Oostatic hormone inhibits biosynthesis of midgut proteolytic enzymes and egg development in mosquitoes

Injection of partially purified oostatic hormone (0.7 μg) into female Aedes aegypti inhibited egg development, proteolytic enzyme activity, and blood digestion in the midgut, whereas control injections of saline or insulin chain A (0.7 μg) did not affect these processes. Oostatic hormone given by enema, on the other hand, did not inhibit proteolytic enzyme activity, indicating that the hormone acts outside the midgut. A single injection of oostatic hormone (0.7 μg) caused a 1.7–1.5‐fold reduction in activity of trypsinlike enzymes during blood digestion, with a 10‐h delay in peak activity. Using [1,3‐ 3 H]diisopropylfluorophosphate (DFP) in the presence of 8 mM tosylamide‐2‐phenylethyl chloromethyl ketone, the synthesis of trypsinlike derivatives was followed in the midgut of female A. aegypti. A 4‐fold reduction in [1,3‐ 3 H]diisopropylphosphoryl‐trypsinlike derivatives was noted after oostatic hormone treatment. Several isozymes that are normally synthesized were absent in the presence of DFP, as assessed by polyacrylamide gel electrophoresis. Injection of oostatic hormone into decapitated and ovariectomized females that did not synthesize ecdysteroids inhibited trypsinlike enzyme synthesis and blood digestion in the midgut, indicating that oostatic hormone inhibits the midgut cells and not the ovary or the brain's endocrine system. Comparison between oostatic hormone and soybean trypsin inhibitor indicated that the former inhibited trypsin synthesis whereas the latter inhibited trypsin activity. A. aegypti oostatic hormone is not species specific and injections of the hormone into Culex quinquefasciatus, Culex nigripalpus , and Anopheles albimanus caused inhibition of egg development, blood digestion, and synthesis of trypsinlike enzymes. A direct relation between oostatic hormone synthesis and the regulation of trypsinlike activity in the midgut is proposed.