Intestinal l-methionine transport in the cultured gilthead bream (Sparus aurata)

• 1.1. The influx and transepithelial movements of l-methionine and its effects on the electrophysiology and Na-Cl-transport in upper and lower intestine of the cultured fish, Spanis aurata, were measured.
• 2.2. The K_m and V_max of l-methionine influx into the tissues were higher in lower intestine than in upper intestine. A prominent diffusion-like transport component was also measured in both segments during influx experiments.
• 3.3. Net transepithelial fluxes of l-methionine (1 mM) were observed in both upper and lower intestine, this transport being Na⁺-dependent.
• 4.4. The two intestinal segments exhibited an electrical potential difference (PD) and a short circuit current (I_sc) serosa negative or near zero. Tissue conductance (G_t) was higher in posterior than in lower intestine.
• 5.5. Addition of l-methionine to the mucosal side of lower or upper intestine did not induce changes in PD in either part.
• 6.6. Isotopic fluxes of Cl⁻ or Na⁺ measurements under short circuit conditions showed that there were no net Cl⁻ or Na⁺ transport in either part.
• 7.7. l-Methionine additions to the mucosa did not induce changes in unidirectional fluxes of Cl⁻ or Na⁺ or in the (I_sc) in either the anterior or posterior intestine.

     

Evaluation of role of the peptide transport system in absorption of dipeptides in the rat small intestine in chronic experiments <Emphasis Type="Italic">in vivo</Emphasis>

Hydrolysis and absorption of glycylglycine and glycyl-L-leucine as well as absorption of glycine and leucine were studied in chronic experiments on rats with their isolated small intestine loop. Values of the “true” kinetic constants (with taking into account effect of the preepithelial layer) were determined to be as follows: (1) K _t = 46.7 ± 4.0 and 2.15 ± 0.59 mM, J _max = 0.74 ± 0.15 and 0.16 ± 0.03 μmol min^?1 cm^?1 (for transport of free glycine and leucine, respectively); (2) K _t = 4.4 ± 0.6 and 4.8 ± 0.9 mM, J _max = 0.24 ± 0.02 and 0.23 ± 0.02 μmol min^?1 cm^?1 (for transport of glycylglycine and glycyl-L-leucine, respectively); (3) K _M = 5.4 ± 1.0 and 38.2 ± 4.4 mM, V _max = 0.09 ± 0.02 and 0.24 ± 0.07 μmol min^?1 cm^?1 (for membrane hydrolysis of these dipeptides, respectively). According to our calculations, in the wide range of the initial glycylglycine concentrations (2.5–40 mM) a part of the peptide component in its total absorption accounts for 0.77–0.80. In the case of glycyl-L-leucine a part of the peptide component in the total glycine absorption decreases from 0.89 to 0.84, while in the total leucine absorption—from 0.86 to 0.71, the initial dipeptide concentration rising from 5 to 40 mM. The obtained results show that the peptide component prevails in absorption of the studied dipeptides in the rat small intestine, but its role is much lesser than what many authors believe. In the case of glycyl-L-leucine, the peptide component can achieve saturation in the range of high substrate concentrations, its part decreasing essentially to become compared with absorption of free amino acids formed as a result of the dipeptide membrane hydrolysis.     

LC–MS/MS-based metabolome analysis detected changes in the metabolic profiles of small and large intestinal adenomatous polyps in <Emphasis Type="Italic">Apc</Emphasis><Superscript><Emphasis Type="Italic">Min</Emphasis>/+</Superscript> mice

Introduction

The adenomatous polyposis coli (APC) gene is a tumor suppressor gene that is inactivated in the initiation of colorectal neoplasia. Apc ^Min/+ mice, which possess a heterozygous APC mutation, develop numerous adenomatous polyps, which are similar to those observed in familial adenomatous polyposis (FAP) in humans. However, unlike FAP patients, Apc ^Min/+ mice predominantly develop adenomatous polyps in the small intestine. The metabolic changes associated with the development of polyps in the small and large intestine remain to be investigated.

Objectives

The objective of this study was to elucidate the metabolic changes associated with intestinal polyp formation.

Methods

We compared the metabolite levels of pairs of polyp and non-polyp tissues obtained from the small intestines (n = 12) or large intestines (n = 7) of Apc ^Min/+ mice. To do this, we analyzed the tissue samples using two methods, liquid chromatography-tandem mass spectrometry (1) with a pentafluorophenylpropyl column for cation analysis, and (2) with a C18 reversed phase column coupled to an ion-pair reagent for anion analysis.

