Inhibition of adenylate cyclase by transglutaminase-catalyzed reactions in pigeon erythrocyte ghosts

We report the occurrence in pigeon erythrocytes of a soluble Ca2+-dependent transglutaminase (TGase) activity. The effect of the erythrocyte ghost protein modifications, determined by TGase-catalyzed reactions, on adenylate cyclase, phospholipid methyltransferase I and II activities and on the lipidic matrix fluidity of the membrane was investigated by using a purified guinea pig liver TGase preparation. The results showed a significant inhibitory effect of such modifications both on the basal and on the variously stimulated (by NaF, Gpp(NH)p alone or in the presence of 1-isoproterenol) adenylate cyclase activity. By contrast, both the phospholipid methylation and the fluidity of the lipidic matrix of the membrane were unaffected by TGase-mediated reactions. These data suggest a new possible inhibitory mechanism of the cyclic AMP synthesis which might be triggered by the enhancement of the cytosolic Ca2+ concentration.

Effect of cyclosporin A on the membrane-associated events in human leukocytes with special reference to the similarity with dexamethasone

The effect of an immunosuppressive drug, cyclosporin A, and dexamethasone was assessed on the enzymatic reactions of membrane phospholipid in normal human lymphocytes and neutrophils. Incubation for 20 min with cyclosporin A markedly suppressed, in a dose dependent manner, phospholipase A2 activity and the release of prostaglandin E2 in lymphocytes, and slightly those in neutrophils, while no inhibition of phosphatidylethanolamine (PE)-N methyltransferase activity was observed. Choline phosphotransferase (CPT) activity was not inhibited by the drug, either. These inhibitory effects on enzyme activities of membrane phospholipid are similar to those of dexamethasone, although different incubation time of the drug was required to induce inhibitory effects. These findings suggest that cyclosporin A acts upon early membrane events in the activation of cells involved in inflammatory reactions; they further suggest that suppression of immune response by cyclosporin A is at least partly due to inhibition of phospholipase A2 in the plasma membrane of inflammatory cells. This inhibition reduces the production of cell membrane lyso-phosphatidylcholine (PC) and arachidonic acid from PC, which is produced by transmethylation of PE and cytidine diphosphate (CDP) choline pathway of which the last reaction to PC is mediated by CPT.

S-Methylation of D- and L-penicillamine by human erythrocyte membrane thiol methyltransferase

Human red blood cell (RBC) membranes contain a thiol methyltransferase activity that catalyzes the S-methylation of 2-mercaptoethanol (2-ME). These experiments were performed to determine whether human RBC membranes contain enzymes that can catalyze the S-methylation of D- and L-penicillamine, to determine whether those enzymes are similar to the RBC membrane thiol methyltransferase that catalyzes the S-methylation of 2-ME, and to determine whether lipophilic conjugates of the S-methyl metabolites of D- and L-penicillamine are formed by RBC membranes. Human RBC membranes were able to catalyze the S-methylation of D- and L-penicillamine. The apparent Michaelis (Km) constants for D- and L-penicillamine were 7.53 and 7.27 mM, respectively. However, the Vmax value for L-penicillamine was more than 2.5 times greater than the Vmax value for D-penicillamine. D- and L-Penicillamine methyltransferases and 2-ME thiol methyltransferase were similar with respect to their subcellular distributions, inhibitor sensitivities, and thermal stabilities. In addition, when methyltransferase activities for 2-ME and for D- and L-penicillamine were measured in RBC membranes from 19 individual subjects, there were highly significant correlations among all three activities (r greater than 0.98, p less than 0.001 for all three comparisons). These observations suggest either that a single enzyme in the human RBC membrane catalyzes the S-methylation of all three compounds, or, less likely, that these reactions are catalyzed by three separate enzymes that are regulated in parallel and have similar properties. Experiments were then performed to identify the products of the penicillamine methylation reactions.(ABSTRACT TRUNCATED AT 250 WORDS)

Human erythrocyte histamine N-methyltransferase: radiochemical microassay and biochemical properties

