Central serotonin agonist actions of LY 165163, 1-(m-trifluoromethylphenyl)-4-(p-aminophenylethyl) piperazine, in rats.

1-(m-Trifluoromethylphenyl)-4-(p-aminophenylethyl)piperazine (LY 156163), reported previously to have selective affinity for the 5-HT1A subtype of serotonin receptor in vitro, was studied at doses of 1.25 to 20 mg/kg i.p. in rats to determine if it had properties characteristic of centrally acting serotonin agonists. LY 165163 decreased whole brain concentrations of the serotonin metabolite, 5-hydroxyindoleacetic acid, but not of serotonin itself, decreased the rate of accumulation of 5-hydroxyindoleacetic acid after probenecid administration to block its efflux from brain, decreased the rate of decline in serotonin concentration after inhibition of serotonin synthesis with alpha-propyldopacetamide and decreased the accumulation of 5-hydroxytryptophan after decarboxylase inhibition by m-hydroxybenzylhydrazine. LY 165163 also decreased 5-hydroxyindoleacetic acid concentrations in two specific brain regions, striatum and hypothalamus. Serum concentrations of corticosterone and prolactin were increased by doses of LY 165163 that reduced serotonin turnover. These effects are all consistent with evidence from other studies that LY 165163 is a centrally acting serotonin agonist. LY 165163 also increased the concentrations of two dopamine metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, measured in whole brain as well as in striatum and hypothalamus, but did not alter dopamine concentration. The accumulation of dopa after decarboxylase inhibition was accelerated by LY 165163. The increases in hormone concentrations in serum and of dopamine metabolite concentrations in brain were not antagonized by pretreatment with metergoline, a serotonin antagonist. The mechanisms of those effects require further study.

N-[2-(o-iodophenoxy)ethyl]cyclopropylamine hydrochloride (LY121768), a potent and selective irreversible inhibitor of type A monoamine oxidase.

The effects of N-[2-(o-iodophenoxy)ethyl]cyclopropylamine hydrochloride (LY121768) on types A and B monoamine oxidase (MAO) assayed with radiocarbon-labeled serotonin and phenylethylamine, respectively, were studied in vitro and in vivo. Type A MAO from rat brain was inhibited in vitro by LY121768 with an IC50 of 4 x 10(-10) M, whereas 2500 times higher concentrations of LY121768 (IC50 = 1 x 10(-6) M) were required to inhibit type B MAO. The inhibition of type A MAO increased with time of incubation of LY121768 with enzyme prior to substrate addition and persisted after dialysis, indicative of irreversible inhibition. The irreversible inactivation was prevented by harmaline, a reversible, competitive inhibitor of type A MAO, indicating a requirement for catalytic activity of MAO in the time-dependent inactivation by LY121768. In rats, LY121768 selectively inhibited type A MAO in brain and in liver at low doses. The inhibition of type A MAO persisted for several days after a single 10 mg/kg i.p. dose of LY121768 and was associated with a significant increase in brain dopamine, norepinephrine and epinephrine concentrations and a significant decrease in the concentration of the dopamine metabolites, homovanillic acid and 3,4-dihydroxyphenylacetic acid. The inactivation of type A MAO by LY121768 in vivo was prevented by co-administration of harmaline, indicating a similar mechanism for the in vivo inactivation as for the in vitro inactivation of MAO by LY121768. A reasonable inference from these data and from previous literature is that LY121768 acts as a "suicide substrate" for MAO and inactivates the enzyme by formation of a reactive intermediate which binds covalently to the enzyme. The presence of iodine in the LY121768 molecule not only confers high selectivity for type A MAO but offers a site for radionuclide introduction that might be a useful means of labeling type A MAO in vitro or in vivo for various purposes.

Effect of cis and trans isomers of 1-amino-2-(p-chlorophenyl)cyclohexane, conformationally restricted analogs of p-chloroamphetamine, on 5-hydroxyindoles in rat brain.

Cis and trans isomers of 1-amino-2-(p-chlorophenyl)cyclohexane, conformationally restricted analogs of p-chloroamphetamine, did not decrease brain serotonin and 5-hydroxyindoleacetic acid concentrations at i.p. doses of .05 and .1 mmole/kg in rats, doses at which p-chloroamphetamine itself decreased the concentrations of these 5-hydroxyindoles to half or less of their initial values. These analogs of p-chloroamphetamine, unlike several others studied previously, apparently lack the ability of the parent compound to inhibit serotonin uptake or synthesis or to release serotonin from intraneuronal granular stores.

