Isoproterenol produces a rapid increase in sialidase activity in rat heart tissue and cardiomyocyte-derived H9c2 cells in culture

The effects of isoproterenol on sialidase activity in rat cardiomyocytes were examined. Administration of isoproterenol to rats (0.2 or 2 mg/kg body weight) produced an increase in sialidase activity in total membrane fraction of heart tissue within 120 min (121+/-13% of the control at 120 min after administration of 0.2 mg isoproterenol/kg, n=5, P<0.05). Sialidase activity in cardiomyocyte-derived H9c2 cells was also increased by treatment with isoproterenol (10 microM) for 60 min. The effect of isoproterenol on sialidase activity was amplified by the addition of 3-isobutyl-1-methylxanthine (IBMX). Sialidase activity in H9c2 cells was elevated by treatment with dibutyryl cAMP plus IBMX without isoproterenol. The content of N-acetylneuraminic acid in cells decreased by 22% after treatment with isoproterenol plus IBMX. These results suggest that sialidase activity in rat cardiomyocytes is regulated by beta-adrenergic stimulators via a cAMP-dependent process. The increased activity of sialidase may account for the reduction of sialic acid content of cells.     

Effect of acute administration of isoproterenol on submandibular salivary gland of female rat

The functions of salivary glands are under the regulation of both sympathetic as well as parasympathetic nerve fibers. Further, it has also been demonstrated that chronic administration of a beta-adrenergic agonist isoproterenol (IPR) results in hypertrophy and hyperplasia of submandibular gland [Schneyer C A, Am J Physiol, 203 (1962) 232]. Specific purpose of the present attempt was to look for metabolic responses of submandibular gland of oestrous female rats at very short intervals after 10 min of administration of 5, 10 and 15 micrograms of IPR to females in oestrous condition; pharmacological action and clearance time being only 8 min. The results indicated significant reduction in case of enzymic activities of phosphorylase, total ATPase and Na(+)-K+ ATPase. Cyclic AMP-specific phosphodiesterase and succinate dehydrogenase activities were suppressed only with 5 micrograms dose, but with rising dose levels the effect was not so apparent. Protein content of the gland was reduced slightly by administration of IPR. Hence, it became clear that submandibular gland responds rapidly to IPR administration. Implications of these observations are discussed.     

Beta-adrenergic regulation of contractility and protein phosphorylation in spontaneously beating isolated rat myocardial cells

Spontaneously beating heart myocytes were prepared from adult rat ventricular tissues to study the correlation between beta-adrenergic receptor-stimulated changes in contractile performance and protein phosphorylation in vitro. The plasma membrane of isolated myocardial cells was permeabilized by saponin in the presence of EGTA and Mg-ATP. The permeabilized myocytes, which formed a homogeneous cell population, retained the rod-cell morphology of heart cells in situ and showed spontaneous cyclic contractions. Their contractile activity in response to extracellularly added cAMP mimicked the effects caused by beta-adrenergic stimulation of the whole heart: both the frequency and longitudinal velocity of free contraction and relaxation of the cells increased. Similar increases were observed when beta-agonist, isoproterenol, and GTP were added to suspending medium. In addition, isoproterenol maximally enhanced the adenylate cyclase activity of the cells in the presence of GTP. Both of these effects of isoproterenol were completely blocked by the beta-antagonist propranolol. cAMP-mediated phosphorylation of proteins in the permeabilized myocytes was investigated under conditions in which the beating frequency increased. cAMP elevated the phosphorylation level of five proteins; three of them with apparent molecular masses of 24, 15, and 12 kDa were membrane proteins and the other two with apparent molecular masses of 150 and 28 kDa were myofibrillar proteins. The 24-kDa phosphoprotein dissociated into 12-kDa molecules when boiled in sodium dodecyl sulfate, suggesting that these proteins are oligomeric and monomeric forms of phospholamban. The phosphorylation of these five proteins was stimulated by isoproterenol. The effect of isoproterenol was enhanced by GTP but completely blocked by propranolol. The time course of their phosphorylation correlated well with that of the increase in the beating frequency of the cells; both were measured after the administration of isoproterenol and GTP. When propranolol was added after the start of the stimulation by isoproterenol, only phospholamban and the 15-kDa protein were rapidly dephosphorylated in close correlation with the decrease of the beating frequency. These results demonstrate for the first time that the permeabilized myocytes retain the functional beta-adrenergic receptor and cellular responses to beta-adrenergic stimulation. They also suggest that cAMP-mediated phosphorylation of proteins, possibly phospholamban and/or the 15-kDa protein, is involved in the increased contractile activity of permeabilized heart cells.     

