[The effect of R(+) limonene on ß-adrenergic signaling in smooth muscles: the significance of oxidative stress index]. / R(+)limonén hatása a ß-adrenerg jelátvitelre a simaizomzatban: az oxidatív stressz index jelentosége.

Reactive oxygen intermediers (ROI) play a role in the signal transduction of beta-adrenergic receptors. We investigated whether an antioxidant (limonene) can reduce the beta-mimetic effect of terbutaline in beta-2-adrenergic receptor (ß2-AR)-regulated smooth muscles. Tissue samples were collected from nonpregnant (trachea) and 22-day-pregnant (myometrium and cervix) rats. Tissue contractility was investigated in an isolated organ bath. In separate groups of animals, the tracheal and uterine ß2-AR activities were upregulated by 17-beta-estradiol valerate (E2) and progesterone (P4), respectively. The total oxidant (TOS) and total antioxidant status (TAS) were also measured. The oxidative stress index (OSI) was defined as the ratio ofTOS and TAS. Terbutaline (10(-10) - 10(-5) M) decreased the spontaneous contractions in the nontreated and the P4-pretreated myometria. The concentration-response curves for terbutaline in the presence of 10-3 M limonene were shifted to the left, but the maximum inhibitory effect was unchanged. Terbutaline (10(-6) M) increased the cervical resistance both in the nontreated and in the P4-treated samples, while limonene reduced this action only in the P4-treated cervices. Terbutaline (10(-9) - 10(-4) M) reduced the tracheal tones both in the nontreated and in the E2-treated tissues, while limonene reduced these effects. The OSI was highest in the trachea and lowest in the pregnant myometrium. Limonene has various influence on terbutaline induced effects in certain tissues. Higher OSI value means, that the antioxidants have greater role in the beta-adrenergic signalmechanism. We assume that the significance of ROI in the signalling process of the ß2-ARs are divergent in the various tissues. Our results suggest that the antiasthmatic effect of beta-mimetics may worsen during parallel limonene administration.

Pulmonary alveolar type II cells isolated from rats. Release of phosphatidylcholine in response to beta-adrenergic stimulation.

It is unclear what factors control the secretion of pulmonary surface active material from alveolar type II cells in vivo. Other workers have suggested that cholinergic stimuli, adrenergic stimuli, and prostaglandins may all stimulate secretion. We isolated type II cells from the lungs of rats by treatment with elastase, discontinuous density centrifugation, and adherence in primary culture. beta-Adrenergic agonists, but not cholinergic agonists, caused an increase in the release of [(14)C]disaturated phosphatidylcholine, the major component of surface-active material, from type II cells in culture. The beta-adrenergic effect was stereo-selective, (-)-isoproterenol being 50 times more potent than (+)-isoproterenol. Terbutaline, 10 muM, a noncatecholamine beta-2 adrenergic agonist, caused a release of 2.0+/-0.5 (mean+/-SD) times the basal release of [(14)C]disaturated phosphatidylcholine in 3 h; the concentration of terbutaline causing half maximal stimulation was 800 nM. The terbutaline effect was blocked by propranolol, a beta-adrenergic antagonist (calculated K(d) = 6 nM), but not by phentolamine, an alpha-adrenergic antagonist. Isobutylmethylxanthine, a phosphodiesterase inhibitor, and 8-Br cyclic AMP, but not 8-Br cyclic guanosine monophosphate, also stimulated release. We conclude that type II cells secrete disaturated phosphatidylcholine in response to treatment with adrenergic stimulation.

Beta 2-adrenergic regulation of prostaglandin D2 receptor in rabbit platelets.

