NPC 15669 inhibits the reversed passive Arthus reaction in rats by blocking neutrophil recruitment.

NPC 15669, N-carboxy-L-leucine,N-[(2,7-dimethylfluoren-9-yl)methyl]ester, has been shown to inhibit several inflammatory reactions that depend upon recruitment of neutrophils into the primary lesion. In the present study we examined the effects of NPC 15669 in the reversed passive Arthus reaction, an inflammatory reaction occurring in the skin of rats in response to intracutaneous injection of antigen followed by intravenous administration of antibody. In this model, immune complex formation activates complement, resulting in rapid recruitment of neutrophils to the site, which releases free radicals and proteases that damage capillaries, resulting in plasma leak. NPC 15669 inhibited the increased capillary permeability occurring in the reversed passive Arthus reaction in a dose-dependent manner, with an ED50 of 4 mg/kg. The agent similarly inhibited the recruitment of radiolabeled neutrophils as well as the accumulation of myeloperoxidase, a neutrophil marker. NPC 15669 in vitro inhibited the adherence of formyl-L-Met-L-Leu-L-Phe- or human recombinant C5a-activated neutrophils to endothelium, with IC50 values of 15 to 30 microM (ca. 4-9 micrograms/ml). Measurement of plasma NPC 15669 showed that at the ED50 dose, the average circulating concentration of drug was 5 micrograms/ml, consistent with the hypothesis that NPC 15669 exerts its anti-inflammatory effects by inhibiting neutrophil adherence to endothelium and recruitment into the inflammatory lesion.

Pharmacologic profile of NPC 168 (naltrexone phenyl oxime), a novel compound with activity at opioid receptors.

NPC 168 (naltrexone phenyl oxime) was synthesized as a novel opioid antagonist and evaluated in several in vitro and in vivo assays. NPC 168 inhibited binding to the mu, delta and kappa subtypes of the opioid receptor with nanomolar potencies. The potency of NPC 168 to antagonize morphine-induced analgesia was slightly less than that of naltrexone and nalmefene following either intraperitoneal (ED50 = 0.07 mg/kg) or oral (ED50 = 0.82 mg/kg) administration. The duration of action of NPC 168 was approximately 8 hr following subcutaneous administration, compared to 4 hr for nalmefene, to antagonize oxymorphonazine-induced analgesia. The long duration of action of NPC 168 was substantiated by pharmacokinetic data that demonstrated rapid uptake and slow clearance of NPC 168 from brain. NPC 168 (5, 10 and 20 mg/kg) also inhibited cumulative 6-hr food intake in rats that were deprived of food for 24 hr, but chronic administration of this compound to rats over a three-week period resulted in a marginal reduction in cumulative body weight gain. NPC 168 at doses of up to 10 mg/kg did not produce a conditioned taste aversion. However, NPC 168 was slightly more toxic than either naltrexone or nalmefene when administered parenterally, and as toxic as nalmefene when administered by the oral route. These data demonstrate that NPC 168 is a novel opioid antagonist with a longer duration of action than either naltrexone or nalmefene.

Bradykinin receptor antagonists.

Bradykinin and its active metabolites are produced at the sites of their actions by kallikreins. They potently elicit a variety of biological effects: hypotension, bronchoconstriction, gut and uterine contraction, epithelial secretion in airway, gut, and exocrine glands, vascular permeability, pain, connective tissue proliferation, and eicosanoid formation. These effects are mediated by at least two broad classes of receptors. The most common is the B2 subtype. The Stewart and Vavrek peptides characterized by a DPhe7 substitution have provided powerful tools for study of bradykinin's actions by competitively and specifically blocking bradykinin B2 receptors. The significance of kinins in certain human diseases is being explored using these new tools and potential therapeutic agents. At present, human clinical trials are underway to test the usefulness of bradykinin receptor antagonists in the symptoms of the common cold and in the pain associated with severe burns. Trials for use in asthma will be initiated in 1990.