A radiochemical assay for the measurement of histamine N-methyltransferase (HNMT) activity in human erythrocytes (RBCs) has been developed. This assay was developed as a first step toward testing the hypothesis that the biochemical properties and regulation of HNMT in an easily obtainable human cell, the RBC, might reflect those of the enzyme in less accessible cells and tissues. The Michaelis (Km) constant in the RBC for histamine, the methyl acceptor substrate for the reaction, was 5.0 X 10(-5) mol/l. The Km constant for S-adenosyl-L-methionine, the methyl donor, was 2.8 X 10(-6) mol/l. The assay was performed at a reaction pH of 7.4 with a potassium phosphate buffer. The product of the reaction was identified as N tau-methylhistamine by high performance liquid chromatography. The Kii for inhibition of the RBC enzyme by amodiaquine, an HNMT inhibitor, was 1.0 X 10(-7) mol/l, while the Kis value was 0.48 X 10(-7) mol/l. Blood samples obtained from 39 randomly selected adult white subjects had a mean activity of 130 +/- 30 U/ml of packed RBCs (mean +/- SD). Enzyme activities varied over a range from 74-213 U. There were no differences between men and women in mean activities, nor was there a significant correlation between RBC HNMT activity and age. The results of experiments in which lysates with 'low' and 'high' activities were mixed gave no indication that individual variations in RBC HNMT activities were due to the effects of endogenous enzyme inhibitors or activators. RBC HNMT activities measured in blood samples from 17 individual subjects four times over 6 wk were quite constant in each subject, with an average coefficient of variation of 6.2%. The availability of this assay will make it possible to test the hypothesis that individual variations in RBC HNMT activity might be used to predict individual differences in HNMT activity in other human cells and tissues.

Thymidylate synthetase of human lymphocytes augmented in vitro by methotrexate

The addition of methotrexate to the assay system of thymidylate synthetase caused a reduction in the activity of the enzyme but addition of methotrexate to the culture of phytohemagglutinin stimulated normal human lymphocytes caused an increase in the activity of the enzyme which was abolished by the addition of actinomycin D or cycloheximide. These studies suggest that the antimetabolite augmented the enzyme activity by modulating the gene for the enzyme. This modulation of the gene could have been achieved by the thymineless state brought about by methotrexate or the antimetabolite could have affected gene reodont or brought about amplification of the gene. The results of the nucleoside incorporation were consistent with a thymidylate synthetase block; however, other explanations are offered.

Characteristics of phospholipid methylation in human erythrocyte ghosts: relationship(s) to the psychoses and affective disorders

Recent studies have shown that patients with a schizophrenic-like illness have a significant deficit in erythrocyte ghost membrane (EGM) phosphatidylcholine (PC); patients with the most severe deficiency showed a marked decrease in Na+-Li+ counterflow activity (Hitzemann et al. 1984a and b). The present study was undertaken to see if the decrement in PC is associated with a decrease in phospholipid methylation activity. Phospholipid methylation in human EGMs is distinctly different from that in rat EGMs (Hirata and Axelrod 1980) in that the human activity is not Mg++-dependent, and apparent methyltransferase I activity is located in the external membrane surface. The patient population consisted of 20 DSM-III schizophrenics (SCZ), 13 DSM-III schizophreniform (SF) disorder patients, and 11 DSM-III manics (M). Twelve age- and sex-matched controls were used for the comparison group. Methylation activity was significantly decreased in all three patient groups, although the M group had significantly higher activity than the SF group. Twenty-four of the SCZ and SF patients entered a Li+ trial. The Li+ responder group (n = 8) showed significantly lower activity than the nonresponder group (n = 16). Overall, we conclude that the decrement in phospholipid methylation activity partially contributes to the decrement in PC levels.

