Bioeffective monoclonal antibody against the decapeptide gonadotropin-releasing hormone: reacting determinant and action on ovulation and estrus suppression.

A monoclonal antibody generated against the decapeptide gonadotropin-releasing hormone (GnRH) was effective in intercepting the bioactivity of the hormone; it blocked ovulation in rats. The antibody reacted optimally with the native hormone. Substitution of amide at the COOH terminus by a carboxyl group decreased immunoreactivity by a factor of 200. The antibody recognized the amino acid sequences 4-6, 7-10, and 4-10 to a variable degree, which suggests that the epitope has a conformation involving the entire molecule, with the NH2- and COOH-terminal regions probably in proximity. The antibody was also competent to suppress the progression of estrus in dogs, an indication that GnRH may play an inductive role in the reproductive function of dogs.