Tylosin inhibits the steroidogenesis in mouse Leydig cells "in vitro"

Former investigations in rats revealed effects of tylosin on the pituitary gonadal axis. After 15 days treatment the animals showed reduced weights of the seminal vesicles, increased pituitary weights, diminished LH/FSH stores in the pituitary and reduced peripheral levels of LH. To investigate if, in addition, the antibiotic exerts a direct effect on the steroidogenesis, the reactivity of Leydig cells was determined: a) after 8 days pretreatment of the donor mice in vivo; b) after addition of the antibiotic in vitro; c) after addition of the antibiotic in vitro in presence of dibutyryl cyclic AMP or hydrocholesterol. Tylosin caused an inhibition of basal and stimulated testosterone production, all the same if it was applied in vivo or in vitro. Moreover the increase in testosterone production caused by dibutyryl cyclic AMP was inhibited as well as that caused by addition of hydrocholesterol. These data give rise to the suspicion that tylosin inhibits directly intracellular steps of testosterone biosynthesis of Leydig cells.