Effect of catecholamines on Na/H exchange in vascular smooth muscle cells

Catecholamines were found to activate Na/H exchange in a concentration-dependent manner in primary cultures of vascular smooth muscle cells (VSMC). The potency order was found to be epinephrine greater than norepinephrine greater than isoproterenol. The major pathway for catecholamine effects appeared to be via interaction with an alpha 1 adrenergic receptor. In addition, it was found that alpha 1 receptor-mediated Na/H exchange in VSMC was increased by angiotensin II and inhibited by 12-O-tetradecanoyl phorbol-13-acetate (TPA). Adrenergic receptors have been shown to be coupled to both adenylate cyclase and to inositol phosphate release (Leeb-Lundberg, L. M. F., S. Cotecchia, J. W. Lomasney, J. F. DeBernadis, R. J. Lefkowitz, and M. G. Caron, 1985, Proc. Natl. Acad. Sci. USA, 82:5651-5655.). It was found that catecholamines increased AMP levels in the potency order isoproterenol greater than norepinephrine greater than epinephrine and the receptor involved was a beta adrenergic receptor. Since these findings did not parallel the results obtained for catecholamine stimulation of Na/H exchange, an increase in AMP levels was probably not the mechanism by which major pathway for catecholamine-stimulated Na/H exchange in VSMC (via the alpha 1 receptor) was activated. When the effects of catecholamines were measured on inositol phosphate release, the potency order for catecholamine stimulation was epinephrine greater than norepinephrine greater than isoproterenol, and the receptor involved was an alpha 1 adrenergic receptor. In addition, angiotensin II increased and TPA inhibited catecholamine-stimulated inositol phosphate release. Since these findings paralleled the results obtained for catecholamine stimulation of Na/H exchange, inositol phosphate release may be the mechanism by which the major pathway for catecholamine-stimulated Na/H exchange in VSMC (via the alpha 1 receptor) was activated.     

Inhibition of cholinergic neurotransmission in human airways by beta 2-adrenoceptors

The purpose of the study was to determine whether catecholamines modulate cholinergic neurotransmission in isolated human airway smooth muscle. Bronchial rings were suspended in organ baths for isometric measurement of tension, and contractions were induced by either electrical field stimulation (EFS) or exogenous acetylcholine (ACh). Isoproterenol, epinephrine, and norepinephrine in that order of potency produced concentration-dependent inhibition of comparable responses to EFS and ACh. However a potency difference of 100-fold for isoproterenol (IC50 = 4.80 X 10(-8) M for EFS and 3.70 X 10(-6) M for ACh) and 10-fold for both epinephrine and norepinephrine was observed for inhibition of responses to EFS compared with responses to ACh. The inhibitory effects of isoproterenol on responses to EFS were prevented by propranolol and ICI 118551 (a beta 2-antagonist) but not by betaxolol (a beta 1-antagonist). Tyramine had no effect on contractions elicited by EFS. These experiments demonstrate that beta-agonists inhibit cholinergic nerve-induced contractions of human bronchi more potently than contractions induced by exogenous ACh, suggesting modulation of cholinergic neurotransmission by prejunctional beta 2-receptors.     

Inhibition of dihydropteridine reductase by catecholamines and related compounds

Catecholamines and related compounds, such as dopamine, 5- or 6-hydroxydopamine, N-methyldopamine, tyramine, octopamine, norepinephrine and epinephrine, inhibit human liver dihydropteridine reductase (NADH:6,7-dihydropteridine oxidoreductase, EC 1.6.99.10) noncompetitively with Ki values ranging from 7.0 X 10(-6) - 1.9 X 10(-4)M (I50 values = 2.0 X 10(-5) - 2.0 X 10(-4)M). The tyrosine analogs alpha-methyltyrosine and 3-iodotyrosine are weak inhibitors of this enzyme (I50 greater than 10(-3)M). The inhibitory effect of catecholamines is slightly decreased by O-methylation of one hydroxyl group, but is essentially abolished by total methylation. The inhibitory strength of the catecholamines and related compounds tested against this enzyme can be arranged in the following order: dopamine, 6-hydroxydopamine, 5-hydroxydopamine, N-methyldopamine greater than tyramine, 3-O-methyldopamine, 4-O-methyldopamine much greater than epinephrine, 3-O-methylepinephrine, norepinephrine, octopamine less than tyrosine much less than alpha-methyltyrosine, 3-iodotyrosine much less than homoveratrylamine. These results suggest that dopamine, norepinephrine and epinephrine may serve as physiological regulators of mammalian dihydropteridine reductase.     

