At least three linear regions but not the zinc-finger domain of U1C protein are exposed at the surface of the protein in solution and on the human spliceosomal U1 snRNP particle.

No structural information on U1C protein either in its free state or bound to the spliceosomal U1 small nuclear ribonucleoprotein (snRNP) particle is currently available. Using rabbit antibodies raised against a complete set of 15 U1C overlapping synthetic peptides (16-30 residues long) in different immunochemical tests, linear regions exposed at the surface of free and U1 snRNP-bound U1C were identified. Epitopes within at least three regions spanning residues 31-62, 85-103 and 116-159 were recognized on free and plastic-immobilized recombinant human U1C expressed in Escherichia coli, on in vitro translated U1C protein and on U1C bound to the U1 snRNP particle present in HeLa S100 extract. Using a zinc affinity labeling method, we further showed that the N-terminal U1C peptide containing a zinc-finger motif (peptide 5-34) effectively binds65Zn2+. The N-terminal region of U1C, which is functional in U1 snRNP assembly, is apparently not located at the surface of the U1 snRNP particle.

Isolation, characterization and chemical synthesis of a new insect defensin from Chironomus plumosus (Diptera).

Injection of low doses of bacteria into the aquatic larvae of the dipteran insect Chironomus plumosus induces the appearance in their hemolymph of a potent antibacterial activity. We have isolated two 36-residue peptides from this hemolymph which are active against Gram-positive bacteria. The peptides are novel members of the insect defensin family and their sequences present marked differences with those of insect defensins isolated from other dipteran species. We have developed a method for efficient renaturation of this cysteine-rich molecule and obtained a highly pure synthetic Chironomus defensin.

Somatostatin blocks the potentiation of TRH-induced TSH secretion from perifused pituitary fragments and the change in intracellular calcium concentrations from dispersed pituitary cells elicited by prepro-TRH (PS4) or by tri-iodothyronine.

TRH and somatostatin (SRIH) are well known to stimulate and to inhibit TSH secretion respectively. However, the mechanisms underlying the effect of SRIH on thyrotrophs are still not understood. We have previously shown in vitro that the TSH response to TRH is potentiated in a Ca(2+)-dependent fashion through the activation of dihydropyridine (DHP)-sensitive Ca2+ channels by the prepro-TRH (160-169) cryptic peptide (PS4) and tri-iodo-L-thyronine (T3), when the hormone was added shortly before a TRH pulse in order to avoid its genomic effect. Using perifused rat pituitary fragments, the present study has shown that SRIH inhibits, in a dose-dependent manner, the TSH response to physiological concentration of TRH (10 nM) and reverses the Ca(2+)-dependent potentiation of that response induced either by PS4 or by T3. We have also demonstrated that the inhibition by SRIH of the T3 potentiation of TRH-induced TSH secretion is pertussis toxin-sensitive. Our data suggest that SRIH inhibits the PS4 and T3 potentiation of TRH-induced TSH secretion through the inactivation of DHP-sensitive Ca2+ channels. Using primary cultures of rat anterior pituitary cells and videomicroscopy, we have already demonstrated that TRH, as well as PS4 and T3, are able to increase intracellular Ca2+ concentration ([Ca2+]i) rapidly, in 15 s. Our study has shown that SRIH is able to abolish the acute rise in [Ca2+]i induced either by PS4 or by T3. Since [Ca2+]i responses to PS4 and T3 are also abolished by the DHP nifedipine, our results suggest that [Ca2+]i changes in PS4- or T3-sensitive pituitary cells depend directly or indirectly on the activation of DHP-sensitive Ca2+ channels and that the inhibitory effect of SRIH may be mediated by inactivation of this type of channel.

Structure-activity analysis of thanatin, a 21-residue inducible insect defense peptide with sequence homology to frog skin antimicrobial peptides.

