- The purposes of the research presented in this thesis were: (1)
to determine the precision with which it is possible to measure
changes in vitamin B6 compounds in the blood and urine following
oral doses of levels of vitamin B6 (as pyridoxine) which are in the
range of the normal daily intake of this vitamin; (2) to compare the
effect of three free forms of vitamin B6 (PL, PM, PN) at these same
levels using the same assays; and (3) to compare the response of
guinea pigs to that of humans when the animals are given three free
forms of vitamin B6 at physiological levels.
The effect of small incremental doses of pyridoxine (PN)
(0.5 - 10 mg) and of equimolar doses of PN, pyridoxamine (PM) and
pyridoxal (PL) were studied in five healthy young men. On the day
before and during the day of the dose, the subjects were on a controlled
diet that supplied 1.6 mg of vitamin B6 each day. During other days of the week, the subjects were on self-selected diets.
Timed blood and urine samples were obtained on the day each
dose was administered. The parameters measured were: plasma
vitamin B6 (PB6), plasma pyridoxal phosphate (PLP), urinary vitamin
B6 (UB6) and urinary 4-pyridoxic acid (4PA). Variables reflecting
the response to each dose for each of these parameters were
calculated in two ways; (1) the percent increase of the maximal
post-response value over the pre-response value; and (2) the area
under the curve bounded by the values obtained and the times of the
For all eight of the variables so calculated, the relationship to
the PN doses given were linear in the 0.5 to 10 mg range. Maximal
levels of plasma PLP and PB6 were reached at 1/2 hr after the dose
for the 0.5, 1, 2, and 4 mg levels of PN. At the 10 mg level, plasma
B6 peaked at 1/2 hr for 3 subjects and at 1 hr for 2 subjects. Plasma
PLP peaked at 1 hr following the 10 mg PN dose. PB6 was much
more responsive to the loading doses than was PLP. The PB6:PLP
ratio was maximal at 1/2 hr following the doses. Maximal values of
urinary 4PA and UB6 were found in the first 3 hr after the dose. The
ratio 4PA:UB6 decreased with increasing PN dose levels and varied
for each collection period following the dose.
The same variables were calculated for the study of a comparison
of 19.44 μmole doses of PN, PM and PL. The PB6 peaks occurred at 1/2 hr for PL and PN, and at 1 hr for PM. The PLP
peaks occurred at the following times: PN, 1/2 hr; PM, 3 hr; and
PL, 1 hr. Maximal levels of UB6 and 4PA were reached in the first
three hr after the dose for all three forms. The percent increase
and area variables were able to distinguish between nearly all the responses
to the three forms of vitamin B6 administered at the 19.44
μmole level. The PB6 response was largest following the PL dose,
but the PLP levels were lower after PL than after either PM or PN.
The 4PA values were highest following the PL dose, indicating that
the PL dose was metabolized to 4PA rather than converted to plasma
Some of the nutrient contents of the self-selected diets were
found to be significantly correlated with some response variables.
There was no relationship found between either body weight and 4PA
excretion on the day before the dose, or between ascorbic acid intake
on the self-selected diets and 4PA excretion on the day before the
Strenuous exercise was found to significantly affect plasma PLP
levels in subjects who had received the loading doses of PN.
In another study, three groups of guinea pigs were each given
their Recommended Dietary Allowance of vitamin B6 as PM, PL or
PN. The same parameters were measured as for the humans. There
were no significant differences between the groups of animals in body weight, organ weights (spleen, liver, kidney, brain), plasma B6 or
PLP, or in formed elements of the blood (hemoglobin, hematocrit,
white blood cells, red blood cells). Urinary 4PA and UB6 were significantly
higher in animals receiving PN.