TESTOSTERONE-INDUCED SUPPRESSION OF LIPOPROTEIN(A) IN NORMAL MEN - RELATION TO BASAL LIPOPROTEIN(A) LEVEL

The concentration of lipoprotein(a) [Lp(a)] in human plasma is largely genetically determined and is inversely correlated to the size of apo lipoprotein(a) [apo(a)]. Additionally, Lp(a) values are relatively sta ble within individuals and are only marginally susceptible to therapeu tic treatment. The aim of our study was to evaluate the effect of exog enous testosterone on plasma Lp(a) concentration. The study was carrie d out on 19 healthy men who were receiving weekly intramuscular inject ions of 200 mg testosterone enanthate. Lp(a) values were determined at multiple time-points by a double monoclonal antibody-based enzyme imm unoassay. This method is not sensitive to variation in Lp(a) size and the values are expressed in nmol/l. Apo(a) size isoforms were determin ed by agarose gel electrophoresis followed by immunoblotting. No corre lation was found between the baseline Lp(a) values and the baseline va lues of testosterone or estradiol. The Lp(a) response to testosterone treatment varied widely among subjects and was dependent upon the pret reatment Lp(a) concentration. For 10 subjects with low Lp(a) values (< 25 nmol/l), no significant decrease in Lp(a) was observed while, for the nine individuals with Lp(a) values > 25 nmol/l, there was a signif icant and consistent reduction in Lp(a) ranging from 25 to 59%. Lp(a) levels returned to baseline values following cessation of testosterone administration. Apo(a) size polymorphism did not appear to play a rol e in the determination of Lp(a) response to testosterone.