Propranolol inhibits the in vitro conversion of thyroxine into triiodothyronine by isolated rat liver parenchymal cells.

A model for the in vitro study of the conversion of thyroxine into triiodothyronine using isolated rat liver parenchymal cells is described. Isolated liver cells (mean protein content 18 mg/ml) convert approximately 0.8% of 1.3 microM exogenously added T4 into T3 during thirty minutes incubation. Carbimazole (50 microM) has no effect on the conversion process, whereas propylthiouracil (50 microM) inhibits the conversion. The beta-adrenoceptor blocking agent propranolol lowers the conversion ratio when added in concentrations of 580 and 1160 microM, but has no inhibitory effect when 290 microM is added.     

Effects of verapamil on lipolysis due to dibutyryl cyclic AMP.

The effects of verapamil, a calcium antagonist, on lipolysis in isolated rat adipocytes were studied. Verapamil (100 microM) potentiated lipolysis due to dibutyryl cyclic AMP (Bt2cAMP) at submaximal concentrations, with or without extracellular Ca2+. Lipolysis due to 0.5 mM-Bt2cAMP was potentiated by verapamil in a dose-dependent manner up to 200 microM, whereas at concentrations higher than 100 microM the stimulatory effect of verapamil was progressively diminished with or without extracellular Ca2+. Verapamil showed only an inhibitory effect on lipolysis due to adrenaline (0.1-10 microM) or 3-isobutyl-1-methylxanthine (IBMX; 25-200 microM). The stimulatory effect of verapamil on lipolysis due to Bt2cAMP was not blocked by alpha-adrenergic antagonists. These results suggest (i) that verapamil has a biphasic effect on lipolysis due to Bt2cAMP and only an inhibitory effect on that due to adrenaline or IBMX, and (ii) that extracellular Ca2+ or alpha-adrenergic receptors are not involved in the action of verapamil.     

Effects of antiarrhythmic drugs on phospholipid metabolism in Jurkat T cells. The potassium channel blocker, clofilium, specifically increases phosphatidylserine synthesis.

Five antiarrhythmic drugs (bretylium, clofilium, propranolol, N-acetylprocainamide and amiodarone) were tested for their ability to modify phospholipid metabolism in Jurkat T lymphocytes. The five drugs, decreased in a dose-dependent mode the biosynthesis of both phosphatidylcholine and phosphatidylethanolamine, this effect was essentially due to impairment of either choline or ethanolamine uptake by the cells. The efficiency of the drugs to inhibit phosphatidylcholine and phosphatidylethanolamine synthesis was in the order: clofilium greater than amiodarone much greater than propranolol = bretylium much greater than N-acetylprocainamide. The IC50 varied from 3-5 microM for clofilium to greater than 200 microM for N-acetylprocainamide. In contrast, only clofilium, a voltage-gated K(+)-channel blocker, was able to increase phosphatidylserine synthesis with an EC50 = 50 microM. The effect of clofilium on phosphatidylserine synthesis thus mimics the effect of three other K(+)-channel blockers, quinine, 4-aminopyridine and tetraethylammonium, suggesting close relationships between phosphatidylserine synthesis and K+ channel activity.     

Modulation by propranolol of the uptake of ethidium bromide by rat submandibular acinar cells exposed to a P2X(7) agonist or to maitotoxin

