Cortisol and testosterone: Inhibitory agents of the mineralocorticoid pathway. Is there a physiopathological meaning in adrenal tumors?

The authors incubated adrenal mitochondria to study the in vitro action of cortisol and testosterone on the transformation of corticosterone and 18-hydroxycorticosterone into aldosterone. The results show that cortisol at concentrations of 5 × 10⁻⁶ and 10⁻⁴ M inhibit the conversion of corticosterone into aldosterone by 23.6 to 90%; testosterone 5 × 10⁻⁵ and 10⁻⁴ M inhibit the reaction by 78.4 and 87.2%, respectively. The inhibition of the conversion of 18-hydroxycorticosterone into aldosterone is 12.5 to 91% by cortisol with concentrations ranging from 5 × 10⁻⁷ to 5 × 10⁻⁵ M and testosterone 5 × 10⁻⁵ and 10⁻⁴ M inhibits the reaction by 87.3 and 91%, respectively. Aldosterone (10⁻⁸ and 10⁻⁶ M) does not inhibit aldosterone biosynthesis from corticosterone or 18-hydroxycorticosterone. It thus appears that cortisol and testosterone have an effect on the aldosterone biosynthesis pathways in mitochondria. This action may be located at the binding site of the cytochrome P450 11β, which catalyzes all hydroxylation steps in the mineralocorticoid biosynthesis pathway. Because cortisol and testosterone may interfere with aldosterone biosynthesis, and since functional zonation is expected in adrenal carcinomas, the presence of these steroids in substantial amounts could explain the very low plasma aldosterone level usually observed, in adrenal carcinomas studies in our laboratory.     

Glutathione-proline activation of feeding behavior in the zoanthid Palythoa psammophilia Walsh & Bowers

Palythoa psammophilia Walsh & Bowers has a well coordinated, stereotyped feeding response, the culminating step of which is ingestion; this may be elicited by the synergistic effect of the tripeptide glutathione and the -imino acid, proline. Either activator acting separately causes responses only at high concentrations (above 10⁻⁵ M for glutathione; above 10⁻⁴ M for proline) in a reduced number of animals and at a low rate (5.00 ± 1.73 min in 5 × 10⁻³ M solutions of glutathione; 11.10±3.74 min in 5 × 10⁻³ M solutions of proline). Highest percentages of response were obtained in combinations where glutathione was at a concentration of 5 × 10⁻³ M and proline at 5 × 10⁻⁴ M or in combinations of glutathione at concentrations 5 × 10⁻⁶ M and proline at 5 × 10⁻⁵ M. The speed of ingestion is considerably enhanced when these activators are combined (1.17±1.18 min).     

Orexins stimulate corticosterone secretion of rat adrenocortical cells, through the activation of the adenylate cyclase-dependent signaling cascade

Orexins-A and B are two novel hypothalamic peptides, which, like leptin and neuropeptide-Y (NPY), are involved in the central regulation of feeding. Since leptin and NPY were found to modulate adrenal function, we have examined whether orexins are able to directly affect rat adrenal steroid secretion. Both orexin-A and orexin-B raised basal corticosterone secretion of dispersed rat zona fasciculata–reticularis (ZF/R) cells, their maximal effective concentration being 10⁻⁸ M. In contrast, orexins did not affect either maximally ACTH (10⁻⁹ M)-stimulated corticosterone production by ZF/R cells or the basal and agonist-stimulated aldosterone secretion of dispersed zona glomerulosa cells. The ACTH-receptor antagonist corticotropin-inhibiting peptide (10⁻⁶ M) annulled corticosterone response of ZF/R cells to ACTH (10⁻⁹ M), but not to orexins (10⁻⁸ M). Orexins (10⁻⁸ M) enhanced cyclic-AMP release by ZF/R cells, and the selective inhibitor of protein-kinase A (PKA) H-89 (10⁻⁵ M) abolished corticosterone responses to both ACTH (10⁻⁹ M) and orexins (10⁻⁸ M). A subcutaneous injection of both orexins (5 or 10 nmol/kg) evoked a clear-cut increase in the plasma concentration of corticosterone (but not aldosterone), the effect of orexin-A being significantly more intense than that of orexin-B. Collectively, these findings suggest that orexins exert a selective and direct glucocorticoid secretagogue action on the rat adrenals, acting through a receptor-mediated activation of the adenylate cyclase/PKA-dependent signaling pathway.     