Antagonists of B2 bradykinin receptors.

Bradykinin and its active metabolites, produced by kallikreins at their sites of action, potently elicit a variety of biological effects: hypotension, bronchoconstriction, gut and uterine contraction, epithelial secretion in airway, gut, and exocrine glands, vascular permeability, pain, connective tissue proliferation, cytokine release, and eicosanoid formation. These effects are mediated by at least two broad classes of receptors. The most common is the B2 subtype. The availability of competitive antagonists of B2 receptors has provided powerful tools for the study of bradykinin's actions. The significance of kinins in certain human diseases is being explored by using these agents as potential therapeutic agents. Human clinical trials are under way to test the usefulness of bradykinin receptor antagonists to treat symptoms of the common cold and the pain associated with severe burns. Trials are also being comtemplated for use in treatment of asthma.

[Arg1-D-Phe7]-substituted bradykinin analogs inhibit bradykinin- and vasopressin-induced contractions of uterine smooth muscle.

The purpose of the present study was to examine the tissue selectivity of several [Arg1-D-Phe7]-substituted analogs of bradykinin. Unlike D-Arg-[Hyp3-D-Phe7]-bradykinin (NPC567), which antagonizes bradykinin-induced contractions both in rat isolated uterus and guinea pig ileum, [D-Nal1-Thi5,8-D-Phe7]-bradykinin (NPC573) was active only in uterine smooth muscle. Binding studies revealed that, unlike several [D-Phe7]-substituted analogs, including NPC567, NPC573 competed with radiolabeled bradykinin neither at receptors in uterus nor ileum. Moreover, no [Arg1-D-Phe7]-substituted analog competed with bradykinin binding in guinea pig ileum, suggesting that these agents, which inhibit uterine but not ileal contractions to bradykinin, may not be bradykinin receptor antagonists. NPC573 inhibited [Arg8]-vasopressin-induced contraction of the uterus more potently than it did bradykinin, although NPC573 (and other [Arg1-D-Phe7]-substituted analogs tested) did not inhibit binding of a vasopressin antagonist either in uterus or liver membranes. We therefore suggest that [Arg1-D-Phe7]-substituted analogs of bradykinin inhibit contractions of uterine smooth muscle by a mechanism other than receptor antagonism. In addition, the tissue selectivity of these agents suggests that the mechanisms underlying bradykinin's contractile effect in uterus are different than in intestinal smooth muscle.

D-Arg-[Hyp3-D-Phe7]-bradykinin, a bradykinin antagonist, reduces mortality in a rat model of endotoxic shock.

The kallikrein-kinin system is activated during endotoxic shock, suggesting that bradykinin plays a role in the pathology of this disease. To test this hypothesis, a bradykinin antagonist, D-Arg-Hyp3-D-Phe7-bradykinin (NPC 567), was studied in conscious, chronically catheterized rats undergoing lipopolysaccharide (LPS)-induced endotoxic shock. LPS treatment resulted in an increase in circulating bradykinin from less than 23 pg/ml to 144 +/- 18 pg/ml at 1 hr. Intravenous administration of LPS resulted in a 38% drop in mean arterial pressure at 1 hr which was partially reversed by NPC 567. NPC 567 did not affect the moderate tachycardia observed following LPS. NPC 567 infusion at 8 nmol/kg/min dramatically reduced mortality from 100% to 50% at 24 hr (P less than 0.01). In response to LPS, blood thromboxane B2 (TXB2) rose from less than 200 pg/ml to 2,298 +/- 64 pg/ml, while 6-keto-prostaglandin-F1 alpha (6kPGF1 alpha) rose from 289 +/- 23 pg/ml to 7,927 +/- 822 pg/ml. NPC 567 reduced the rise in 6kPGF1 alpha by 42% (P less than 0.05), without affecting TXB2. In summary, NPC 567 reduced mortality in rats treated with LPS, reduced the rise in 6kPGF1 alpha and partially reversed the hypotensive effects. These results suggest that bradykinin plays a significant role in the pathology of endotoxic shock.

