Gonadorelin-Induced Testosterone Release: A Biological Assay for Quality Assurance of Gonadorelin in Veterinary Medicine

Abstract

Two experiments were conducted with bulls administered norgestomet and gonadorelin to determine if the gonadorelin-induced release of testosterone could be developed into a biological assay for quality assurance of gonadorelin. Implants containing norgestomet (0 to 36 mg) reduced the episodic release (r = −.81; P <. 05) and mean concentrations of testosterone (r = −.82; P <. 05). Gonadorelin-induced testosterone release increased (r = −.99; P <. 05) with increasing dosage of gonadorelin (up to 5 μg) in norgestomet-implanted bulls (36 mg). Maximal testosterone was released (>sixfold increase) with 5 to 40 μg of gonadorelin. In summary, the gonadorelin-induced testosterone release in bulls administered a synthetic progestin is a sensitive (0.008 μg per kg body weight for 5 μg of gonadorelin) biological assay with a rapid turnaround time for the confirmation of gonadorelin potency. Based on a per-kg-body-weight basis, the norgestomet-treated bull is the most sensitive biological assay model.