Effects of bedrest and centrifugation of humans on serum thyroid function tests.

Changes in plasma volume and protein concentration have been reported when normal subjects are bedrested or centrifuged. Since thyroid hormones are transported by specific plasma proteins, each of these procedures could be expected to change plasma levels of these hormones. In this study centrifugation of normal healthy human subjects produced an increased concentration of total protein and albumin. When these same subjects were bedrested for six days, no change in total protein, albumin or thyroxine binding globulin were found although there was an eight per cent decrease in plasma volume. Centrifugation and, to a lesser extent, bedrest produced changes in serum T-4 levels and the T-3 test results. The direction of these changes (decreased % T-3 values and increased T-4 levels) indicate that these two situations produce an increased plasma concentration of thyroxine binding sites.