THE EFFECTS OF SELECTED PROCTOLIN ANALOGS ON CONTRACTIONS OF LOCUST (LOCUSTA-MIGRATORIA) OVIDUCTS

We have examined the ability of some selected proctolin analogues to m imic the basal contraction induced by proctolin (Arg-Tyr-Leu-Pro-Thr) on a locust oviduct. The criterion of agonist-induced basal contractio n was used to construct dose-response relationships for these selected analogues. Three of the analogues were modified in the [Tyr2]-positio n, two were modified in the [Arg1]-position, and one was a tetrapeptid e lacking the N-terminal arginine, Tyr(3'-NH2)-Leu-Pro-Thr. All were c hosen because of their differing rank orders of activity on two other insect preparations. [L-Dopa2]proctolin, [Phe(pNH2)2]proctolin and [Ph e(pNMe2)2]proctolin were all capable of mimicking proctolin, as too we re [Lys1]proctolin and [homo-Arg1]proctolin, although with varying thr esholds, half-maxima and maxima. The tetrapeptide was a very poor agon ist, resulting in only a minor basal contraction at the high dose of 1 0(-5) M. The rank orders, based upon doses required for half-maxima an d maximal contraction were different from either a cockroach heart or a mealworm heart. The results support the suggestion for subtypes of p roctolin receptors within insects, and indicate that these analogues m ay be useful tools for comparing these sub-types.