[3H]Prostaglandin D2 binding to rabbit platelets was increased by about 150% in the presence of beta-adrenoceptor agonist, isoproterenol. The isoproterenol-induced potentiation of the [3H]prostaglandin D2 binding gave a bell-shaped dose-response relationship (maximum response at 3 X 10(-8) M) in a stereospecific manner. Similar and moderate potentiation was obtained with terbutaline. On the other hand, beta-adrenoceptor antagonists such as alprenolol, propranolol and butoxamine (beta 2-specific) had no potentiating effect on [3H]prostaglandin D2 binding; rather, they abolished the isoproterenol-induced increase of [3H]prostaglandin D2 binding. The beta 1-specific antagonist, metoprolol, did not have any effect. Rabbit platelets were found to possess one [3H]prostaglandin D2 binding site (Kd = 6 X 10(-7) M, Bmax = 787 fmol/mg protein). In the presence of isoproterenol at 3 X 10(-8) M, Bmax was increased with unaltering Kd value. Isoproterenol did not increase [3H]prostaglandin E1, [3H]prostaglandin E2 and [3H]prostaglandin F2 alpha bindings to platelets. The potential effect of isoproterenol was mimicked by forskolin, theophylline, dibutyryl cyclic AMP, prostaglandin E1 and prostaglandin I2, but it was abolished by 2', 5'-dideoxyadenosine, an inhibitor of adenylate cyclase, indicating that elevated level of cyclic AMP may be available for the induction of the increase of [3H]prostaglandin D2 binding. Prostaglandin D2-induced cyclic AMP synthesis and antiaggregation activity were also augmented in the presence of isoproterenol. These results suggest a beta 2-adrenoceptor-mediated cyclic AMP-dependent mechanism for the regulation of prostaglandin D2 receptor binding in rabbit platelets.

Positive inotropic effects of the beta 2-adrenoceptor agonist terbutaline in the human heart: effects of long-term beta 1-adrenoceptor antagonist treatment.

OBJECTIVES: This study was conducted to determine whether activation of cardiac beta 2-adrenoceptors increases contractility in humans and whether this is affected by long-term beta 1-adrenoceptor antagonist treatment. BACKGROUND: Coexistence of beta 1- and beta 2-adrenoceptors in the human heart is generally accepted. The functional importance of cardiac beta 2-adrenoceptors for increases in contractility in humans, however, has not been completely established. METHODS: We studied 1) the beta-adrenoceptor subtype mediating positive inotropic effects of the beta 2-adrenoceptor agonist terbutaline in vitro (on right atrial and left ventricular preparations from nonfailing human hearts) and increases in contractility (by measurement of systolic time intervals) in vivo in seven healthy male volunteers; and 2) in vivo whether long-term treatment of volunteers with the beta 1-adrenoceptor antagonist bisoprolol affects terbutaline-induced increases in contractility. RESULTS: In vitro terbutaline caused a concentration-dependent increase in atrial and ventricular adenylate cyclase activity and force of contraction. Terbutaline effects were antagonized only by the beta 2-adrenoceptor antagonist ICI 118,551, indicating that they were mediated by beta 2-adrenoceptor stimulation. In vivo intravenous infusions of terbutaline (dose range 25 to 300 ng/kg body weight per min for 15 min) dose dependently increased heart rate and shortened the pre-ejection period and heart rate-corrected electromechanical systole (QS2) time. These effects are mediated predominantly by beta 2-adrenoceptor stimulation because they were only marginally affected by the beta 1-adrenoceptor antagonist bisoprolol (1 x 10 mg orally), either given 2 h before infusion or long term for 3 weeks. CONCLUSIONS: Stimulation of cardiac beta 2-adrenoceptors in humans causes not only in vitro but also in vivo positive inotropic effects. Long-term beta 1-adrenoceptor antagonist treatment does not considerably affect beta 2-adrenoceptor-mediated in vivo increases in contractility. Thus, it may be possible to treat patients with chronic heart failure and long-term beta 1-adrenoceptor antagonist therapy with beta 2-adrenoceptor agonists if immediate inotropic support is needed.

Effects of terbutaline on NGF formation in allergic inflammation of the rat.