Immune challenge to the insect Podisus maculiventris induces synthesis of a 21-residue peptide with sequence homology to frog skin antimicrobial peptides of the brevinin family. The insect and frog peptides have in common a C-terminally located disulfide bridge delineating a cationic loop. The peptide is bactericidal and fungicidal, exhibiting the largest antimicrobial spectrum observed so far for an insect defense peptide. An all-D-enantiomer is nearly inactive against Gram-negative bacteria and some Gram-positive strains but is fully active against fungi and other Gram-positive bacteria, suggesting that more than one mechanism accounts for the antimicrobial activity of this peptide. Studies with truncated synthetic isoforms underline the role of the C-terminal loop and flanking residues for the activity of this molecule for which we propose the name thanatin.

Dihydropyridine-like effects of amiodarone and desethylamiodarone on thyrotropin secretion and intracellular calcium concentration in rat pituitary.

Amiodarone (AM) and its major metabolite desethylamiodarone (DEA) are structurally similar to biologically active thyroid hormones. Amiodarone therapy is frequently associated with impairment of thyrotropic function, whose mechanisms are still controversial. Besides its effect on nuclear thyroid hormone binding. AM is able to displace dihydropyridine (DH) binding on membrane preparations from several tissues. By perifusing rat pituitary fragments and measuring thyrotropin (TSH) release we examined: the effect of AM on Ca(2+)-dependent and DHP-sensitive potentiation of the TSH response to thyrotropin-releasing hormone (TRH) induced by either triiodothyronine (T3, perifused for only 30 min before a TRH pulse) or by the prepro-TRH peptide 160-169 (PS4); and the effect of DEA on TRH-induced TSH response in the presence or absence of the DHP nifedipine. We show that AM reverses T3 or PS4 potentiation of the TSH response to TRH; this effect is specific because AM does not modify ionomycin potentiation of that response. In contrast, DEA significantly potentiates the TSH response to TRH and the DHP nifedipine reverses that potentiation. We also tested whether AM would change the acute T3-induced increase in intracellular Ca2+ concentration by measuring intracellular Ca2+ ([Ca2+])i with fura-2 imaging on primary cultures of pituitary cells. We show that AM reverses the effect of T3 on [Ca2+]i as well as the PS4-induced increase in [Ca2+]i. In contrast, DEA increases [Ca2+]i and nifedipine reverses this effect. Our results suggest that AM and DEA display DHP-like effects on TRH-induced TSH release, behaving either as a Ca2+ channel blocker (AM) or as a Ca2+ channel agonist (DEA).

Triiodo-L-thyronine enhances TRH-induced TSH release from perifused rat pituitaries and intracellular Ca2+ levels from dispersed pituitary cells.

There is now increasing evidence that Ca2+ serves as the first messenger for the prompt and non-genomic effects of 3,5,3' triiodo-L-thyronine (T3) in several tissues. We have previously shown that the first phase of thyroid stimulating hormone (TSH) release in response to thyrotropin-releasing hormone (TRH) can be potentiated by messengers of hypothalamic origin, by a Ca(2+)-dependent phenomenon involving the activation of dihydropyridine-sensitive Ca2+ channels. By perifusing rat pituitary fragments, we have investigated whether T3 would modify TSH release when the hormone is applied for a short time (i.e. 30 min) before a 6 min pulse of physiological concentration of TRH, thus excluding the genomic effect of T3. We show that: (1) increasing concentrations of T3 (100 nM-10 microM) in the perifused medium potentiates the TRH-induced TSH release in a dose-dependent manner; (2) the T3 potentiation is not reproduced by diiodothyronine and T3 does not potentiate the increase if TSH release induced by a depolarizing concentration of KCl; (3) the protein synthesis inhibitor cycloheximide, does not significantly modify the effect of T3; (4) addition of Co2+, nifedipine, verapamil, or omega-conotoxin in the medium, at a concentration which does not modify the TSH response to TRH, reverses the T3 potentiation of that response. We also tested whether T3 would change intracellular concentrations of Ca2+, by measuring [Ca2+]i with fura-2 imaging on primary cultures of dispersed pituitary cells, either in basal conditions or after stimulation by TRH or/and T3. Both substances induced a fast increase of [Ca2+]i, with a peak at 15 s, followed by a subsequent progressive decay with TRH and a rapid return with T3. Our data suggest that T3 enhances TRH-induced TSH release by a protein synthesis-independent and Ca(2+)-dependent phenomenon, probably due to an increase in Ca2+ entry through the activation of dihydropyridine- and omega-conotoxin-sensitive Ca2+ channels. They also show that T3 may acutely enhance [Ca2+]i in pituitary cells. These findings support the idea of the occurrence of a prompt and stimulatory role of T3 at the plasma membrane level in normal rat pituitary gland.

