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NEW BRUNSWICK, NEW JERSEY\ EVERAL RECENT STUDIES from this laboratory offer strong support of the belief (i) that at least two gonadotropins can be isolated from extracts of pituitary glands. Preliminary evidence was obtained from experiments with extracts of hog glands digested by proteolytic enzymes permitting differentiation of gametogenic ('follicle stimulating') and interstitial cell'Stimulating effects depending upon the en' zyme used and the extent of digestion (2). Physicochemical methods were next em' ployed to separate the gonadotropins from hog pituitary extracts which had not undergone preliminary enzymic hydrolysis (3). The interstitial cell'Stimulating hor' mone as a pure protein was isolated (4). The gametogenic hormone was separated as a substance with only one apparent biological effect; however, the purest preparations contained small proportions of two contaminating impurities.Work in the University of California (5) likewise led to the isolation of interstitial cell'Stimulating hormone from pituitary glands of another mammal, the sheep. We have had the opportunity of making a limited examination of the potency and bio' logical action of this extract believed, like our hog pituitary protein, to be a pure sub' stance.In this report and the two which follow it, the term thylakentrin will be used to refer to the gametogenic hormone (FSH or follick'Stimulating hormone) and the term metakentrin will refer to the interstitial cell'Stimulating hormone (ICSH and, in a restricted sense only, luteinizjng hormone). The basis for suggesting these names is given by Coffin and van Dyke (6).The results of a ramified investigation of the biological action of pure metakentrin as well as more restricted and less elaborate biological experiments with thylakentrin will be described in this first report. The second report will deal completely with a simplified method of securing pure metakentrin. Physicochemical evidence of purity as well as additional biological data important for demonstrating that the protein is the hormone will also be presented. The third and last report will offer immunological evidence not only of the purity of hog metakentrin but also of its striking immunologi' cal difference from sheep metakentrin whether in crude extract or in pure form.Unless otherwise noted, the metakentrin was the pure protein derived from hog pituitary glands and the thylakentrin, of similar origin, was about 80 per cent pure. 1

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