BIOLOGICALLY ACTIVE LUTEINIZING HORMONE (LH) IN PLASMA

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Abstract
An in vitro bioassay method for measuring LH activity was applied to male plasma. This method is based on the specific testosterone [T] response to LH activity by interstitial cells from mouse testes. In contrast to assays conducted on female plasma, non-parallel response lines were obtained between serial dilutions of untreated male plasma and the International Reference Preparation for Human Pituitary Gonadotropins (FSH [follicle stimulating hormone] and LH/ICSH [interstitial cell stimulating hormone]) for bioassay (code no. 69/104). To eliminate this source of error, which would invalidate the assays, plasma was subjected to either ether extraction or charcoal adsorption prior to assay. While ether extraction was ineffective, charcoal treatment eliminated the source of non-parallelism. The inclusion of a charcoal pre-treatment step provides an assay method for LH which fulfils the recognized criteria of reliability when applied to male plasma. An investigation of the likely causes of non-parallelism was undertaken by incubating mouse interstitial cells with various steroids and steroid sulfates at concentrations likely to be present in plasma. While most of the presumed precursors of T were converted to T steroid sulfates (dehydroepiandrosterone sulfate and pregnenolone sulfate) at high concentrations as present in male plasma were the most active compounds in forming T. The amount of T produced from these precursors under controlled conditions was insufficient to account entirely for the deviation from parallelism observed with male plasma. The non-parallelism observed with untreated plasma samples cannot be entirely explained by the presence of steroidal T precursors in male plasma.