Diapause Hormone Levels in Subesophageal Ganglia of Uni-, Bi- and Poly-voltine Races during Pupal-adult Development of Bombyx mori, and the Effects of Ouabain, an Inhibitor of Na⁺-K⁺ ATPase, on the Hormone Levels

Abstract

In the silkworm, Bombyx mori, diapause hormone (DH) produced in the female subesophageal ganglion (SG) and released into the hemolymph primarily determines embryonic diapause by targeting developing ovaries. DH consists of 24 amino acid residues with an amidated C-terminus and belongs to the FXPRLamide peptide family. In order to quantify DH levels, we previously developed a sandwich enzyme-linked immunosorbent assay (ELISA) using mouse monoclonal and rabbit polyclonal antibodies to the N- and C-terminal regions of DH, respectively. This procedure demonstrated that DH levels in SG during the middle pupal stage decreased markedly in the diapause-egg producers when compared with the nondiapause-egg producers from a bivoltine race, Daizo, thus indicating active release of DH into the hemolymph. In this study, in order to further confirm this result, we measured and compared DH levels in SGs of diapause- and nondiapause-egg producers from Bombyx three races. When DH release into hemolymph was stimulated by administration of the Na⁺-K⁺ ATPase inhibitor ouabain, DH levels in SG were decreased. These results suggest that the reduced levels of DH in SG during the middle pupal stage are the result of active release of DH into the hemolymph.