and dobutamine (DOB) were 10.6 +/- 0.12, 8.55 +/- 0.02, and 7.0 +/- 0.20, respectively. Metoprolol caused a shift in the concentration-effect curves for the three agonists. In spontaneously beating rat right atria, pD2 values of GP-2-128, ISO, and DOB are 10.4 +/- 0.24, 8.82 +/- 0.18, and 6.92 +/- 0.18, respectively. The affinity constant (KA) of GP-2-128, ISO, and DOB for cardiac beta 1-adrenoceptors was determined by competition binding assays to be 8.09, 6.04 and 4.49, respectively. In guinea pig trachea precontracted with histamine, GP-2-128 and ISO produced a concentration-dependent relaxation. pD2 values were 10.0 +/- 0.1 and 8.2 +/- 0.1, respectively. DOB was more potent than GP-2-128 in contracting isolated rat aortic rings (alpha 1 effect) and in displacing [3H]rauwolscine (alpha 2 effect). We also studied the interactions of GP-2-128 and ISO with the atypical beta-adrenoceptors (beta 3) in guinea pig ilea and rat and hamster adipocytes. Both agents inhibited twitches produced by transmural nerve stimulation in the presence of 10(-5) M nadolol. The EC30 for GP-2-128 and ISO at this atypical receptor site were 4.25 x 10(-10) and 5.05 x 10(-8) M, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of S-dobutamine on venous blood return and organ nutrient blood flow.

The selective contractile effects of s-dobutamine were studied in vitro in selected canine arteries and vein preparations; propranolol was included to block potential beta-mediated vasodilation. These in vitro data were expanded by quantifying the in vivo effects of s-dobutamine on venous blood return and redistribution of regional nutrient blood flow (NBF) and non-nutrient blood flow (non-NBF) in anesthetized dogs. In in vitro studies with isolated canine arteries and veins, s-dobutamine exhibited vein-selective constriction. At maximally efficacious concentrations of agonist, contractions of carotid, coronary, and femoral arteries in response to s-dobutamine were only 7, 25 and 45% as great as those elicited by norepinephrine (NE). Similarly, in jugular vein, s-dobutamine-mediated contractions were 55% as great as those obtained in response to NE. Coronary and femoral arteries precontracted with NE were relaxed in a dose-related manner by increasing concentrations of s-dobutamine. Effects of NE and s-dobutamine on venous blood return (VR) were compared in dogs. s-Dobutamine increased VR by 49 +/- 10 ml, whereas NE increased VR by 14 +/- 6 ml during 5-min infusion. s-Dobutamine significantly increased coronary NBF in left ventricular (LV) endocardium from 115 +/- 10 to 194 +/- 13 and 263 +/- 9 ml/min/100 g at doses of 10 and 20 micrograms/kg/min, respectively. In addition, LV epicardium flow was increased from 87 +/- 8 to 189 +/- 15 and 262 +/- 11 ml/min/100 g at 10 and 20 micrograms/kg/min, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Actions of the opioid antagonist, nalmefene, and congeners on reperfusion cardiac arrhythmias and regional left coronary blood flow.

Opioid antagonists have been shown to prevent the occurrence of lethal arrhythmias following coronary reperfusion. In this study, we have examined the effect of a new, long-lasting, potent opioid antagonist, nalmefene, and congeners in the prevention of reperfusion arrhythmias in dogs. Nalmefene given at a dose of 1 mg/kg i.v. reduced the incidence of reperfusion arrhythmias significantly when compared to the saline control. Neither N-methyl nalmefene, a quaternary analog that does not cross the blood brain barrier, nor (+) nalmefene, an isomer with no anti-opioid actions, provided any protection against reperfusion arrhythmias. Regional myocardial blood flow profiles, during and after coronary occlusion, were not different between the nalmefene- and saline-treated groups. We conclude that nalmefene prevents the occurrence of reperfusion-induced arrhythmias by blocking opioid receptors in the brain.

Antagonism of fentanyl-induced respiratory depression with nalmefene.

We determined the ability of a new opioid antagonist, naimefene, to prevent fentanyl-induced respiratory depression in 8 healthy male volunteers. Ventilation and pulmonary function were measured with the respiratory inductive plethysmograph (RIP), which is non-invasive and requires no connection to the airway. Each volunteer was tested two times on different days. During the first session, each volunteer was monitored for one hour of baseline measurement followed by 4 hourly injections of fentanyl (1 microgram/kg) administered in an open-label manner. In the second session, the subjects were monitored for one hour after 1 mg of intravenous nalmefene was administered. Intravenous fentanyl or identical placebo were then given in a double-blind manner as in the first session. Progressive and profound respiratory depression occurred with fentanyl administration alone. In the absence of nalmefene, fentanyl converted normal breathing pattern to an irregular breathing pattern. When the subjects were treated with nalmefene prior to fentanyl administration, all of these changes were almost completely prevented. Pulmonary variables which reflected this difference between the fentanyl-alone group and the nalmefene-pretreated groups included frequency (p less than 0.001), tidal volume (p less than 0.001), percent rib cage contribution to tidal volume (p less than 0.001) and expiratory time (p less than 0.001). This study showed that nalmefene is an effective long-acting opioid antagonist, and that RIP accurately measures changes in respiration caused by opioid administration.

