The Effect of Clomiphene Citrate on the 24-Hour LH Secretory Pattern in Normal Men

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Abstract
Plasma luteinizing hormone (LH) was measured by radioimmunoassay at 20-min intervals for 24-hr in 5 normal men before and after the daily administration of 100 mg clomiphene citrate for 7 days. The results showed that clomiphene caused a significant (P < 0.001) increase in the 24-hr mean LH concentration in all 5 subjects. The range of the percent increase was 135–245 with a mean of 180%. In spite of the highly significant increase in the 24-hr mean LH concentration there were instances of overlap of isolated LH values in the control and clomiphene studies. Analysis of the 24-hr plasma curves showed that the increased mean LH concentration was achieved by either increasing the amount of LH secreted per secretory episode or the number of major secretory episodes or both. Calculation of the LH production rate from the 24-hr LH secretory patterns showed a mean percent increase of 189% with a range of 149–259. Estimation of the LH “half-life” from the declining phase of the secretory episodes showed a clustering of estimates into 2 groups. The group of lower estimates of 30–78 min agreed with previous reports where LH half-life was determined by either disappearance of labelled LH or endogenous LH after hypophysectomy. These estimates were considered the “true” half-life and were used for calculation of the mean half-life. This assumption is supported by the findings from 5-min sampling studies which show the longer half-lives (80–160 min) almost uniformly are associated with continued secretion during the declining phase of a secretory episode. Comparison of the mean “true” half-life estimates during the control and clomiphene studies showed no significant difference.