Recent reports have described two types of plasma absorption curves following the oral administration of vitamin B1.,. With microbiologic assay methods, after massive doses of vitamin. Bs, early significant plasma levels have been found indiscriminately in both pernicious anemia patients and control subjects (1, 2). On the other hand, two independent laboratories, using radio-labeled cyanocobalamin, have successfully determined plasma absorption curves after the oral administration of only 0.46 to 1.0 microgram doses (3, 4).With these small amounts of vitamin B12 a distinctly different type of absorption curve was found in normal subjects and in pernicious anemia patients when intrinsic factor was added. This curve was characterized by little or no plasma radioactivity during the first four hours of the test and a peak concentration in the 8-to 12-hour interval. Furthermore, there was clear differentiation between control subjects and patients with pernicious anemia, because at these dosage levels the latter without added intrinsic factor showed insignificant plasma radioactivity.In this investigation plasma absorption curves were obtained in pernicious anemia patients with and without intrinsic factor, as well as in control subjects after the oral administration of test doses of radio-labeled cyanocobalamin which ranged from 0.56 to 500 micrograms. This included a dosage range not previously examined.
MATERIAL AND METHODSCobalt'-labeled vitamin B. 2 used in test doses had an initial specific activity of 1,137 microcuries per mg., while that of the Cotm-labeled vitamin Bn-2 used was 893 microcuries per mg. Crystalline non-radioactive vitamin B,2 was added as necessary to make up the desired test
A new method for the determination of the absorption of vitamin B12 has been described using measurement of radioactivity in the blood or plasma after the ingestion of physiologic test doses of Co60 labeled vitamin B12.
Although doses of 1.0 µc. (0.92 µg. vitamin B12) gave higher counts, equally reliable results were obtained with 0.5 µc. (0.46 µg. vitamin B12). The radioactivity was found in the plasma portion of the blood.
With this method it was possible to differentiate between all of nine patients with pernicious anemia and 36 control subjects.
In non-pernicious anemia subjects and in pernicious anemia patients given intrinsic factor, there was a relatively delayed rise in the blood or plasma radioactivity until a peak was reached in the 8 to 12 hour interval after the ingestion of the test dose. This absorption curve was quite different from the early rise observed by others after massive oral doses of vitamin B12, indicating a different mode of absorption.
Following the peak blood concentration the radioactivity gradually declined and small amounts usually persisted for as long as one week, quite different from the rapid disappearance after parenteral administration previously reported.
This method appears valuable in the diagnosis of pernicious anemia and other vitamin B12 malabsorptive states, in the evaluation of intrinsic factor activity, and in studies of various aspects of the metabolism of vitamin B12.
Magnetic resonance imaging protocol including dynamic sequence for the characterization of parotid gland lesion yielded nonsignificant increases in sensitivity, specificity, or positive predictive values, and negative predictive values over noninjected protocol.
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