Israel Lyon Chaikoff

Chaikoff was born in London in 1902.[1] He pursued advanced scientific training in Canada, earning both a PhD and an MD from the University of Toronto.[1] He subsequently joined the faculty of the University of California, Berkeley, and died in Berkeley on January 25, 1966.[1]

Chaikoff's most extensively documented contributions concern the biochemistry of thyroid hormone synthesis. A 1943 paper co-authored with M. E. Morton, published in the Journal of Biological Chemistry, reported the conversion of radioactive inorganic iodine into radiothyroxine and radiodiiodotyrosine by excised, surviving thyroid tissue from sheep, dogs, and rats.[2] The experimental protocol placed thyroid tissue in bicarbonate-Ringer's solution containing tracer radioactive iodine, and products were identified through repeated recrystallization to constant specific activity.[2]

The quantitative results revealed notable species differences. Rat thyroid showed the highest conversion rates, incorporating as much as 12 percent of the added radioactive iodine into thyroxine and 60–71 percent into diiodotyrosine during three-hour incubations.[2] Sheep thyroid converted up to 6 percent into thyroxine and up to 37 percent into diiodotyrosine, while dog thyroid converted up to 4 percent into thyroxine and 21–24 percent into diiodotyrosine.[2] Comparisons between intact slices and disrupted preparations found no radiothyroxine formation in homogenized sheep or rat thyroid tissue. The authors concluded that iodine incorporation failed when the tissue's organization was disrupted by homogenization.[2]

A second paper in the same volume, co-authored with Morton, W. O. Reinhardt, and Evelyn Anderson, examined the formation of thyroxine and diiodotyrosine in completely thyroidectomized animals.[2]

By the mid-1950s, Chaikoff and collaborators studied how ionizing radiation affects the thyroid. A study co-authored with G. D. Potter and A. Taurog administered radioactive iodine doses ranging from 5 to 300 microcuries to rats and examined the irradiated thyroids two to five weeks later against normal controls.[3] The investigators assessed six parameters: iodide concentration, synthesis of organic radioiodine compounds, response to propylthiouracil, response to cold exposure, response to thyroid-stimulating-hormone injection, and cytological appearance.[3]

The most sensitive indicator of radiation damage was a reduced capacity for hypertrophy and hyperplasia, with cytological changes appearing at low radiation levels.[3] By contrast, large doses were required before iodide trapping or the formation of organic iodides such as thyroxine was measurably impaired. Even the most heavily irradiated thyroids retained a normal distribution of I-131 among the various iodine compounds.[3] The authors interpreted these findings to mean that thyroid processes governing growth were more sensitive to irradiation than those governing iodine metabolism.[3]

A 1956 study co-authored with O. H. Taurog, H. Hama, and H. Tong investigated the selective uptake of I-131-labeled thyroxine and triiodothyronine in the neurohypophysis of rabbits and dogs.[3] The study reported that I-131 thyroxine concentration in the posterior pituitary reached 20–60 times that measured in the cerebral cortex and 2–4 times the plasma level. Triiodothyronine entered all parts of the brain more rapidly than thyroxine.[3]

Chromatographic analysis indicated that neither thyroxine nor triiodothyronine was chemically altered by the posterior pituitary.[3] Stalk sectioning and inhibition of the posterior pituitary with large doses of alcohol had no effect on thyroxine uptake, whereas surgical thyroidectomy increased the posterior pituitary's avidity for thyroxine.[3]

Chaikoff also contributed to lipid biochemistry. A 1952 paper co-authored with S. Hotta, titled "Cholesterol synthesis from acetate in the diabetic liver" and published in the Journal of Biological Chemistry, was cited in a 1957 discussion of cholesterol synthesis in diabetes.[3] That discussion connected the paper with findings that liver slices from alloxan-diabetic rats showed a tenfold increase in the conversion of labeled acetate into cholesterol.[3]

Chaikoff's documented research ranged from radioactive-tracer studies of thyroid hormone formation to experiments on radiation damage, neurohypophyseal hormone uptake, and cholesterol synthesis.[2][3] His 1943 work with Morton was especially notable for showing that intact thyroid-tissue organization was required for the observed in vitro incorporation of radioactive iodine into thyroxine and diiodotyrosine.[2]

Chaikoff's surname became associated with the Wolff-Chaikoff effect through thyroid research conducted with Jan Wolff. A later critical account identifies an influential 1948 paper and describes the effect as the proposition that high iodine exposure suppresses thyroid function.[4]

That account disputes the conventional interpretation of the experiments. Drawing on Guy Abraham's critique, it alleges that the researchers claimed iodine-induced goiter in rats at doses 20 times the recommended daily allowance even though thyroid hormone levels were not measured and no evidence of enlarged thyroid or disease was reported.[4] It further states that Wolff extrapolated the findings to humans in 1969 and that the interpretation was subsequently taught to generations of physicians.[4] These statements represent the book's explicitly critical characterization and are not independently established by the archival journal sources cited elsewhere in this article.