Results

Pathway mapping of the metabolites whose levels were significantly altered revealed that the polyp tissue of the small intestine contained significantly higher levels of intermediates involved in glycolysis, the pentose phosphate pathway, nucleotide metabolism, or glutathione biosynthesis than in the equivalent non-polyp tissue. In addition, significantly higher levels of methionine cycle intermediates were detected in the polyp tissues of both the large and small intestines. Organ-dependent (small vs. large intestine) differences were also detected in the levels of most amino acids and urea cycle intermediates.

Conclusion

Our results indicate that various metabolic changes are associated with polyp development, and understanding these alterations could make it possible to evaluate the treatment response of colorectal cancer earlier.

     

Increased intracellular calcium level and impaired nutrient absorption are important pathogenicity traits in the chicken intestinal epithelium during <Emphasis Type="Italic">Campylobacter jejuni</Emphasis> colonization

Although a high number of chickens carry Campylobacter jejuni, the mechanistic action of colonization in the intestine is still poorly understood. The current study was therefore designed to investigate the effects of C. jejuni on glucose uptake, amino acids availability in digesta, and intracellular calcium [Ca²⁺]_i signaling in the intestines of broiler chickens. For this, we compared: control birds (n?=?60) and C. jejuni-infected birds (n?=?60; infected orally with 1?×?10⁸ CFU of C. jejuni NCTC 12744 at 14 days of age). Our results showed that glucose uptake was reduced due to C. jejuni infection in isolated jejunal, but not in cecal mucosa at 14 days postinfection (dpi). The decrease in intestinal glucose absorption coincided with a decrease in body weight gain during the 2-week post-infectious period. A reduction in the amount of the amino acids (serine, proline, valine, leucine, phenylalanine, arginine, histidine, and lysine) in ileal digesta of the infected birds at 2 and/or 7 dpi was found, indicating that Campylobacter utilizes amino acids as a carbon source for their multiplication. Applying the cell-permeable Ca²⁺ indicator Fluo-4 and two-photon microscopy, we revealed that [Ca²⁺]_i was increased in the jejunal and cecal mucosa of infected birds. The muscarinic agonist carbachol induced an increase in [Ca²⁺]_i in jejunum and cecum mucosa of control chickens, a response absent in the mucosa of infected chickens, demonstrating that the modulation of [Ca²⁺]_i by Campylobacter might be involved in facilitating the necessary cytoskeletal rearrangements that occur during the bacterial invasion of epithelial cells. In conclusion, this study demonstrates the multifaceted interactions of C. jejuni with the gastrointestinal mucosa of broiler chickens. For the first time, it could be shown that a Campylobacter infection could interfere with intracellular Ca²⁺ signaling and nutrient absorption in the small intestine with consequences on intestinal function, performance, and Campylobacter colonization. Altogether, these findings indicate that Campylobacter is not entirely a commensal and can be recognized as an important factor contributing to an impaired chicken gut health.     

α-Glucosidase Inhibitor from the Seeds of Balsam Pear (Momordica charantia) and the Fruit Bodies of Grifola frondosa

α-Glucosidase inhibitory activities were found in aqueous methanol extracts of the seeds of Momordica charantia and the fruit bodies of Grifola frondosa. An active principle against the enzyme prepared from rat small intestine acetone powders was isolated and characterized. The structure of the isolated compound was identified as D-(+)-trehalose by FDMS, ¹H-, ¹³C-NMR, and [α]_D measurements. The inhibitory activity of trehalose was compared with 1-deoxynojirimycin. Trehalose showed 45% inhibitory activity at the concentration of 2×10^?3 M, but 1-deoxynojirimycin had 52% inhibitory activity at 1×10^?7 M.     

