Pituitary hormones dependent expression of insulin-like growth factors I and II in the immature hypophysectomized rat testis

Since insulin-like growth factors I (IGF-I) and II (IGF-II) appeared involved in paracrine or autocrine regulation of both cell multiplication and differentiation of the rat testis, we have investigated the pituitary hormonal dependence of IGF-I and IGF-II mRNA production in the testis of immature hypophysectomized rats (22 days old) supplemented with highly purified FSH, LH, GH or PRL. Our data show that testicular expression of IGF-I mRNA as measured by dot-blot hybridization, is increased by LH, FSH or GH treatments of 7-, 6-, and 4-fold, respectively, above controls. Intensity of the signal was 3-fold lower after PRL treatment than in hypophysectomized control rats. On the contrary, IGF-II mRNA expression, was found low in the immature hypophysectomized rat testis and unmodified by any hormonal treatment. In contrast to the increase of IGF-I expression in the testis no significant change in the IGF-I plasma concentration was observed after LH or FSH supplementation. GH treatment, as expected, increased 4-fold the IGF-I plasma concentration of the experimental animals. Since we have previously shown that LH, FSH, and GH exhibit selective cell multiplication and differentiation in the testis of our animal model, it is proposed that testicular IGF-I expression could be the tissue response to pituitary hormone in these phenomena.