Rat natriuretic peptide stimulates cGMP production in a dose-dependent manner in Malpighian tubules isolated from Rnor\Npr1Scer\UAS.cKa; Scer\GAL4c42 or Rnor\Npr1Scer\UAS.cKa; Scer\GAL4tsh-c724 flies. This is acompanied by an increase in fluid secretion from the tubules.