The inhibitory effect of picrotoxin on basal and cold-induced thyrotropin secretion involves somatostatin mediation.

This work was undertaken to investigate whether the inhibitory tone exerted by GABA on somatostatin (SRIH) release operates in the control of thyrotropin (TSH) secretion in both basal and cold-stimulated conditions. In a first group of animals (G1) undergoing both carotid and third ventricle push-pull cannulation, i.vt. injection of picrotoxin (10(-5) M) induces a significant decrease in plasma TSH level under basal conditions (0.09 +/- 0.02 versus 0.27 +/- 0.4 ng/100 microliters; P < 0.03, n = 5). In a median eminence (ME) push-pull cannulated group of rats (G2), picrotoxin, peripherally administered, blocks cold-induced inhibition of SRIH release (35.0 +/- 1.8 versus 7.4 +/- 3.3 pg/15 min; P < 0.005; n = 5). In a third group of intact rats (G3), peripheral administration of picrotoxin (2 mg/kg i.p.) blunts the cold-induced TSH release (0.17 +/- 0.03 versus 0.46 +/- 0.04 ng/100 microliters; P < 0.001; n = 5). Our results strongly suggest that a decrease in SRIH release is involved in the GABAergic control of basal and cold-induced TSH secretion.

[Inhibition of ecdysone biosynthesis by synthetic molecules]. / Inhibition de la biosynthèse de l'ecdysone par des molécules synthétiques.

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.

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.

[New studies on 3-dehydroecdysteroids in the biosynthetic pathway of ecdysone in Locusta migratoria]. / Nouvelles études sur les 3-déshydroecdystéroöides dans la voie de biosynthèse de l'ecdysone chez 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)

Chronic stress affects in vivo hypothalamic somatostatin release but not in vitro GH responsiveness to somatostatin in rats.

One week after stereotaxical implantation of a push-pull cannula into the median eminence (ME), rats were stressed by immobilization for 2 h daily for 7 days. Thereafter, ME was perfused for 1 h in basal, stress and recovery conditions, respectively, and somatostatin (SRIH) was measured in perfusate fractions. Pituitaries were in vitro perifused to assess GH responsiveness to SRIH. In the stressed group, basal SRIH release was significantly higher than in the control group and stress caused a significant sharp peak in neurohormone release. GH responsiveness to SRIH was not affected in pituitaries obtained from stressed donors. High SRIH levels secreted under chronic stress thus did not impair the GH pituitary response to SRIH.

Effects of bilateral superior cervical ganglionectomy on thyroid and gonadal functions in the edible dormouse Glis glis.

1. The annual profiles of plasma thyroid-stimulating hormone (TSH), thyroxine (T4), luteinizing hormone (LH) and testosterone (T) concentrations in control and ganglionectomized (SCGx) dormice were analyzed to determine whether the pineal gland affects thyroid-gonadal interactions in response to the seasonal influence of environmental factors. 2. Dormice ganglionectomized in September, around the time of prehibernation when hormonal activity is minimal had significantly disturbed annual cycles of plasma T4, LH and T, while the TSH cycle was unchanged. 3. SCGx performed after breeding season (June), only affected the T4 variations, while the T and LH titers were similar to those of controls. 4. We conclude that the annual cycles of T4 and testosterone are controlled by the sympathetic nervous system via the superior cervical ganglion which innervates both the pineal gland and the thyroid. 5. During the start of seasonal gonadal activity, which is strongly dependent on thyroid-gonadal interactions, the inhibitory action of the pineal gland on the neuroendocrine thyroid axis, or most probably a direct inhibition of the thyroid by the sympathetic innervation from SCG, might influence the timing of the reproduction cycle. 6. The lack of thyroid-gonadal interaction at the end of the breeding season suggests that the thyroid disturbance caused by ganglionectomy in June does not cause gonadal perturbation at this time.

