Thyroid stimulator rabbits

Solomon, D. H., and Beall, G. N., Thyroid-stimulating activity in the serum of immunized rabbits. II. Nature of thyroid-stimulating material. J. Clin. Endocrinol. Metab. 28, 1496-1502 (1968). 

PRODUCTION OF A THYROID STIMULATOR BY IMMUNIZING RABBITS WITH HUMAN THYROID... 

The adjusted logarithm is usually expressed as the antilogarithm — counts per minute (cpm) — for convenience in presentation of data. Since the bioassay mice vary markedly both in their responsiveness to thyroid stimulation and to inert control materials (7), a response is taken as significant only if it differs (P-<0,05 or <0.01 as indicated) from that seen with a variety of control materials tested concomitantly in the same batch of assay mice routinely in the studies reported here groups of mice were given injections of 3 doses (0.05 mu, 0.2 mu and 0.8 mu) of thyrotropin (NIH S3 or B4) and 1% and 5% albumen solutions as well as other appropriate materials such as extracts of normal rabbit serum. 

Characteristically (7) thyrotropin in this bioassay gives a response greater at 2 hr than at 9 hr and the reverse is seen with the long-acting thyroid stimulator. However, as previously reported (7), this is not always a clear-cut distinction — hence the concern with the data obtained with some rabbit material reported below. 

The data in Fig. 1 illustrate that the thyroid-stimulating activity of the immunized rabbit serum is not inhibited by a dose of antithyrotropin antiserum which inhibited the concentration of rabbit thyrotropin giving a similar 2 hr response in the bioassay. Further, the activity was apparently bound to thyroid microsomes when the extract of rabbit serum was incubated with a human thyroid microsome preparation and the microsome pellet resedimented by ultracentrifugation, the supernatant contained no thyroid stimulating activity [distinct from results (not shown) found with a human liver microsome preparation which did not bind the thyroid stimulator]. The importance of the latter data is marginal since. 

To date inhibition of the thyroid-stimulating activity in the serum of thyroid-immunized rabbits by antiserum to rabbit IgG has been inconstant and unconvincing. This is, however, not unexpected because of two factors 1) if it is assumed that there is a thyroid stimulating IgG in the serum of the immunized rabbits, it presumably is a small proportion of the total IgG 2) one is restricted in the total quantity of anti IgG antiserum (or gamma globulin) which may be added to the rabbit serum extract before iv injection into the mouse because of the artifactual effects seen with quantities of protein much in excess of the equivalent of 0.5... 

To summarize the results of the experiments described above, it appears that 1) in response to injections of thyroid gland homogenate an antibody was formed in rabbits which acted as a thyroid stimulator when injected into mice 2) the thyroid-stimulating antibody affected the host rabbit s own thyroid function so that it became "non-suppressible" by the injection of thyroxine. 

There is no evidence that the rabbits with thyroid-stimulating antibody in their blood were hyperthyroid and, indeed, the normal release rate of thyroid radioiodine probably indicates they were not. It would therefore be reasonable to question why they were not hyperthyroid or, in a similar vein, if they are likely to become so. The following points may be relevant to these considerations. 

It is perhaps to be wondered at that an antibody to a human antigen should cross-react with (presumably) the same component in the rabbit thyroid — although this wonder is surpassed by the surprise that it apparently has sufficient trans-species crossreactivity to act in the mouse. Consequently, although such crossreactivity appears to exist, it is only to be expected that there is loss of sensitivity (in terms of thyroid stimulation) in the various crossings from species to species so that a potent effect on the rabbit thyroid (or on the mouse gland) might require an inordinate titre of antibody. 

Guillemin et al. (G9) reported that they had extracted and purified a substance from the hypothalamus of sheep which stimulated thyroid function in the rat. Others showed that crude hypothalamic extracts would stimulate thyroid function in mice and rabbits, and Schreiber (S6) reported that a crude extract of bovine hypothalamus would release TSH from rat pituitaries in vitro. Schally et al. (S3) obtained a more purified TRF factor from 100,000 porcine hypothalami. TRF is apparently a small molecular weight substance and, although originally thought to be a protein (G8, S2), more recent evidence suggests that... 

---