1. The aim of this study was to determine the effects of the beta adrenergic agonist terbutaline on NGF increase caused by allergic inflammation in rats. 2. Intraplantar antigen injection in sensitized rats increased paw volume and stimulated NGF biosynthesis in the skin of the injected paw as determined 3 and 6 h after injection. Treatment of rats with terbutaline (0.1 - 0.3 mg kg(-1), s.c.) had no significant effect on the NGF concentration in non-inflamed skin, but reduced oedema, and at 0.3 mg kg(-1) also NGF mRNA and immunoreactive NGF in the skin of the inflamed paw in a propranolol-reversible manner. In carrageenan-induced inflammation, terbutaline did not significantly reduce the inflammation-induced increase of NGF in paw skin. 3. Exposure of sensitized rats to aerosolized antigen (twice, 24 h interval) increased protein content, eosinophil leukocytes, and immunoreactive NGF in the bronchoalveolar lavage fluid (BAL, obtained 16 h after the second antigen exposure). Treatment of rats with terbutaline (0.3 mg kg(-1), s.c. 30 min before the second antigen challenge) suppressed antigen-induced elevation of protein and eosinophil leukocytes, and reduced the concentration of NGF in BAL to values similar to those found in non-sensitized rats. 4. The present results demonstrate anti-allergic properties of terbutaline in rats that were accompanied by a marked reduction of antigen-induced NGF increase in skin and BAL, respectively. These results are compatible with the assumption that terbutaline primarily suppressed the immune response to antigen thereby attenuating the release of vasoactive mediators and the stimulation of NGF biosynthesis.

Effects of terbutaline on force and intracellular calcium in slow-twitch skeletal muscle fibres of the rat.

1. The effect of the alpha2-adrenoceptor agonist, terbutaline, was investigated on simultaneously measured force and intracellular free calcium ([Ca2+]i) in intact rat soleus muscle fibres, and on contractile protein function and Ca2+ content of the sarcoplasmic reticulum (SR) in skinned fibres. 2. Terbutaline (10 microM) had no significant effect on either resting force or [Ca2+]i. Exposure to terbutaline increased both the integral of the indo-1 ratio transient and peak twitch force by 37%. 3. At sub-maximal (10 Hz) stimulation frequencies, terbutaline accelerated force relaxation but had highly variable effects on tetanic force amplitude. The corresponding indo-1 ratio transients were significantly larger, and faster to decay than the controls. 4. Terbutaline increased tetanic force at near maximal stimulation frequencies (50 Hz) by increasing tetanic [Ca2+]i. Force relaxation was accelerated at this frequency with no significant change in the indo-1 ratio transient decay rate. 5. All of terbutaline's effects on force and indo-1 ratio transients in intact fibres were completely blocked and reversed by ICI 118551 (1 microM). 6. Mechanically skinned fibres isolated from intact muscles pre-treated with terbutaline showed no significant changes in SR Ca2+ content, myofilament [Ca2+]i-sensitivity or maximum force generating capacity. 7. The results suggest that terbutaline primarily modulates force by altering the amplitude and decay rate of the [Ca2+]i transient via phosphorylation of both the ryanodine receptor (RR) and the SR pump regulatory protein, phospholamban (PLB). The high variability of responses of slow-twitch muscles to beta2-agonists probably reflects individual differences in basal phosphorylation levels of PLB relative to that of RR.

Beta-adrenergic regulation of renin expression in differentiated U-937 monocytic cells.

Previous studies from our laboratories demonstrated that human decidual macrophages and peripheral mononuclear cells express renin. In the present study, we found that U-937 monocytes, induced to differentiate into macrophage-like cells by treatment with phorbol dibutyrate (PDBU), express renin mRNA and release renin (95%, of which is in the form of prorenin). Treatment of these PDBU-exposed cells with dibutyryl-cAMP (1 mM) caused a 20-fold increase in renin mRNA and a 10-fold increase in prorenin release. Forskolin (10 microM), an activator of adenylyl cyclase, and terbutaline (100 microM), a beta2-adrenergic agonist known to increase cAMP levels, also increased renin mRNA and prorenin release. The secretory response to terbutaline was potentiated by the type IV cyclic AMP-phosphodiesterase (PDE) inhibitor Ro 20-1724 (50 microM). Angiotensin II agonist inhibited the stimulatory effect of terbutaline on renin secretion as did the cytokines tumor necrosis factor-alpha and lipopolysaccharide plus interferon-gamma. Since other studies have shown that U-937 cells possess beta2-adrenergic receptors and express mainly the type IV PDE, the present findings strongly suggest that beta-adrenergic receptors in mononuclear cells are coupled to renin expression via the cAMP transduction pathway. The results support a possible role for the renin-angiotensin system in macrophage function and suggest potential autocrine regulatory mechanisms in prorenin expression.