Role of adrenergic and cholinergic mediators in salivary phospholipids secretion.

The influence of adrenergic and cholinergic mediators on phospholipid secretion in rat sublingual salivary gland cells maintained in the presence of [3H]choline was investigated. The secretion of [3H]choline-containing phospholipids over 30 min period averaged 1.93% of the total cellular labeled phospholipids in the absence of any mediator, and was enhanced by beta-adrenergic agonist, isoproterenol, to a greater extent than the cholinergic agonists, pilocarpine and carbachol. A 2.9-fold increase in phospholipid secretion occurred with isoproterenol, while pilocarpine and carbachol evoked only 1.3-fold increase. The effect of isoproterenol was inhibited by alprenolol and that of pilocarpine and carbachol by atropine. In contrast to pilocarpine and carbachol, the enhanced phospholipid secretion due to isoproterenol was accompanied by an increase in cAMP concentration. The secretion of phospholipids was also stimulated by dibutyryl-cAMP and the protein kinase C activator, phorbol myristate acetate, but not by 4 alpha-phorbol 12,13-didecanoate which does not activate protein kinase C. Furthermore, the effects of dibutyryl-cAMP and phorbol myristate acetate were additive. The phospholipids secreted in response to isoproterenol exhibited a 52% decrease in lysophosphatidylcholine, while those secreted in response to pilocarpine and carbachol showed a 21-23% lower content of phosphatidylcholine, and were enriched in lysophosphatidylcholine (2.6-2.8-fold) and sphingomyelin (1.5-1.6-fold). The results indicate that salivary phospholipid secretion remains mainly under beta-adrenergic regulation, while the phospholipid makeup of the secretion is under cholinergic control.     

Regulation of platelet-activating factor receptor and platelet-activating factor receptor-mediated biological responses by cAMP in rat Kupffer cells

Treatment of cultured Kupffer cells with the beta-adrenergic agonist isoproterenol (10 microM) for a short period of time (30 min) attenuated the subsequent platelet-activating factor (PAF)-induced arachidonic acid release and cyclooxygenase-derived eicosanoid (e.g. thromboxane B2 and prostaglandin E2) production. This effect of isoproterenol was highly specific since the alpha-adrenergic agonist phenylephrine and the beta-adrenergic antagonist propranolol had no effect on the stimulatory effect of 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (AGEPC). The inhibitory effect of isoproterenol on the AGEPC-induced arachidonic acid release was demonstrated through the use of a specific beta-adrenergic subtype agonist and antagonist to be mediated by beta 2-adrenergic receptors on Kupffer cells. These inhibitory effects of isoproterenol can be mimicked by dibutyryl cAMP but not by dibutyryl cGMP, suggesting that a cAMP-dependent mechanism is likely involved in the regulatory action of isoproterenol. Ligand binding studies indicated that short term (i.e. 30 min) treatment of the cultured Kupffer cells with either isoproterenol or dibutyryl cAMP had no effect on the specific [3H]PAF binding. However, long term incubation (9-24 h) with dibutyryl cAMP caused down-regulation of the PAF receptors in rat Kupffer cells. Forskolin (0.1 mM), an adenylyl cyclase activator, down-regulated the surface expression of the AGEPC receptors more rapidly, decreasing the specific [3H]AGEPC binding by approximately 40% within 2 h. The receptor regulatory effect of dibutyryl cAMP and forskolin was time- and concentration-dependent. These observations suggest that a cAMP-dependent mechanism coupled with beta 2-adrenergic receptors may have important regulatory effects on the PAF receptor and post-receptor signal transducing mechanisms for PAF in hepatic Kupffer cells.     