beta-Adrenergic receptors in rabbit liver plasma membranes. Predominance of beta 2-receptors and mediation of adrenergic regulation of hepatic glycogenolysis

[3H]Dihydroalprenolol was used to study beta-adrenergic binding sites in plasma membranes isolated from rabbit liver. Specific binding was measured at 25 degrees C as the difference between total binding and binding in the presence of 2 microM dl-propranolol or 10 microM l-isoproterenol. Binding was saturable and stereoselective. The maximum number of binding sites (Bmax) was 434 +/- 41 fmol/mg of protein. The Kd for this binding as determined by Scatchard analysis was 1.39 +/- 0.09 nM. This value agreed well with the Kd value (1.27 +/- 0.12 nM) determined by kinetic analysis. The potency order for the displacement of bound [3H]dihydroalprenolol was isoproterenol greater than epinephrine greater than norepinephrine, indicative of beta 2-receptors. Use of beta 1- and beta 2-subtype-selective inhibitors also supported the interpretation that the binding characteristics are those of beta 2-receptors. Computer-aided analysis of this inhibition indicated that the beta-receptors in this membrane are predominantly, if not exclusively, of the beta 2-subtype. That these receptors are responsible for mediating catecholamine stimulation of hepatic glycogenolysis was deduced from the inhibition of agonist-stimulated glycogenolysis, in isolated hepatocytes, by beta-receptor subtype-selective antagonists. Thus, the hydrochloride of (t-butylamino-3-ol-2-propyl)oximino-9 fluorene, a beta-antagonist which has higher affinity at beta 2-sites than at beta 1-sites, was 3 orders of magnitude more potent in inhibiting isoproterenol-stimulated glycogenolysis than either atenolol or practolol, both of which are beta 1-selective antagonists. These results resemble the inhibition of [3H]dihydroalprenolol binding in plasma membranes. The glycogenolytic effects of catecholamines occurred with the potency order isoproterenol greater than epinephrine greater than norepinephrine. Thus, both by radioligand binding studies and by metabolic studies, the functional adrenergic receptor in the rabbit liver is shown to be of the beta 2-subtype.     

Human apolipoprotein A-II: nucleotide sequence of a cloned cDNA, and localization of its structural gene on human chromosome 1

[3H]yohimbine, a potent and selective alpha 2-adrenergic antagonist was used to label alpha-adrenoceptors in intact human lymphocytes. Binding of [3H]yohimbine was rapid (t1/2 1.5 -2.0 min) and readily reversed by 10 microM phentolamine (t1/2 = 5 - 6 min) and of high affinity (Kd = 3.7 +/- 0.86 nM). At saturation, the total number of binding sites was 19.9 +/- 5.3 fmol/10(7) lymphocytes. Adrenergic agonists competed for [3H]yohimbine binding sites with an order of potency: clonidine greater than (-) epinephrine greater than (-) norepinephrine greater than (+) epinephrine much greater than (-) isoproterenol; adrenergic antagonists with a potency order of yohimbine greater than phentolamine greater than prazosin. These results indicate the presence of alpha 2-adrenoceptors in human lymphocytes.     

Characterization of the beta-adrenergic receptor of the rat peritoneal macrophage

The beta-adrenergic receptor was characterized on BCG-activated rat peritoneal macrophage membranes by radio-ligand binding studies. Saturable binding with [125I]iodocyanopindolol (125I-ICYP) was demonstrated. With Scatchard analysis, rat macrophages demonstrate approximately 1000 receptors per cell with a Kd of 5 X 10(-11) M for 125I-ICYP. Competition curves with (-) and (+) propranolol at concentrations below 10(-6) M confirmed stereospecificity. The potency of various ligands to compete for 125I-ICYP binding sites followed the order: propranolol greater than isoproterenol greater than epinephrine greater than norepinephrine with apparent Kd of 2.0 X 10(-9), 3.9 X 10(-7), 1.0 X 10(-5), and 2.5 X 10(-5) M, respectively. Isoproterenol-stimulated adenylate cyclase activity was two-fold above basal activity. The potential physiologic significance of a beta-adrenergic receptor on rat peritoneal macrophages was suggested by a dose-dependent decrease in phagocytosis of soluble, model immune complexes (aggregated gamma-globulin) by macrophages incubated with metaproterenol. We conclude that the rat macrophage has a beta-adrenergic receptor and that catecholamines may thereby modulate macrophage function.     