D-Phe7-substituted peptide bradykinin antagonists are not substrates for kininase II.

The bradykinin receptor antagonists [D-Phe7]bradykinin, D-Arg[Hyp3,D-Phe7]bradykinin and D-Arg[Hyp3,Thi5,8,D-Phe7]bradykinin were tested for their ability to serve as substrates for kininase II (angiotensin converting enzyme) purified from rabbit lung. By HPLC, the peptides were not measurably degraded over 30 minutes. Under identical conditions, bradykinin was completely degraded to bradykinin (1-7). When hippuryl-His-Leu was used as a substrate for kininase II, the D-Phe7-substituted bradykinins acted as weak noncompetitive inhibitors. While the peptides were poor substrates for kininase II, they were short-lived when injected intravenously. D-Arg[Hyp3,D-Phe7]bradykinin was completely degraded to small fragments in less than 2 minutes. In diluted serum in vitro, a single product was observed with elution consistent with loss of arginine, suggestive of metabolism by kininase I.

Bradykinin as a pain mediator: receptors are localized to sensory neurons, and antagonists have analgesic actions.

Autoradiographic studies localize [3H]bradykinin receptor binding sites to the substantia gelatinosa, dorsal root, and a subset of small cells in both the dorsal root and trigeminal ganglia of the guinea pig. [3H]Bradykinin labeling is also observed over myocardial/coronary visceral afferent fibers. The localization of [3H]bradykinin receptors to nociceptive pathways supports a role for bradykinin in pain mediation. Several bradykinin antagonists block bradykinin-induced acute vascular pain in the rat. The bradykinin antagonists also relieve bradykinin- and urate-induced hyperalgesia in the rat paw. These results indicate that bradykinin is a physiologic mediator of pain and that bradykinin antagonists have analgesic activity in both acute and chronic pain models.

Distinct bradykinin receptors mediate stimulation of prostaglandin synthesis by endothelial cells and fibroblasts.

Bradykinin-stimulated prostaglandin synthesis was investigated in Swiss albino 3T3 fibroblasts (Swiss 3T3 cells) and bovine pulmonary artery endothelial cells (CPAE). Previous studies have indicated that bradykinin stimulates arachidonic acid release in Swiss 3T3 cells by activating phospholipase A2 and by activating phosphatidylcholine-specific phospholipase C in CPAE cells. The dose-response for bradykinin-stimulated prostaglandin synthesis was similar in Swiss 3T3 cells and CPAE cells. Marked differences were found in the effects of several bradykinin analogs in Swiss 3T3 cells and CPAE cells. des-Arg9-bradykinin was a partial agonist in CPAE cells whereas it was completely inactive in Swiss 3T3 cells. [p-chloro-D-Phe6-D-Pro7]-Bradykinin was a full agonist in Swiss 3T3 cells, but only a partial agonist, exhibiting a bell-shaped curve, in CPAE cells. The bradykinin antagonist, [D-Arg0-Hyp3-D-Phe7]-bradykinin, was a several-fold more potent antagonist in Swiss 3T3 cells, compared to CPAE cells. The effects of these bradykinin analogs on prostaglandin synthesis do not fit the previously described BK1, BK2 bradykinin receptor classification. These findings suggest that there are at least two bradykinin receptors which stimulate prostaglandin synthesis. Previous studies have indicated that these two bradykinin receptors may be coupled to different transduction pathways for the release of arachidonate.

Effect of cysteine on the persistent depletion of brain monoamines by amphetamine, p-chloroamphetamine and MPTP.