Beta-adrenergic receptor-mediated phospholipase C activation independent of cAMP formation in turkey erythrocyte membranes.

The effect of the beta-adrenergic receptor agonist isoproterenol on guanine nucleotide-dependent phospholipase C (PLC) activity was examined in turkey erythrocyte membranes prepared from [3H]inositol-labeled turkey erythrocytes. In the presence of guanosine 5'-(gamma-thiotriphosphate) (GTP[S]) isoproterenol caused a dose-dependent stimulation of [3H]inositol phosphate ([3H]InsP) formation. The activation of PLC by GTP[S] occurred after an initial lag period of 1-2 min and was followed by a sustained rate of [3H]InsP formation which remained linear for 4-5 min. Isoproterenol decreased the lag period for GTP[S]-induced [3H]InsP formation and increased PLC activity at all time points following this lag. Consequently, isoproterenol shifted the dose-response curve for GTP[S] to the left (10-fold) and increased the maximal response. The EC50 value for isoproterenol-induced activation of PLC was 104 +/- 17 nM. Isoproterenol also potentiated GTP-dependent PLC activity but was ineffective in stimulating the enzyme in the presence of AIF4-. The PLC activation by isoproterenol was completely inhibited by propanolol and atenolol but was unaffected by prazosin or yohimbine. Although GTP[S] and isoproterenol could increase cAMP formation in this membrane preparation, the isoproterenol-induced stimulation of PLC occurred in the absence of ATP and was independent of cAMP formation. Furthermore, addition of cAMP, 8-bromo-cAMP, forskolin, or either the regulatory or catalytic subunits of cAMP-dependent protein kinase failed to stimulate [3H]InsP formation and had no effect on the responses elicited by GTP[S] and isoproterenol. Isoproterenol also stimulated [3H]InsP2 and [3H]InsP3 production in intact erythrocytes. Cholera toxin had no effect on [3H]InsP formation in the intact cells under conditions where it stimulated cAMP accumulation. In addition, the activation of PLC by GTP[S] and isoproterenol was unaffected in membranes prepared from cholera toxin-treated erythrocytes. These data demonstrate that stimulation of turkey erythrocyte beta-adrenergic receptors by isoproterenol results in a direct activation of guanine nucleotide-dependent PLC.     

Beta-adrenergic stimulation of C6 glioma cells: effects of cAMP overproduction on cellular metabolites. A multinuclear NMR study.

We used 31P-NMR spectroscopy to investigate the response of living C6 glioma cells to stimulation by a beta-adrenergic agonist, isoproterenol. In the presence of 3-isobutyl-1-methylxanthine, stimulation induced an accumulation of cAMP, making possible the NMR detection of the second messenger in living cells grown on microcarrier beads and perfused in the NMR tube. The cAMP signal rose to a maximum level within 20-25 min of stimulation; thereafter it decreased to the detection threshold within 60 min. At the same time, 40% increases of phosphomonoester and diphosphodiester signals were observed, whereas no significant change in phosphocreatine and nucleotide signals was detected. The kinetics of changes of the cellular content in phosphorylated metabolites were analyzed after recording 31P-NMR spectra of cell perchloric acid extracts as a function of time of stimulation. cAMP accumulation in stimulated cells was evidenced by a near linear increase of its NMR signal as a function of incubation time (from 0 to 60 min). Concomitantly with the production of cAMP, the data showed 30% decreases of phosphocreatine and ATP levels within 60 min of stimulation, and an unexpected redistribution of pyrimidine and purine nucleoside triphosphates. At the same time, levels of phosphomonoesters (phosphorylcholine and phosphorylethanolamine) and phosphodiesters (glycerophosphorylcholine and glycerophosphorylethanolamine) rose (50% increase). 13C-NMR spectra of cell perchloric acid extracts prepared after isoproterenol stimulation of cells incubated in the presence of [1-13C]glucose indicated a higher glucose content in stimulated cells, whereas the resonance of ribose C1 was diminished. Moreover, the resonances of C1 of ethanolamine and choline (and their derivatives) were increased in spectra of stimulated cells, whereas that of C3 of serine was decreased. In addition, the 13C-NMR data indicated that neither the pattern of glutamate carbon enrichment nor the glutamate/glutamine ratio was modified in stimulated cells. On the other hand, the heteronuclear coupling pattern of the lactate (methyl group) resonance in 1H-NMR spectra of cell incubation media indicated that no change occurred in the carbon flux through the pentose-phosphate shunt under stimulation. The results of this multinuclear NMR approach are discussed in terms of metabolic responses of C6 cells to beta-adrenergic stimulation and cAMP overproduction.     

