Eur. J. Entomol. 90 (1): 23-35, 1993
Effects of proctolin on autonomic physiological functions in insects
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The pharmacological effects of proctolin, [L-Dopa2]-proctolin, [Phe(OMe)2]-proctolin and [Cha(4-OMe)2]-proctolin were studied on pupae of the mealworm, Tenebrio molitor. The results were obtained by prolonged monitoring of extracardiac pulsations in haemocoelic pressure. These pulsations revealed the functions of the autonomic nervous system (coelopulse). The administration of proctolin in 100 nM to 5 µM concentrations increased the amplitude of haemocoelic pressure pulsations up to six-fold, within a few minutes. With dosages corresponding to 1 µM concentrations, the effects of proctolin culminated between the 2nd and 3rd hour post-treatment, with a successive decline to the original level within the next 15-20 hrs. The frequency of pulsations and duration of resting periods were unaffected. The [L-Dopa2]-proctolin analogue was slightly-more effective than proctolin itself, although its action was retarded for 20-30 min. The remaining two proctolin derivatives were completely inactive.
Large doses of proctolin or [L-Dopa2]-proctolin (more than 5 µM concentrations in the body) produced pathophysiological symptoms of ''hyperproctolinism'', manifested by paralysis of all haemocoelic pulsations for several hours. The findings of considerable in vivo persistence of proctolin are in conflict with some general views upon the rapid inactivation of proctolin by enzymes present in the haemolymph or tissues. It is possible that proctolin may be a valid neurohormone, involved in the regulation of homeostatic physiological functions, and this is discussed.
Keywords: Neuropeptides, proctolin, L-Dopa-proctolin, autonomic nervous system, haemocoelic pulsations, Tenebrio molitor (Coleoptera: Tenebrionidae)
Accepted: September 28, 1992; Published: March 25, 1993 Show citation
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