The biological action of thyroxine on embryonic bones grown in tissue culture / by Honor B. Fell and E. Mellanby.

  • Fell, Honor B.
Date:
[1955?]
Catalogue details

Licence: In copyright

Credit: The biological action of thyroxine on embryonic bones grown in tissue culture / by Honor B. Fell and E. Mellanby. Source: Wellcome Collection.

    19/26 page 443
    thyroxine content of X2 medium must have been about 21-26/xg/100 ml., which would raise it to a concentration of human hyperthyroidic serum. The XG plasma, on the other hand, only had an additional lpg/lOOml., which would increase its total amount to 6-11 pg/100 ml. and thus leave the plasma equivalent to that of a normal individual. It would appear, therefore, that the thyroxine content of the culture media fell within the limits normally met with in biological conditions and was not exceptionally high. The results have shown that under these conditions thyroxine has a direct action on skeletal tissue in vitro, where all systemic effects are eliminated. The same concentration of the added hormone, e.g. 16pg/100ml., may be in¬ effective, stimulatory or toxic according to the stage of differentiation of the tissue at the beginning of treatment and the particular bone rudiment exposed. We will consider first the stimulatory effect. In general, the young rudiments were more susceptible to stimulation by thyroxine than the older primordia and, as recorded in Table 1, the blastemata were affected even by the addition of a concentration as low as lp,g/100ml. (A6). Of all the rudiments, the humerus responded best and differentiation was accelerated, not only in those explanted at the blastematous stage, but also in the older rudiments during the first few days of cultivation. Of the other wing-bones, the radii were occasionally stimulated in the blastemata and in all the older explants; the ulna was not affected in the blastemata but was often stimulated in groups III and IV. In the tibiae and femora maturation of the cartilage was sometimes hastened in the blastemata but only very slightly at the older stage. The older explants were more liable to toxic action than the blastemata, but here again the various rudiments responded differently to the same dose. Thus the leg-bones were always more severely affected than those of the wing. Of the wing-bones, the humerus was the most susceptible and next the ulna; the radius was the most resistant, and even when exposed to a concentration of 400 /xg/100 ml., which produced regressive changes in all the other rudiments, it remained healthy during the period of the experiment and was more highly differentiated than its control. As stated above, Willier (1924) grafted fragments of thyroid gland on to the chorio-allantoic membranes of chick embryos in ovo, and noted emaciation of the entire chick and shortening of the limbs. Although the author gives no histological data, his results appear to agree with ours in that the leg-bones of the host were more affected by the graft than the skeleton: 'when the host embryo is only slightly affected by the thyroid graft, the modifications show up most clearly in the legs’. On the other hand, when Beyer (1952) injected thyroxine into unincubated eggs, he found that the development and growth of the embryos were accelerated. It seems probable that the disparity between Willier’s and Beyer’s results is due to the fact that the former produced hyperthyroidism
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