A new perspective in the assessment of vitamin B-6 nutritional status during pregnancy in humans

Plasma pyridoxal-5'-phosphate (PLP) concentration has been suggested as a valid indicator to assess vitamin B-6 nutritional status. Animal and human studies have shown that plasma PLP concentrations decrease progressively during pregnancy and large doses of vitamin B-6 supplementation are required to maintain plasma PLP at early or prepregnant levels. PLP is known to be hydrolyzed to pyridoxal (PL) by alkaline phosphatase (ALP), resulting in an inverse relationship between PLP and ALP. The object of this study was to compare the PLP-PL equilibrium in a group of healthy pregnant females with that of an age-matched nonpregnant control group from a similar socioeconomic background. The mean plasma PLP level was 37% lower, (P less than 0.0001), whereas the mean PL level was almost 90% higher (P less than 0.001) in the pregnant group than in the nonpregnant control group. The total amount of plasma PLP and PL levels, however, did not differ significantly (P greater than 0.24) between the two groups. Because the PL vitamer is regarded as the ultimate transport form of vitamin B-6, it may serve as a readily available source of vitamin B-6 to meet possible increased metabolic demands. Therefore, the estimation of plasma PLP alone does not permit an accurate assessment or understanding of the nutritional status and the physiology of vitamin B-6 in conditions associated with altered vitamin B-6 homeostases.     

Compartmentalization of pyridoxal-5′-phosphate during the acute phase of myocardial infarction

Summary Vitamin B6 nutritional status is assessed by measuring the plasma concentration of one of its vitamers, pyridoxal-phosphate (PLP). Several conditions, e.g., myocardial infarction (MI), can disturb the dynamic equilibrium between the different vitamers resulting in transiently low plasma PLP levels. An important question is whether these low plasma PLP levels observed during MI represent a transient state of deficiency and what the possible clinical consequences of such a fall in plasma PLP could be. Since the main metabolic function of PLP is to act as an intracellular coenzyme, it was decided to monitor the changes not only of PLP but also of PL (transport form of vitamin B6) in both the plasma and red blood cells (RBCs) in patients with myocardial infarctions (MI): 16 patients with proven MI were investigated measuring the aforementioned parameters at regular intervals. It was found that the approximately 40% fall in plasma PLP levels was accompanied by an equivalent increase in RBC PLP levels. Subsequently plasma PLP concentrations returned to normal but RBC PLP values were maintained at the newly elevated steady state (without any vitamin supplementation). Since membranes are impermeable to PLP, the only way in which PLP could have been redistributed to the intracellular compartment was through hydrolysis to PL and rephosphorylation once inside the RBCs. This compartmentalization could be an important adaptive response since it has been shown that PLP reduces O₂ affinity of deoxygenated hemoglobin, thereby facilitating O₂ delivery to the tissues. In addition it would also enhance the proposed storage function of RBCs for PLP and PL which is said to be an important source for muscle vitamin B6 which again is essential for energy production by the muscle cells during ischemia.Abbreviations AST Aspartate Aminotransferase (EC 2.6.1.1) - CK Creatine Kinase (EC 2.7.3.2) - CV coefficient of variation - HPLC high performance liquid chromatography - LD lactate dehydrogenase (EC 1.1.1.27) - MI myocardial infarction - MRC Medical Research Council - NAD⁺ oxidized nicotinamide adenine dinucleotide - NADH reduced nicotinamide adenine dinucleotide - PL pyridoxal - PLP pyridoxal-5-phosphate - PLSC pyridoxal semicarbazone - PLPSC pyridoxal-5-phosphate semicarbazone - PM pyridoxamine - PMP(PNP)-oxidase pyridoxamine-phosphate- (pyridoxine-phosphate) — oxidase - PN pyridoxine - RBCs red blood cells - SEM standard error of the mean     

ATTITUDES OF AUSTRALIAN DENTAL STUDENTS TOWARDS THE ELDERLY

The attitudes of Sydney dental students towards elderly persons was studied using a semantic differential questionnaire developed by Rosencranz and McNevin in 1969. U.S. dental students from two Universities were used as a comparison group. The control age group was the attitude of the students towards persons aged 32 years. Knowledge about ageing was also obtained from the study population through the use of Palmore's (1977) Facts on Aging Quiz. Analysis of the data indicated that the Sydney dental students viewed persons aged 32 as being less independent and autonomous than did their U.S. counterparts. However they also saw persons aged 65 and over BS more ineffective, less autonomous and less personally effective than the U.S. students. The Sydney students were significantly less well informed about ageing than the U.S. dental students as measured by the number of correct answers on the Facts on Aging Quiz. The possible meaning of these findings is discussed and some explanations suggested.