Heterogeneity of plasma gonadotropins. Consequences on immunological properties of LH

The pituitary gonadotropins FSH and LH are secreted into blood as dimeric glycoproteins which display a wide heterogeneity when submitted to technique of separation based on electric charge. That supports the assumption of a major role of the carbohydrates moieties as a source of heterogeneity. No clear difference however has been demonstrated in the biological potency of the different isoforms occurring in blood. On the contrary, important discrepancies in immunological activity have been evidenced, mainly as far as LH is concerned. This is particularly important from a practical point of view since some monoclonal sandwich assays widely used for the measurement of LH levels fail to detect LH in samples from certain subjects. The description of the so-called "invisible LH" phenomenon should prompt international organizations to incite the manufacturers of commercial kits to improve the standardization in gonadotropin assays.