The differential regulation of aldosterone output in hamster adrenal by angiotensinII and adrenocorticotropin.

Aldosterone was isolated from hamster adrenal cells and was identified by high performance liquid chromatography and thermospray mass spectroscopy analysis. Basal outputs from adrenal cell suspensions were of the same order of magnitude, 8.4 ± 1.9 ng and 8.0 ± 0.7 ng/2 h/50,000 cells, for aldosterone and corticosteroid, respectively. The outputs of aldosterone and corticosteroid increased with K⁺ concentrations to reach maxima of 3.3- and 1.6-fold at 10 meq/l of K⁺. Angiotensin_II (A_II) produced dose-dependent increases in aldosterone and corticosteroid outputs with maxima of 3- and 4-fold, respectively. In contrast, ACTH induced relatively no changes in aldosterone output, whereas dose-dependent increases in corticosteroid output were found. In time study experiments, with 10⁻⁸ M A_II, aldosterone and corticosteroid outputs were maximally increased after 1 h (6-fold) and 3 h (1.8-fold), respectively. At 10⁻⁸ M, ACTH had a small stimulatory effect on aldosterone output after 6 h, whereas it provoked a gradual increase in corticosteroid output (up to 7-fold after 8 h of incubation). The effects of A_II and ACTH on adrenal cytochrome P-450_11β involved in the last steps of aldosterone formation were evaluated by c combined in vivo andin vitro experiments. The P-450_11β mRNA level was increased by a low sodium intake but not by a 24 h ACTH stimulus. These results taken together indicate that ACTH and A_II differentially regulate P-450_11β. It is postulated that these two regulatory peptides regulate the hamster adrenal steroidogenesis by different P-450 genes.     

Induction of chromosomal aberrations, sister-chromatid exchanges and cell-cycle delay in cow peripheral blood lymphocytes treatment with two N-nitroso compounds in vitro

We investigated the effect of NDMA and DNSGU on the induction of chromosomal aberrations and sister-chromatid exchanges (SCEs), as well as the influence of the former compound on cell-cycle kinetics in cultured cow peripheral lymphocytes. A clastogenic effect was observed in treated cell cultures at 6 or 12 × 10⁻⁵ M concentrations of NDMA and DNSGU, respectively, but no increase of chromosomal breaks was seen at the lowest dose. NDMA at 6 × 10⁻⁴ M was toxic to cow lymphocytes. NDMA and DNSGU induced statistical increases of SCEs at the test doses (6 or 12 × 10⁻⁶ and 6 or 12 × 10⁻⁵ M, respectively). In addition, treatment with NDMA at a dose of 6 × 10⁻⁵ M revealed significant heterogeneity of the first, second and third metaphases between treated and untreated groups. A reduction of the proliferation index and proliferation delay per cycle was shown too.     

Lack of comutagenicity by norharman and other compounds on revertants induced by photolabeling with 2-azido-9-fluorenone oxime

Mutations were induced by photolabeling 2-azido-9-fluorenone oxime in Salmonella typhimurium tester strain TA1538. Since the critical adducts were formed directly by the photogenerated nitrene, metabolic activation was bypassed. The bacteria themselves possessed the deep rough cell wall and uvrB⁻ mutations, thereby minimizing comutagenic effects resulting from transport or DNA repair. This technique thus permitted detection of comutagenicity resulting from altneration in the binding of the mutagen to its critical receptor. No compound tested increased mutagenicity. Cholic acid had no effect at low dose, but inhibited mutagenicity at 10⁻⁴ M, while trans-retinol had no effect at any concentration. Harman, norharman and ethidium reduced the number of mutants only slightly at concentrations from 10⁻⁶ to 10⁻⁵ M.     

Effects of peptide YY and its analogues on chloride ion secretion in fed and fasted rat jejunum

