Coherence between biosynthesis and secretion of insect adipokinetic hormones.

The importance of the process of continuous biosynthesis of locust adipokinetic hormones (AKHs) for the availability of these peptide hormones for release was assessed in vitro by inhibiting this biosynthesis followed by secretory stimulation. Inhibition of the biosynthetic activity for AKHs by brefeldin A caused a considerable inhibition of the AKH release induced by the endogenous crustacean cardioactive peptide (CCAP). After brefeldin A treatment followed by potassium depolarization, CCAP-induced AKH release was completely abolished.

Cell biology of the adipokinetic hormone-producing neurosecretory cells in the locust corpus cardiacum.

The adipokinetic cells are neuron-like unipolar cells, the cell bodies and cell processes of which are intermingled within the glandular part of the corpus cardiacum. In Schistocerca gregaria, they produce two adipokinetic hormones, AKH-I and -II, whereas in Locusta migratoria an additional hormone, AKH-III, is present. The three AKHs are produced by the same cells and are co-localized in secretory granules.

Adipokinetic hormones of insect: release, signal transduction, and responses.

Flight activity of insects provides an attractive yet relatively simple model system for regulation of processes involved in energy metabolism. This is particularly highlighted during long-distance flight, for which the locust constitutes a well-accepted model insect. Peptide adipokinetic hormones (AKHs) are synthesized and stored by neurosecretory cells of the corpus cardiacum, a neuroendocrine gland connected with the insect brain.

Absence of coupling between release and biosynthesis of peptide hormones in insect neuroendocrine cells.

Adipokinetic hormone (AKH)-producing cells in the corpus cardiacum of the insect Locusta migratoria represent a neuroendocrine system containing large quantities of stored secretory peptides. In the present study we address the question whether the release of AKHs from these cells induces a concomitant enhancement of their biosynthesis. The effects of hormone release in vivo (by flight activity) and in vitro (using crustacean cardioactive peptide, locustamyoinhibiting peptide, and activation of protein kinase A and C) on the biosynthetic activity for AKHs were measured.

Intracisternal granules in the adipokinetic cells of locusts are not degraded and apparently function as supplementary stores of secretory material.

The intracisternal granules in locust adipokinetic cells appear to represent accumulations of secretory material within cisternae of the rough endoplasmic reticulum. An important question is whether these granules are destined for degradation or represent stores of (pro)hormones. Two strategies were used to answer this question.