Cellular electrophysiology of clofilium, a new antifibrillatory agent, in normal and ischemic canine Purkinje fibers.

Intracellular electrophysiological studies were performed on isolated canine cardiac tissues to investigate further the reported ability of clofilium (3 X 10(-8)--10(-6) M) to selectively increase action potential duration (APD) and refractoriness. In Purkinje fibers from normal dogs, clofilium did not influence (1) the rate of rise of the action potential (Vmax) elicited from normal or depolarized (10 mM potassium) resting potentials, (2) the Vmax of premature potentials elicited during the repolarization phase of a previous action potential or (3) the rate of diastolic depolarization of spontaneously firing Purkinje fibers. The diastolic interval was altered by inserting a single premature impulse during diastole or by varying the basic cycle length. Clofilium (3 X 10(-7) M) slightly reduced the time constant for the relation between diastolic interval and APD in concentrations that caused a maximal increase in APD of nonpremature impulses. In dogs subjected to occlusion of the left anterior descending coronary artery 48 hr before study, the APD of surviving Purkinje fibers was longer in the infarcted zone than in the normal zone. Clofilium (3 X 10(-8) M) increased APD in both zones but more so in the normal areas, thus reducing the disparity of APD between zones. Similarly, clofilium (3 X 10(-8) and 3 X 10(-7) M) increased the effective refractory period in both zones but more so in the normal area. The increase of APD and refractoriness in normal as well as depolarized or ischemic tissues in the absence of marked changes in Vmax and conduction may decrease the likelihood of reentrant arrhythmias and underlie the antifibrillatory effects in anesthetized dogs.

Ihibition of rat brain norepinephrine N-methyltransferase in vitro and in vivo by chloro-substituted 1-aminoindans.

Norepinephrine N-methyltransferase from rat brain stem was inhibited in vitro by 1-aminoindans with chlorine substituents on the aromatic ring. The order of inhibitory potency among these compounds was 4.5-dichloro greater than 4-chloro greater than 5-chloro approximately or equal to 5,6-dichloro approximately or equal to 6,7-dichloro greater than 6-chloro greater than 7-chloro. All except the 7-chloro compound were more potent inhibitors than the parent unsubstituted 1-aminoindan. 4,5-Dichloro-1-aminoindan was a competitive inhibitor in kinetic studies with L-norepinephrine as the variable substrate; its Ki value determined from a Dixon plot was 3.3 x 10(-7) M. At doses of 10-40 mg/kg i.p., this compound inhibited brain stem and hypothalamic norepinephrine N-methyltransferase in vitro and lowered hypothalamic concentrations of epinephrine in rats, effects that lasted for several hours. 4,5-Dichloro-1-aminoindan may be a useful pharmacologic tool for studies of epinephrine-forming neurons in brain.

A32390A, a new biologically active metabolite. II. Isolation and structure.

An inhibitor of dopamine-beta-hydroxylase, designated A32390A, was isolated from the culture broth of a Pyrenochaeta species. The inhibitor showed antimicrobial activity against fungi and gram-positive bacteria. Spectroscopic analysis and chemical degradation studies indicated that the structure was 1,6-di-O-(2-isocyano-3-methylcrotonyl)-D-mannitol.

Biological disposition of rigid analogs of amphetamine.

Tissue levels of amphetamine and of amphetamine analogs with a rigid conformation (2-aminoindan, 2-aminotetralin, and 2-aminobenzocycloheptene) were measured in rats by a spectrofluorometric method involving the reaction of the primary amine group with fluorescamine. All drugs were concentrated in tissues, the order of distribution being lungs greater than kidneys greater than liver=spleen=brain greater than muscle greater than fat=heart greater than blood. In brain, amphetamine and 2-aminoindan were present mostly in the supernatant fraction after high speed centrifugation onbrain homogenates; the two higher molecular weight drugs were present at slightly greater concentrations in the particulate fraction. All four drugs disappeared from rat brain with half-lives of 1-2 hr. Iprindole pretreatment increased drug levels in brain and prolonged the half-lives by two- to threefold. The data suggest that the biological disposition of the rigid analogs resembles generally that of amphetamine and that all of the drugs are probably metabolized by ring hydroxilation in the rat.