The aim of our study was to determine whether a meal modifies the antisecretory response induced by PYY and the structural requirements to elicit antisecretory effects of analogue PYY(22–36) for potential antidiarrhea therapy. The variations in short-circuit current (Isc) due to the modification of ionic transport across the rat intestine were assessed in vitro, using Ussing chambers. In fasted rats, PYY induced a dose- and time-dependent reduction in Isc, with a sensitivity threshold at 5 × 10⁻¹¹ M (ΔIsc −2 ± 0.5 μA/cm²). The reduction was maximal at 10⁻⁷ M (Isc −23 ± 2 μA/cm²), and the concentration producing half-maximal inhibition was 10⁻⁹ M. At 10⁻⁷ M, reduction of Isc by PYY reached 90% of response to 5 × 10⁻⁵ M bumetanide. The PYY effect was partly reversed by 10⁻⁵ M forskolin (Isc +13.43 ± 2.91 μA/h·cm², p < 0.05) or 10⁻³ M dibutyryl adenosine 3′,5′ cyclic monophosphate (Isc +12 ± 1.69 μA/cm², p < 0.05). Naloxone and tetrodotoxin did not alter the effect of PYY. In addition, PYY and its analogue P915 reduced net chloride ion secretion to 2.85 and 2.29 μEq/cm² (p < 0.05), respectively. The antisecretory effect of PYY was accompanied by dose- and time-dependent desensitization when jejunum was prestimulated by a lower dose of peptide. The antisecretory potencies exhibited by PYY analogues required both a C-terminal fragment (22–36) and an aromatic amino acid residue (Trp or Phe) at position 27. At 10⁻⁷ M the biological activity of PYY was lower in fed than fasted rats (p < 0.001). Our results confirm the antisecretory effect of PYY, but show that the fed period is accompanied by desensitization, similar to the transient desensitization observed in the fasted period with cumulative doses. This suggests that PYY may act as a physiological mediator that reduces intestinal secretion.     

Bradykinin counteracts the stimulatory effect of angiotensin-(1-7) on the proximal tubule Na+ -ATPase activity through B2 receptor

Recently, we demonstrated that angiotensin-(1–7) (Ang-(1–7)) stimulates the Na⁺-ATPase activity through a losartan-sensitive angiotensin receptor, whereas bradykinin inhibits the enzyme activity through the B₂ receptor [Regul. Pept. 91 (2000) 45; Pharmacol. Rev. 32 (1980) 1]. In the present paper, the effect of bradykinin (BK) on Ang-(1–7)-stimulated Na⁺-ATPase activity was evaluated. Preincubation of Na⁺-ATPase with 10⁻⁹ M Ang-(1–7) increases enzyme activity from 7.9±0.9 to 14.1±1.5 nmol Pi mg⁻¹ min⁻¹, corresponding to an increase of 79% (p<0.05). This effect is reverted by bradykinin in a dose-dependent manner (10⁻¹⁴–10⁻⁸ M), reaching maximal inhibitory effect at 10⁻⁹ M. Des-Arg⁹ bradykinin (DABK), an agonist of B₁ receptor, at the concentrations of 10⁻⁹–10⁻⁷ M, does not mimic the BK inhibitory effect, and des-Arg⁹-[Leu⁸]-BK (DALBK), a B₁ receptor antagonist, at the concentrations of 10⁻¹⁰–10⁻⁷ M, does not prevent the inhibitory effect of BK on Ang-(1–7)-stimulated enzyme. On the other hand, HOE 140, an antagonist of B₂ receptor, abolishes the inhibitory effect of BK on the Ang-(1–7)-stimulated enzyme in a dose-dependent manner, reaching maximal effect at 10⁻⁷ M. Taken together, these data indicate that stimulation of B₂ receptors by BK can counteract the stimulatory effect of Ang-(1–7) on the proximal tubule Na⁺-ATPase activity.     

Highly potent and specific inhibitors of human renin

We have designed and synthesized a series of small peptides containing a perfluoroalkyl ketone group at the C-terminal position of the angiotensin I sequence as inhibitors of human renin. From this series of compounds, 8 and 10 showed strong inhibition of human renin (IC₅₀ = 3 × 10⁻⁹, 7 × 10⁻⁹ M, respectively). Compound 10 did not inhibit pepsin and cathepsin D at 10⁻⁴ M. Comparison of the IC₅₀ of compound 8 and compound 11 (8.7 × 10⁻⁷ M) demonstrated the marked effect of the perfluoropropyl group on the potency of inhibition on renin, presumably due to the strong electron-withdrawing effect causing the ketone in 8 to exist predominantly as the hydrate — thus mimicking the tetrahedral transition state during hydrolysis of the scissile Leu¹⁰—Val¹¹ amide bond.     