Cardiovascular effects of KM-13, a new, orally effective, cardiotonic sympathomimetic amine.

Dobutamine's chemical structure was modified to make it orally effective, while its pharmacological profile was preserved. Testing on anesthetized dogs showed that replacement of the para hydroxyl group with carboxyamide at the phenyl end of the molecule increased inotropic potency threefold, but it introduced pressor activity that spoiled the inotropic selective profile of dobutamine. However, shifting carboxyamide to the meta position avoided pressor activity and further enhanced inotropic potency to nine times that of dobutamine. When administered orally to conscious dogs, this compound, KM-13 (5 mg/kg), produced a sustained increase in left ventricular dP/dt with only immediate changes in heart rate; 10 mg/kg dobutamine was without cardiovascular effects. The (-) isomer of KM-13 contained twice the inotropic activity of the (+) isomer; in contrast, the (-) isomer had no effect on diastolic blood pressure, while the (+) isomer lowered blood pressure. The inotropic and chronotropic effects of dobutamine and KM-13 are both largely due to beta-adrenergic stimulation as shown by propranolol blockade. In contrast to dobutamine, KM-13 is an agent that is active by either oral or buccal administration and has greater inotropic potency.

Noninvasive delivery of a novel inotropic catecholamine: iontophoretic versus intravenous infusion in dogs.

Using a newly developed iontophoretic delivery device, a novel inotropic catecholamine, pharmacologically similar to dobutamine, has been successfully administered to dogs by noninvasive transdermal infusion for periods of up to 1.5 h. The technique was compared with intravenous infusion and shown to be capable of achieving the same degree of cardiac contractility and steady-state plasma concentrations of the inotrope. There was also a good linear relationship between the applied current and the resulting steady-state plasma concentrations of the inotrope. Approximately 2 mA of applied current during transdermal iontophoresis produced a response equivalent to an intravenous infusion of 1 micrograms/kg/min of the drug.

The role of endogenous opioids in congestive heart failure: effects of nalmefene on systemic and regional hemodynamics in dogs.

We studied the role of endogenous opiates and their interrelationships with the sympathetic nervous system in an experimental preparation of right-sided congestive heart failure (CHF) produced by surgical tricuspid avulsion and progressive pulmonary arterial constriction. Three groups of dogs with CHF and one group of sham-operated dogs were studied. One group of dogs with CHF was given normal saline as pretreatment, while the other two groups were pretreated with either propranolol alone (beta-blockade) or propranolol plus prazosin (alpha- plus beta-blockade). CHF was characterized by weight gain, ascites, elevated right atrial pressure, tachycardia, and reduced cardiac output. Compared with sham-operated animals, animals with CHF exhibited significantly higher baseline levels of plasma beta-endorphin and cortisol. Furthermore, only the animals with CHF responded to the opiate receptor-antagonist nalmefene with significant increases in plasma beta-endorphin, cortisol, and adrenocorticotropic hormone. Administration of nalmefene increased aortic blood pressure, cardiac output, left ventricular dP/dt and dP/dt/P, and blood flow to the myocardium, skeletal muscle, and kidneys in dogs with CHF, but had no appreciable effects in sham-operated dogs. beta-Receptor blockade abolished the increase in cardiac output, left ventricular performance, and blood flow produced by nalmefene, but had no effect on the pressor response to nalmefene. The increase in mean aortic pressure in the beta-blockade group was accompanied by an increase in skeletal muscle vascular resistance. Addition of prazosin in the alpha- plus beta-blockade group abolished the increases in mean aortic pressure and skeletal muscle vascular resistance, suggesting that the changes after propranolol probably resulted from unmasking of alpha-receptor-mediated vasoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)

Conditioning effects of chronic infusions of dobutamine. Comparison with exercise training.