Inhibitory effects of dapsone on enzymatic activities of membrane phospholipids in human blood cells

In order to elucidate the action mechanism of dapsone on blood cell membranes, we assessed the dose-dependent effect of dapsone on the activities of choline phosphotransferase (which mediates the production of the structural phospholipid, phosphatidylcholine) and methyltransferase (which produces phosphatidylcholine from phosphatidylethanolamine, representing the dynamics of the cells) in the membranes of red cells, lymphocytes, and neutrophils obtained from 16 healthy human subjects. The methyltransferase activity of lymphocyte and neutrophil cell membranes was slightly inhibited by dapsone, although only at a high concentration (1 mM), while that of red cells was not affected. On the other hand, dapsone significantly decreased the choline-phosphotransferase activity of red-cell membranes in a dose-dependent fashion, but did not significantly inhibit that of lymphocytes or neutrophils. The mechanisms of the hemolytic side effect of dapsone on erythrocytes and its anti-inflammatory effect on neutrophils are discussed in connection with its inhibitory effect on the enzymatic activities of membrane phospholipids.

Activity of cyclic AMP phosphodiesterase and methyltransferases in leukocyte membranes from allergic patients

Cyclic AMP metabolism and methylation of phospholipids are central events which occur at the membrane level. Since a dysfunction of cell membranes seems to characterize some allergic diseases, we investigated cyclic AMP phosphodiesterase and methyltransferase activities in leukocyte membrane fractions obtained from healthy volunteers and from allergic patients. The allergic group presented a significantly decreased methyltransferase activity compared with a control group, whereas cyclic AMP phosphodiesterase and noradrenaline (NA)-stimulated methyltransferase were found to be increased with respect to the control group. A significant correlation has been found between cyclic AMP phosphodiesterase and NA-stimulated methyltransferase with both control and allergic subjects, which suggests close relationships between these two enzymes within the cell membrane.

Phospholipid transmethylation in the membrane of human neutrophils and lymphocytes

Phospholipid transmethylation in the microsomal fraction of stimulated and unstimulated human leukocytes was measured in a recently developed assay system. Microsomal fraction was prepared from neutrophils, unseparated lymphocytes, T lymphocytes, and non-T lymphocytes by sonication and subsequent ultracentrifugation. Two hundred micrograms of microsomal protein was reacted with S-adenosyl-L-[methyl-3H]methionine. In unstimulated cells, incorporation of methyl-3H into phospholipid was 0.60 +/- 0.06 pmol min-1 mg protein in neutrophil membrane, 0.84 +/- 0.075 in unseparated lymphocytes, 1.23 +/- 0.17 in T lymphocytes, and 0.71 +/- 0.085 in non-T lymphocytes (mean +/- SE). Stimulation of neutrophils with opsonized zymosan or concanavalin A (Con A), and of lymphocytes with Con A, phytohemagglutinin, or pokeweed mitogen increased 15 to 30%. The resulting methylated phospholipids were identified and quantitated by two-dimensional thin-layer chromatography. The inhibitor 5'-S-isobutyl-5'-deoxyadenosine (SIBA) inhibited transmethylation 47-55%. This assay system appears to measure specifically the activity of methyltransferases which mediate the transmethylation of membrane phospholipid; the assay should find important applications in the study of membrane lipid metabolism in human health and disease.

Thiol methylation pharmacogenetics: heritability of human erythrocyte thiol methyltransferase activity

Thiol methylation of aliphatic sulfhydryl drugs is catalyzed by thiol methyltransferase (TMT), an enzyme activity that can be measured in the human erythrocyte (RBC) membrane. As a first step toward determining the possible role of inheritance in the regulation of individual variations in the S-methylation of drugs in man, the heritability of human RBC membrane TMT activity was determined. RBC TMT activity was measured in blood samples from 231 first-degree relatives in 47 randomly selected families. The frequency distribution of enzyme activities was unimodal, with a fivefold variation within +/- 2 SDs. RBC TMT activity did not correlate with either age or sex. Heritability in the "narrow" sense (h2) was estimated by comparing correlations of RBC TMT activities in first-degree relatives with theoretical values expected for a trait under total additive genetic control. The correlation between RBC TMT activities in mothers and fathers in these families was only 0.04, a finding that made shared environment a less likely explanation for significant correlations among other family members. However, sibling-sibling (S-S), parent-offspring (P-O), and midparent (average of two parental values)-offspring (M-O) correlations were 0.49, 0.49, and 0.69.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlation of low and high affinity thiol methyltransferase and phenol methyltransferase activities in human erythrocyte membranes