Adrenergic versus VIPergic control of cyclic AMP in human colonic crypts

The actions of catecholamines on VIP-induced cyclic AMP is studied in human colon. We show that: (1) Epinephrine in the 10(-7)-10(-3) M concentration range (ED50 = 11.10(-6) M) inhibits VIP-induced cyclic AMP rise in isolated colonic epithelial cells; the maximal inhibition reaches 30% of VIP effect; epinephrine alters the efficacy of the peptide and does not modify its potency; epinephrine also reduces the basal cyclic AMP level. (2) The inhibition is found with other alpha adrenergic agonists with the order of potencies epinephrine greater than norepinephrine greater than phenylephrine. Clonidine has a poor intrinsic activity but antagonizes the action of epinephrine. (3) The inhibition of VIP action by epinephrine is reversed by the alpha antagonists dihydroergotamine, phentolamine and the alpha 2 antagonist yohimbine, while unaffected by the beta antagonist propranolol and the alpha 1 antagonist prazosin, (4) Epinephrine inhibits VIP-stimulated adenylate cyclase activity in preparations of colonic plasma membranes. Thus catecholamines exert through an alpha 2 adrenoreceptor a negative control on basal and VIP-stimulated cyclic AMP formation in human colon. We suggest that colonic cyclic AMP metabolism undergoes a dual control: VIPergic, activator and adrenergic, inhibitor.     

ACCUMULATION OF CYCLIC ADENOSINE 3', 5'-MONOPHOSPHATE IN CEREBRAL CORTICAL SLICES FROM RAT AND MOUSE: STIMULATORY EFFECT OF α- AND β-ADRENERGIC AGENTS AND ADENOSINE

Abstract— Norepinephrine, epinephrine, isoproterenol, and adenosine elicit enhanced accumulations of cyclic AMP in incubated slices of rat cerebral cortex. Combinations of norepinephrine, epinephrine, isoproterenol, or histamine with adenosine have a greater than additive effect on cyclic AMP levels. The effects of isoproterenol appear to be mediated via a classical β-adrenergic receptor whereas the effects of norepinephrine appear due to interactions with both α- and β-adrenergic receptors. The presence of the phosphodiesterase inhibitor, isobutylmethylxanthine, potentiates the effects of the catecholamines and reveals a histamine-mediated increase in cyclic AMP levels. After an initial stimulation of cyclic AMP formation with norepinephrine, followed by washing of the slices, the cyclic AMP-generating system is unresponsive to norepinephrine but does respond to an adenosine-norepinephrine combination. In mouse cerebral cortical slices, catecholamines appear to elicit an accumulation of cyclic AMP primarily via interaction with a β-adrenergic receptor.     

Stereostructure activity relationships of catecholamines on human platelet function

