No abstract

The effects of ingesting the aromatic amino acid L-tyrosine on excretion of unconjugated catecholamines (dopamine, norepinephrine, and epinephrine) and tyrosine were studied. (Tyrosine is the circulating precursor for the catecholamines, but only a small fraction of the tyrosine in the body is utilized for catecholamine synthesis.) In 10 of 11 normal volunteer subjects, ingestion of 100 mg/kg tyrosine (in three divided doses, preceding each meal, between 8 AM and 5 PM) for 1 day increased the 24-h excretions of total catecholamines by 25%. Only 0.42% of the tyrosine dose was excreted unchanged, but this was sufficient to increase urinary tyrosine by 138%. Both tyrosine and catecholamine excretions varied diurnally; 60% or more of the total output occurred during the day. Since urinary catecholamines reflect molecules synthesized outside the central nervous system, these findings indicate that tyrosine administration can accelerate catecholamine synthesis in the human sympathoadrenal system, probably by enhancing saturation of tyrosine hydroxylase. Therefore, tyrosine may be useful therapeutically in diseases characterized by peripheral catecholamine deficiencies.

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _Growing dogs were divided into three groups and were fed on nutritionally-balanced diets. Control dogs were fed on a rice diet, the cassava (gari) group ate a diet in which gari provided the carbohydrate source, while the rice +cyanide group consumed the rice diet to which hydrocyanic acid (equivalent to that present in gari) was added. Each group consumed its diet for 14 weeks, during which plasma thiocyanate concentration and total serum triiodothyronine (T3) were monitored. At the end of the experiment the concentrations of the plasma free amino acids phenylalanine and tyrosine, the thyroid weights and histology were determined. While plasma thiocyanate remained undetectable in control dogs, animals consuming both gari and rice +cyanide generated significant amounts. In the control dogs and the gari group, total serum T, increased 40 and 38.8 % respectively from the basal level by the end of the period (P < 0.02). In contrast there was a decrease in T, by 36 % in the dogs fed on rice + cyanide (P < 0.05).This group also showed significant thyroid enlargement and a histological picture consistent with parenchymatous goitre, whereas the gari group was essentially normal. The relatively low mean thyroid weight, the rise in total serum T, level and the normal histological appearance of the gland indicate that dogs that consumed the gari diet were essentially normal with respect to their thyroid function, in spite of their high blood thiocyanate content. In contrast, dogs that consumed rice with cyanide suffered from hypothyroidism and goitre. It is suggested that the gari diet, despite generating thiocyanate endogenously, when taken in a nutritionally-balanced diet with high-quality animal protein, has no deleterious effects on thyroid function.Thyroid: Cassava diet: Dog

Tyrosine administration to rats causes dose-related increases in urinary catecholamine levels without reducing tissue catecholamines. Pretreatment with carbidopa, a peripheral inhibitor of aromatic-L-amino acid decarboxylase, reduces basal urinary catecholamine levels and blocks of urinary catecholamine increases caused by tyrosine administration or cold exposure. DOPA excretion, which is usually undetectable by our methods, becomes significant after carbidopa, and rises a further four-fold when rats are also given tyrosine. These observations suggest that tyrosine availability can affect both catecholamine synthesis in and release from the sympathoadrenal apparatus.

Ascorbic acid levels in 30 subjects in their third trimester of pregnancy were estimated. Their haematological parameters (packed cell volume, haemoglobin and mean cell haemoglobin concentration) were also determined. The values were compared with that of 30 non-pregnant women (control group). The ascorbic acid status of newly born babies using cord blood were determined along with that of their mothers at delivery. The ascorbic acid level of 0.92+0.37 mg/dl was reported in third trimester. This value was not significantly (P>0.05) lower than in the control group (1.04+0.4 mg/dl). The result showed that the ascorbic acid level at delivery was significantly (P<0.05) higher than that of the control group. The ascorbic acid levels in the cord blood of the newly born babies were significantly (P<0.01) higher than the maternal level. There was insignificant difference in the haematological parameters between the pregnant and non-pregnant women.