The development of an amperometric microbial biosensor using Acetobacter pasteurianus for lactic acid

A microbial biosensor, using Acetobacter pasteurianus cells and an oxygen electrode, was developed for the determination of lactic acid. The bacterial cells were retained on a nylon membrane and attached to the surface of the oxygen electrode. In view of response time, stability and sensitivity, the biosensor performed best at 26°C and in pH 6 phthalate buffer containing magnesium sulfate. The activity of the retained cells was stable for approximately 170 h and was regenerable. The biosensor exhibited a hyperbolic response to both D- and L-lactic acid in the range of 10⁻⁴ M to 25 × 10⁻³ M. However, in the range 10⁻⁴ M to 15 × 10⁻⁴ M the response was linear. The microbial biosensor was applicable for detecting lactate concentration in yogurt and milk, since it was not sensitive to lactose, sucrose and glucose — three major components of such dairy products.     

Stimulatory effect of vasoactive intestinal peptide (VIP) on the secretory activity of dispersed rat adrenocortical cells. Evidence for the interaction of VIP with ACTH receptors

VIP dose-dependently increased basal, but not submaximally ACTH (10⁻¹⁰ M)-stimulated, aldosterone (ALDO) and corticosterone (B) secretion of dispersed rat capsular and inner adrenocortical cells, respectively. The maximal stimulatory effect (60–70% rise) was obtained with a VIP concentration of 10⁻⁸ M. [4-Cl-D-Phe⁶,Leu¹⁷]-VIP, a VIP-receptor antagonist (VIP-A), and corticotropin inhibiting peptide (CIP), an ACTH receptor antagonist (both 10⁻⁶ M), completely annulled VIP (10⁻⁸M)-evoked rises in basal ALDO and corticosterone secretions. The ACTH (10⁻¹⁰ M)-enhanced (about 5-fold) production of both hormones was completely reversed by CIP (10⁻⁶ M) and only partially reduced (about −30%) by VIP-A (10⁻⁶ M). The hypothesis is advanced that the weak secretagogue effect of VIP on dispersed rat capsular and inner adrenocortical cells may be due to its positive interaction with ACTH receptors.     

Is an endothelin a neurotoxic factor in the brain?

A possible role for endothelin in the pathogenesis of hypoglycemic brain damage in rats was evaluated using an in vitro model with which we could directly monitor the release of dopamine from striatal slices. There was no evidence of impairment in case of non-exposure of the slices to endothelin-3 during 20–40 min of hypoglycemia. The response all but disappeared in striatal slices stimulated twice with 10⁻⁵ M endothelin-3 during 20 min of hypoglycemia. Hypoglycemic damage triggered by endothelin-3 was not observed in the absence of extracellular Ca²⁺. Nifedipine (10⁻⁶ M), but not verapamil (10⁻⁵ M) nor diltiazem (10⁻⁵M), protected striatal tissue from this damage. Our findings provide evidence that endothelins might be etiological factors in the development of hypoglycemic/ischemic brain injury by stimulating dihydropyridine-regulated Ca²⁺ influx.     

Synthetic peptide analogs to barnacle settlement pheromone

Barnacle pheromone enhances the rate of settlement and metamorphosis of larvae of Balanus amphitrite Darwin. Analogs to the heterogeneous pheromone peptides were sought. Settlement assays were used to assess both the pheromone and the potential analogs. The pheromone has a lower threshold of activity at a concentration of 0.2 μg BSA protein equivalence l⁻¹. Treatment with carboxypeptidase eliminates biological activity. Series of dipeptides were tested to determine if dipeptides could promote settlement. Combinations of acidic, neutral, and basic amino acids in dipeptides were examined. Specific small peptides can mimic barnacle pheromone. Only peptides with a basic carboxy-terminal amino acid and either a neutral or a basic amino-terminal amino acid enhance settlement. Six peptides were shown to mimic pheromone activity at concentrations comparable to the native molecule. Some peptides were more potent than others. The most effective peptides were L-leucyl-L-arginine and L-histidyl-L-lysine which had a lower threshold of settlement enhancement of 2.0×10⁻¹⁰ M and caused a 130% increase in settlement rate at 2.0×10⁻⁸ M. Glycyl-glycyl-L-arginine, glycyl-L-histidyl-L-lysine, L-leucyl-glycyl-L-arginine and L-tyrosyl-L-arginine had thresholds between 2.0×10⁻⁸ M and 2.0×10⁻⁹ M. Peptide pheromone analogs should be useful in determining the nature and mechanism of barnacle pheromone receptor interactions.     

