Gonadorelin-induced testosterone release: A biological assay for quality assurance of gonadorelin in veterinary medicine

Two experiments were conducted with bulls administered norgestomet and gona dorelin to determine if the gonadorelin-induced release of testosterone cou ld be developed into a biological assay for qualify assurance of gonadoreli n. Implants containing norgestomet (0 to 36 mg) reduced the episodic releas e (r = -.81; P < .05) and mean concentrations of testosterone (r = -.82; P < .05). Gonadorelin-induced testosterone release increased (r = .99; P < .0 5) with increasing dosage of gonadorelin (up to 5 mu g) in norgestomet-impl anted bulls (36 mg). Maximal testosterone was released (>sixfold increase) with 5 to 40 mu g of gonadorelin. In summary, the gonadorelin-induced testo sterone release in bulls administered a synthetic progestin is a sensitive (0.008 mu g per kg body weight for 5 mu g of gonadorelin) biological assay with a rapid turnaround time for the confirmation of gonadorelin potency. B ased on a per-kg-body-weight basis, the norgestomet-treated bull is the mos t sensitive biological assay model.