We have compared the formation of pores in rat submandibular acinar cells in response to 2',3'-O-(4-benzoylbenzoyl) adenosine 5'-triphosphate (Bz-ATP) and maitotoxin. Bz-ATP (100 microM) permeabilized the cells to ethidium bromide. The uptake of ethidium increased to 29+/-1% of maximal uptake in 10 min. DL-Propranolol (300 microM) inhibited the Bz-ATP-induced uptake of ethidium bromide by 40% without affecting the P2X(7)-gated cation channel. The inhibitory effect of DL-propranolol on the formation of pores by Bz-ATP was reproduced by D-propranolol, an optical isomer with very poor beta-blocking activity. Tenidap, an antiinflammatory drug, enhanced the permeabilization in response to Bz-ATP. Propanolol inhibited the response to tenidap plus Bz-ATP. The effect of propranolol was reproduced by labetolol, a beta-adrenergic antagonist with membrane-stabilizing properties, but not by atenolol, which blocks beta-adrenergic receptors but has no effect on the stability of the membrane. In the presence of extracellular calcium, maitotoxin also increased the uptake of ethidium bromide. Tenidap had no effect on this response, which was delayed by propranolol. In conclusion, we have shown that propranolol, in a range of 10-300 microM, inhibits the pore-forming activity of the P2X(7) receptor without affecting the opening of the cation channel coupled to this receptor. This inhibition is not related to its beta-adrenergic blocking activity but rather to its membrane-stabilizing properties. Propranolol also delays the uptake of ethidium bromide in response to maitotoxin. This is in agreement with the current view that P2X(7) agonists and maitotoxin share a common pore.     

Propranolol has direct antithyroid activity: Inhibition of iodide transport in cultured thyroid follicles

The effect of propranolol on the process of thyroid hormone formation was studied in a physiological culture system. Porcine thyroid follicles were preincubated with propranolol for 24 h. Iodide transport, iodine organification, and de novo thyroid hormone formation were measured by incubating these follicles with the mixture of carrier-free 0·1 μCi Na ¹²⁵I and 50 nM NaI for 2 to 6 h at 37°C. A concentration of propranolol greater than 100 μM inhibited iodide transport in a dose-dependent manner; this inhibition was non-competitive with iodide and independent of thyrotropin (TSH). Reduced iodine organification and thyroid hormone formation was seen with 150 μM propranolol or greater. The inhibitory action of propranolol was not caused by beta-blocking activity, since D -propranolol (devoid of beta-blocking activity) inhibited iodide transport, and other beta-blockers (metoprolol, atenolol, and labetalol) did not inhibit iodide transport. The inhibition of iodide transport was most likely caused by membrane stabilizing activity since quinidine, which possess the same membrane stabilizing activity as propranolol, also inhibited iodide transport. TSH-mediated cAMP generation and Na ⁺K⁺ ATPase activity, membrane functions for iodide transport, were unaffected by propranolol. Our study has shown, for the first time, that propranolol has a direct antithyroid action, namely inhibition of iodide transport in the intact thyroid follicle.     

Absence of negative feedback control of bile acid biosynthesis in cultured rat hepatocytes

The effect of individual bile acids on bile acid synthesis was studied in primary hepatocyte cultures. Relative rates of bile acid synthesis were measured as the conversion of lipoprotein [4-14C]cholesterol into 4-14C-labeled bile acids. Additions to the culture media of cholate, taurocholate, glycocholate, chenodeoxycholate, taurochenodeoxycholate, glycochenodeoxycholate, deoxycholate, and taurodeoxycholate (10-200 microM) did not inhibit bile acid synthesis. The addition of cholate (100 microM) to the medium raised the intracellular level of cholate 10-fold, documenting effective uptake of added bile acid by cultured hepatocytes. The addition of 200 microM taurocholate to cultured hepatocytes prelabeled with [4-14C]cholesterol did not result in inhibition of bile acid synthesis. Taurocholate (10-200 microM) also failed to inhibit bile acid synthesis in suspensions of freshly isolated hepatocytes after 2, 4, and 6 h of incubation. Surprisingly, the addition of taurocholate and taurochenodeoxycholate (10-200 microM) stimulated taurocholate synthesis from [2-14C]mevalonate-labeled cholesterol (p less than 0.05). Neither taurocholate nor taurochenodeoxycholate directly inhibited cholesterol 7 alpha-hydroxylase activity in the microsomes prepared from cholestyramine-fed rats. By contrast, 7-ketocholesterol and 20 alpha-hydroxycholesterol strongly inhibited cholesterol 7 alpha-hydroxylase activity at low concentrations (10 microM). In conclusion, these data strongly suggest that bile acids, at the level of the hepatocyte, do not directly inhibit bile acid synthesis from exogenous or endogenous cholesterol even at concentrations 3-6-fold higher than those found in rat portal blood.     

