ZUR WIRKUNG DER SEXUALHORMONE AUF WACHSTUM UND DIFFERENZIERUNG

Abstract

Summary Investigations made up to the present time on the action of male and female sex hormones on non‐sexual cells have been reviewed and the mode of action of these hormones discussed. The studies were made on rabbit fibrocytes and on amphibian eggs in various stages of development. The action of testosterone and of some of its derivatives was studied, together with that of oestradiol, and also of stilboestrol which is strongly oestrogenous although it does not occur in the animal body. The hormones were used in concentrations of i: 20,000 to 1: 1,000,000. 1. Action of the male sex hormones Testosterone and its derivatives scarcely slowed down growth in cultures of fibrocytes. Damage to cells showed itself by a characteristic change in the mechanism of mitosis, involving an increase in abnormal metaphases. According as the damage was weak or strong, fewer or more chromosomes failed to become attached to the spindle and lay outside the area of division. In experiments with Amphibia, the eggs of Triton alpestris were used in various stages of cleavage and at the beginning of gastrulation. The action of testosterone always began to show itself in the course of gastrulation and was most pronounced in the neurula stage. In 55% of cases neurulation was abnormal, in 19% of these embryos the medullary plate was defective on both sides and in 81% on one side only. In extreme cases half‐embryos arose, which appeared externally to be a mere pad of muscle. Sections showed that internally too they were only organized on one side, the mesoderm being undeveloped on the unorganized side while on the other side it was normally segmented. These disturbances of neurulation were correlated with an inhibition of growth. In the half‐embryos there were noticeably fewer mitoses on the undeveloped side, while with bilateral disturbances the number of mitoses was diminished on both sides. The abnormalities in mitosis were of the same nature as in the fibrocyte cultures. 2. Action of the female sex hormones Oestrone and oestradiol were noticeably more effective than testosterone even at weaker concentrations. At higher concentrations (i: 10,000 to 1: 50,000) there was a complete standstill in 9 hours, while with weaker doses the metaphase was delayed and chromosome scattering became almost the rule, so that at the end of the period of observation up to 82 % of the equatorial plates were abnormal. Stilboestrol had a considerably stronger action than oestradiol and even in a concentration of 1: 200,000 led to a marked lengthening of the period of mitosis, owing to a blocking of early metaphase. The critical concentration was 1: 125,000; below this there was no effect. Female sex hormones acted much more strongly on amphibian eggs than on fibrocyte cultures. They already became effective in the course of cleavage, acting within a few hours from the beginning of an experiment. They upset the rhythm of cleavage in proportion to their concentration. Either the whole egg was affected or certain blastomeres were selected. Mitoses were always abnormal. The spindle was often loosened and the spindle fibres irregularly arranged. Among the pathological metaphases there occurred, together with equatorial plates with detached chromosomes, other types of injury such as an irregular arrangement of the chromosomes, incomplete dissolution of the resting nuclei, dwindled spindles and giant metaphases. Just as often the ana‐telophases were upset, in that delayed parting of the daughter chromosomes or incomplete dissolution of isolated sections of the nucleus were evident. The resting nuclei, too, were at times abnormal, but prophases were never affected. Besides the damage to nuclei, especially evident during mitosis, disturbances due to cytoplasmic damage were observed. These were evident above all in blastomeres of eggs which had been exposed to large doses of stilboestrol (1: 300,000 to 1: 500,000). They were apparent as early as 4 to 8 hours after the beginning of experiments and consisted in displacement of pigment, secondary dissolution of cell boundaries and the formation of cysts. In strongly damaged cells the spindle was absent, so that chromosomes lay in the middle of the yolk. Similar phenomena were observed in the egg of Tubifex. Here it was sufficient to place the eggs in the solution during metaphase for a breakdown of the whole nuclear apparatus to result. 3. Influence of female sex hormones on the development of eggs Only those eggs which had been exposed to strong doses of hormone showed abnormalities in morphogenesis. Gastrulation was often made impossible by an insufficiently developed or absent blastocoele. Only those embryos developed further which had completed an undisturbed gastrulation. But the medullary plates were mostly narrow and the medullary folds rudimentary. At best such embryos attained only the tail‐bud stage. To test the action of oestradiol and stilboestrol on growth and differentiation, newt embryos at Glasner's stage 29 were exposed to the hormone action. The disturbances occurred in all organs in which cell multiplication was active. Stil‐boestrol caused a stoppage of growth in the limb blastemas, while in the neural tube and in the retina the typical standstill occurred only in the matrix, with subsequent cell degeneration. In the central regions those cells which had already begun to differentiate proceeded no further. 4. Action of the sex hormones A possible connection between damage to mitosis and structural formulae was first investigated. For male hormones it was shown that unsaturated bonds always act by damaging mitoses, saturated bonds never. It was further shown that hormone specificity and damage to mitosis are wholly independent. Thus the damage caused by single male or female hormones is unaffected by the presence of a hormone of the opposite sex. In relation to the place of action of the harmful hormones, it was pointed out that carcinogenous hydrocarbons which cause the same damage to mitoses as sex hormones accumulate in certain lipophil cell structures, which may well be identical with mitochondria. The question of the relationship of the active steroids to nucleic acid metabolism was particularly studied. During gastrulation and neurulation there is a very intensive synthesis of nucleoproteids. Embryos treated with stilboestrol or oestradiol showed a disturbance in the distribution of nucleoproteids in single (? particular) cells and in the whole embryo. From this fact it was concluded that developmental processes and normal nucleoproteid metabolism are closely linked. In support of a direct connection there is the fact that an addition of nucleic acid to the harmful hormones is able completely or partially to neutralize their action. The observation that on the unorganized side of half‐neurulae produced by testosterone treatment there is a distinct decrease in the number of pyroninafnne granules lends support to the idea of a connection between nucleic acid metabolism and the mode of action of sex hormones. On a basis of the experimental results we arrive at the following scheme for the mode of action of sex hormones. The sex hormones accumulate inside cells at those places which are distinguished by their content of nucleoproteids, SH‐proteins and various enzyme systems, and which are important as metabolic centres in the life of the cell. The SH‐proteins which accompany nucleoproteids and play a decisive part in development are important in the detoxication of the harmful compounds but are not the primary point of attack of these hormones. The places at which sex hormones accumulate may be the mitochondria. Certain steroids are able to influence the synthesis and breakdown of nucleic acid through their structural peculiarities. The necessary preliminaries for the complete or partial synthesis of thymonucleic acid are thereby disturbed, just as by the use of the cytoplasmic nucleic acids. As a consequence abnormalities arise in the course of mitosis, with degeneration phenomena in the cytoplasm.