Isoproterenol potentiates exercise-induction of Hsp70 in cardiac and skeletal muscle

The response to exercise stress is characterized by an increase in circulating catecholamines and rapid synthesis of the inducible member of the 70 kDa family of heat shock proteins (Hsp70). Cell culture studies indicate that Hsp70 expression is influenced by beta-adrenergic receptor intermediates including cyclic AMP (cAMP) and cAMP dependent protein kinase (PKA). Thus, in the present investigation, the effect of a beta-adrenergic agonist, isoproterenol (ISO; 10 mg/kg) and a beta-adrenergic antagonist, nadolol (NAD; 25 mg/kg), on the in vivo expression of Hsp70 in rodent cardiac and skeletal muscle following moderate (MOD; 17 m/min) and exhaustive (EXH; 30 m/min) exercise was examined. While ISO alone did not induce Hsp70 synthesis, ISO treatment potentiated Hsp70 expression following MOD in the white vastus and heart (395+/-29 and 483+/-29% greater than control respectively, P < 0.05). Furthermore, this effect was reversed with combined beta-adrenergic agonist and antagonist treatment (ISO+NAD) indicating that the isoproterenol induced increase in post-exercise Hsp70 expression was mediated via beta-adrenergic receptor activity. However, there were no differences in Hsp70 levels among treatment groups following EXH. The failure of NAD to attenuate Hsp70 accumulation following EXH suggests that beta-adrenergic receptor activity is not the main signal in the induction of Hsp70 following exercise. Hsp70 induction was dependent on exercise intensity and ISO administration prior to MOD resulted in Hsp70 levels similar to those observed following EXH. The results from the present investigation indicate that beta-adrenergic receptor stimulation does not induce Hsp70 synthesis per se, but may be one factor involved in the complex regulation of the stress response to exercise in vivo.     

Induction of DNA synthesis by dichloroisoproterenol without initial rise of the cAMP level in the parotid gland of mouse

The increase in the cAMP concentration in the parotid gland of mouse, observed shortly after administration of isoproterenol, was not detected after dichloroisoproterenol, a β-adrenergic blocking agent. The latter compound, however, could induce DNA synthesis which was comparable to that induced by IPR in several respects. The results strongly suggest that the initial rise of cAMP concentration in the parotid gland after IPR injection is not related directly to the initiation of the stimulated DNA synthesis.     

Control of salivary phospholipid content and composition.

The mediation of phospholipid secretion in rat sublingual salivary gland cells maintained in the presence of [3H]choline was investigated. The secretion of [3H]choline-containing phospholipids was enhanced by beta-adrenergic agonist, isoproterenol, to a greater extent than the cholinergic agonist carbachol. A 2.9-fold increase in phospholipid secretion occurred with isoproterenol, while carbachol evoked only about 1.3-fold increase. In contrast to carbachol, the enhanced phospholipid secretion due to isoproterenol was accompanied by an increase in cAMP concentration. The secretion of phospholipids was also stimulated by dibutyryl-cAMP and the protein kinase C activator, phorbol myristate acetate, but not by 4 alpha-phorbol 12, 13-didecanoate which does not activate protein kinase C. Furthermore, the effects of dibutyryl-cAMP and phorbol myristate acetate were additive. The phospholipids secreted in response to isoproterenol exhibited a 52% decrease in lysophosphatidylcholine, while those secreted in response to carbachol showed a 23% lower content of phosphatidylcholine, and were enriched in lysophosphatidylcholine (2.8-fold) and sphingomyelin (1.4-fold). The results suggest that salivary phospholipid secretion remains mainly under beta-adrenergic control, while the phospholipid makeup is under cholinergic regulation.     

