Effects of human choriogonadotropin on mitochondrial and microsomal cytochrome P-450 levels in mouse testes.

The mitochondrial and microsomal cytochrome P-450 contents of C57B1/6 mouse testis have been measured using difference spectroscopy on stable enzyme preparations containing the ferrous-carbon monoxide complex. Results were obtained on control animals (52 +/- 3 days of age) and on animals injected subcutaneously with human choriogonadotropin (0.017 micrograms/g body weight 24 h prior to sacrifice). The high ratio of testicular mitochondrial cytochrome oxidase to P-450, which has previously precluded measurements of basal P-450 levels, was overcome by using N,N,N',N'-tetramethyl-p-phenylene diamine to bypass site II, in combination with antimycin A to prevent reverse electron flow. The basal levels of mitochondrial and microsomal P-450 in mouse testis were 37.9 +/- 3.5 and 28.9 +/- 1.6 pmol/mg protein, respectively. Following administration of a desensitizing dose of gonadotropin, the respective values were lowered to 19.9 +/- 1.4 and 19.6 +/- 2.1 pmol/mg protein in 24 h. This is the first report of a gonadotropin-mediated decrease in mitochondrial P-450 and thus demonstrates that desensitization leads to alterations in both microsomal and mitochondrial P-450 in mouse testis.