We studied the conditioning effects of chronic infusion of dobutamine and exercise training in three groups of chronically instrumented dogs. One group was infused with normal saline, a second group was infused with dobutamine (40 mug/kg per min), and the third group was exercised on a treadmill at 4 mph, up a 10 degrees incline. Each group was either infused or exercised for 2 h a day, 5 d a week for 5 consecutive wk. Resting heart rate and arterial blood lactate concentration, measured at weekly intervals, decreased progressively in the dobutamine and exercise groups, but not in the group that received normal saline infusion. Cardiovascular responses to submaximal treadmill exercise were not changed by 5 wk of normal saline infusion. However, the increases in heart rate, cardiac output, mean aortic blood pressure, arterial blood lactate, plasma renin activity, and norepinephrine concentration during exercise were significantly smaller after 5 wk of conditioning with either dobutamine or exercise training. After conditioning, the increases in arteriovenous oxygen difference during exercise were larger in the latter two groups, but the increases in total body oxygen consumption did not differ before and after conditioning. To assess ventricular function, we intravenously infused methoxamine both before and after conditioning. The slope of the line that related systolic aortic blood pressure and mean left atrial pressure increased in the animals conditioned with either dobutamine or exercise, indicating enhanced myocardial contractility. Left ventricular blood flow was lower in these two groups of animals than it was in the normal saline group. Left ventricular weight did not differ among the three groups. Our results show that chronic infusion of dobutamine produced cardiovascular and metabolic conditioning effects like those produced by exercise training, and further suggest that sympathetic stimulation during exercise plays a role in physical conditioning.

Differential beta adrenergic sensitivity of atrial and ventricular tissue assessed by chronotropic, inotropic, and cyclic AMP responses to isoprenaline and dobutamine.

Cat atrial tissue was more sensitive to isoprenaline (USP:isoproterenol) and dobutamine than ventricular tissue. Chronotropic response of atrial strips occurred at lower agonist concentrations than inotropic responses of papillary muscle. Cyclic AMP responses in atrial slices also occurred at lower agonist concentrations and were of much greater magnitude than the cyclic AMP responses in ventricular slices. However, the disporportionately greater sensitivity of atrial tissue was more marked with isoprenaline than with dobutamine.

Effect of dobutamine in postperfusion cardiac failure in the dog.

The effect of dobutamine on cardiac function of dogs was investigated. Sixteen dogs were submitted to cardiopulmonary bypass. The aorta of each dog was cross-clamped for 1 hour; attempt was not made to perfuse the heart. After 1 hour, 8 of the 16 dogs were randomly selected and treated with dobutamine (5 mug/kg/min). The other 8 dogs were designated the control group and were given placebo. Postperfusion failure and death were used as end point criteria. Dogs given dobutamine responded remarkably well, with significantly decreased postperfusion low output syndrome. Evidence of cardiac function 5 minutes after the removal of the bypass was the criterion used to determine survival of the surgical cross-clamp procedure; however, this did not necessarily indicate survival of the dog. Of the 8 dogs given dobutamine, 6 (75%) survived the surgical cross-clamp, whereas of the 8 dogs not given dobutamine, 3 (37.5%) survived the surgical procedure. Seemingly, the effect of dobutamine is not mainly chronotropic, but is rather a direct aid to myocardial strength.

Dobutamine: development of a new catecholamine to selectively increase cardiac contractility.

We systematically modified isoproterenol's chemical structure to reduce chronotropic, arrhythmogenic, and vascular side effects. Experiments on dogs showed that the resulting drug, dobutamine, had an inotropic efficacy as great as that of epinephrine due to a direct action on beta1 cardiac receptors. However, unlike epinephrine, dobutamine's effect on alpha and beta2 vascular receptors was slight. At equivalent inotropic doses, dobutamine had less than a fourth of the chronotropic effect of isoproterenol. Desmethylimipramine (DMI), which blocks the sympathetic nerve fiber uptake mechanism, had no effect on dobutamine's actions. In contrast, DMI antagonized dopamine's inotropic effect, and marked chronotropic and pressor responses occurred when we used doses of dopamine large enough to elicit a direct inotropic effect. Dobutamine increased the contractility of isolated cat papillary muscles more but the automaticity less than did isoproterenol. In ischemic dog hearts, dobutamine lacked significant arrhythmic activity, whereas dopamine, norepinephrine, and isoproterenol caused severe ectopic activity. In dogs with experimentally induced low cardiac contractility, low cardiac output, and hypotension, dobutamine produced dose-related increases in cardiac contractility and output, restored arterial blood pressure, and reduced total peripheral resistance slightly. In contrast, isoproterenol failed to restore blood pressure, had only a meager effect on cardiac contractility and output, cuased extreme tachycardia, and lowered peripheral resistance more than did dobutamine. Norepinephrine, which did not increase cardiac contractility or output as much as dobutamine, excessively elevated peripheral resistance and arterial blood pressure.