The concentration-dependent effects of clonidine, isomers of epinephrine, norepinephrine (NE), isoproterenol, cobefrin and alpha-methyldopamine, and related desoxy analogs (epinine, dopamine, N-isopropyldopamine) were examined on human platelets. The rank order of aggregatory potency (pD2 values) was R(-)-epinephrine (6.3) greater than R(-)-NE (5.9) greater than (+/-)-erythro-cobefrin (5.3) greater than S(+)-epinephrine (4.7) = S(+)-NE (4.7) = clonidine (4.7) = dopamine (4.6) greater than epinine (4.4) greater than S(+)-alpha-methyldopamine (4.3) = R(-)-alpha-methyldopamine (4.3) greater than (+/-)-threo-cobefrin (3.7). The isoproterenol isomers and N-isopropyl-dopamine were inactive as agonists. In 9 of 16 platelet-rich plasma preparations, R(-)-epinephrine, R(-)-NE, and (+/-)erythro-cobefrin were agonists and the remaining analogs blocked R(-)-NE-induced aggregation with a rank order of inhibitory potencies (pKB values) of clonidine (6.2) greater than S(+)-alpha-methyldopamine (5.0) greater than dopamine (4.6) = R(-)-alpha-methyldopamine (4.4) greater than or equal to S(+)-NE (4.3) greater than N-isopropyldopamine (4.1) greater than S(+)-isoproterenol (3.7) = R(-)-isoproterenol (3.5). Each compound was also able to reverse prostaglandin E1 (PGE1) (0.1 microM)-induced blockade of the maximal aggregation response to ADP. At high concentrations, R(-)-isoproterenol was more potent than either the S(+)-isomer or desoxy analog, N-isopropyldopamine, in the reversal of PGE1 inhibition of ADP aggregation. Phentolamine blocked these alpha 2-adrenoceptor-mediated actions against PGE1 on ADP aggregation. The rank order of potency for the reversal of PGE1-mediated inhibition of ADP aggregation by these catecholamines was similar to that observed for platelet aggregation. Our results indicate that (i) the stereochemical requirements for the interaction of catecholamines with platelet alpha 2-adrenoceptors are in agreement with the Easson-Stedman hypothesis and other alpha-adrenoceptor tissues; (ii) catecholamines lacking a benzylic hydroxyl group in the R-configuration and/or possessing an N-isopropyl group were alpha 2-adrenoceptor antagonists; (iii) clonidine gave quantitatively different responses compared with catecholamines for interaction with alpha 2-adrenoceptors; and (iv) inhibition of platelet adenylate cyclase is correlated to the inhibition of epinephrine-induced aggregation response for this series of compounds.     

Characterization of beta-adrenergic receptors by (3H) isoproterenol in adipocytes of humans and rats

The specific binding of (3H) isoproterenol to isolated fat cells of human and rat was characterized. Binding of (3H) isoproterenol to isolated fat cells of rat was saturable with 420 pmol of (3H) isoproterenol bound/100 mg of lipid. Half-maximal saturation occurred at 5 microM providing an estimate of the equilibrium dissociation constant, KD, for the interaction of (3H) isoproterenol with its binding sites. Kinetic analysis of (3H) isoproterenol binding provided a value of 2.01 x 10(4) min-1. M-1 for the forward bimolecular rate constant, k1. Dissociation of (3H) isoproterenol was a first order reaction with a rate constant, k2, of 0.62 x 10(-1) min-1. The ratio k2/k1 = 3.07 microM provides an independent measurement of the KD for the interaction of (3H) isoproterenol with its binding sites which is in agreement with the values obtained by steady state analysis (3 to 5 microM). The apparent equilibrium dissociation constant, KD, for the interaction of (3H) isoproterenol with its receptor in human fat cells obtained by steady state analysis was 1 to 0.9 microM. Scatchard- and Hill-analysis suggest the possibility of different negatively cooperative interactions among the binding sites in human and rat. beta-Adrenergic agonists competed for the binding sites. The order of potency was isoproterenol greater than epinephrine greater than norepinephrine. Compounds such as DOPA, dopamine and (m-Hydroxyphenyl)2-methyl-aminoethanol which are structurally related to catecholamines had little or no affinity for (3H) isoproterenol binding sites.     

Beta 1-adrenoceptors in rat hepatoma. Desensitization by isoproterenol and phorbol-myristate-acetate

The beta-adrenergic responsiveness of hepatocytes obtained from hypothyroid rats and of a transplantable hepatoma cell line (AS-30D) were studied by measuring the accumulation of cyclic AMP. The potency order for agonists in hepatocytes was: isoproterenol greater than epinephrine much greater than norepinephrine whereas in the hepatoma cells the potency order was: isoproterenol greater than norepinephrine greater than or equal to epinephrine. The effect of isoproterenol was antagonized in hepatocytes by low concentrations of ICI 118551 and only partially by concentrations of atenolol as high as 100 microM. In hepatoma cells the effect of isoproterenol was inhibited by both antagonists with the potency order atenolol greater than ICI 118551. These data indicate that in hepatocytes the effect is mediated by beta 2-adrenoceptors whereas in hepatoma cells it is through beta 1-adrenoceptors. Preincubation of hepatoma cells with isoproterenol or phorbol-myristate-acetate diminished the subsequent beta-adrenergic responsiveness of the cells. Interestingly, when both isoproterenol and phorbol-myristate-acetate were present during the preincubation the beta-adrenergic desensitization observed was bigger than that induced by any of these agents alone.     