Human red blood cell (RBC) membranes have been reported to contain both high and low affinity 'forms' of the drug metabolizing enzyme thiol methyltransferase (TMT). The biochemical characteristics of the two 'forms' of human RBC TMT were compared. Apparent Km constants of the high affinity activity for 2-mercaptoethanol and S-adenosyl-L-methionine, cosubstrates for the TMT reaction, were 0.38 mumol/l and 2.6 mumol/l, respectively. These constants may be compared with values of 20 mmol/l and 43 mumol/l, respectively, previously reported for the low affinity form of RBC TMT activity. The properties and regulation of the two forms of TMT were then compared with each other and also with those of two 'control' enzymes, phenol methyltransferase (PMT) and beta-glucuronidase. When high and low affinity TMT, PMT and beta-glucuronidase activities were measured in RBC membranes from 22 individual subjects, there were highly significant correlations among all three methyltransferase activities (all r values greater than 0.95), but beta-glucuronidase activity did not correlate significantly with any of the methyltransferase activities (all r values less than 0.40). The thermal stabilities of the three methyltransferases were very similar. They were all inactivated approximately 50% by incubation at 48 degrees C for 15 min. beta-Glucuronidase activity was approximately 50% inactivated by incubation at 76 degrees C for 15 min. PMT and both TMT activities had similar subcellular distributions and similar responses to ions and to enzyme inhibitors. These results suggested that high and low affinity TMT and PMT activities might be catalyzed by the same enzyme. Alternatively, these three RBC membrane methyltransferase activities might be regulated in a parallel fashion.

Enzymatic properties of phospholipid methylation in rabbit platelets

The enzymatic properties of phospholipid methylation in rabbit platelets were examined using S-adenosyl-L-[methyl-3H]methionine as a substrate. pH optimum for the methylation was around 10.5 under Tris-HCl and glycine-NaOH buffer systems. When Tris-HCl buffer was replaced by phosphate buffer, pH optimum shifted to around 8.0 and the methylation was increased approximately threefold, compared with that in the case of Tris-HCl buffer at pH 8.0. The formation of the 3H-methylated phospholipids was increased by addition of exogenous phosphatidyl-N-monomethylethanolamine or phosphatidyl-N,N-dimethylethanolamine, intermediates of the biosynthesis of phosphatidylcholine from phosphatidylethanolamine. However, the increase in product formations by addition of exogenous intermediates was all but equal under Tris-HCl and phosphate buffer systems at pH 8.0. These results suggest that phosphate ion stimulates the first step of the successive methylation to form phosphatidyl-N-monomethylethanolamine from phosphatidylethanolamine. The methylation in platelets was inhibited to 30% of the basal value with Ca2+ (0.2 mM). However, Ca2+ showed different effects on the methylation in various tissues (activation to 150% of the basal value in the adrenal gland and slight inhibition to 82-88% of corresponding basal values in the liver, lung, kidney and brain).

Enzymatic methylation of chicken erythrocyte DNA modified by two carcinogens, 2-(N-acetoxyacetylamino) fluorene and methylnitrosourea

Both DNA-AAF and MNU-alkylated DNA are methylated less than nonmodified DNA by rat brain nuclei cytosine 5-methyltransferase purified either by chromatography on DEAE cellulose or by Dyematrex. The inhibition of methylation is proportional to the modification of the DNA, and DNA having a given percentage of bases modified with MNU is less methylated than DNA modified to the same extent with AAF. Moreover, DNA-AAF irreversibly inhibits the methylation of native DNA, whereas MNU-alkylated DNA does not inhibit the methylation of native DNA. The AAF-substituted DNA has a higher affinity for the enzyme than native DNA. However, this is probably not due to the AAF-induced local destabilization of the DNA helix, since heat-denatured DNA shows a lower affinity for the enzyme than double-stranded DNA. Addition of DNA-AAF to the enzyme preincubated with native DNA inhibits methylation, but only after a lag period. This agrees with the model in which the methylase walks along the strand to methylate cytosine residues before being detached from the DNA. AAF bound to guanine residues may block the movement of the enzyme along the helix. The in vitro hypomethylation of DNA, caused by carcinogens, could explain the in vivo observations made by several authors and could have significance in gene activity, cellular differentiation, and oncogenesis.