Hormonal stimulation of cyclic AMP accumulation and glycogen phosphorylase activity in calcium-depleted hepatocytes from euthyroid and hypothyroid rats.

Activation of glycogen phosphorylase by hormones was examined in hepatocytes isolated from euthyroid and hypothyroid female rats and incubated by Ca2+-free buffer containing 1 mM-EGTA. Basal glycogen phosphorylase activity was decreased in Ca2+-free buffer. However, the activation of hepatocyte glycogen phosphorylase, in the absence of extracellular Ca2+, in response to adrenaline, glucagon or phenylephrine was slightly lower, whereas that by vasopressin was abolished. The activation of glycogen phosphorylase by phenylephrine, adrenaline or isoproterenol (isoprenaline) in hepatocytes from euthyroid rats incubated in the absence of Ca2+ was not accompanied by any detectable increase in total cyclic AMP. The log-dose/response curves for activation of phosphorylase by phenylephrine or low concentrations of adrenaline were the same in hepatocytes from hypothyroid as compared wit euthyroid rats, whereas the response to isoproterenol was greater in hepatocytes from hypothyroid rats. However, the increases in total cyclic AMP accumulation caused by adrenaline or isoproterenol were greater in hepatocytes from hypothyroid rats than in hepatocytes from euthyroid rats. The increases in cyclic AMP accumulation caused by adrenaline or isoproterenol in Ca2+-depleted hepatocytes from hypothyroid rats were blocked by propranolol, a beta-adrenergic antagonist. In contrast, propranolol was only partially effective asan inhibitor of the activation of glycogen phosphorylase by phenylephrine or adrenaline in hepatocytes from hypothyroid rats and ineffective on phosphorylase activation in cells from euthyroid rats. These data indicate that the alpha-adrenergic activation of glycogen phosphorylase is not affected by the absence of extracellular Ca2+, and the extent to which total cyclic AMP was increased by adrenergic amines did not correlate with glycogen phosphorylase activation.     

Lipophilic beta-blockers inhibit monocyte and endothelial cell-mediated modification of low density lipoproteins.

The effects of propranolol, pindolol and metoprolol on the modification of low density lipoprotein (LDL) by U937 monocyte-like cells, endothelial cells and copper ions were studied by determination of the lipid peroxidation product content and measurement of the relative electrophoretic mobility of the particle. Propranolol and pindolol inhibited LDL oxidation by U937 cells in a dose-dependent manner from 10 to 100 microM, whereas metoprolol had no effect. In the case of LDL modification by endothelial cells, all the three beta-blockers were efficient within the same range of concentrations, and the order of potency was propranolol greater than pindolol greater than metoprolol. In vitro oxidation of LDL in the presence of copper ions was also inhibited by propranolol; pindolol and metoprolol had no significant protective effect in this system. These results concerning the inhibitory action of beta-blockers were confirmed by testing the degradation of modified LDL by J774 macrophages. Although the concentrations of the drugs utilized in this study are relatively high, in long-term treatment beta-blockers might accumulate in target tissues, and the protective effect of propranolol against LDL oxidation might be involved in its inhibitory action on atherosclerosis previously reported in animal models.     

D-propranolol and DL-propranolol both decrease conversion of L-thyroxine to L-triiodothyronine.

The effects of propranolol (DL-propranolol) and D-propranolol on thyroid hormone metabolism were studied in six euthyroid volunteers receiving L-thyroxine (T4) and six hypothyroid patients receiving T4 replacement. D-propranolol as well as propranolol decreased L-triiodothyronine (T3) concentrations and the ratio of T3 to T4 in the euthyroid subjects, and D-propranolol decreased these variables in the subjects with hypothyroidism (propranolol was not given to this group). It is concluded from this study and from parallel invitro investigations that the effect of propranolol on the conversion of T4 to T3 is unrelated to its beta-adrenergic blocking activity, and that at low therapeutic doses propranolol may exert appreciable "membrane-stabilising" effects in vivo.     