Bradykinin dilates rat middle cerebral artery and its large branches via endothelial B2 receptors and release of nitric oxide

Ring segments of rat middle cerebral artery (MCA) were prepared for measurement of isometric force and precontracted with 10⁻⁴ M uridine triphosphate (UTP). Concentration-effect curves (CEC) were constructed for bradykinin (BK, 10⁻⁸–10⁻⁵ M) in segments with functionally intect (E+) or denuded (E−) endothelium. E− segments did not dilate to BK. The BK receptor was characterized by application of specific B₁ or B₂ antagonists [des-Arg⁹-Leu⁸] BK (10⁻⁵ M) and [ -Arg⁰-Hyp³-Thi⁵- -Tic⁷-Oic⁸] BK (HOE140,3 × 10⁻⁷ M), respectively, or B₁ agonist [des-Arg⁹] BK (10⁻⁸–10⁻⁴ M). Involvement of nitric oxide (NO) was tested with N^G-nitro- -arginine (LNNA, 10⁻⁴ M). BK induced concentration-dependent relaxation with a maximal effect (E_max) of 40.86 ± 1.50% at 10⁻⁶ M and a pD₂ (−log₁₀ EC₅₀) of 6.818 ± 0.044. This relaxation could be prevented with HOE140 or LNNA, but was not influenced by [des-Arg⁹-Leu⁸] BK. [des-Arg⁹] BK did not induce any effect. These results demonstrate that BK induced relaxation via endothelial B₂ receptors and release of NO in isolated rat MCA.     

Nitric oxide stimulates prostaglandin synthesis in cultured rabbit gastric cells

Both prostaglandins (PGs) and nitric oxide (NO) have cytoprotective and hyperemic effects in the stomach. However, the effect of NO on PG synthesis in gastric mucosal cells is unclear. We examined whether sodium nitroprusside (SNP), a releaser of NO, stimulates PG synthesis in cultured rabbit gastric mucus-producing cells. These cells did not release NO themselves. Co-incubation with SNP (2 × 10⁻⁴, 5 × 10⁻⁴, 10⁻³ M) increased PGE₂ synthesis, and SNP (10⁻³ M) increased PGI₂ synthesis in these cells. Hemoglobin, a scavenger of NO, (10⁻⁵ M) eliminated the increase in PGE₂ synthesis by SNP, but methylene blue, an inhibitor of soluble guanylate cyclase, (5 × 10⁻⁵ M) did not affect the increase in PGE₂ synthesis by SNP. 8-bromo guanosine 3′ : 5′-cyclic monophosphate (8-bromo cGMP), a cGMP analogue, (10⁻⁶, 10⁻⁵, 10⁻⁴, 10⁻³ M) did not affect PGE₂ synthesis. These findings suggest that NO increased PGE₂ and PGI₂ synthesis via a cGMP-independent pathway in cultured rabbit gastric cells.     

Effect of ascorbic acid, sodium citrate, sodium bicarbonate, and their combination effect on the binding of Fe and Fe to plasma membrane of lactating mouse mammary gland

Isolated plasma membranes of lactating mouse mammary gland were treated with different concentrations of ascorbate, sodium citrate, sodium bicarbonate, combinations of them (from 16 x 10⁻¹⁰ to 4 x 10⁻⁶ moles/L) and studied for the binding of ⁵⁹Fe²⁺ and ⁵⁹Fe³⁺ at pH 7.4. The results show that the Fe³⁺ form of iron is under a greater influence of anions used in these experiments. The Fe²⁺ form of iron is weakly bounded and affected. It is suggested that the form with a greater positive electric charge is more effectively bound to the receptors in plasma membranes.     

Redox potentials of the pyridine-haem c system

1. Haem c was synthesized and purified. It was shown unequivocally that the method gives a product with the cysteine residues on the -carbon atoms at the 2 and 4 positions of the haem.

2. Redox potentials of haem c in the presence of 2.5 M pyridine were determined in the pH range 1.5–13; it was found necessary to add cetyl trimethyl ammonium bromide (CTAB) to prevent precipitation in the acid range below about pH 4. The E_m vs pH curve shows three slopes (−dE/dpH) of value, 0.18, 0.01 and 0.06 with points of inflexion at pH 3.8 and 10.6. The potentials are intermediate between those of protohaem and mesohaem obtained under similar conditions.

3. With constant haem c concentration (a) 10⁻⁴ M and (b) 10⁻⁵ M and varying pyridine concentration (0.12–5 M) it was found at pH 9.0 that E_m values increased as the pyridine concentration was increased and there was a tendency to reach a plateau value. The explanation appears to be that pyridine binds more firmly to ferroporphyrin c than to ferriporhyrin c.