Basic properties of beta adrenergic receptors mediating melanosome dispersion of melanophores in a cyprinid fish, Zacco temmincki

In melanophores of a cyprinid fish, Zacco temmincki, receptor mechanisms of melanosome dispersion induced by catecholamines were examined. While possessing a melanosome-aggregating action in higher concentrations, isoproterenol and epinephrine in lower concentrations acted to disperse melanosomes. Norepinephrine, epinine and dopamine altered their action from melanosome aggregation to melanosome dispersion after alpha adrenergic blockade. The catecholamine-induced melanosome dispersion was inhibited by beta adrenergic blocking agents. Mediation of dispersion is regulated through beta adrenergic receptors. The beta adrenergic responses were unaffected by mersalyl, a sulfhydryl inhibitor. A prospective substance acting in dispersing melanosomes appears to be adrenaline, but not noradrenaline.     

ß-Adrenergic Receptor Activation Increases Acetylcholine Receptor Number in Cultured Skeletal Muscle Myotubes

Treatment of embryonic chick muscle myotubes with the beta-adrenergic agonist isoproterenol increased the number of surface membrane nicotinic cholinergic receptors. Receptor degradation was unaffected by isoproterenol, suggesting that receptor synthesis was increased. The effect of isoproterenol appears to be mediated by the beta-adrenergic receptor adenylate cyclase system for the following reasons: (a) The response to isoproterenol was dose-dependent and stereospecific. (b) The response to catecholamines followed the order isoproterenol greater than epinephrine greater than norepinephrine. (c) Alprenolol, a beta-adrenergic antagonist, but not phentolamine, an alpha-antagonist, abolished the effect. (d) The maximal effects of isoproterenol and cholera toxin, an activator of adenylate cyclase, were not additive. These results suggest that under certain physiological states catecholamines may play an important role in the regulation of cholinergic receptors.     

Effects of vasoactive intestinal polypeptide, monoamines, prostaglandins, and 2-chloroadenosine on adenylate cyclase in rat cerebral microvessels

Abstract: Adenylate cyclase in microvessels isolated from rat cerebral cortex was stimulated by guanine nucleotides, catecholamines, prostaglandin E₁, prostaglandin E₂, and 2-chloroadenosine. Catecholamine stimulation was mediated by interaction with β-adrenergic receptors. The order of relative potency was: isoproterenol > epinephrine > norepinephrine. Activation of microvessel adenylate cyclase by prostaglandins E₁ and E₂ as well as by 2-chloroadenosine was dose related. Twenty-two peptides were tested for possible effects on the microvessel adenylate cyclase. Only vasoactive intestinal polypeptide (VIP) was stimulatory. No inhibitory action was observed. Activation by VIP required guanosine triphosphate and was dose dependent from 10 n M to μ M (ED₅₀= 0.1 μ M ). At 30°C, stimulation of adenylate cyclase by the peptide increased linearly with time for up to 15 min. The effect of VIP was not inhibited by phentolamine or propranolol, suggesting that its action was not elicited by interaction with α- or β-adrenergic receptors. Activation achieved by VIP and isoproterenol, prostaglandin E₁, or 2-chloroadenosine was the sum of the individual stimulations, suggesting that receptors for VIP were distinct from those for isoproterenol, prostaglandin E₁, and 2-chloroadenosine.     

Identification of adenylate cyclase-coupled beta-adrenergic receptors in the developing mammalian palate