Vitamin B12-dependent methyltetrahydrofolate: homocysteine methyltransferase activity in normal and leukemic human hematopoietic cells

The cyanogen bromide method was applied to the assay of vitamin B12-dependent methyltetrahydrofolate:homocysteine methyltransferase activity in normal and leukemic human hematopoietic cells. Normal peripheral lymphocytes and leukemia cells of lymphoid origin wuch as CLL and ALL, contained higher levels of enzyme activity than did normal human bone marrow cells. Normal granulocytes and leukemia cells of myeloid origin, such as CML in the chronic phase and AML, contained lower enzyme activity. Leukemia cells of CML in blast crisis showed higher mean activity than in the chronic phase of the disease.

Thiol S-methylation in uremia: erythrocyte enzyme activities and plasma inhibitors

Thiopurine methyltransferase (TPMT) catalyzes thiopurine S-methylation, an important metabolic pathway for drugs such as 6-mercaptopurine. Thiol methyltranferase (TMT) catalyzes the S-methylation of a variety of aliphatic sulfhydryl compounds. Erythrocyte (RBC) TPMT activity is elevated in the blood of uremic patients on maintenance hemodialysis, 15.83 +/- 0.90 U/ml RBCs (mean +/- SEM, n = 41), whereas in blood from randomly seleted nonuremic subjects it was 12.76 +/- 0.16 U/ml (n = 298, p < 0.001). RBC TPMT activity is not affected by hemodialysis. The plasma of uremic patients reversibly inhibits RBC TPMT activity to a greater extent than normal plasma does and contains higher concentrations of endogenous methyl acceptors than normal plasma. Plasma TPMT inhibitors are not removed by hemodialysis. There are large individual variations in inhibition of RBC TPMT by plasma from patients with renal failure. Inhibition varied from 1% to 93% in 20 microliters of plasma from each of 20 randomly selected uremic patients. There was a positive correlation between the inhibition of TPMT and the content of endogenous methyl acceptors in uremic plasma (r = 0.914, n = 20, p < 0.001), but there was no significant correlation between degree of inhibition and urea nitrogen, serum creatinine, or hematocrit. The ability of plasma from individual uremic patients to inhibit TPMT also correlated with its ability to inhibit two other drug metabolizing methyltransferases in the RBC, catechol-O-methyltransferase and phenol-O-methyltransferase, RBC TMT activity is not altered in patients with uremia. The results of these and other studies of methyl conjugation in renal failure focus attention on the accumulation of methyl acceptor substrates in some of these patients and on the possible effects of these methyl acceptors on a variety of methylation reactions.

Human erythrocyte thiol methyltransferase: radiochemical microassay and biochemical properties

A radiochemical microassay for the measurement of thiol methyltransferase (TMT) activity in human red blood cell (RBC) membranes has been developed. Both 2-mercaptoethanol and dithiothreitol were used as substrates for the enzyme. The pH optimum of the reaction was approximately 9.0 when glycine NaOH was used as a buffer. The apparent Michaelis-Menten (KM) value for the methyl donor for the reaction, S-adenosyl-L-methionine, was 43 mumol/l. Human RBC TMT activity was neither activated nor inhibited by Ca2+, Mg2+, or tropolone, but the enzyme was inhibited by SKF 525A and by reagents that react with sulfhydryl groups. The mean TMT activity in blood from 289 randomly selected adult white subjects was 10.93 +/- 3.22 units per mg protein (mean +/- S.D.). The activity was the same in samples from men and women. The results of experiments in which TMT activity was measured in mextures of RBC membranes with relatively "low" and relatively "high" activities provided no evidence that individual variations in the enzyme activity were due to variations in endogenous TMT activators or inhibitors.

