Changes in the qualitative and quantitative secretion of luteinizing hormone (LH) following orchidectomy in man

The effect of orchidectomy and thus withdrawal of testicular hormones on the biological and immunological properties of plasma LH was studied. Plasma samples were obtained from five men (mean age 71, range 65-81 years) with advanced carcinoma of the prostate, before orchidectomy and 1, 4, 8 and 16 weeks after surgery. LH bioactivity was estimated by a mouse Leydig cell bioassay and immunoreactivity by radioimmunoassay, using the same human pituitary LH standard 68/40. FSH and testosterone were measured by radioimmunoassay. Similar baseline data were obtained from a group (n = 17) of normal adult men (26, 19-36 years). Baseline bioactive (40 IU/l, median) and immunoreactive (10.8 IU/l) LH levels in the patients were higher (P less than 0.01) than in the controls (15.1 and 5.7 IU/l respectively), but bioactive to immunoreactive (B:I) LH ratios (3.4 +/- 0.2 versus 2.8 +/- 0.7) and testosterone levels (15.3 vs 18.7 nmol/l) were no different, consistent with compensated Leydig cell failure in the elderly men. After orchidectomy there was a greater increase in immunoreactive (46.6 IU/l at 16 weeks) than bioactive (80.3 IU/l) LH levels i.e. a fourfold vs twofold increase from baseline values. Consequently the B:I LH ratio decreased significantly (1.8 +/- 0.4 at 16 weeks) from the baseline ratio (P less than 0.0001) and that of the controls (P less than 0.01). These data indicate that acute withdrawal of testicular sex steroids results not only in quantitative change in LH secretion but also in qualitative change that decreases the biopotency of the LH molecules.