GAS-CHROMATOGRAPHIC MASS-SPECTROMETRIC (GC-MS) ANALYSIS OF GONADAL-STEROIDS IN PLASMA OF THE MALE AFRICAN CATFISH, CLARIAS-GARIEPINUS - EFFECTS OF CASTRATION OR TREATMENT WITH GONADOTROPIN-RELEASING-HORMONE ANALOG

To identify testicular steroids that may be involved in the feedback m echanisms of the hypothalamus-pituitary-gonad axis in African catfish, Clarias gariepinus, steroids, which are known to be produced by the t estis in vitro, were identified and quantified in blood plasma before and after castration using gas chromatography followed by mass spectro metry. Before castration 20 testicular steroids were detected. Quantit atively dominant steroids were testosterone (16.9 +/- 4.3 ng/ml), andr ostenedione (12.0 +/- 3.9 ng/ml), and 11-ketotestosterone (6.7 +/- 1.8 ng/ml). After castration, only these steroids showed a strong decreas e in plasma, indicating that they are of testicular origin. Assuming t hat steroids involved in the feedback to the pituitary are under gonad otropic control, fish were injected with two doses of a salmon gonadot ropin releasing hormone analogue (sGnRHa). The lower sGnRHa dose (0.25 mu g/kg body weight) increased plasma GTH-II levels in the same range as those induced by castration, resulting in a significant increase i n plasma levels of testosterone, androstenedione, and 11-ketotestoster one. After injection of a higher dose of sGnRHa (5.0 mu g/kg body weig ht), there was a greater increase in plasma GTH-II level, as well as a significant increase in most of the other steroids studied. The decre ased levels of testosterone, androstenedione, and 11-ketotestosterone after castration and the significant increase in these steroids follow ing moderate GTH stimulation, suggest that one or more of these steroi ds plays a role in the feedback mechanism within the hypothalamus-pitu itary-gonad axis. (C) 1994 Academic Press, Inc.