Influence of caffeine on arecoline-induced SCE in mouse bone-marrow cells in vivo

The effect of exposure of mice for 5, 10 and 15 days to arecoline or/and caffeine on the frequency of sister-chromatid exchanges (SCEs) in bone-marrow cells was evaluated by using the fluorescence plus Giemsa technique. There was a significant increase in the frequency of SCEs after exposure to either arecoline or caffeine. When these two alkaloids were given in combination, the SCE frequency-enhancing effect was additive. The implications of coffee/tea drinking and betel chewing on oral cancer are discussed.     

Effects of epidermal growth factor on the syntheses of DNA and polyamine in isoproterenol-stimulated murine parotid gland

The effects of epidermal growth factor (EGF) on isoproterenol (IPR)-stimulated DNA synthesis and the activities of the rate limiting enzymes of polyamine synthesis (ornithine and S-adenosylmethionine decarboxylases) in parotid glands were investigated in vitro in cultured rat parotid explants and in vivo in submandibulectomized mice (mice after bilateral removal of the submandibular and sublingual glands). When the explants were cultured on siliconized lens paper floating on chemically defined synthetic medium, IPR caused the increases of both tissue cAMP level and the two decarboxylase activities in the prereplicative period and the stimulation of DNA synthesis with similar time courses to those observed in vivo. Dibutyryl cyclic AMP (DBcAMP) also increased the enzyme activities, but not DNA synthesis. EGF (1-2 ng/ml) had little effect on the IPR- and DBcAMP-dependent increases of amylase secretion and the enzyme activities, but it markedly enhanced IPR-stimulated DNA synthesis. Moreover, increase in DNA synthesis by DBcAMP was clearly observed in the presence of EGF when the explants were treated with this nucleotide analogue only during the early prereplicative period. In in vivo experiments, IPR-dependent increase in DNA synthesis was less in submandibulectomized mice than in intact animals. This decreased response to IPR of DNA synthesis was completely reversed by administration of EGF, though EGF alone did not induce either the enzymes or DNA synthesis. In submandibulectomized mice, although increases in the enzyme activities 8 h after injection of IPR were lower and they were significantly reversed by EGF, the activities at 12 h and the changes in polyamine levels at 8 and 12 h were almost the same as those in intact mice and were not affected by EGF treatment. These results obtained in vitro and in vivo suggest that EGF participates in the maximal response of IPR-dependent DNA synthesis but is not involved in the change of polyamine synthesis induced by IPR in murine parotid glands.     

Reactivation of chick erythrocyte nuclei in heterokaryons with rat hepatoma cells

The concentration of adenosine 3′,5′-cyclic monophosphate (cAMP) was measured in the parotid gland of the mouse after intraperitoneal injection of a beta-adrenergic drug, isoproterenol. A marked elevation of cAMP was observed 10 min after the administration, followed by a return to the control level within 40 min. A small peak was found around 14 h, onset of the stimulated DNA synthesis being observed at 20 h. A close relationship was found between the cAMP level at 10 min and the rate of DNA synthesis at 24 h in animals given different doses of the drug. However, DNA synthesis could not be induced by adrenalin in spite of a significant increase in the cAMP concentration. Furthermore, X-irradiation or certain metabolic inhibitors (actinomycin D and cycloheximide), administered prior to isoproterenol, completely inhibited the stimulated DNA synthesis without affecting the cAMP elevation at 10 min. It is concluded that the critical step in the initiation of stimulated DNA synthesis may be located at a period later than the initial cAMP elevation.     

