Natriuretic and depolarizing effects of a stable fly (Stomoxys calcitrans) factor on Malpighian tubules

Abstract A two-step HPLC purification procedure resulted in a factor from the stable fly that depolarizes the lumen-negative transepithelial voltage (V t ) of the adult stable fly Malpighian tubule. When applied to tubules of the female mosquito, Aedes aegypti , this factor partially mimics the electrophysiological actions of the mosquito natriuretic factor (MNF). It also selectively increases active transepithelial Na transport by the mosquito Malpighian tubule. The blood meal causes a transient increase in hemolymph Na and Cl contents and hemolymph volume during the course of the 24-h post-feeding period. The level of a factor that is immunologically cross-reactive with the human atrial natriuretic peptide (ANP) increases more than 6-fold within 6 h following a blood meal by the stable fly. The temporal pattern of the levels of the ANP-immunoreactive factor closely parallels the blood meal-induced rise and subsequent fall in hemolymph NaCl content and hemolymph volume, suggesting a functional correlation between the ANP-immunoreactive factor and the rate of NaCl and fluid loss from the hemolymph.