The identification of monoiodotyrosine, diiodotyrosine and thyroxine in extracts of the endostyle of the ascidian, Ciona intestinalis L

Abstract

Specimens of Ciona intestinalis have been maintained in sea water containing 131 I, and the iodinated compounds present in extracts of their endostyles studied by chromatography, using two different two-dimensional systems. Before chromatographic analysis, the extracts have been purified by acetic acid elution from an anion exchange resin, using a procedure based upon that described by Pitt-Rivers & Sacks (1962). The reliability of the technique has been confirmed by prior tests with extracts of the thyroid gland of rats. 3-Monoiodotyrosine and 3,5-diiodotyrosine have been readily identified in 1% and 10% acetic acid eluates of endostylar extracts. There is no evidence that 3, 5, 3' -triiodothyronineis present, but small amounts of thyroxine have been identified in 50% acetic acid eluates; in this instance positive results are only obtained if close attention is given to the conditions in which the experimental animals are maintained. Other radioactive spots are present in the chromatograms, but it has not so far been possible to characterize them . Some reference is made to results obtained with extracts of the remainder of the pharynx, and of the cuticular layer of the tunic. The results are discussed in relation to previous autoradiographic and chromatographic studies of protochordates, and in the light of the well-known development of the thyroid gland of lampreys from the endostyle of the ammocoete larva. Much further investigation of the complex problem of the origin of thyroidal biosynthesis is still needed, but it is concluded at this stage that thyroxine is probably synthesized in the endostyle of Ciona , and that this process is associated with the presence in that organ of a zone of specialized iodinating epithelium . It is, however, impossible as yet to determine whether or not this is a true thyroidal biosynthesis.