Proctolin, its presence in and action on the oviduct of an insect.

Proctolin has been isolated from oviduct extracts of Leucophaea maderae by HPLC. Quantitative bioassay with the hindgut of L. maderae demonstrated a proctolin titre of 0.93 +/- 0.15 ng/oviduct. Exposure to proctolin produced three changes in the spontaneous contractile activity of the oviduct: an increase in muscle tonus, an increase in the amplitude and frequency of phasic contractions. The sensitivity of the oviduct to proctolin was compared with the hindgut and foregut organ preparations from the same insect. Oviducts were responsive to proctolin in a calcium-free medium and the peptide also appeared to facilitate the reentry of calcium after depleted preparations were returned to normal levels of external calcium.