Jacques Proux

Identification of an arginine vasopressin-like diuretic hormone from Locustamigratoria

We have identified two neuropeptides (F1 and F2) from suboesophageal and thoracic ganglia of Locusta migratoria, which we isolated earlier based on their immunological similarity to arginine vasopressin. The more abundant and hydrophilic factor, F1, has sequence Cys-Leu-Ile-Thr-Asn-Cys-Pro-Arg-Gly-NH2, but its biological role is unknown. The less abundant factor, F2, is an antiparallel dimer of F1, and functions as a diuretic hormone of this species. It appears to act through the intermediacy of cyclic AMP. The properties of the native neuropeptides were identical with those of samples synthesized from appropriately protected L-amino acids.

Enhancement of excretion across locust malpighian tubules by a diuretic vasopressin-like hormone.

Abstract Haemolymph volume of 20-day-old adult locusts was measured in vivo using a dye dilution method. It is close to 200 μl. The rate of dye excretion in vivo by Malpighian tubules exhibited an almost twofold increase after injection of crude or purified extracts from two suboesophageal ganglia. The stimulatory factor is immunologically related to the vasopressin molecule; nevertheless, synthetic vasopressin had no effect on dye excretion. Corpora cardiaca extracts and suboesophageal ganglionic extracts depleted of their stimulatory factor were without effect on dye excretion. Malpighian tubules appear to respond to the suboesophageal ganglion extracts in a dose-dependent way, suggesting a specific effect. An in vitro test, founded on the excretion of primary urine by the isolated Malpighian tubules, was also performed. It shows that a corpora cardiaca material permits the release of the suboesophageal ganglion vasopressin-like factor which increases directly the Malpighian tubules diuresis.

Evidence for vasopressin-like molecule in migratory locust. Radioimmunological measurements in different tissues: correlation with various states of hydration.

Abstract Biochemical studies were carried out and measurements taken of an antigenically related vasopressin molecule in the brain, nervous ventral cord, rectum, Malpighian tubules, and hemolymph of the migratory locust. The molecular weight of this substance was close to that of vasopressin. Correlations with immunofluorescence observations reported in the literature make it possible to believe that this molecule is synthesized in the suboesophageal ganglion, transported to the brain and nervous ventral cord, and released into the hemolymph. Enzymatic degradation occurring in the rectum and Malpighian tubules suggests the presence of target cells in these organs. When variations in the measured levels were correlated with relative humidity we found that this substance may be implicated in the water regulation process, although it did not exhibit an antidiuretic effect as has been described for vasopressin in mammals.

Antidiuretic factor from the nervous corpora cardiaca of the migratory locust: Improvement of an existing in vitro bioassay

Nervous lobes of the migratory locust corpora cardiaca contain an antidiuretic (AD) factor which increases the fluid reabsorption of isolated recta in a dose-dependent manner. Several extraction procedures were developed and compared. The very satisfactory thermostability of the AD factor was demonstrated. By using a succession of different incubating media on the same preparation, we improved our bioassay. The developed variant is faster and more sensitive than the existing test and saves time and biological material.

Diuretic activity of a newly identified neuropeptide—The arginine-vasopressin-like insect diuretic hormone: Use of an improved bioassay

Abstract A new bioassay using Locusta migratoria Malpighian tubules in vitro has been developed. It permits the measurement of excretion of primary urine over a long period of time (from 2 to several hours). We used it to test the diuretic roles of the newly identified arginine-vasopressin-like peptides, so-called because of their immunological relationship with arginine-vasopressin, the antidiuretic hormone of most mammals. One of them, the arginine-vasopressin-like insect diuretic hormone, has comparable diuretic activity as both the natural and synthetic forms. A possible involvement of these substances at the rectal level (where reabsorption of fluid from the gut takes place) was investigated using a bioassay of the rectum in vitro . None of these substances appeared to promote fluid reabsorption. In addition, the immunological relationship between each of the available arginine-vasopressin-like substances, either natural or synthetic, and the authentic arginine-vasopressin was established with the help of a radioimmunoassay.

