Myotropic Peptides Research Articles

Isolation and partial characterization of a second myotropic peptide from the hindgut of the cockroach, Leucophaea maderae

1. 1. Proctolin and a second myotropic peptide were extracted from the hindgut of the cockroach Leucophaea maderae with methanol-water-acetic acid (90:9:1). The two peptides were easily separated by HPLC on a μ-Bondapak-phenyl column. 2. 2. Like proctolin, the second peptide was heat stable and was inactivated by the exopeptidases aminopeptidase M and carboxypeptidase Y. 3. 3. The response of the isolated hindgut to the new peptide was distinguishable from the response to proctolin by the following features: (a) a longer interval following application (1–4 min) to reach a maximum contraction, and (b) a much larger amplitude for single phasic contractions. Like proctolin, the new peptide could cause a protracted stimulation of the hindgut for more than 2 hr.

Isolation and high-performance liquid chromatographic purification of a myotropic peptide from the hindgut of the crayfish, Procambarus clarkii

Isolation and high-performance liquid chromatographic purification of a myotropic peptide from the hindgut of the crayfish, Procambarus clarkii

Analogs of the insect myotropic peptide proctolin: Synthesis and structure-activity studies

Fifteen pentapeptides structurally related to the insect myotropic substance proctolin synthesized by solution methods were assayed for proctolin activity on cockroach proctodeal muscle. [Phe( p -OMe) 2 ]-Proctolin was almost three times as potent as the natural pentapeptide; other analogs ranged from 15% as active to almost inactive. Related shorter chain-length peptides had little or no activity. None of the synthetic peptides acted as antagonists.

Evidence for proctolin and a second myotropic peptide in the cockroach, Leucophaea maderae, determined by bioassay and HPLC analysis

Purification and analytical HPLC methods were developed for quantitatively determining proctolin in extracts of foreguts, hindguts, and heads of Leucophaea maderae. The system will measure as little as 30 ng of proctolin from extracts containing up to 50 organs. Comparison of analytical results with bioassay data indicates that all of the myogenic activity in these foregut and hindgut extracts can be accounted for by proctolin (0.83 ng/foregut, 3.3 ng/hindgut). Proctolin was absent from head extracts but these extracts contained another myogenically active peptide, the hindgut-stimulating neurohormone. Proctolin and neurohormone caused an increase in the frequency, amplitude, tonus and coordination of contractions of the hindgut. Both peptides produced a protracted excitation of the hindgut. Both proctolin at 3 × 10 −10 M and HSN at 0.5 head equivalents/ml evoked responses that lasted for 65 min before the preparations were rinsed in fresh saline solution.

The oviduct musculature of the horsefly, Tabanus sulcifrons, and its response to 5‐hydroxytryptamine and proctolin

ABSTRACT. A delicate lace‐like membrane covers the ovaries of Tabanus sulcifrons. These membranes were found to contain muscle fibres that provide the organs with motile properties. The lateral oviducts consist of a single layer of longitudinal muscles that form a structural syncytium by means of an extensive anastomosis of the fibres comprising it. The common oviduct is composed of two muscle layers, an outer sheath of circular muscle and an inner substratum of longitudinal muscle. Both of these layers showed evidence of a structural syncytium. When isolated in saline, the oviduct was spontaneously active and gave a simple phasic pattern of contraction. Such muscle preparations were sensitive to both 5‐hydroxytryptamine (5HT) and the insect myotropic peptide, proctolin. Excitation was generally indicated by a rise in muscle tonus or an increase in the frequency and amplitude of individual phasic contractions, or all three characteristics. The threshold for activation with 5HT was variable, ranging from as low as 4 × 10‐9M to 1 × 10‐7M. Proctolin evoked a noticeable increase in the tonus of most oviducts at 10‐10M. However, several preparations responded to as little as 3 × 10‐11M proctolin.

Proctolin: A peptide transmitter candidate in insects

The slow, striated muscles of the proctodeum (hindgut) of the cockroach, Periplaneta americana (L.), were examined pharmacologically with reference to the responses evoked by nerve stimulation, glutamate, 5-HT, and proctolin, a myotropic peptide from Periplaneta recently isolated and identified. The graded contractions evoked by repetitive nerve stimulation were simulated by 5-HT and proctolin at threshold concentrations of about 10 −7 and 10 −9 M respectively; responses to glutamate (∼10 −4 M) were not similarly graded. The 5-HT receptors are distinct from other receptors, including the post-synaptic receptors, since they were specifically blocked by bromolysergic acid diethylamide. Proctolin was fully active on TTX-treated or surgically denervated muscle indicating that the proctolin receptors are located on the muscle fibre membrane. Tyramine, at threshold levels 5×10 −8 M, reversibly antagonized the responses evoked by proctolin and by nerve stimulation but was without effect on the 5-HT and glutamate responses. Neurally evoked responses were potentiated by subthreshold concentrations of proctolin but not by glutamate. Pharmacologically, the proctolin and post-synaptic receptors appear to be identical and distinct from the glutamate and 5-HT receptors. Since proctolin is known to be a constituent of an efferent pathway of the proctodeal nerves, the evidence suggests that it may function as an excitatory transmitter substance. Peptidergic transmission is discussed in relation to the ultrastructural organization of the proctodeal nerve terminals which contain neurosectory granules in addition to electron-lucent, synaptic vesicles.