Synthesis of phosphatidylcholines in rat hepatocytes. Possible regulation by norepinephrine via an alpha-adrenergic mechanism

The effect of norepinephrine on phosphatidylcholine and phosphatidylethanolamine formation was investigated in short-term incubations with freshly isolated rat hepatocytes. In the presence of dl-propranolol, norepinephrine decreases the incorporation of [methyl-14C]choline into phosphatidylcholines in a dose-dependent manner. At a concentration of 50 microM, norepinephrine (plus 20 microM propranolol) inhibits the incorporation of [methyl-14C]choline over a wide range of choline concentrations (59% inhibition at 5 microM choline; 34% inhibition at 1 mM choline). Norepinephrine also decreases the incorporation rates of [1-14C]palmitic acid and [1-14C]oleic acid into phosphatidylcholines. The effect of norepinephrine is mediated through an alpha-adrenergic receptor. Norepinephrine (plus propranolol) does not decrease the uptake or phosphorylation rate of [methyl-14C]choline. Pulse-label and pulse-chase studies indicate that the conversion rate of phosphocholine to CDP-choline, catalyzed by CTP:phosphocholine cytidylyltransferase, is diminished by norepinephrine. In contrast with the inhibitory effect of norepinephrine on phosphatidylcholine synthesis, this hormone stimulates the formation of phosphatidylethanolamines from [1,2-14C]ethanolamine. This increased incorporation rate is apparent at ethanolamine concentrations above 25 microM. A combination of norepinephrine and propranolol decreases, however, the synthesis of phosphatidylcholines from [1,2-14C]ethanolamine. The results indicate that alpha-adrenergic regulation dissociates the synthesis of phosphatidylcholines from that of phosphatidylethanolamines.     

Evidence for a beta-adrenoceptor-mediated regulation of human natural killer cells

Pretreatment of lymphocytes (16 hr, 37 degrees C) with adrenaline at final concentrations of 10(-7) to 10(-9) M, followed by removal of the drug, increased natural killer (NK) cell activity vs K562 leukemic cells in a 4-hr 51Cr-release assay. The most efficient concentration of adrenaline was 10(-8) M; mean increase of NK activity over base-line activity for all donors examined was 30%. However, the individual response to adrenaline pretreatment was variable; in some donors, the effect was equal to maximal interferon (IFN) stimulation. Effects of adrenaline pretreatment were consistently reduced to base-line activity by co-incubation with the nonselective beta-adrenoceptor antagonist propranolol at 100-fold higher concentrations. The enhancing effect of adrenaline (10(-8) M) pretreatment was also observed after 1-hr pretreatment; this effect was prevented by simultaneous incubation with propranolol but was not affected by dex-propranolol. Direct addition of adrenaline to lymphocyte/target cell mixtures was inhibitory at 10(-6) M adrenaline concentration. The inhibitory effect of adrenaline in this assay was again completely prevented by propranolol and unaffected by dex-propranolol. The observed stimulatory effect of adrenaline pretreatment could not be ascribed to IFN production. Data presented indicate a dual effect of adrenaline on NK cell activity and suggest both a positive and a negative beta-adrenoceptor-mediated regulation of human NK cells.     

Iloprost (ZK 36374) modulates the responses to beta-adrenoceptor agonists in guinea-pig airways and pulmonary vasculature

The effect of iloprost on airway smooth muscles and its influence on the actions of beta-agonists and histamine were studied in the isolated perfused lung and isolated tracheal strips from guinea-pigs. Bolus injection of iloprost into the pulmonary artery elicited a concentration-dependent decrease in pulmonary perfusion pressure and an increase in airway resistance. These effects are not mediated through cholinergic, serotoninergic and histaminergic receptors. A rapid tachyphylaxis affected the effect of iloprost in airway resistance but not in pulmonary perfusion pressure. Iloprost did not induce a response in the isolated tracheal strips and did not alter the effect of histamine in both tracheal strips and airway resistance. This compound, however, caused an inhibition in the airway resistance-reducing effect of adrenaline and isoprenaline in the isolated perfused lung and a potentiation in the perfusion pressure-increasing effect of adrenaline. Iloprost also inhibited the relaxing effect of adrenaline and isoprenaline in the isolated tracheal strips precontracted with histamine and potentiated the inhibitory effect of propranolol against adrenaline and isoprenaline. From these results it was concluded that: Iloprost, a stable analogue of prostacyclin, modulates the beta-adrenoceptor blocking effect of propranolol in both airway smooth muscles and pulmonary vasculature.     

