Prolonged histamine deficiency in histidine decarboxylase gene knockout mice affects Leydig cell function

The present study focuses on histaminergic regulation of Leydig cell physiology, since limited information is available so far. To evaluate the dependency of Leydig cells on histamine (HA), we performed experiments using highly purified Leydig cells in culture, isolated from wild type (WT) and histidine decarboxylase (Hdc) gene knockout (HDC KO)-so HA-deprived-mice. HDC KO Leydig cells showed lower basal and human choriogonadotropin (hCG)-induced testosterone production compared to WT Leydig cells, presumably due to altered P450scc gene (Cyp11a1) expression levels. Moreover, in HDC KO cells, hCG did not increase basal expression levels of HA H1 and H2 receptor genes, while the hormone showed a significant inducing effect in WT cells. Based on these findings, we propose that prolonged HA deficiency in HDC KO mice affects various aspects of Leydig cell physiology, most importantly the response to hCG, providing definite evidence that HA plays a role as direct modulator of Leydig cell function and steroid synthesis in the testis. Also, the results presented herein constitute the first molecular evidence for the expression of HA H1 and H2 receptor subtypes in isolated Leydig cells.