Nacl flux in the flounder (Pseudopleuronectes americanus) intestine: Effects of ph and transport inhibitors

• 1.1. The effects of extracellular pH on Na⁺ and Cl⁻ absorption were studied in vitro in the small intestine of the winter flounder, Pseudopleuronectes americanus.
• 2.2. Reductions in bathing solution pH inhibited J_ms^na (mucosal-to-serosal flux) and J_net^na (net flux) (r = 0.90) and J_net^Cl (r = 0.92) [due to an increase in J_sm^Cl, (serosal-to-mucosal)] and decreased short circuit current (Isc).
• 3.3. Luminal bumetanide (0.1 mM) and amiloride (1 mM) inhibited Na⁺ and Cl⁻ absorption by reducing J_ms.
• 4.4. Luminal barium (5mM) and luminal copper (100 μM) decreased J_ms^Cl and increased J_sm^Cl.
• 5.5. We conclude that reductions in extracellular pH inhibit a luminal membrane NaCl absorptive process (Na⁺-K⁺-2Cl⁻) and stimulate an electrogenic Cl⁻ secretory process.

     

The biliary excretion of circulating asialoglycoproteins in the rat.

Following intravenous injection into the rat a small proportion (0.5 – 3.0%) of asialo α₁-acid glycoprotein, asialo fetuin, asialo CEA¹ and native CEA are excreted in an apparently unchanged form in the bile. The maximum excretion rate occurs one hour after injection in all cases. The possibility of a novel pathway for glycoprotein uptake by the liver is discussed.     

NHERF3 (PDZK1) Contributes to Basal and Calcium Inhibition of NHE3 Activity in Caco-2BBe Cells

Elevated intracellular Ca²⁺ ([Ca²⁺]_i) inhibition of NHE3 is reconstituted by NHERF2, but not NHERF1, by a mechanism involving the formation of multiprotein signaling complexes. To further evaluate the specificity of the NHERF family in calcium regulation of NHE3 activity, the current study determined whether NHERF3 reconstitutes elevated [Ca²⁺]_i regulation of NHE3. In vitro, NHERF3 bound the NHE3 C terminus between amino acids 588 and 667. In vivo, NHE3 and NHERF3 associate under basal conditions as indicated by co-immunoprecipitation, confocal microscopy, and fluorescence resonance energy transfer. Treatment of PS120/NHE3/NHERF3 cells, but not PS120/NHE3 cells, with the Ca²⁺ ionophore, 4-bromo-{"type":"entrez-nucleotide","attrs":{"text":"A23187","term_id":"833253","term_text":"A23187"}}A23187 (0.5 μm): 1) inhibited NHE3 V_max activity; 2) decreased NHE3 surface amount; 3) dissociated NHE3 and NHERF3 at the plasma membrane by confocal immunofluorescence and fluorescence resonance energy transfer. Similarly, in Caco-2BBe cells, NHERF3 and NHE3 colocalized in the BB under basal conditions but after elevation of [Ca²⁺]_i by carbachol, this overlap was abolished. NHERF3 short hairpin RNA knockdown (>50%) in Caco-2BBe cells significantly reduced basal NHE3 activity by decreasing BB NHE3 amount. Also, carbachol-mediated inhibition of NHE3 activity was abolished in Caco-2BBe cells in which NHERF3 protein expression was significantly reduced. In summary: 1) NHERF3 colocalizes and directly binds NHE3 at the plasma membrane under basal conditions; 2) NHERF3 reconstitutes [Ca²⁺]_i inhibition of NHE3 activity and dissociates from NHE3 in fibroblasts and polarized intestinal epithelial cells with elevated [Ca²⁺]_i; 3) NHERF3 short hairpin RNA significantly reduced NHE3 basal activity and brush border expression in Caco-2BBe cells. These results demonstrate that NHERF3 reconstitutes calcium inhibition of NHE3 activity by anchoring NHE3 basally and releasing it with elevated Ca²⁺.In normal digestive physiology, the brush border (BB)² Na⁺/H⁺ exchanger, NHE3, mediates the majority of the NaCl and NaHCO₃ absorption in the ileum (1). Sequential inhibition and stimulation of NHE3 occur as part of digestive physiology. Short-term regulation of NHE3 activity is achieved through a variety of factors that affect NHE3 turnover number and/or surface expression and often involve a role for the cytoskeleton and accessory proteins, including the multi-PDZ domain containing proteins, NHERF1 and NHERF2 (1, 2). However, many details of this regulation are not understood.The NHERF (Na⁺/H⁺ exchanger regulatory factor) family of multi-PDZ domain containing proteins consists of four evolutionarily related members, all of which are expressed in epithelial cells of the mammalian small intestine (2). NHERF1 and NHERF2 have been previously shown to contribute to acute NHE3 stimulation and inhibition (3–10). Recently, two additional PDZ domain containing proteins, termed NHERF3/PDZK1 and NHERF4/PDZK2/IKEPP, have been demonstrated to possess sequence homology with NHERF1 and NHERF2 (11–14). However, unlike NHERF1 and NHERF2, which are comprised of two tandem PDZ domains flanked by a C-terminal ezrin/radixin/moesin binding domain, NHERF3 and NHERF4 consist of four PDZ domains but no other protein-protein interacting domains (12).NHERF3 was initially identified by a yeast two-hybrid screen from a human kidney cDNA library using the membrane-associated protein MAP17, as bait (12). NHERF3 is expressed in the brush border of epithelial cells of the kidney proximal tubule and the small intestine (12). NHERF3 associates with and, in a few cases, has been shown to regulate the activity of multiple apical membrane ion transporters including the cystic fibrosis transmembrane regulator (CFTR), urate anion exchanger 1 (URAT1), sodium-phosphate cotransporter type IIa (NaP_iIIa), proton-coupled peptide transporter (PEPT2), and organic cation/carnitine cotransporter (OCTN2) (15–19). Furthermore, NHERF3 directly binds the C terminus of NHE3 (20). Recent studies have begun evaluating the effect of NHERF3 on mouse intestinal Na⁺ and Cl⁻ transport. Basal electroneutral sodium absorption was decreased by >40% in the NHERF3 null mouse jejunum (21) and by >80% in the colon (22). In addition, Cinar et al. (22) demonstrated that cAMP and [Ca²⁺]_i inhibition of NHE3 activity was abolished in the NHERF3 null mouse colon. However, the mechanism by which NHERF3 regulates NHE3 activity was not resolved.Several physiological and pathophysiological agonists, acting through [Ca²⁺]_i-induced second messenger systems, are known to inhibit electroneutral NaCl absorption in the small intestine (1, 23). Elevation of [Ca²⁺]_i has previously been demonstrated to inhibit NHE3 activity in a NHERF2-, but not NHERF1-dependent manner (5). NHERF2 regulation of NHE3 involves the formation of multiprotein complexes at the plasma membrane that include NHE3, NHERF2, α-actinin-4, and PKCα, which induce endocytic removal of NHE3 from the plasma membrane by a PKC-dependent mechanism (5, 24). Because multiple PDZ proteins exist in the apical pole of epithelial cells (2), the current study was designed to determine whether NHERF3 could reconstitute Ca²⁺ regulation of NHE3 activity and to define how that occurred.     