Relationship between the displacement of phosphatidate phosphohydrolase from the membrane-associated compartment by chlorpromazine and the inhibition of the synthesis of triacylglycerol and phosphatidylcholine in rat hepatocytes

Glycerolipid synthesis was studied in isolated hepatocytes by using 177 microM [14C]oleate and 1 mM [3H]glycerol. Chlorpromazine (25-400 microM) inhibited the synthesis of phosphatidylcholine and triacylglycerol. This was accompanied by an average increase of 12-fold in the accumulation of the labelled precursors in phosphatidate at 200 microM chlorpromazine and a decrease in the conversion of phosphatidate to diacylglycerol of 76%. These results indicate that part of the inhibition of the synthesis of phosphatidylcholine and triacylglycerol occurs at the level of phosphatidate phosphohydrolase. The relative rate of triacylglycerol synthesis at different concentrations of chlorpromazine was approximately proportional to the rate of conversion of phosphatidate to diacylglycerol. Phosphatidylcholine synthesis increased at higher rates of conversion of phosphatidate to diacylglycerol, but it was relatively independent of the latter rate when this was inhibited by more than about 30% with chlorpromazine. The addition of oleate to the hepatocytes caused a translocation of phosphatidate phosphohydrolase from the cytosol to the membrane-associated compartment. Chlorpromazine had the opposite effect and displaced the phosphohydrolase from the membranes in the presence or absence of oleate. There was a highly significant correlation between the activity of phosphatidate phosphohydrolase that was associated with the membranes of the hepatocytes and the calculated conversion of [3H]phosphatidate to diacylglycerol. Chlorpromazine also antagonized the association of the phosphohydrolase with microsomal membranes when cell-free preparations were incubated with combinations of oleate and spermine. Furthermore, it inhibited the transfer of the soluble phosphohydrolase to microsomal membranes that were labelled with [14C]phosphatidate and thereby decreased diacylglycerol production. It is concluded that part of the action of chlorpromazine in inhibiting the synthesis of triacylglycerol and phosphatidylcholine occurs because it prevents the interaction of the soluble phosphatidate phosphohydrolase with the membranes on which glycerolipid synthesis occurs. This in turn prevents the conversion of phosphatidate to diacylglycerol.     

Heterogeneity among beta-adrenoreceptor blockers in the modulation of energy-dependent uptake of the organic cation amantadine by rat renal tubules.

Eight representative beta-adrenoreceptor blocking drugs, acebutolol, atenolol, labetalol, metoprolol, nadolol, pindolol, propranolol, and timolol, were studied in vitro with respect to their potential to block energy-dependent uptake of [3H]amantadine into proximal and distal rat renal tubule fragments in the presence and absence of bicarbonate. Five of the eight beta-adrenoreceptor blockers showed a dose-dependent inhibition of renal tubule accumulation of amantadine: labetalol, metoprolol, pindolol, propranolol, and timolol. Labetalol was the only beta-adrenoreceptor blocker with greater inhibitory potency in phosphate-based buffer than in bicarbonate-based buffer. Propranolol was the most potent inhibitor of renal tubule amantadine accumulation with IC50 values of 15 +/- 10 and 31 +/- 11 microM for proximal and distal tubule fragments, respectively, in a bicarbonate-based buffer environment. Inhibition in a phosphate-based buffer was less potent only in proximal tubules, with an IC50 of 76 +/- 30 microM. Kinetic studies of propranolol inhibition of amantadine uptake were consistent with both uncompetitive and competitive inhibition mechanisms in bicarbonate-based buffer in both proximal and distal renal tubule segments. There was no chiral preference between the R and S forms of propranolol for the inhibitory effects observed. These data suggest that there is potential for selection among the beta-adrenoreceptor blocking drugs to minimize or restrict the inhibition of amantadine energy-dependent uptake at the organic cation ion uptake sites characterized by amantadine in the presence and absence of bicarbonate.     

beta-Adrenergic receptor subtypes in melanophores of the marine gobies Tridentiger trigonocephalus and Chasmichthys gulosus.