The administration of L-cysteine (500 mg/kg i.p.) 30 min before and 5 h after the administration of (+)-amphetamine sulfate markedly attenuated the persistent decreases in striatal dopamine (DA), dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in rats one week after the administration of a single dose of amphetamine (9.2 mg/kg i.p.) to iprindole-treated animals and in mice one week after the last of four daily injections of amphetamine (30 mg/kg i.p.). Cysteine prevented the persistent decreases in striatal serotonin (5HT) and 5-hydroxyindoleacetic acid (5HIAA) one week after the administration of p-chloroamphetamine to rats, but failed to alter the persistent decreases in striatal DA, DOPAC and HVA in mice one week after the last of four daily doses of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, 30 mg/kg s.c.). The results suggest that the mechanisms by which amphetamine and p-chloroamphetamine, but not MPTP, produce persistent depletions of striatal monoamines involve the generation of neurotoxic electrophilic intermediates which can be inactivated by the administration of cysteine.

Central and peripheral catecholamine depletion by 1-methyl-4-phenyl-tetrahydropyridine (MPTP) in rodents.

1-Methyl-4-phenyl-tetrahydropyridine (MPTP) given in single doses to rats depleted norepinephrine concentration in heart and mesenteric artery but had little effect on catecholamine concentration in brain. MPTP did not share with amphetamine the ability to cause persistent depletion of striatal dopamine in iprindole-treated rats. Administration of MPTP via osmotic minipumps implanted s.c. for 24 hrs after a loading dose of MPTP in rats resulted in depletion of striatal dopamine and its metabolites one week later. MPTP in vitro was a reasonably potent, competitive and reversible inhibitor of MAO-A (monoamine oxidase type A). MPTP appeared to inhibit MAO-A in rat brain in vivo as determined by its antagonism of the inactivation of MAO-A by pargyline and by its antagonism of the increase in dopamine metabolites resulting from the administration of Ro 4-1284, a dopamine releaser. The inhibition of MAO-B by MPTP in vitro was noncompetitive, time-dependent, and not fully reversed by dialysis, consistent with the findings of others that MPTP is acted upon by MAO-B. In mice, four successive daily doses of MPTP is acted upon by MAO-B. In mice, four successive daily doses of MPTP given s.c. resulted in marked depletion of dopamine and its metabolites one week later, and the depletion of dopamine was completely prevented by pretreatment with deprenyl, which inhibited MAO-B but not MAO-A. These and other studies in rodents may help in elucidating the mechanisms involved in the destructive effects of MPTP on striatal dopamine neurons that lead to symptoms of Parkinson's disease in humans and in monkeys.

A pivotal role for serotonin (5HT) in the regulation of beta adrenoceptors by antidepressants: reversibility of the action parachlorophenylalanine by 5-hydroxytroptophan.

An acute reduction in the synaptic availability of serotonin (5HT) by p-chlorophenylalanine (PCPA) nullifies the decrease in the density of cortical beta adrenoceptors caused by desipramine (DMI) but does not appreciably alter the attenuation of the norepinephrine (NE) sensitive adenylate cyclase. The analysis of competition-binding curves of [3H]-dihydroalprenolol shows that the affinity of the agonist (-)-isoproterenol for cortical beta adrenoceptors is profoundly reduced following PCPA. This reduction in agonist affinity is enhanced by DMI. Resupplying 5HT by by-passing tryptophan hydroxylase inhibition, by administering 5-hydroxytryptophan, converts a DMI non-responsive to a DMI responsive beta adrenoceptor population and shifts the markedly decreased agonist affinity towards the affinity values found in control preparations. The results demonstrate the pivotal role of 5HT in the regulation of the density and agonist affinity characteristics of cortical beta adrenoceptors and contribute to the scientific basis of the 'serotonin-norepinephrine link hypothesis' of affective disorders.

Effects of antipsychotic drugs on the long-term effects of amphetamine on nigro-striatal dopamine neurons in iprindole-treated rats.