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.

Seasonal changes in thyroid-gonadal interactions in the edible dormouse, Glis glis.

This study was conducted to determine changes in thyroid-gonadal interaction in the edible dormouse during the phase of the annual cycle that corresponds to the end of the breeding season (from June to September). We evaluated intra-hypothalamic luteinizing hormone-releasing hormone (LHRH) content, and plasma concentrations of luteinizing hormone (LH), testosterone, thyroid-stimulating hormone (TSH) and thyroxine (T4) in three groups of dormice: (1) controls; (2) dormice receiving sufficient T4 supplementation to maintain June levels in control animals until September, thus counteracting the seasonal reduction of T4 that normally begins in July; and (3) thyroidectomized dormice. The effect of thyroidectomy was only detectable in June, when plasma T4 concentration in the control group was maximal, and consisted of a significant decrease in plasma testosterone levels. This provides strong support for the hypothesis that thyroid function positively influences gondal function during the breeding season. The T4 supplementation resulted in a decrease in hypothalamic LHRH concentration, suggesting that an increased LHRH release led to the observed stimulated hypophyseal secretion of LH in June and September and the increased circulating testosterone levels in September. There was no detectable effect in July and August. These results show that thyroid axis activation of the hypothalamic-pituitary-gondal system is only possible during certain phases of the annual cycle, particularly evidenced here during the breeding season. They also reinforce our conclusions drawn from the thyroidectomy results. Conversely, the summer testicular regression which normally occurs after the breeding season is no longer controlled by plasma T4 levels.(ABSTRACT TRUNCATED AT 250 WORDS)

[Involvement of 3-dehydroecdysteroids in the ecdysone biosynthetic pathway in Locusta migratoria, in vitro]. / Implication des 3-déhydroecdystéroïdes dans la voie de biosynthèse de l'ecdysone chez Locusta migratoria, in vitro.

Prothoracic glands of the locus, Locusta migratoria, incubated in vitro converted tritiated 3-dehydrocetodiol (22,23,24,25 3H4-14 alpha-hydroxy-5 beta-cholest-7-en-3,6-dione) into ecdysteroids and 3-dehydroecdysteroids as far as the final products of the two series, ecdysone and 3-dehydroecdysone. In the two series, the different compounds are formed in the same quantities, except for 2,22-desoxy-products, the nature of which could not have been determined. Converted 3-dehydroecdysone issued from 3-dehydrocetodiol is transformed into ecdysone after several hours incubation with Locusta last instar larvae hemolymph. Till now is has been impossible to determine if the reduction of 3-dehydroecdysteroids took place into the prothoracic glands or in the incubation medium. In no case is 3-dehydrocetodiol converted into cetodiol. Conversion rates of the different compounds, either issued from cetodiol or from 3-dehydrocetodiol as precursors, are of same importance, so that a weak specificity of the hydroxylation enzymes must be considered.

A prepro-TRH connecting peptide (prepro-TRH 160-169) potentiates TRH-induced TSH release from rat perifused pituitaries by stimulating dihydropyridine- and omega-conotoxin-sensitive Ca2+ channels.

