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.

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    statistically significant. The growth rate then declined relatively to that of control humeri until it fell below that of the controls. The T-treated femora, on the other hand, grew at the same rate as their controls during the first 6 days, after which there was a sudden drop in the growth rate (statistically significant) and the thyroxine curve fell below that of the control. As described above, chondroblastic hypertrophy always causes a rapid expansion of the cartilage in which it occurs, and it is probable that the sharp rise in the rate of elongation of the T-treated humeri between the 2nd and 4th day was associated with the marked stimulation of hypertrophy produced by thyroxine in all the twelve rudiments measured. Of the ten T-treated femora from which the average growth curve was obtained, hypertrophy was present in only two. The fact that in the presence of thyroxine the growth rate of both the humeri and femora fell below that of the controls after the 6th day, suggested that more prolonged exposure to the hormone was harmful. This was supported by the observation that by the 8th day of cultivation the zone of outgrowth from the connective tissue surrounding the skeleton was sparse and unhealthy in contrast to its appearance in the controls. The effect of thyroxine on explanted rudiments of groups III and IV Development. When first removed from the embryo, the long-bone rudiments of group III (Text-fig. 4) were short and stumpy and showed little anatomical or histological differentiation; those of group IV were better developed and had begun to assume their characteristic shapes, while with transmitted light yellowish areas of hypertrophic cartilage were seen in the femur, humerus and sometimes in the other primordia. When grown in control medium, the humerus in group III formed its head and trochanter, the distal end acquired a fairly normal outline and the shaft elongated rapidly and became curved as in vivo, though usually the curvature was abnormally pronounced in vitro. In this group, however, some of the radii and ulnae failed to develop anatomically or to ossify and merely enlarged to form an oval nodule of small-celled cartilage; most of the radii and ulnae had fairly well-shaped proximal ends, but owing to the difficulty of separating them cleanly from the carpus, the distal ends were either imperfect or associated with carpal fragments. The femur formed its pulley-like condyles, a head and sometimes a trochanter, though the primordium of the trochanter was often destroyed during dissection. In the explanted tibiae, the general outline and relative sizes of the ends were fairly normal. This capacity of the rudiments for self-differentiation has been discussed elsewhere (Fell, 1939, 1952). During the first 2 days in vitro, the development of the rudiments grown in medium containing 16/xg/100 ml. of thyroxine resembled that of the controls, but by the 4th day the shaft of the femur, and often of the tibia also, was seen to be shorter than in the corresponding explants in control medium; the ends