Prolonged treatment with the GnRH analogue buserelin does not affect alpha-subunit production by the pituitary gonadotroph.

Seven patients with metastatic prostatic cancer were treated with biodegradable implants of the GnRH analogue buserelin and six were treated with buserelin intranasally. After 4-24 weeks of treatment mean serum testosterone concentrations were significantly lower in the patients treated with implants than in those treated intranasally (0.7 vs 1.7 nmol/l respectively; P less than 0.01). Also, serum LH concentrations were significantly lower in the group treated with implants. Serum alpha-subunit concentrations were significantly higher than pretreatment values during buserelin treatment. However, the sum of the concentrations of alpha-subunit present either as free alpha-subunit or as a part of LH did not differ significantly from pre-treatment values after 8 weeks or more of buserelin treatment. During buserelin treatment serum LH concentrations measured by radioimmunoassay (RIA) were higher than those measured by immunoradiometric assay (IRMA). Cross-reactivity of alpha-subunit in the LH RIA accounted for many, but not all, of the observed discrepancies. We conclude that: (1) the principal long-term effect of prolonged buserelin administration on the pituitary gonadotroph is the suppression of LH beta production, while alpha-subunit production is not affected; (2) the serum concentrations of bioactive LH are better reflected by LH concentrations measured by IRMA than by those measured by RIA. (3) Subcutaneous application of biodegradable buserelin implants is more effective in suppressing serum LH and testosterone concentrations than intranasal buserelin application.