Phospholipid methylation unmasks cryptic beta-adrenergic receptors in rat reticulocytes

The effect of phospholipid methylation on the number of beta-adrenergic receptor binding sites was examined in rat reticulocyte membranes. Stimulation of phosphatidylcholine synthesis by the introduction of the methyl donor S-adenosyl-L-methionine into reticulocyte ghosts increased the number of beta-adrenergic receptor sites. The appearance of beta-adrenergic binding sites was dependent on the formation of phosphatidylcholine by the enzyme that converts phosphatidyl-N-monomethylethanolamine from phosphatidylethanolamine. Both the synthesis of phosphatidylcholine and the unmasking of cryptic receptors were time and temperature dependent and did not occur in the presence of the methyl transferase inhibitor, S-adenosyl-L-homocysteine.

Human erythrocyte phenol O-methyltransferase: radiochemical microassay and biochemical properties

A radiochemical microassay for the determination of phenol O-methyltransferase (PMT) activity in human red blood cell membranes has been developed. Acetaminophen was used as the substrate. The apparent Michaelis-Menten (KM) value for acetaminophen was 21.2 X 10(-3) M. The apparent KM value for S-adenosyl-L-methionine, a co-substrate for the reaction, was 4.8 X 10(-6) M, and the pH optimum of the reaction was approximately 9.0 with four different buffer systems. Phenol was also tested as a substrate and had an apparent KM value of 2.0 X 10(-3) M. Human erythrocyte (RBC) membrane PMT activity did not have the biochemical characteristics of catechol O-methyltransferase, another RBC membrane methyltransferase enzyme activity. Blood samples obtained from 212 randomly selected adult white subjects had a mean activity of 134.5 +/- 41.5 pmol of p-acetanisidide formed per mg protein per hour (mean +/- S.D.). Activities varied from 44 to 282 units. There were no differences in the mean activities of samples from men and women. Experiments in which mixtures of "low" and "high" activity RBC membrane preparations were assayed for PMT provided no evidence that the variations in enzyme activity were due to the presence of endogenous PMT activators or inhibitors. RBC membrane PMT activity in blood from 9 patients with renal failure, a pathological state in which there are elevated circulating levels of phenols, was found to be significantly decreased with average activity of 76.2 +/- 9.7 (mean +/- S.E.M., P less than 0.001).

Human erythrocyte thiopurine methyltransferase: radiochemical microassay and biochemical properties

A radiochemical micromethod for the determination of thiopurine methyltransferase (TPMT) activity in human red blood cells (RBC) is described. Both 6-mercaptopurine and 6-thioguanine were substrates for the TPMT activity in the human RBC. Apparent Michaelis-Menten (KM) values for 6-mercaptopurine and 6-thioguanine were 3.2 X 10(-4) M and 2.0 X 10(-4) M, respectively. The apparent KM value for S-adenosyl-L-methionine, a co-substrate for the reaction, was 1.7 X 10(-6) M. The pH optimum for the reaction was approximately 7.5. Blood samples from 73 randomly selected adult subjects had a mean activity of 10.2 +/- 2.4 (mean +/- S.D.) units/ml packed red blood cells. The range of activities was from 4.6 to 14.2 units/ml. The results of experiments in which partially purified human kidney TPMT was added to RBC lysates and of experiments in which "low" and "high" activity lysates were mixed gave no indication that individual variations in RBC TPMT activity were due to endogenous inhibitors or activators of the enzyme.

Enzymatic synthesis and rapid translocation of phosphatidylcholine by two methyltransferases in erythrocyte membranes

The synthesis of phosphatidylcholine from phosphatidylethanolamine is carried out by two methyltransferases in erythrocyte membranes. The first enzyme uses phosphatidylethanolamine as a substrate, requires Mg2+, and has a high affinity for methyl donor, S-adenosyl-L-methionine. The second enzyme methylates phosphatidyl-N-monomethylethanolamine to phosphatidylcholine and has a low affinity for S-adenosyl-L-methionine. The first enzyme is localized on the cytoplasmic side of the membrane and the second enzyme faces the external surface. This asymmetric arrangement of the two enzymes across the membrane makes possible the stepwide methylation of phosphatidylethanolamine localized on the cytoplasmic side and facilitates the rapid transmembrane transfer of the final product, phosphatidylcholine, to the external surface of the membrane. A mechanism for an enzyme-mediated flip-flop of phospholipids from the cytoplasmic to the outer surface of erythrocyte membranes is described.

