[New studies on 3-dehydroecdysteroids in the biosynthetic pathway of ecdysone in Locusta migratoria]

Prothoracic glands of the locust, Locusta migratoria, incubated in vitro, converted in the same manner 3-dehydroketodiol (14 alpha-hydroxy-5 beta-cholest-7-en-3,6-dione) tritiated either on the side chain (22,23,24,25)3H4 or on the nucleus (1,2)3H2. Conversion products always appeared in two forms: one oxidized at C-3 corresponding with 3-dehydroecdysteroids, and the other corresponding with "classical" ecdysteroids which are usually obtained by conversion of ketodiol. All the different intermediate ecdysteroids between ketodiol and ecdysone are presents. A non-hemolymphatic reductase is conceivably responsible for the conversion of 3-dehydroecdysteroids at one or several places in the course of the biosynthetic pathway. Quantitatively the two forms (oxidized or hydroxylated at C-3) appeared in changeable ratios according to the different ecdysteroids but with a prevailing tendency to 1:1. The specificity of the conversion from nucleus-tritiated-dehydroketodiol depended on an enormous production of polar degradation products (more than 50% of total radioactivity). Consequently the quantities of 3-dehydro- and 3-hydroxy-ecdysteroids were lower than those which could be obtained after the conversion of side-chain-tritiated-3-dehydroketodiol. By means of an incubation with locust-larval-hemolymph, each 3-dehydroecdysteroid was totally (or at least in a great part: 3-dehydro-2-deoxyecdysone) converted into the corresponding reduced ecdysteroid. This fact confirms the reducing function of the hemolymph.(ABSTRACT TRUNCATED AT 250 WORDS)

[Inhibitory activity of allene cholesteryl derivatives on the biosynthesis of ecdysone]

Prothoracic glands of the migratory locust Locusta migratoria during the postembryonnic development, are the biosynthetic source of ecdysone. The production of ecdysone by these glands in vitro has been used to evaluate the inhibitory activity of four cholesteryl derivatives with an allenic function on the side chain at C-22. These molecules were devised as potential inhibitors of hydroxylation at C-22 which is an obligate step in the biosynthesis of ecdysone. Three of the four molecules tested induce a marked depressory effect of the production of ecdysone. The effect of the compound with the higher activity was dose dependent and irreversible.

[Comparison of the morphogenic effects of JH-I and JH-III during the solitary phase of Locusta migratoria]

After injection of oiled solutions of JH-I metamorphosis was much more disturbed than following the same treatment with JH-III. The two hormones reduced in the same way the mortality which occurred after injection of pure peanut oil in the first hours of a larval stage. JH-1 and JH-III seemed to have the same effect on the two phases of Locusta.

[Cardiotropic effects of C 18 synthetic juvenile hormone of Hyalophora cecropia on Locusta migratoria L]

C 18 Cecropia juvenile hormone injected at doses of 50 and 100 mug/animal in larval instar and of 200 mug/animal in the adults, increases the heartbeat of the fifth instar and males and females of Locusta migratoria in the same way as the implantation of one pair of corpora allata.

[Inhibition of ecdysone biosynthesis by synthetic molecules]