The decrease in striatal dopamine (DA) at 1 week after the administration of a single injection of (+)-amphetamine sulfate (9.2 mg/kg) to iprindole-treated (10 mg/kg of iprindole hydrochloride) rats was prevented by haloperidol (0.2 mg/kg), sulpiride (32 mg/kg), pimozide (2 mg/kg), chlorpromazine hydrochloride (3.5 mg/kg), fluphenazine 2-hydrochloride (0.25 mg/kg) and (+)-butaclamol hydrochloride (1 mg/kg) but not by (-)-butaclamol hydrochloride (1 mg/kg) or clozapine (40 mg/kg). The same dose of sulpiride did not significantly attenuate the rotational behavior induced by the administration of (+)-amphetamine sulfate (9.2 mg/kg) to iprindole-treated rats with unilateral aspiration lesions of the striatum. The concentration of amphetamine in the brains of iprindole-treated rats at 8 h after (+)-amphetamine sulfate (9.2 mg/kg) administration was not altered by the coadministration of haloperidol (1 mg/kg), sulpiride (32 mg/kg), pimozide (2 mg/kg) or clozapine (40 mg/kg). Recovery of striatal DA after depletion by alpha-methyl-m-tyrosine (alpha MMT) (50 mg/kg) was facilitated by haloperidol (0.2 mg/kg) and sulpiride (32 mg/kg) but not by clozapine (40 mg/kg). The possibility that neuroleptic drugs antagonize both the short-term depletion of striatal DA produced by alpha MMT and the long-term depletion of striatal DA produced by amphetamine in iprindole-treated rats by an effect on the nerve impulse-mediated release of vesicular transmitter is discussed.

Long-term effects of a priming dose and short-term infusion of amphetamine on striatal dopamine neurons in rats.

A priming dose (15 mg/kg i.p.) of (+)-amphetamine sulfate combined with a 16 h subcutaneous infusion of 1.36 mg of the drug per hour to rats via its release from osmotic minipumps produced marked decreases in striatal dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and the synaptosomal uptake of [3H]DA which lasted for at least 12 weeks. The decrease in striatal DA persisted through 24 weeks after drug treatment. In contrast, striatal levels of DOPAC, HVA and synaptosomal DA uptake recovered to control levels by 24 weeks after amphetamine treatment.

Drug discrimination in rats: evidence for amphetamine-like cue state following chronic haloperidol.

Two groups of male Sprague-Dawley rats were trained to discriminate which of two levers to press for milk reinforcement on a VI-20 sec schedule of reinforcement on the basis of whether they were injected intraperitoneally with d-amphetamine (0.50 mg/kg or 1.50 mg/kg) or saline 15 min prior to daily 30 min training sessions. Following acquisition of the discrimination, dose-response functions were generated for both training-dose groups during 5 min test sessions. All subjects were then injected with 1.0 mg/kg of haloperidol for ten consecutive days and retested on either saline or intermediate doses of amphetamine on days 1, 2, 4 and 7 following the final haloperidol injection. The results indicated that chronic haloperidol enhanced the discriminative stimulus properties of amphetamine in both training groups. More importantly, when tested on saline, subjects in both training groups made significantly more responses on the d-amphetamine lever than observed prior to chronic haloperidol. On the basis of linear regression analysis of the dose-response curves it was shown that rats in both groups responded as though they had been injected with 0.18 mg/kg of d-amphetamine. In a second experiment this increase in amphetamine-lever responding when animals were tested with saline following chronic haloperidol was replicated and in addition it was observed that chronic amphetamine had the opposite effect on this measure.

Role of serotonergic input in the regulation of the beta-adrenergic receptor-coupled adenylate cyclase system.

The action of desipramine on the norepinephrine-sensitive adenylate cyclase system and the density of beta-adrenergic receptors in rat cortex was studied after selective lesioning of serotonergic neurons with 5,7-dihydroxytryptamine. In animals with lesions desipramine failed to reduce the density of beta-adrenoceptors but decreased the response of adenosine 3',5'-monophosphate to isoproterenol and norepinephrine to the same degree as in animals without lesions. The results demonstrate a functional linkage between serotonergic and noradrenergic systems in the rat cortex, with beta-adrenergic receptors and neurohormonal sensitivity of the adenosine 3',5'-monophosphate-generating system being under separate regulatory control.