Plasma indolethylamine-n-methyltransferase activity and growth hormone level during sleep: a pilot study

Polygraphic recordings and sequential growth hormone (GH) samplings were performed in eight healthy adult males. In the plasma samples from seven of the subjects, indolethylamine-N-methyltransferase (INMT) activity was also determined. Five of eight subjects showed significant fluctuation in plasma GH level, and six of seven subjects showed significant fluctuation in plasma INMT activity level. There were also significant positive correlations between plasma GH and INMT activity level during the second episode of NREM sleep stage 1 and during the third episode of NREM sleep stage 2. A significant negative correlation between plasma GH and INMT activity level during the seventh episode of sleep stage 2 and during the fifth episode of post sleep-onset wake was found. In view of a previous finding that INMT activity in the serum of psychiatric patients is positively correlated with severity of delusions, the observation that NREM sleep is associated with mental activity characterized by repetitive thoughts, and the result that GH level in plasma is increased in NREM sleep early at night, our present findings suggest the hypotheses that increased plasma INMT activity during sleep is indicative of both increased INMT activity in the central nervous system (CNS) and the activation or maintenance of NREM mental activity during sleep. Additional research will be needed in order to validate our observations and test these hypotheses.

Octopamine plasma levels and hepatic encephalopathy: a re-appraisal of the problem

An investigation on the blood levels of octopamine was carried out on 70 adult individuals. There was a statistically significant correlation between the levels of octopamine and hepatic encephalopathy. Normal subjects had values below 1 ng/ml, while patients with grade 3 or grade 4 encephalopathy constantly showed values above 3.2 ng/ml. In these two groups the distribution was fairly homogeneous. Through the differences between cirrhotics without neurologic involvement and those with grade 1 or 2 hepatic encephalopathy displayed statistical significance, distribution of values in these groups was rather non-homogeneous. Octopamine levels paralleled variations in mental state in 3 out 4 cases. No difference was found between venous and arterial values. The reaction of transmethylation used in the assay of octopamine was constantly found to be inhibited by the presence of plasma. This inhibition is probably due to the presence of one or more beta-hydroxyphenylethanolamines other than octopamine.

A test of the transmethylation hypothesis in acute schizophrenic patients

Keeping biochemical determinations and clinical judgements independent, the authors investigated three aspects of the transmethylation hypothesis. They found that 26 acutely schizophrenic patients were no more likely to have bufotenine or N,N-dimethyltryptamine present in urine or elevated serum indolethylamine N-methyltransferase activity than 10 normal control subjects. The authors conclude that these are naturally occurring substances which are equally likely to be present in normal and schizophrenic subjects.

Biochemical studies in early infantile autism

In four series of studies on schizophrenic patients and normals we found that all the schizophrenics eliminated N, N-dimethyltryptamines in their urine while none of the normals did so. Similarly, with early infantile autism (Studies I and II) and normal controls, this separation between patiens and normals still held. But ten parents of the five autistic children positive for bufotenin revealed that one or both parents, i.e., seven of ten were positive. The Psychiatric Assessment Interview, the Minnesota Multiphasic Personality Index, and the Rorschach indicated no significant evidence of psychopathology. Thus, individuals who revealed no psychopathology could still be positive for bufotenin. In studies III and V, 1 of 13 normals and 13 of 27 normals were positive, respectively. Study IV showed that 6 of 18 autistic children were positive for bufotenin.

Indolethylamine-N-methyltransferase activity in psychiatric patients and controls

The level of INMT activity was determined in the sera of 29 psychiatric patients and 11 healthy controls from St. Louis; and in 13 psychiatric patients and 15 healthy controls from Chicago. The level of enzyme activity in the serum of paranoid schizophrenics in the St. Louis group was significantly higher than in other types of schizophrenics. The mean level of enzyme activity in the serum in nonschizophrenic psychiatric patients in the Chicago group was significantly higher than that in the same group of patients from St. Louis. The serum level of INMT activity in all psychiatric patients and schizophrenic patients from St. Louis was positively correlated with severity of delusions. The only significant difference in the Chicago patients was that the occurrence of depressive features was greater in the group of patients with a low serum INMT level than in the group with a high enzyme level.