Decreased autophagy: a major factor for cardiomyocyte death induced by β1-adrenoceptor autoantibodies

Cardiomyocyte death is one major factor in the development of heart dysfunction, thus, understanding its mechanism may help with the prevention and treatment of this disease. Previously, we reported that anti-β₁-adrenergic receptor autoantibodies (β₁-AABs) decreased myocardial autophagy, but the role of these in cardiac function and cardiomyocyte death is unclear. We report that rapamycin, an mTOR inhibitor, restored cardiac function in a passively β₁-AAB-immunized rat model with decreased cardiac function and myocardial autophagic flux. Next, after upregulating or inhibiting autophagy with Beclin-1 overexpression/rapamycin or RNA interference (RNAi)-mediated expression of Beclin-1/3-methyladenine, β₁-AAB-induced autophagy was an initial protective stress response before apoptosis. Then, decreased autophagy contributed to cardiomyocyte death followed by decreases in cardiac function. In conclusion, proper regulation of autophagy may be important for treating patients with β₁-AAB-positive heart dysfunction.Heart dysfunction is the terminal stage of various cardiovascular diseases, and it is characterized by a complicated etiology and high mortality. Recent studies indicate that cardiomyocyte death was a leading contributor to the development of heart dysfunction.¹ Because systolic and diastolic function is directly affected by myocardial cell loss, understanding how cardiomyocyte death occurs will inform treatment strategies to prevent or treat heart dysfunction.Since the 1990s, studies have revealed that diverse cardiovascular diseases are correlated to anti-β₁-adrenergic receptor autoantibodies (β₁-AABs).^{2, 3} We reported that β₁-AABs were induced by myocardial remodeling in heart dysfunction,⁴ and that its long-term presence significantly decreased cardiac function in vivo.⁵ β₁-AABs also caused cell death of cultured adult rat ventricular myocytes and this was attributed to apoptosis.⁶ Recently, work from our laboratory⁷ and others⁸ indicated that β₁-AABs induced myocardial apoptosis. However, β₁-AAB-induced cardiomyocyte death was not completely reversed with the caspase inhibitor Z-VAD-fmk,⁶ indicating that other factors were involved in β₁-AAB-induced cardiomyocyte death.Presently, we observed that β₁-AABs decrease myocardial autophagy that maintains cellular homeostasis.⁹ Deficiencies in autophagy allow the accumulation of damaged, denatured or aging proteins¹⁰ and organelles,¹¹ and this will cause cell death. To date, the role of β₁-AAB-induced changes in autophagy as related to cardiac function and cardiomyocyte death is unclear. Therefore, we characterized β₁-AAB-induced changes in myocardial autophagy and identified a role for this in cardiac function and cardiomyocyte death. Our data will inform future studies of β₁-AAB-positive heart dysfunction and suggest a treatment window for autophagy regulation.     