In vivo effects of catecholamines and glucocorticoids on mouse thymic cAMP content and thymolysis

In vivo administration of the beta-adrenergic agonist, isoproterenol, induced a rapid, dose-dependent increase in the mouse thymic cyclic AMP (cAMP) content. Hydrocortisone (1 mg/animal), at a concentration which by itself did not alter the cAMP content of the thymus, markedly potentiated the effect of isoproterenol (5 micrograms/animal). Isoproterenol or hydrocortisone treatment led to a significant decrease in thymic weight and an even greater decrease in thymocyte number. In addition, the simultaneous administration of both agents produced additive effects on thymic atrophy. It appears from these results that glucocorticoids and catecholamines exert a negative control on the thymic size by increasing the programmed cell death of some cell subpopulations. Thus, glucocorticoids and catecholamines, either alone or in association, may influence the immune system under physiological or pathophysiological conditions.     

Desensitization of beta receptor mediated cyclic AMP response of cultured fibroblasts by partial agonists.

Two novel beta-adrenergic myocardial stimulants of general structure: Formula: (see text), where R is a phenyl or benzyl group were investigated for their ability to stimulate and desensitize the cyclic AMP response of C6 glioma cells. Compound ICI 89, 963 (R:phenyl) which elicited less than 1% of the maximum increase in cAMP produced by isoproterenol, was strikingly effective as a desensitizer of the isoproterenol response. This desensitization was markedly reduced by propranolol. Compound ICI 119,033 (R: benzyl) which was a more effective stimulant of cAMP synthesis than ICI 89,963, was also a more effective desensitizer of the isoproterenol response of C6 cells. The kinetics of the desensitization by ICI 89,963 were comparable with those for isoproterenol reaching a maximum in 2 to 3 hours. The data indicate that beta-adrenergic agonists are more potent as desensitizers of the cyclic AMP response than as stimulants of that response.     

Effects of catecholamines and glucagon on glycogen metabolism in human polymorphonuclear leukocytes.

Addition of 10 micron of the alpha-adrenergic agonist phenylephrine to polymorphonuclear leukocytes suspended in glucose-free Krebs-Ringer bicarbonate buffer (pH 6.7) activated phosphorylase, inactivated glycogen synthase R maximally within 30 s, and resulted in glycogen breakdown. Phenylephrine increased 45Ca efflux relative to control of 45Ca prelabelled cells, but did not affect cyclic adenosine 3',5'-monophosphate (cAMP) concentration. The effects of phenylephrine were blocked by 20 micron phentolamine and were absent in cells incubated at pH 7.4. The same unexplained dependency of extracellular pH was observed with 2.5 nM--2.5 micron glucagon, which activated phosphorylase and inactivated synthase-R, but in addition caused a 30-s burst in cAMP formation. 25 nM glucagon also increased 45Ca efflux. The activation of phosphorylase by phenylephrine and possibly also by glucagon are thought mediated by an increased concentration of cytosolic Ca2+ activating phosphorylase kinase. The effects of 5 micron isoproterenol or 5 micron epinephrine were independent of extracellular pH 6.7 and 7.4 and resulted in a sustained increase in cAMP, an activation of phosphorylase and inactivation of synthase-R within 15 s, and in glycogenolysis. The effects of both compounds were blocked by 10 micron propranolol, whereas 10 micron phentolamine had no effect on the epinephrine action. The efflux of 45Ca was not affected by either isoproterenol or epinephrine. The beta-adrenergic activation of phosphorylase is consistent with the assumption of a covalent modification of phosphorylase kinase by the cAMP dependent protein kinase. Phosphorylation of synthase-R to synthase-D can thus occur independently of increase in cAMP, but the evidence is inconclusive with respect to the cAMP dependent protein kinase also being active in this phosphorylation.     

Trypanosoma cruzi: alteration of cAMP metabolism following infection of human endothelial cells.