4. When the pyridine concentration was kept constant (2.5 M) and the haem c concentration was varied in the range 7 · 10⁻⁴–7 · 10⁻⁶ M, it was found that a decrease in haem c concentration brought about an increase in redox potential. The results are explained as being due to dimerization of the oxidized form.

5. The results are discussed in comparison with a number of related haem systems.     

Biphasic regulation by N, 2′-O-dibutyryl adenosine 3′, 5′-cyclic monophosphate (dbcAMP) of steroid 21-hydroxylase activity in rat hepatocytes

Steroid 21-hydroxylase activity has been identified in many tissues, including liver. But it is possible that the enzyme found in the liver is different from adrenal 21-hydroxylase. In the adrenal cortex, steroid 21-hydroxylase activity is increased by corticotropin (ACTH); the effect of ACTH is mediated by cyclic AMP (cAMP), and presumably involves a cAMP-dependent protein kinase (PKA). It is not yet clear, however, how extra-adrenal steroid 21-hydroxylase activity is regulated. In the present study, we examined the effect of N⁶, 2′-O-dibutyryl adenosine 3′,5′-cyclic monophosphate (dbcAMP), forskolin, N-[2-(methylamino)ethyl]5-isoquinolinesulfonamide (H-8) and 12-O-tetradecanoylphorbol-13-acetate (TPA) on steroid 21-hydroxylase activity in primary cultures of rat hepatocytes to determine the nature of regulation of extra-adrenal steroid 21-hydroxylase activity. Steroid 21-hydroxylase activity in hepatocytes incubated with 10⁻¹¹M dbcAMP for 24 h was 1.6 times higher than that in control hepatocytes untreated with dbcAMP. On the other hand, steroid 21-hydroxylase activity decreased by 20 and 50% when the cells were incubated with 10⁻⁵ and 10⁻³ M dbcAMP, respectively. The stimulatory effect of 10⁻¹¹ M dbcAMP was not blocked by 10⁻⁵ M H-8 (PKA inhibitor), but the inhibitory effect of 10⁻⁵ or 10⁻³ M cAMP was. TPA did not alter the activity of steroid 21-hydroxylase. These findings indicate that the steroid 21-hydroxylase in rat liver is regulated by mechanisms different from those in the adrenal glands.     

Vasopressin and oxytocin modulation of melatonin secretion from rat pineal glands

The rat pineal gland is known to release melatonin in response to noradrenergic stimulation. Since vasopressin (VP)- and oxytocin (OT)-containing fibers innervate the pineal gland, the effects of VP and OT on melatonin release from perifused rat pineal glands were investigated. VP (10⁻⁷ M) and OT (10⁻⁶ M) decreased the basal melatonin secretion. No dose-dependent effect was observed. At high concentrations (10⁻⁵) these peptides potentiated the isoproterenol-induced increase of melatonin secretion. Below 10⁻⁵ M no potentiation was observed. Fragments of VP {[pGlu⁴,Cys⁶]VP(4–9)} and OT {[pGlu⁴,Cys⁶]OT(4–9)} did not display any effect on the isoproterenol-induced melatonin secretion.     

Inhibition of antennal esterases of the egyptian armyworm Spodoptera littoralis by trifluoromethyl ketones

A series of aliphatic and aromatic trifluoromethyl ketones has been tested as inhibitors of the antennal esterases of the Egyptian armyworm Spodoptera littoralis, by evaluation of the extent of hydrolysis of [1-³H]-(Z,E)-9, 11-tetradecadienyl acetate (1), a tritiated analog of the major component of the sex pheromone. The most active compounds with a long chain aliphatic structure were 3-octylthio-1,1,1-trifluoropropan-2-one (2) (IC₅₀ 0.55 μM) and 1,1,1-trifluorotetradecan-2-one (4) (IC₅₀ 1.16 μM). The aromatic compounds were generally less potent inhbitors than the coressponding aromatic ones, although β-naphthyltrifuloromethyl ketone (10) exhibited a remarkable inhibitory activity (IC₅₀ 7.9 μM). Compounds 2, 4 and 10 exhibit a competitive inhibition with K_i values of 2.51×10⁻⁵ M, 2.98×10⁻⁵ M and 2.49×10⁻⁴ M, respectively. Some of the trifluoromethyl ketones tested were slow-binding inhibitors and compounds 2 and 10 are described as inhibitors of the antennal esterases of a moth for the first time.