Theoretical investigation on exciton-dissociation and charge-recombination processes of PC<Subscript>61</Subscript>BM-PTDPPSe interface

Designing and synthesizing novel electron-donor polymers with the high photovoltaic performances has remained a major challenge and hot issue in organic electronics. In this work, the exciton-dissociation (k _dis ) and charge-recombination (k _rec ) rates for the PC₆₁BM-PTDPPSe system as a promising polymer-based solar cell candidate have been theoretically investigated by means of density functional theory (DFT) calculations coupled with the non-adiabatic Marcus charge transfer model. Moreover, a series of regression analysis has been carried out to explore the rational structure–property relationship. Results reveal that the PC₆₁BM-PTDPPSe system possesses the large open-circuit voltage (0.77 V), middle-sized exiton binding energy (0.457 eV), and relatively small reorganization energies in exciton-dissociation (0.273 eV) and charge-recombination (0.530 eV) processes. With the Marcus model, the k _dis , k _rec , and the radiative decay rate (k _s ), are estimated to be 3.167×10¹¹ s^?1, 3.767×10¹⁰ s^?1, and 7.930×10⁸ s^?1 respectively in the PC₆₁BM-PTDPPSe interface. Comparably, the k _dis is as 1～3 orders of magnitude larger than the k _rec and the k _s , which indicates a fast and efficient photoinduced exciton-dissociation process in the PC₆₁BM-PTDPPSe interface.

Open image in new window

Graphical Abstract PTDPPSe is predicted to be a promising electron donor polymer, and the PC₆₁BM-PTDPPSe system is worthy of further device research by experiments.

     

Effect of cold adaptation of α-and β-adrenergic responses of blood pressure in hindlimb and small intestine in situ and systemic blood pressure in rabbits

Changes in the main parameters of α-and β-adrenergic responses, sensitivity to agonists (EC ₅₀) and maximum response (P _m) of hindlimb and small intestinal blood pressure in situ and systemic blood pressure were studied in rabbits adapted to cold for 1–30 days (daily exposures to ?10°C for 6 h). The responses to phenylephrine, noradrenaline, adrenaline, clonidine (α-agonists), and isopropylnoradrenaline (β-agonist) corresponded to the equation p = (P _m A ⁿ )/(EC ₅₀ ⁿ + A ⁿ ) (1) with n = 1 and n = 2, respectively. Cold adaptation induced reciprocal changes in the response of both EC ₅₀ and P _m to α-agonists and in the response of P _m alone to isopropylnoradrenaline. The significant differences of the parameters from control observed during the first 5 days of adaptation gradually decreased by day 30. After 10 days of adaptation, the efficiency (E = P _m/2EC ₅₀) of response to α-and β-agonists of adrenoceptors significantly increased.     

