Frances Larin

Brain catechol synthesis - Control by brain tyrosine concentration

Brain catechol synthesis was estimated by measuring the rate at which brain dopa levels rose following decarboxylase inhibition. Dopa accumulation was accelerated by tyrosine administration, and decreased by treatments that lowered brain tyrosine concentrations (for example, intraperitoneal tryptophan, leucine, or parachlorophenylalanine). A low dose of phenylalanine elevated brain tyrosine without accelerating dopa synthesis. Our findings raise the possibility that nutritional and endocrine factors might influence brain catecholamine synthesis by controlling the availability of tyrosine.

Daily rhythms in the concentrations of various amino acids in human plasma.

Abstract Blood was collected at intervals during a 24-hour period from 23 healthy male volunteers on diets containing various amounts of protein; the plasma was assayed for 16 amino acids. Among subjects receiving 0.71 or 1.5 gm of protein per kilogram of body weight, the concentrations of tyrosine, phenylalanine and tryptophan tended to be lowest at 2:00 and highest at or after 10:30 a.m. Volunteers given a diet containing less than 0.04 gm of protein per kilogram showed similar fluctuations in the concentrations of the above amino acids and methionine, but peak plasma levels were observed somewhat earlier in the morning. All the amino acids studied showed some tendency to vary with time of day. Tyrosine, tryptophan, phenylalanine, methionine, cysteine and isoleucine underwent the greatest per cent changes; the amino acids whose plasma concentrations were highest (that is, alanine, glycine and glutamic acid) showed the least tendency to vary.

Correlation between brain tryptophan and plasma neutral amino acid levels following food consumption in rats

Abstract Brain tryptophan increases significantly within two hr of the time that rats begin to consume a diet containing carbohydrate and fat, but fails to rise if the diet also contains 18–24% protein. The effects of particular diets on brain tryptophan are not well correlated with plasma tryptophan concentrations alone, but do correlate well with the ratio of plasma tryptophan to individual neutral amino acids (leucine, isoleucine, valine, tyrosine, phenylalanine) or to their sums. (These amino acids compete with tryptophan for uptake into the brain.) Carbohydrate ingestion raises brain tryptophan by elevating plasma tryptophan and depressing the plasma levels of the competing neutral amino acids; protein consumption prevents an increase in brain tryptophan by raising the plasma concentrations of the competing amino acids more than of tryptophan.

Brain H3‐catecholamine metabolism in experimental cerebral ischemia

Unilateral ligation of a common carotid artery in gerbils causes a major depletion of brain dopamine, which is most marked in brain regions known to receive dopaminergic projections. To determine whether this depletion reflects release of stored dopamine, a radioactive label (H3-dopamine) was introduced into brain dopamine pools 4 hours prior to ligation. Twenty-four hours later, brain H3-catecholamines were profoundly depressed ipsilateral to the lesion among animals exhibiting clinical signs of stroke. Within brain regions known to receive dopaminergic projections, common carotid ligation also was associated with a selective decrease in the concentration of H3-deaminated metabolites. These data suggest that cerebral ischemia is associated with release of catecholamines, as well as with impaired oxidative metabolism of catecholamines.

Daily variations in the concentrations of individual amino acids in rat plasma.

Abstract Daily rhythms have been described in the plasma concentrations of tyrosine and phenylalanine in the rat (1), and of tryptophan and total amino acids in the mouse (2,3). However, no data appear to be available on daily variations in the concentrations of other plasma amino acids except in the chicken and the human (4,5,6,7). The determination of whether diurnal rhythmicity is common to the plasma levels of most amino acids, and most mammals, or whether such temporal changes are associated in rats only with tyrosine and phenylalanine is essential for the characterization of the physiological mechanisms that control plasma amino acid levels. It would also be useful in assessing the significance of changes in plasma amino acid levels observed in rats several hours after particular experimental manipulations. This study describes the daily rhythmic changes that occur in the concentrations of 12 amino acids in rat plasma.

Mechanism of changes in brain norepinephrine levels following olfactory bulb lesions

Rats killed 27 days after an olfactory bulb is transected show characteristic alterations in the quantities of norepinephrine in certain brain regions (1,2). In the ipsilateral telencephalon, the locus of most of the axons which leave the olfactory bulb (3), norepeniphrine levels decrease. This effect probably reflects a loss of noradrenergic nerve endings, since the ability of the telencephalon to take up and retain 3H-norepinephrine placed in the lateral cerebral ventricles also declines. In the brain stem, norepinephrine levels increase. This region is not known to receive a significant number of nerve fibers originating in the olfactory bulb (3); hence the elevation in its norepinephrine content must result from a trans-synaptic mechanism. This communication provides information on the time-course of the changes in brain norepinephrine levels after olfactory bulb lesions and on the anatomic and biochemical mechanisms responsible for these changes.

A sensitive and specific isotopic assay for the estimation of tyrosine transaminase.

Tyrosine transaminase activity estimation by radioactive isotopic assay method, discussing application to rat liver and other organs

Influence of feeding habits and adrenal cortex on diurnal rhythm of hepatic tyrosine transaminase activity

Summary The amplitude of the 24-hr rhythm in hepatic tyrosine transaminase activities of rats fed hourly was markedly reduced when compared to the activities of the enzyme in rats eating ad libitum. Reversing the lighting schedule reversed the rhythms but did not change their amplitudes. The TT rhythm of adrenalectomized rats eating ad libitum was reduced in amplitude and the rhythm extinguished in animals fed hourly. Hourly feedings did not influence the cyclicity of the corticosterone content of the adrenal. It is concluded that rhythms in food ingestion and adrenal cortical secretions play roles in the generation of the rhythmicity of hepatic tyrosine transaminase activities but that the diurnal variation in adrenal corticosterone content is not related to the cyclicity of food intake.

Stimulation of(14C)serotonin synthesis from (14C)tryptophan by mescaline in rat pineal organ cultures.

Abstract Addition of mescaline to the nutrient medium of rat pineal glands in organ culture produces a marked increase in pineal synthesis of serotonin from [ 14 C] tryptophan. By contrast, addition of psilocybin or lysergic acid diethylamide (LSD) has no effect on [ 14 C] serotonin synthesis by these cultures. Mescaline has no effect on pineal [ 14 C] serotonin synthesis when [ 14 C] 5-hydroxytryptophan is substituted for [ 14 C] trytophan as the labelled substrate. Mescaline does not inhibit the deamination of [ 14 C] serotonin to 5-hydroxyindoleacetic acid and has no significant effect on the intracellular content of [ 14 C] tryptophan or its conversion to [ 14 C] protein. It is concluded that mescaline stimulates pineal [ 14 C] serotonin synthesis via a primary stimulatory action on the enzymatic conversion of [ 14 C] tryptophan to 5-hydroxytryptophan, rather than by effects on other steps in the indole pathway or on cellular uptake of [ 14 C] tryptophan.