We studied the putative inhibitory activity of about 50 synthetic molecules on the biosynthesis of ecdysone. Most of these molecules had been synthesized according to the conceptual framework of suicide substrate type inhibitors. They potentially react either with well-known catalytic mechanisms (hydroxylations at C-22 and C-25) or with more hypothetic ones (introduction of the keto group at C-6 and the hydroxylation at C-14). The two hydroxylations which take place on the side chain at C-22 and C-25 in the last steps of the ecdysone biosynthetic pathway, and which are catalysed by cytochrome P-450 dependent monooxygenases, can be effectively affected. The essential chemical arrangement which produced a consequent inhibitory effect included an acteylenic or an allenic inhibitory function, near the hydroxylation to inhibit, with a hydroxyl group, preferably grafted in C-20. In order to increase the inhibitory effect, several characteristics gradually appeared: shortness of the side chain, hydroxyl group in position (R) at C-20 and at C-22, if necessary; in the proximal shortening side chain molecules, hydroxyl group at C-17 in position beta; lowering steric hindrance at C-20. It seemed that a molecule bearing a side chain in a relative position behind the midplan of the steroid nucleus induced a more important inhibitory effect. On the contrary, the form of the steroid nucleus itself (as in cholesterol, 7-dehydrocholesterol, 3-dehydrocholesterol, or in a molecule with a saturated B cycle) did not play a deciding part in the activity of the compound. Only the molecules with a typical ecdysteroid nucleus showed a poor inhibitory effect. Molecules acting as suicide substrate type inhibitors on the ecdysone biosynthesis should produce an irreversible inactivation of the enzyme and show a biosynthetic inhibition specifically linked to ecdysteroid. It was not the case of all the tested molecules. Some of them induced a very important inhibition without possessing the other characteristics of a suicide substrate type compound. Other derived chemicals, which were not synthesized according to the framework of the suicide substrate type molecules, showed all the characteristics of this type of molecules. In the course of this work, it has been possible to point out several molecules showing an important inhibitory effect on ecdysone biosynthesis.

Blockade of potassium or calcium channels provokes modifications in TRH-induced TSH release from rat perifused pituitaries

The aim of the present study was to determine the functional relationship between blockade of potassium or calcium channel activity and the initial burst of TSH secretion in response to TRH. Perifused rat pituitary fragments were stimulated by a 6-min pulse of physiological concentration of TRH (10 nM) in the presence or absence of pharmacological blockers of K+ or Ca2+ channels. Blockade of Ca(2+)-activated K+ channels with TEA (10 mM and 30 mM), apamin (200 nM), or charybdotoxin (50 nM) completely or partially blunted TRH-induced TSH release. By contrast, blockade of voltage-dependent K+ channels with 4-aminopyridine (4-AP) (500 microM) or with dendrotoxin (DTX) (350 nM) significantly increased TSH response. Moreover, blockade of T-type voltage-sensitive Ca2+ channels (VSCC) with NiCl (3 mM) or with diphenylhydantoin (100 microM) significantly (P < 0.01) reduced TSH response to TRH, whereas blockade of L-type Ca2+ channels with verapamil (50 microM) was ineffective. Our results suggest that secretion of TSH in response to nanomolar concentrations of TRH is correlated with stimulation of Ca(2+)-activated K+ channels, and inhibition of 4-AP-and DTX-sensitive voltage-dependent K+ channels; furthermore TSH response seems to depend on the activation of T-type VSCC.

A cryptic peptide of TRH prohormone inhibits TRH-induced GH release

The effects of two cryptic peptides from pro-TRH: Ps4 (160-169) and Ps5 (178-199) were investigated on basal and secretagogue (GRH and TRH)-induced releases of GH from perifused fragments of rat adenohypophysis. Validation of the perifusion system was done by measuring: (1) the dose-dependent effect of GRH and TRH on GH release; and (2) the stimulation of that release by forskolin (to mimic the adenylate cyclase pathway) or by phorbol ester (to mimic the protein kinase C pathway). We show that: (1) Ps4 and Ps5 (1 microM) do not modify basal GH release; (2) Ps4 (1 microM) changes neither GRH (10 nM)- nor TRH (100 nM)-induced release of GH; (3) Ps5 (100 nM and 1 microM) significantly decreases the release of GH induced by equimolar concentrations of TRH but not that induced by GRH.

[Effect of 5-HT on insect cardiac activity in vivo]

Injection of the Insect Locusta migratoria with 10 mul of normal saline produces an important (10 per cent) but short (1 min) increase of the cardiac rhythm. Adding various concentrations of 5-HT with the saline always results during the following ten minutes in a greater increase of the cardiac rhythm than the controls.

[The effect of an injection of synthetic juvenile hormone on Locusta migratoria L]

Hyalophora cecropia synthetic juvenile hormone (Demoute and al., 1973) is injected at doses of 50, 100 or 200 mug in 10 mul of pure peanut oil in fourth stadium of Locusta migratoria migratorioides. This synthetic juvenile hormone shows high chromatotropic, gonadotropic, and juvenilizing actions which are very similar to those of one pair of corpora allata of the species.