The subtype of beta-adrenergic receptors in melanophores of the marine gobies Tridentiger trigonocephalus and Chasmichthys gulosus was studied. Pigment of denervated melanophores in isolated, split caudal fins was preliminarily aggregated by incubating the specimens in a physiological saline containing 10 microM phentolamine and 30-100 microM verapamil or 2-10 nM melatonin, and the responses of the melanophores to a beta-adrenergic agonist added to the incubating medium were recorded photoelectrically. The beta-adrenergic agonists noradrenaline, adrenaline, isoproterenol, salbutamol and, dobutamine were all effective in evoking a dispersion of melanophore pigment in the presence of phentolamine and verapamil or melatonin. The pigment-dispersing effect of noradrenaline (beta 1-selective agonist) was inhibited by metoprolol (beta 1-selective antagonist), propranolol,- and butoxamine. Whereas, the effect of salbutamol (beta 2-selective agonist) was hardly inhibited by metoprolol, though it was considerably inhibited by propranolol and ICI-118551. It was estimated that beta 1- and beta 2-adrenergic receptors coexist at ratios of 8.6:91.4, in the melanophore of Tridentiger trigonocephalus, and 25:75, in the melanophore of Chasmichthys gulosus, through the analyses of Hofstee plots of the effects of the beta-adrenergic drugs. It was suggested that the relation between the pigment-dispersing effect of a beta-adrenergic agonist on the melanophores and the concentration of the drug follows mass action kinetics, when the effect is mainly caused by the activation of beta 2-adrenergic receptors of the melanophores. However, when it is mainly caused by the activation of beta 1-adrenergic receptors of the melanophores, the relation does not follow mass action kinetics.     

Calcium metabolism in rat hepatocytes.

1. The total calcium concentration in rat hepatocytes was 7.9 microgram-atoms/g dry wt.; 77% of this was mitochondrial. Approx. 20% of cell calcium exchanged with 45Ca within 2 min. Thereafter incorporation proceeded at a low rate to reach 28% of total calcium after 60 min. Incorporation into mitochondria showed a similar time course and accounted for 20% of mitochondrial total calcium after 60 min. 2. The alpha-adrenergic agonists phenylephrine and adrenaline + propranolol stimulated incorporation of 45Ca into hepatocytes. Phenylephrine was shown to increase total calcium in hepatocytes. Phenylephrine inhibited efflux fo 45Ca from hepatocytes perifused with calcium-free medium. 3. Glucagon, dibutryl cyclic AMP and beta-adrenergic agonists adrenaline and 3-isobutyl-1-methyl-xanthine stimulated calcium efflux from hepatocytes perifused with calcium-free medium. The effect of glucagon was blocked by insulin. Insulin itself had no effect on calcium efflux and it did not affect the response to dibutyryl cyclic AMP. 4. Incorporation of 45Ca into mitochondria in hepatocytes was stimulated by phenylephrine and inhibited by glucagon and by carbonyl cyanide p-trifluoromethoxyphenylhydrazone. The effect of glucagon was blocked by insulin. 5. Ionophore A23187 stimulated hepatocyte uptake of 45Ca, uptake of 45Ca into mitochondria in hepatocytes and efflux of 45Ca into a calcium-free medium.     