Inhibition of phosphatidylcholine secretion by stilbene disulfonates in alveolar type II cells.

Various agents stimulate the secretion of lung surfactant from alveolar type II cells by increasing intracellular Ca2+, cyclic adenosine-3':5'-monophosphate (cAMP), or diacylglycerol. A few agents, including the purified surfactant protein A, are known to inhibit the secretion by an unknown mechanism. In the present study, we demonstrated that stilbene disulfonic acids, 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) and 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid (SITS), are potent but reversible inhibitors of lung surfactant secretion. The inhibition was concentration dependent, and the EC50 was 5 microM for DIDS and 50 microM for SITS. The inhibition was not specific to agonists for any one type of receptor, and was also observed for secretion stimulated by 8-bromo-cAMP, or tetradecanoyl phorbol acetate, suggesting that the site of inhibition was distal to the generation of intracellular second messengers. This was also supported by the failure of DIDS to block the stimulus-mediated increase in diacylglycerol content of type II cells. Further, DIDS and SITS were also inhibitory for basal secretion. Based on the reversibility of inhibition and the fact that inhibition was observed with both basal and stimulated secretion, we suggest that stilbene disulfonic acids affect a component of the exocytosis process that occurs at or near the plasma membrane.

The effects of enalapril and spironolactone on terbutaline-induced hypokalemia.

OBJECTIVE: To investigate whether enalapril (E) 10 mg and spironolactone (S) 100 mg attenuate the hypokalemic effect of inhaled terbutaline (T). DESIGN: Randomized single-blind crossover. Subjects received the following treatment combinations: (a) placebo (P), (b) T alone, (c) T + E, or (d) T + S. SETTING: University Department of Clinical Pharmacology. PARTICIPANTS: Twenty healthy volunteers (ten male, ten female) of mean age 22.8 +/- 3.1 years. MAIN OUTCOME MEASURES: Serum potassium, magnesium, ECG changes (R-R interval, T wave, and QTc interval) for 4 h after terbutaline inhalation. MAIN RESULTS: Baseline serum potassium levels were higher following prior treatment with E and S; P, 3.78 mmol/L (3.67 to 3.88); T + E, 3.93 mmol-1 (3.82 to 4.03); and T + S, 4.03 mmol/L (3.93 to 4.14) (p less than 0.05). Mean potassium concentrations over 4 h were also higher following prior treatment with E and S; T, 3.58 mmol/L (3.54 to 3.63); T + E, 3.68 mmol/L (3.64 to 3.72) (p less than 0.05); and T + S, 3.73 mmol/L (3.68 to 3.78) (p less than 0.01). CONCLUSIONS: Enalapril and spironolactone protect against the fall in serum potassium over 4 h by elevating baseline potassium concentration. These potassium-sparing drugs, however, should not be used to prevent the hypokalemic and electrocardiographic sequelae of inhaled beta 2-agonists.

Effects of timolol on terbutaline- and VIP-stimulated aqueous humor flow in the cynomolgus monkey.

The effects of timolol on terbutaline- and VIP-stimulated aqueous humor flow were investigated in cynomolgus monkeys, with a labeled albumin dilution method. The maximal increase in aqueous humor flow caused by intracameral (100 micrograms/ml) or intravenous (0.4 micrograms/kg/min) administration of terbutaline was about 100%. The effect of intravenously infused terbutaline was completely abolished by intracameral administration of timolol, 0.1 mg/ml. The same dose of timolol also abolished the effect of intravenously infused VIP, 50 ng/kg/min. Intravenous administration of timolol, 0.2 mg/kg, had no effect on VIP-stimulated aqueous humor flow, when VIP (90 micrograms) was given intracamerally, but abolished completely the effect of intracameral terbutaline, 100 micrograms/ml. The results suggest that the effect of intravenously infused VIP on aqueous humor flow is secondary to activation of the sympathetic nervous system, while the effect of intracameral administration of VIP is a direct effect on the ciliary epithelium. The maximal aqueous humor flow achieved with terbutaline is comparable to that in conscious cynomolgus monkeys.

Analysis of the beta-receptor mediated effect on slow-contracting skeletal muscle in vitro.