A direct radioligand binding technique utilizing a beta-adrenergic antagonist [3H]Dihydroalprenolol [( 3H]DHA) was employed in the identification and characterization of fetal palatal beta-adrenergic receptors. [3H]DHA binding was saturable (Bmax 16 fmol/mg protein) with high affinity and an apparent equilibrium dissociation constant (KD) of 1.5 nM. Binding of [3H]DHA was displaced by the competitive beta-adrenergic antagonist propranolol in a concentration-dependent manner. Dissociation kinetic studies demonstrated almost complete reversibility of radioligand binding within 60 min. The functionality of these beta-adrenergic receptors was demonstrated by showing that fetal palatal mesenchymal cells responded to catecholamine agonists with dose-dependent accumulations of intracellular cAMP. This effect could be entirely blocked by the beta-antagonist, propranolol. The relative potency order of catecholamines in eliciting an elevation of cellular cAMP was characteristic of a beta 2-adrenergic receptor-mediated response: (-) isoproterenol greater than (-) epinephrine greater than (-) norepinephrine. In addition, this response was found to be stereospecific with (-) isoproterenol being significantly more potent than (+) isoproterenol. Both the [3H]DHA binding characteristics and the catecholamine sensitivity of fetal palatal tissue support the presence of adenylate cyclase-coupled beta-adrenergic receptors in the developing mammalian secondary palate.     

Beta-adrenergic receptors and stimulatory effects of (-) isoproterenol on testosterone production in fetal mouse Leydig cells

Beta-adrenergic receptors were characterized in freshly excised fetal mouse testis using the radioiodinated antagonist iodocyanopindolol (ICYP). [125I]-CYP bound to a single class of high affinity sites with a KD value of 42.2 +/- 7.0 pM. Adrenergic agonists competed for ICYP binding sites with the following order of potency: (-)isoproterenol greater than (-)epinephrine much greater than (-)norepinephrine which is typical for a beta 2-adrenergic receptor. A selective beta 2-receptor antagonist ICI 118-551 showed an approximately 200 fold higher affinity than the beta 1-selective compound, betaxolol. The beta-adrenergic agonist (-)isoproterenol did not or slightly affect testosterone production by freshly isolated fetal Leydig cells. The ability of fetal Leydig cells to respond to (-)isoproterenol increased during culture. This change in responsiveness was not accompanied either by modification of the number of binding sites or by change in the binding affinity. Taken together these data suggest that i) the stimulatory effect of (-)isoproterenol on testosterone production by cultured fetal Leydig cells is mediated through beta 2-adrenergic receptors ii), the inability of freshly Leydig cells to respond to catecholamines is probably due to post receptor events.     

Cerebrovascular smooth muscle culture. II. Characterization of adrenergic receptors linked to adenylate cyclase

Cultured and propagated smooth muscle cells contain adenylate cyclase (AC) responsive to catecholamines and their analogues. Isoproterenol and zinterol were the most effective stimulants of AC activity with EC50 = 8.5 X 10(-8)M. They were followed by epinephrine, phenylephrine and norepinephrine (EC50 = 7.5 X 10(-7)M, 6.5 X 10(-6)M and 4 X 10(-6)M, respectively). When the selective antagonists for beta 1 and beta 2 receptors (beta 1-type practolol and atenolol, beta 1/beta 2-type propranolol and beta 2-type butoxamine) were tested against isoproterenol, epinephrine and norepinephrine stimulation of AC activity, the beta 1 in contrast to beta 2 antagonists were found ineffective. The alpha-blockers (phentolamine alpha 1/alpha 2-type antagonists) and yohimbine (alpha 2-type antagonist) alone or in the presence of propranolol did not significantly inhibit the catecholamine-induced enhancement of cAMP formation. On the other hand, prazosine (alpha 1-type antagonist) blocked the stimulatory effect of epinephrine and norepinephrine on AC system. Similarly, the alpha 2-agonist, clonidine, did not affect the catecholamines' stimulated AC activity while alpha 1 agonist, phenylephrine, induced an additive enhancement of norepinephrine production of cAMP. The findings of beta-2- and alpha-1-type adrenergic receptors in the cultured cerebrovascular smooth muscle provide additional support for the implicated involvement of adrenergic innervation in the regulation of cerebral blood flow and/or systemic blood pressure.     

