Preliminary isolation of mosquito natriuretic factor.

A natriuretic factor that triggers diuresis in isolated Malpighian tubules of the mosquito was isolated from the head of the yellow-fever mosquito Aedes aegypti by passing a saline extract of mosquito heads through low-pressure and then high-pressure liquid chromatography (HPLC) columns. Three fractions with biologic activity eluted during a reverse-phase HPLC linear acetonitrile gradient run. Fraction I depolarized the transepithelial voltage (Vt) of isolated perfused Malpighian tubules but did not not stimulate fluid secretion in the Ramsay assay (J. A. Ramsay, J. Exp. Biol. 31: 104-113, 1954). Fraction II depolarized and fraction III hyperpolarized Vt, and both stimulated fluid secretion three- to fourfold. Even though the effects of fractions II and III on Vt differed, both stimulated fluid secretion by increasing the rate of NaCl secretion without affecting K secretion. The selective stimulation of active secretory Na transport by fraction III is mimicked by cyclic AMP (cAMP), suggesting the second messenger role of cAMP in the effects of fraction III. Because fraction III stimulates a NaCl-rich, as opposed to KCl-rich, fluid, the term mosquito natriuretic factor is proposed for this active fraction.