We have previously reported that Trypanosoma cruzi infection of endothelial cells results in alterations in the metabolism of Ca2+, inositol triphosphate (IP3), and prostacycline (PGI2). In this report, we demonstrate that infection also alters the metabolism of cAMP. Infection of endothelial cells does not significantly alter beta-adrenergic receptor density or affinity, adenylate cyclase activity, and whole-cell cAMP levels. However, incubation of infected endothelial cells with the phosphodiesterase inhibitor isobutylmethylxanthine (IBMX) resulted in less than a 60% increase in cell cAMP in contrast to the greater than a 100% increase observed in uninfected endothelial cells under otherwise identical reaction conditions. Infected endothelial cells demonstrated a twofold increase in phosphodiesterase activity when measured directly. Moreover, homogenates prepared from infected endothelial cells previously incubated with isoproterenol for 20 min showed little or no change in PDE activity. In contrast, homogenates prepared from uninfected endothelial cells treated under otherwise identical reaction conditions showed a 5.7-fold increase in PDE activity. In the presence of IBMX, isoproterenol-dependent stimulation of cAMP levels in infected endothelial cells reached a maximum level at 5 min of incubation, and thereafter rapidly declined. In contrast, cAMP levels in uninfected endothelial cells reached a maximum at 2 min of incubation, and thereafter remained elevated throughout the duration of the incubation. Infection-associated changes in isoproterenol dependent stimulation of cAMP accumulation appear to relate, in part, to changes in PDE activity.     

Effects of nonspecific beta-adrenergic stimulation and blockade on blood coagulation in hypertension.

A hypercoagulable state might contribute to increased atherothrombotic risk in hypertension. The sympathetic nervous system is hyperactive in hypertension, and it regulates hemostatic function. We investigated the effect of nonspecific beta-adrenergic stimulation (isoproterenol) and blockade (propranolol) on clotting diathesis in hypertension. Fifteen hypertensive and 21 normotensive subjects underwent isoproterenol infusion in two sequential, fixed-order doses of 20 and then 40 ng. kg(-1). min(-1) for 15 min/dose. Thirteen subjects were double-blind studied after receiving placebo or propranolol (100 mg/day) for 5 days each. In hypertensive subjects, isoproterenol elicited a dose-dependent increase in plasma von Willebrand factor (vWF) antigen [F(2,34) = 5.02; P = 0.032] and a decrease in D-dimer [F(2,34) = 4.57; P = 0.040], whereas soluble tissue factor remained unchanged. Propranolol completely abolished the increase in vWF elicited by isoproterenol [F(1,12) = 10.25; P = 0.008] but had no significant effect on tissue factor and D-dimer. In hypertension, vWF is readily released from endothelial cells by beta-adrenergic stimulation, which might contribute to increased cardiovascular risk. However, beta-adrenergic stimulation alone may not be sufficient to trigger fibrin formation in vivo.     

Role of microtubules in surfactant secretion

In the isolated perfused rat lung and cultured type II cells, surfactant secretion and cellular adenosine 3',5'-cyclic monophosphate (cAMP) content was stimulated by beta-adrenergic agonists. Isoproterenol-induced surfactant secretion was inhibited by the antimicrotubule agents colchicine and vinblastine. Incorporation of [3H]glycerol into disaturated phosphatidylcholine was augmented by beta-adrenergic agents but was not significantly different from the enhanced incorporation rate when colchicine was present. This suggests that the augmented incorporation of [3H]glycerol into disaturated phosphatidylcholine was a secondary response to storage depletion rather than direct cAMP stimulation. beta-Adrenergic agents shifted the equilibrium in the isolated perfused rat lung and cultured type II cells to favor microtubules. The stimulatory effect of 1.0 microM isoproterenol on tubulin polymerization was observed as early as 1 min and was augmented 2.8-fold at a half-maximal stimulation of 4 nM in cultured type II cells. Cytochalasin B, an antimicrofilament agent, potentiated the isoproterenol-induced secretion. These results suggest that an intact microtubule-microfilament system may be obligatory for enhanced surfactant secretion and that beta-adrenergic agents not only induce surfactant release but also tubulin polymerization.