Cyclic AMP: the second messenger of an antidiuretic hormone from the glandular lobes of the migratory locust corpora cardiaca

Abstract Cyclic AMP levels in the rectum of the migratory locust were measured by means of a radioimmunoassay. An antidiuretic factor, extracted from the glandular lobes of the corpora cardiaca, enhances water reabsorption across the rectal wall in vitro (maximal response with 0.5 gland 10 μ l of bathing medium). The same extract also elicits an increase in the cyclic AMP of the rectal tissue (60% with 0.05 gland 10 μ l of bathing medium). Two analogues of cyclic AMP (2′- O -dibutyryl-cyclic AMP 1 mM and 8-Br-cyclic AMP 1 mM) enter the rectal cells and mimic this antidiuretic effect. Forskolin (0.1 mM) stimulates an increase of the cyclic AMP concentration at the rectal level by activating the adenylate cyclase. IBMX (0.2 mM), by inhibiting phosphodiesterase activity, dramatically potentiates the forskolin effect. Furthermore, forskolin mimics the action of the antidiuretic factor. These results lead us to conclude that cyclic AMP is a likely second messenger of the antidiuretic factor contained in the glandular lobes of the corpora cardiaca.

Biochemical characterization of a vasopressin-like neuropeptide in Locusta migratoria. Evidence of high molecular weight protein encoding vasopressin sequence

The biochemical characterization of a diuretic neurohormone, immunologically related to the mammalian vasopressin (AVP) and present in Locusta migratoria has been performed. The results have been obtained using an AVP radioimmunoassay as method of detection and quantification. The AVP like molecule exhibits the same C terminal moiety: the tetrapeptide 1/2 Cys-PrO-Arg-Gly NH2. 125I-radiolabelling allows us to demonstrate the presence of a tyrosyl residue. The molecular weight of this molecule is estimated by gel filtration to 2500 +/- 400 Daltons. The isoelectric point is 7.5 and the electrophoretic migration lead to conclude to the presence of amino acid residues lacking in the vasopressin hormone. We have demonstrated the presence of a vasopressin sequence included in high molecular weight protein which have been quantified in suboesophageal ganglion (biosynthetic site) and in the nervous ventral cord (release site).

Cyclic AMP: A second messenger of the newly characterized AVP-like insect diuretic hormone, the migratory locust diuretic hormone

An AVP-like neurohormone was extracted from suboesophageal and thoracic ganglia of Locusta migtatoria, isolated, characterized and synthesized. It functions as a diuretic hormone in this species by enhancing the excretion of urine from the MT. It appears to act by increasing cyclic AMP; synthetic AVP-like IDH increases cyclic AMP of the MT in vitro in a time-dependant, dose-dependant and very specific manner. 8-BR-cyclic AMP, an analog of cyclic AMP known to enter the cells, mimics the diuretic action of the AVP-like IDH. Furthermore, the combined actions of forskolin (the activator of the adenylate cyclase) and IBMX (the inhibitor of the phosphodiestherase activity) increase both MT cyclic AMP level and excretion of the primary urine. We conclude from these results that cyclic AMP is a second messenger of the AVO-like IDH.

Influence of hydration on the concentration of two arginine-vasopressin-like neuropeptides coexisting in the ventral nerve cord of the migratory locust, Locusta migratoria

Abstract Two neurosecretory cells of the ventral nerve cord of Locusta migratoria contain two neuropeptides structurally related to mammalian arginine-vasopressin: a monomer, nonapeptide without any known biological activity and a dimer, the antiparallel homodimer of monomer, previously named arginine-vasopressin-like insect diuretic hormone. We established that their concentrations in the ganglia of the ventral nerve cord are influenced by hygrometric conditions. A dry environment (low r.h. and dehydrated food) decreases concentration and supplying of dimer, monomer being predominant in the nervous tissues. A damp environment (high r.h. and hydrated food) stimulates dimer production which becomes predominant in the tissues and is available in great amount to increase diuresis. The relationship between monomer-dimer and water content-live weight was established to discuss the involvement of monomer and dimer in water regulation.

Neurotransmitters and stimulation of fluid reabsorption in migratory locust rectal cells

Several biogenic amines enhance fluid reabsorption and the accumulation of cyclic adenosine-monophosphate (cAMP) in the rectum of the migratory locust but only 5-hydroxytryptamine (5-HT) acts in a dose-dependent manner at low concentrations (between 10(-8) and 5.10(-7) M). Cyclic AMP is a second messenger of 5-HT, and its actions on fluid reabsorption are calcium-dependent. Polymyxin B (a protein kinase C inhibitor) mimics the actions of 5-HT on fluid reabsorption and on calcium-dependent cAMP accumulation. This suggests the presence of other sources of calcium and a possible relationship between several transduction systems within different rectal cells. The second messenger system mediating the 5-HT antidiuretic message differs from those involved in the transduction of the known locust antidiuretic hormones.