Generation of C3- and C2-deuterated l-lactic acid by human erythrocytes exposed to d-[1-13C]glucose,d-[2-13c]glucose and d-[6-13C]glucose in the presence of D2O

• 1.1. The generation of C₂- and C₃-deuterated l-lactate was monitored by ¹³C NMR in human erythrocytes exposed to d-[1-¹³glucose, d-[2-¹³C]glucose or d-te-¹³C]glucose and incubated in a medium prepared in D₂O.
• 2.2. The results suggested that the deuteration of the C₁ of d-fructose 6-phosphate in the phosphoglucoisomerase reaction, the deuteration of the C₁ of d-glyceraldehyde-3-phosphate in the sequence of reactions catalyzed by triose phosphate isomerase and aldolase and the deuteration of the C₃ of pyruvate in the reaction catalyzed by pyruvate kinase were all lower than expected from equilibration with D₂O.
• 3.3. Moreover, about 40% of the molecules of pyruvate generated by glycolysis apparently underwent deuteration on their C₃ during interconversion of the 2-keto acid and l-alanine in the reaction catalyzed by glutamate-pyruvate transaminase.
• 4.4. The occurrence of the latter process was also documented in cells exposed to exogenous [3-¹³C]pyruvate.
• 5.5. This methodological approach is proposed to provide a new tool to assess in intact cells the extent of back-and-forth interconversion of selected metabolic intermediates.

     

Effects of ligands of α<Superscript>2</Superscript>-adrenoceptors on mRNA level of apoptotic proteins in developing rat brain

The effects of antagonist of α²-adrenoceptors yohimbine and their agonist clonidine on Bax and Bcl-X _L mRNA levels in neonatal rat brain were studied. Yohimbine decreased Bax mRNA level in the cerebellum, increased the ratio between Bcl-X _L and Bax mRNA levels in the cerebellum, cortex, and hippocampus, and increased Bcl-X _L mRNA level in the cortex and hippocampus of 6-day-old-rat pups 24 h after injection. Administration of clonidine 20 min after yohimbine administration abolished its effect on Bcl-X_L mRNA level in the hippocampus. The data obtained indicate that the blockade of α²-adrenoceptors induces antiapoptotic changes in the developing rat brain, some of which can be abolished after coadministration with the agonist of these receptors.     

Modulation of alfa-adrenoceptor activity by beta-adrenoceptor agonists and antagonists in rat brain cortex membranes

The influence of β-adrenoceptor activation and inhibition by isoprenaline and propranolol on the specific binding of nonselective α₁- and α₂-adrenoceptor antagonists [³H]prazosin and [³H]RX821002 in rat cerebral cortex subcellular membrane fractions was studied. It was established that for the α₁- and α₂-adrenoceptors the ligand–receptor interaction corresponds to the model of one affinity pool of receptors and binding of two ligand molecules by one dimer receptor. The parameters of [³H]prazosin binding to α₁-adrenoceptors were: K _d = 1.85 ± 0.16 nM, B _max = 31.14 ± 0.35 fmol/mg protein, n = 2. The parameters of [³H]RX821002 binding to α₂-adrenoceptors were: K _d = 1.57 ± 0.27 nM, B _max = 7.2 ± 1.6 fmol/mg protein, n = 2. When β-adrenoceptors were activated by isoprenaline, the binding of radiolabelled ligands with α₁- and α₂-adrenoceptors occurred according to the same model. The affinity to [³H]prazosin and the concentration of active α₁-adrenoceptors increased by 27% (K _d = 1.36 ± 0.03 nM) and 84% (B _max = 57.37 ± 0.28 fmol/mg protein), respectively. The affinity of α₂-adrenoceptors to [³H]RX821002 decreased by 56% (K _d = 3.55 ± 0.02 nM), and the concentration of active receptors increased by 69% (B _max = 12.24 ± 0.06 fmol/mg protein). Propranolol alters the binding character of both ligands. For [³H]prazosin and [³H]RX821002, two pools of receptors were detected with the following parameters: K _d1 = 1.13 ± 0.09, K _d2 = 6.07 ± 1.06 nM, B _m1 = 11.36 ± 1.77, Bm2 = 51.09 ± 0.41 fmol/mg protein, n = 2 and K _d1 = 0.61 ± 0.02, K _d2 = 3.41 ± 0.13 nM, B _m1 = 1.88 ± 0.028, B _m2 = 9.27 ± 0.08 fmol/mg protein, n = 2, respectively. The concentration of active receptors (B _max) increased twofold for both ligands. It was suggested that α₁- and α₂-adrenoceptors in rat cerebral cortex subcellular membrane fractions exist as dimers. A modulating influence of isoprenaline and propranolol on the specific binding of the antagonists to α₁- and α₂- adrenoceptors was revealed, which was manifested in the activating effect on the [³H]prazosin binding parameters, in the inhibitory effect on the [³H]RX821002 binding parameters, and in a change of the general character of binding for both ligands.