Dose-response curves vitamins

Fig. 4. Dose-response correlation in cats of the effects of U-74006F on post-traumatic (compression injury) spinal cord lipid peroxidation (i.e., loss of reduced vitamin E) and on progressive white matter ischemia at 4 hours post-injury (data from ref. [24]) versus chronic (4-week) neurological recovery (data from ref. [46]). Doses indicated were administered at 30 minutes post-injury. Doses in parentheses under the chronic recovery dose-response curve indicate the total 48-hour dosing regimen that these cats received. All values are mean standard error. Numbers of animals are given in parentheses in each bar. Asterisks indicate p < 0.05 vs vehicle-injured animals by ANOVA.

Each of the methods outlined in the following sections has significant problems in determining a dose-response curve for a vitamin. Table... 

The potencies of various tocopherols, K vitamins, ubiquinones, and similar substances in the prevention of respiratory decline have been assayed by supplementation of graded dose levels to the whole homogenate system. For each dose level, averages of at least four experiments were established. From the dose-response curves, the 50 % effective dose (EDbo) was derived. The EDso for df-a-tocopherol was found to be 1.1 ng per 3 ml of medium containing 50 mg of homogenized liver (Table VII). A comparison of the potencies of a-, /3-, 7-, and 5-tocopherols gave the same relative order of activity as the resorption sterility assay for vitamin E. df-a-To-copheryl acetate demonstrated only 3 % of the activity of the free vitamin. a-Tocopherylquinone was about 10% as active as tocopherol itself. The Simon metabolite (Simon et al., 1956) (Fig. 4) showed 40% of the activity of di-a-tocopherol, in spite of the fact that it was supplied in the quinone form. 

In some cases, e.g. for carcinogenic materials, traee elements and vitamins, the dose-response curves are more complex. 

Fig. 4. Dose response curve to graded doses of vitamin Bu (spaced logarithmically). Continuous line — expected response according to formula. Difference between observed means and expected increase is shown by vertical lines. Dot = initial count length of line = deviation from expected response arrow shows whether deviation was above or below expectation. The relationship between response and log dose did not hold for doses below 5 (from Ungley, C. C., and Campbell, H. 1949. Brit. Med. J. 2, 1370-1377).

A standard dose-response curve is prepared by plotting the average of the turbidity values found at each level of the vitamin standard against the amount of vitamin present. The vitamin content of a sample is determined by interpolating the response to the known amount of the test solution onto this standard curve. The vitamin content per milliliter of the test solution is now calculated for each of the triplicate sets of tubes, and the vitamin content of the sample is calculated from the average of the values. 

Any transformation that could be affected for such curves so that they would yield linear graphs would have manifest advantages, because it would afford a sound mathematical basis for computation, which is a desirable consideration for any analytical method. In any type of microbiological assay of vitamin Bu the results should be plotted to test whether a dose-response, a log dose-response, or a log dose-log response curve is sufficiently linear to make possible the use of statistical methods. In the assay of vitamin B12 activity in crude materials, however, the most pertinent problem at present is to relate this activity to certain defined substances rather than to obtain the highest accuracy in measuring the Bu activity. 

---