The stimulation of TSH secretion by TRH involves the phosphatidylinositol second messenger pathway via activation of phospholipase C. This effect is mediated by a GTP-binding protein and leads to a mobilization of intracellular Ca2+ stores and an activation of protein kinase C. However, TRH stimulation also results in an influx of extracellular Ca2+. Since we have previously demonstrated that a non-TRH fragment of the prepro-TRH molecule, the connecting peptide PS4 (prepro-TRH 160-169), was able to potentiate the TRH-induced TSH release in a dose-dependent manner, we attempted to determine whether this potentiation might be due to a Ca(2+)-dependent phenomenon and whether a specific class of voltage-dependent Ca2+ channels, the L type Ca2+ channels, might be involved in the effect of PS4. This was studied by perifusing normal pituitary fragments with medium containing either the Ca2+ ionophore, ionomycin, and Co2+ ions, or organic compounds well known to block L-type Ca2+ channels, and by measuring the TSH response to a pulse of TRH (10 nM) in the presence or absence of PS4 (100 nM).(ABSTRACT TRUNCATED AT 250 WORDS)

Aspects of chronic oral treatment with thyrotropin-releasing hormone: the hypothalamic-pituitary-thyroid axis in rats. A study with a pharmacological dose of thyrotropin-releasing hormone.

The effects of 16 days of oral treatment with thyrotropin-releasing hormone (TRH, 1 mg/24 h) on serum levels of thyrotropin (TSH), thyroxine (T4) and triiodothyronine (T3) and the kinetics of TRH in the blood were studied in normal rats. A second group of animals served as controls. TRH was dissolved by sonification (10 mg/l) and was stable in tap water. TRH was measured by a radioimmunoassay procedure (normal range: 20-80 pmol/l, antiserum K2B9 1:120,000 final dilution). An increase in basal TSH (7,200 +/- 440 ng/l, mean +/- SD) was found after 2 days of treatment (11,420 +/- 810 ng/l), but a significant increase was observed after 5 days of treatment (12,530 +/- 640 ng/l, p less than 0.001). T4 serum concentrations remained in the normal range during the entire period of study, whereas T3 serum concentrations (0.76 +/- 0.1 micrograms/l) were increased to 1.22 +/- 0.2 micrograms/l on day 5 (p less than 0.001). A subsequent decline of TSH, T4 and T3 up to the end of the study was observed. TRHmax concentrations were registered on day 5 (790 +/- 24 pmol/l). The mean value of TRHmax was 723 +/- 34 pmol/l. To improve the stability of TRH in tap water, 1-ml samples of drinking water with dissolved TRH were measured. The mean TRH concentration in drinking water was 73 +/- 1.5% (SD). No significant correlations were found between the area under the curve of TSH (184,340 ng.l-1.24 h) and that of TRH (14,954 pmol.l-1.24 h).(ABSTRACT TRUNCATED AT 250 WORDS)

Involvement of dihydropyridine-sensitive calcium channels in the GABAA potentiation of TRH-induced TSH release.

The effects of gamma-aminobutyric acid (GABA) and isoguvacine on the thyrotropin (TSH) secretion stimulated by thyrotropin releasing hormone (TRH), were investigated in vitro with perifused rat pituitaries. At nanomolar concentrations the two agonists induced potentiation of the TRH-induced TSH release. The potentiation was blocked by SR 95531 a specific GABAA antagonist. The isoguvacine potentiation of the TSH response to TRH failed to occur when cobalt (Co2+) was added to the perifused medium. Nifedipine completely blocked the GABA or isoguvacine potentiation of the TSH response while omega-conotoxin did not modify it. Pre-perifusion of the pituitaries with pertussis toxin did not change the TSH response to TRH but completely inhibited the isoguvacine potentiation of the response. Our results demonstrate that the GABA potentiation of TRH-induced TSH release occurring through the stimulation of GABAA receptor sites is a calcium (Ca2+)-dependent phenomenon, probably mediated by activation of dihydropyridine (DHP)-sensitive, omega-conotoxin-insensitive Ca2+ channels involving a pertussis toxin-sensitive G protein.

[Inhibitory activity of allene cholesteryl derivatives on the biosynthesis of ecdysone]. / Etude de l'activité inhibitrice de dérivés allénques du cholestérol sur la biosynthèse de l'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.