Effects of imipramine, nomifensine and d-amphetamine on type B monoamine oxidase, cyclic AMP phosphodiesterase and dopamine-beta-hydroxylase

The three dissimilar structural antidepressant drugs, imipramine, nomifensine and d-amphetamine, were compared for their effects on type B monoamine oxidase, cyclic AMP phosphodiesterase and dopamine-beta-hydroxylase. Three antidepressant drugs caused a dose-dependent inhibition on type B monoamine oxidase. Of the three drugs, imipramine had a most potent effect. Unlike d-amphetamine, both imipramine and nomifensine inhibited the cyclic AMP phosphodiesterase activity at concentrations more than 10(-4)M. No effect was observed below this concentration. All drugs seemed to have little or no effects on the partially purified dopamine-beta-hydroxylase activity. The weak inhibitory effects of nomifensine on these three enzymes may not be attributable to its antidepressant properties. Morphine had no effect on the three enzyme activities.

Extraction of an inhibitory substance from rat liver on rat brain ATPase

A substance, which can be extracted from rat liver and partially purified, has been tested for its effect on the activity of ATPase in rat brain. This substance inhibited the ATPase activity significantly, and the inhibitory effect was not eliminated by the addition of catecholamines such as epinephrine and dopamine.

Effects of various agents on synaptosomal adenylate cyclase activity in the absence and presence of the boiled supernatant

A study was made of the effects of various agents on adenylate cyclase in synaptosomes in both the absence and presence of the boiled supernatant from rat cerebral cortex. The activity of adenylate cyclase in these preparations was inhibited by the sulfhydryl reactive agent p-chloromercuribenzoate. Sulfhydryl compounds such cysteine, glutathione and Coenzyme A stimulated the enzymic activity in both the absence and presence of the boiled supernatant. The chelating agent 1.2-bis-(2-dicarboxymethylaminoethoxy)ethane caused a stimulation of the enzymic activity with and without the presence of the boiled supernatant. Adenine nucleotide (adenine, adenosine, AMP and ADP), GTP, Pi and carbamylcholine seemed to have little effect. The stimulatory substance in the boiled supernatant was estimated to have a molecular weight in the range of 1,000-1,300.

Inhibitory substance (substance I) in rat liver of dopamine-beta-hydroxylase and its effect on the rat blood pressure

In a series of experiments undertaken to investigate the naturally occurring inhibitors of dopamine-beta-hydroxylase, we extracted some active substance from rat liver. This substance was named "substance I" because of its inhibitory effect on the dopamine-beta-hydroxylase. Substance I had some hypotensive effect on the rat blood pressure.

Inhibition of dopamine-beta-hydroxylase by carnosine

Dopamine-beta-hydroxylase was partially purified from bovine adrenal medulla and the effect of carnosine on the dopamine-beta-hydroxylase activity was investigated. Carnosine significantly inhibited the enzyme activity at the concentrations higher than 0.5 mM. According to the Lineweaver-Burk plots, the inhibition observed appeared to be a non-competitive type with the substrate, tyramine.

The stimulatory effect of the boiled supernatant on cyclic AMP formation in synaptosomes from rat cerebral cortex

The effect of the boiled supernatant on synaptosomal adenyl cyclase activity of rat cerebral cortex was investigated. The boiled supernatant markedly increased the accumulation of cyclic AMP in synaptosomes when added to adenyl cyclase system by a mechanism presumably unrelated to inhibition of cyclic AMP phosphod iesterase or adenosine triphosphatase. Magnesium ion was required for synaptosomal adenyl cyclase activity and its stimulation by the boiled supernatant. The result discerned by doubl reciprocal plots showed an increase in Vmax value of adenyl cyclase by addition of the boiled supernatant without significantly altering the affinity for substrate. The enzyme activity was not stimulated by dopamine, histamine and serotonin in either the absence and presence of the boiled supernatant.