Spermatogenesis in the vitamin A-deficient rat: possible interplay between retinoic acid receptors, androgen receptor and inhibin alpha-subunit.

In order to understand the mechanisms of retinol action on the testis, testicular retinoic acid receptor alpha, beta(RAR alpha and beta), androgen receptor (AR) and inhibin alpha-subunit were studied in normal, vitamin A-deficient (VAD) and vitamin A-supplemented rats by immunohistochemistry and immunoblotting. Compared to the normal testis, expression of 110 K AR was up-regulated by vitamin A withdrawal, whereas 51 K RAR alpha remained unchanged. An additional 55 K RAR alpha signal was observed. Readministration of retinol caused a marked decrease of AR in the VAD testis. By 24 h, AR declined to below the normal level. Although the 51 K RAR alpha signal remained unchanged, the 55 K band was slightly up-regulated at 6 h after retinol administration. A 51 K RAR beta protein was seen in the VAD but in not the normal testis. The intensity of the 51 K RAR beta band remained constant before and after the administration of retinol, but it had a slight up-shift at 6 h after retinol injection, suggesting post-translational modification of the receptor. The inhibin alpha-subunit of 18 K protein was undetectable in the VAD testis and increased to above normal level at 24 h after retinol administration. Immunohistochemically, nuclear AR immunostaining was more intense in the VAD testis than in the normal testis. The intensity of immunostaining declined in all AR-positive cells after the injection of retinol, but the decrease was more evident in Sertoli than in other cells. At 24 h after retinol the immunostaining was undetectable in most Sertoli cells. The regulation of the inhibin alpha-subunit by retinol in the cytoplasm of Sertoli cells detected by immunohistochemistry was correlated to the results in immunoblotting. These results suggest a possible interplay between retinoids, androgen and inhibin signalling systems in Sertoli cells in the regulation of spermatogenesis during retinol action.