Differential effects of catecholamines on in vitro growth of pathogenic bacteria

Supplementation of minimal medium inoculated with bacterial cultures with norepinephrine, epinephrine, dopamine, or isoproterenol resulted in marked increases in growth compared to controls. Norepinephrine and dopamine had the greatest enhancing effects on growth of cultures of Pseudomonas aeruginosa and Klebsiella pneumoniae, while epinephrine and isoproterenol also enhanced growth to a lesser extent. The growth of Escherichia coli in the presence of norepinephrine was greater than growth in the presence of the three other neurochemicals used in the study. Growth of Staphylococcus aureus was also enhanced in the presence of norepinephrine, but not to the same degree as was the growth of gram negative bacteria. Addition of culture supernatants from E. coli cultures that had been grown in the presence of norepinephrine was able to enhance the growth of K. pneumoniae. Addition of the culture supernatant fluid culture from E. coli cultures that had been grown in the presence of norepinephrine did not enhance growth of P. aeruginosa or S. aureus. Culture supernatant fluids from bacteria other than E. coli grown in the presence of norepinephrine were not able to enhance the growth of any bacteria tested. The results suggest that catecholamines can enhance growth of pathogenic bacteria, which may contribute to development of pathogenesis; however, there is no uniform effect of catecholamines on bacterial growth.     

Norepinephrine-induced down regulation of alpha 1 adrenergic receptors in cultured rabbit aorta smooth muscle cells

Drug-induced refractoriness of alpha-adrenergic receptor-mediated vasoconstriction may be a clinically important phenomenon. We have investigated the possible molecular mechanisms underlying this phenomenon in cultured vascular smooth muscle cells derived from the rabbit aorta. alpha 1-Adrenergic receptors were identified in membranes prepared from these cells by [125I]HEAT binding. The radioligand bound to a high affinity site (Kd = 140 pM) in a saturable fashion (202 fmol/mg protein). Adrenergic agonists and antagonists competed for binding of [125I]HEAT with the expected order of potency for an alpha 1-receptor, (-)epinephrine greater than or equal to (-) norepinephrine greater than (+)epinephrine greater than isoproterenol and prazosin greater than phentolamine greater than yohimbine. Exposure of cells for 26 hours to 10 microM norepinephrine resulted in a 70% decrease in the number of alpha 1-receptors as measured by [125I]HEAT binding without any significant change in the affinity of the receptor for the ligand. When the alpha-receptors were blocked with 10 microM phentolamine the loss of receptors induced by norepinephrine was completely prevented. Similar down-regulation of the [125I]HEAT binding sites was observed when the alpha 1-agonist phenylephrine was used instead of norepinephrine. It is concluded that alpha-agonists induce down-regulation of aortic smooth muscle alpha 1-receptors. This reduction of alpha-receptors could be important in the mechanisms by which vascular smooth muscle develops refractoriness to alpha-adrenergic stimulation.     

Beta 2-adrenergic stimulation of androgen production by cultured mouse testicular interstitial cells

The present studies characterized the beta-receptor subtype involved in androgen production by cultured mouse testicular interstitial cells and explored the possible stimulation of androgen release by alpha-adrenergic agonists. During a 3-hour incubation period, LH and a non-specific beta-adrenergic agonist, L-isoproterenol steadily increased androgen production with a similar time-course. Isoproterenol, epinephrine, norepinephrine and a specific beta 2-receptor agonist, salbutamol stimulated androgen release in a concentration-dependent manner. The concentrations of the agonists required for half-maximum stimulation (EC50) were approximately 1 nM (isoproterenol), 8 nM (epinephrine), 9 nM (salbutamol) and 2 microM (norepinephrine) giving an order of potency of isoproterenol greater than epinephrine = salbutamol much greater than norepinephrine. L- but not the D-isomer of isoproterenol induced androgen production. A non-selective beta-receptor antagonist, propranolol, abolished androgen production induced by isoproterenol. A selective beta 2-receptor antagonist ICI 118,551 inhibited the isoproterenol effect in a concentration-dependent manner with half-maximum inhibition (IC50) at approximately 23 nM. The beta 1-receptor antagonists, metoprolol and atenolol had no effect on isoproterenol-induced androgen release. The stimulatory effect of norepinephrine (an alpha- and beta-agonist) was completely (100%) abolished by propranolol, unaffected by the alpha-antagonist phentolamine and only partially (35%) inhibited by phenoxybenzamine. Phenoxybenzamine and the alpha 2-agonist, clonidine reduced basal androgen production. These studies indicate that androgen production by primary cultures of mouse testicular interstitial cells occurs exclusively via the beta 2-receptor subtype and that alpha-receptor agonists do not stimulate androgen release by these cells.