A Growth Factor in Corpus Luteum Powder for Goitrogen-fed Rats

When a commercial preparation of corpus luteum powder was included in the diet, it reinstated growth of growth-arrested, sulfaguanidine-fed rats. A study was made, therefore, to determine whether the growth response to corpus luteum powder was due to thyroid hormones. The corpus luteum powder was hydrolyzed with acid. The acid-insoluble residue was extracted with alcohol and the addition of AgNO3 produced a precipitate which contained a growth factor capable of reinstating growth of growth-arrested, sulfaguanidine-fed and of thyroidectomized rats. One microgram of 3,5,3′-triiodo-L-thyronine produced the same growth response as 3.3 mg of the growth factor preparation. No iodine could be detected on paper chromatograms of the growth factor and the growth factor differed from triiodothyronine in its ability to prevent goiter. Two enzymes were used to compare the growth factor with triiodothyronine. Inosine monophosphate dehydrogenase was inhibited by 10-9M triiodo-L-thyronine but the growth factor had no effect on this enzyme. Adenylosuccinate synthetase was stimulated by 10-9M triiodo-L-thyronine, whereas the growth factor inhibited this enzyme. These results are taken as evidence that corpus luteum contains a growth factor which is capable of substituting for thyroid hormones insofar as growth is concerned but the growth factor is not an iodinated thyronine.