Noradrenaline Antagonizes and Ouabain Potentiates the Effects of iV-Methyl-D-Aspartate on Rat Cerebellar Cyclic GMP Production

Noradrenaline potently antagonizes the effects of N-methyl-D-aspartate (NMDA) (80 microM) on cyclic GMP production in immature rat cerebellar slices in vitro (IC50 = 0.6 microM). The effect is stereospecific (D-noradrenaline, IC50 = 100 microM), and also observed with adrenaline (IC50 = 0.5 microM) and isoprenaline (IC50 = 1.2 microM). The alpha 1-adrenoceptor agonists methoxamine or phenylephrine or the mixed alpha 1/alpha 2 agonists oxymetazoline or xylometazoline (100 microM) do not block the effects of NMDA, but the alpha 2-adrenoceptor agonist clonidine is weakly active (IC50 = 200 microM). Salbutamol and terbutaline were also inactive except at high concentrations (300 microM), as were a number of other catechol and phenylethylamine derivatives. The antagonistic effects of noradrenaline on the NMDA response were insensitive to phentolamine, atenolol, or propranolol (up to 100 microM), but were blocked by the alpha 2 antagonist idazoxan (1-10 microM). The Na+,K+-ATPase inhibitor ouabain (0.1-10 microM) markedly potentiates the effects of NMDA in this model, and also antagonizes and reverses the ability of noradrenaline (10 microM) to block the effects of NMDA. The results suggest that noradrenaline and Na+,K+-ATPase activity have potent modulatory effects on the NMDA response.     

Adrenaline stimulates H2O2 generation in liver via NADPH oxidase

It is known that adrenaline promotes hydroxyl radical generation in isolated rat hepatocytes. The aim of this work was to investigate a potential role of NADPH oxidase (Nox) isoforms for an oxidative stress signal in response to adrenaline in hepatocytes. Enriched plasma membranes from isolated rat liver cells were prepared for this purpose. These membranes showed catalytic activity of Nox isoforms, probably Nox 2 based on its complete inhibition with specific antibodies. NADPH was oxidized to convert O(2) into superoxide radical, later transformed into H(2)O(2). This enzymatic activity requires previous activation with either 3 mM Mn(2+) or guanosine 5'-0-(3-thiotriphosphate) (GTPgammaS) plus adrenaline. Experimental conditions for activation and catalytic steps were set up: ATP was not required; S(0.5) for NADPH was 44 microM; S(0.5) for FAD was 8 microM; NADH up to 1 mM was not substrate, and diphenyleneiodonium was inhibitory. Activation with GTPgammaS plus adrenaline was dose- and Ca(2+)-dependent and proceeded through alpha(1)-adrenergic receptors (AR), whereas beta-AR stimulation resulted in inhibition of Nox activity. These results lead us to propose H(2)O(2) as additional transduction signal for adrenaline response in hepatic cells.     

The roles of alpha- and beta-adrenoceptors in the chronotropic responses to norepinephrine in carp heart (Cyprinus carpio)

1. The chronotropic effect of norepinephrine was studied in isolated spontaneously beating atrial preparations of carp (Cyprinus carpio) heart. 2. Norepinephrine, 0.1 microM, caused a positive chronotropic effect, while at 1 microM it caused either a positive or a negative chronotropic effect. The positive chronotropic effect, observed in 13 preparations, was potentiated by phentolamine and almost completely blocked by propranolol. 3. The negative chronotropic effect observed in the other 5 preparations was greater in the presence of propranolol, reduced by phentolamine and not affected by atropine. 4. These results indicate that alpha- and beta-adrenoceptors may coexist, mediating the negative and positive chronotropic effects, respectively, in isolated atrial preparations of carp heart.     

Effect of the beta-adrenoblocker propranolol on adrenaline-stimulated lipolysis in the adipose tissue of spontaneously hypertensive rats

The effect of the beta-adrenoblocker propranolol on adrenaline-stimulated lipolysis was studied in the adipose tissue of spontaneously hypertensive rats (SHR) and control rats. The lipolytic activity was estimated from the increase in glycerol concentration in the incubation medium in vitro. The adipose tissue of SHR responded to adrenaline similarly to that of control rats, but the concentration of adrenaline inducing the half-maximum response (KA) was 2 times less for SHR than KA for normotensive controls. Under propranolol effect this parameter was increased more significantly in SHR than in controls. These data indicate higher sensitivity of SHR adipose tissue to propranolol that may well be relative to alteration of the properties of beta-adrenergic receptors of adipose tissue in this form of hypertension.