Sex-segregated grouping of DBA/2, BALB/c, and CBA males caused rapid amyloid development and early death as compared with segregated grouped females or with males living individually in cages with several females. Grouping of several males in a cage with females also caused early death in amyloidosis indicating that the exposure of males to males and not the sexual isolation was important for the amyloid development. Both reserpine treatment and castration prolonged the survival time of sex-segregated grouped males. Estrogen treatment retarded amyloid development in sex-segregated males while spayed and androgen-treated spayed females showed only small amounts of amyloid. Treatment with chlortetracycline did not prevent amyloid development in grouped males. Thymectomy of sex-segregated males at 1 month of age gave inconclusive evidence of a prolongation of survival time. Egg-transferred DBA/2 mice reacted as conventional DBA/2 mice when grouped by sex segregation. Cells with abundant PAS-positive cytoplasm were found in the spleen, liver, and ovaries of mice of all strains but most prominently in CBA mice. Evidence for a direct conversion of these cells to amyloid was found. Estrogen-treated BALB/c males developed testicular tumors and thymus alterations including necrosis and depletion of lymphocytes, depletion of PAS cells, formation of large cysts containing necrotic nuclei, and intralobular fibrosis.

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