Biphasic effect of orchiectomy on pro-opiomelanocortin gene expression in the hypothalamus

Previous studies have shown that the hypothalamic concentration of pro-opiomelanocortin (POMC) mRNA and several POMC-derived peptides increases in the rat 4 weeks after orchiectomy and that this increase can be prevented by testosterone replacement. In this study, we have examined the short-term effects of orchiectomy on POMC gene expression in the medial basal hypothalamus (MBH). Adult male rats were studied at various time points between 1 day and 4 weeks after orchiectomy and compared to sham-orchiectomized rats. The MBH was homogenized and, after an aliquot was removed for beta-endorphin (beta-EP) radioimmunoassay, the RNA was isolated and the amount of POMC mRNA was measured using a solution hybridization S1 nuclease protection assay. In the first experiment, POMC mRNA was significantly higher 4 weeks after orchiectomy compared to that of the intact controls: 1.34 +/- 0.14 vs. 0.86 +/- 0.04 pg/micrograms RNA (p less than 0.01). Three days after orchiectomy, POMC mRNA was somewhat lower, 0.71 +/- 0.06 pg/micrograms RNA, but not significantly different from the controls. In a second experiment, POMC mRNA levels were measured 1, 2, 3, 4 and 7 days after orchiectomy. At 1 and 2 days after orchiectomy, POMC mRNA was lower than the controls: 0.51 +/- 0.02 and 0.52 +/- 0.06 vs. 0.70 +/- 0.09 pg/micrograms RNA. Levels then steadily increased to 0.61 +/- 0.04, 0.70 +/- 0.09 and 0.78 +/- 0.11 pg/micrograms RNA at 3, 4 and 7 days after orchiectomy, respectively. The mean level at 1-2 days after orchiectomy was significantly less than the controls (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)