THE EFFECT OF CASTRATION ON STEADY-STATE LEVELS OF LUTEINIZING-HORMONE-RELEASING HORMONE (LHRH) MESSENGER-RNA AND PROLHRH PROCESSING - TIME-COURSE STUDY UTILIZING SEMIQUANTITATIVE REVERSE TRANSCRIPTION POLYMERASE CHAIN-REACTION/

Many studies have consistently shown that castration induces a prompt increase in serum levels and pituitary content of the gonadotropins, l uteinizing hormone (LH) and follicle-stimulating hormone (FSH), as wel l as a concomitant rise in steady state levels of the messenger RNAs d irecting their synthesis. The reports of effects of castration on the overall physiology of hypothalamic luteinizing hormone-releasing hormo ne (LHRH)-steady state levels of LHRH mRNA, post-translational process ing and secretion-have, however, not been consistent. The goal of the studies reported here was to provide the first analysis of the effect of castration, at multiple post-operative time points, on steady state levels of LHRH mRNA and on the levels of hypothalamic proLHRH. All th ese data are correlated with hypothalamic levels of the mature LHRH de capeptide and with serum and pituitary levels of immunoreactive LH and FSH. Adult male rats were either castrated or sham-castrated (control s) and then sacrificed at 1, 3, 5, 7, 14, 21 or 28 days postoperativel y. As expected, there was a prompt and sustained rise in serum immunor eactive LH and FSH in castrates compared with sham-operated animals. I ntrapituitary LH levels rose above levels in the sham-operated animals by 14 days post castration. Intra-pituitary FSH showed a biphasic res ponse, first falling significantly below control levels, then rising a bove control levels at 21 days. Steady state levels of LHRH mRNA in ca strates, measured by reverse transcription/polymerase chain reaction, were increased about 2-fold above control levels by 1 day postoperativ ely, but were virtually identical to control levels at each of the oth er time points despite marked changes in the gonadotropins. ProLHRH co ntent in castrates was 1.8-times that seen in controls at 1 day post c astration (P<0.05), concomitant with the rise in steady state levels o f LHRH mRNA at that time point. However, proLHRH content in castrates was no different from that seen in controls at each of the later time points examined. LHRH content was' unchanged through 7 days after cast ration, but then fell significantly to 57% of control levels in hypoth alami from animals gonadectomized 14 to 21 days previously (P<0.001 vs control), and to 54% of sham-operated levels at 28 days postoperative ly (P<0.001). We conclude that: (1) changes in steady state levels of LHRH mRNA after castration are small and transient and (2) increased p roLHRH coupled with unchanged LHRH levels at 1 day post castration, an d castrate animal proLHRH at control levels coupled with falling LHRH at later post-castration time points indicate that the effect of gonad ectomy on post-translational processing of proLHRH to LHRH is, likewis e, small and transient. In aggregate our data suggest that most of the increase in serum LH and FSH seen in male rats after castration is no t mediated at the hypothalamic level.