Subtetanic contractions of the guinea-pig isolated soleus, a slow-contracting skeletal muscle, were evoked by transmural field-stimulation. Isoprenaline caused a dose-dependent depression of the contractions. This effect was inhibited by propranolol and H 35/25 (1-(p-tolyl-2-isopropylamino-1-propanol) but not by practolol. Similar results were obtained for terbutaline. Tazolol and H 80/62 (1-isopropylamino-3-(p-hydroxyphenoxy)-2-propanol (HCl), selective beta1-agonists, had no effect per se but inhibited the effect of terbutaline. Adrenaline, noradrenaline, and dopamine all caused a dose-dependent decrease in the force of the soleus contractions, their potencies being in that order. Tyramine did not appreciably affect the contractions nor did it inhibit the effect of terbutaline. Pretreatment with reserpine, if anything, increased the response to terbutaline. It is concluded, in conformity with previous in vivo studies, that the adrenergic receptor mediating the effect on the soleus muscle contractions is of the beta2-type. Indirect sympathomimetic effects do not contribute to the responses observed on the isolated soleus muscle.

Tocopherol inhibits the relaxing effect of terbutaline in the respiratory and reproductive tracts of the rat: the role of the oxidative stress index.

AIMS: Reactive oxygen species play a role in the signal transduction of beta-adrenergic receptors. We investigated whether an antioxidant (tocopherol) can reduce the effect of terbutaline in beta-2-adrenergic receptor (ß2-AR)-regulated smooth muscles. MAIN METHODS: Contractility of the tissues from nonpregnant (trachea) and 22-day-pregnant (myometrium and cervix) rats was investigated in an isolated organ bath. The tracheal and uterine ß2-AR expressions were increased by 17-beta-estradiol valerate (E2) and progesterone (P4), respectively. The accumulation of cyclic-AMP (cAMP), and the total oxidant (TOS) and total antioxidant status (TAS) were also measured. The oxidative stress index (OSI) was defined as the ratio of TOS and TAS. KEY FINDINGS: Terbutaline (10(-10)-10(-5)M) decreased the contractions in the nontreated and the P4-pretreated myometria, but tocopherol (10(-7)M) did not alter these actions. Terbutaline (10(-6)M) increased the cervical resistance both in the nontreated and in the P4-treated samples, while tocopherol reduced this action only in the P4-treated cervices. Terbutaline (10(-9)-10(-4)M) reduced the tracheal tones both in the nontreated and in the E2-treated tissues, while tocopherol reduced these effects. The changes in the intracellular cAMP levels of the tissues were in harmony with the isolated organ results. The OSI was highest in the trachea and lowest in the pregnant myometrium. SIGNIFICANCE: A higher OSI is linked to a higher tocopherol sensitivity of beta-mimetic-induced relaxation. Our results suggest that the antiasthmatic effect of beta-mimetics may worsen, while their tocolytic effect may remain unchanged during parallel tocopherol administration.

Immunologic release of histamine from dog lung: comparison of in vivo and in vitro responses in the same animal.

The purpose of this study was to compare, for the first time, antigen-induced histamine release from the lung in the same natively allergic dogs both in vitro and in vivo. In six dogs, maximal antigen-induced histamine release from the lung correlated closely in vitro and in vivo (r = 0.94), although it varied widely between dogs (0% to 75.5% of total tissue histamine content); similarly, the antigen concentration to produce 50% of maximal histamine release varied sixfold between dogs (40 micrograms/ml to 250 micrograms/ml). In each of five other dogs, terbutaline sulfate administered intravenously caused a dose-dependent inhibition of antigen-induced histamine release from lung fragments in vitro: the maximal inhibition produced by 1 mg/kg was 60 +/- 4.5% (mean +/- SEM). In these same dogs, 10(-5)M terbutaline incubated with lung fragments in vitro caused inhibition of antigen-induced histamine release comparable to 1 mg/kg terbutaline in vivo. Increasing the dose of terbutaline in vitro produced maximal inhibition at 10(-4)M with no greater effect of the drug at 10(-3)M (71.4 +/- 3.8% inhibition). In both experimental situations propranolol caused a dose-dependent inhibition of beta-adrenergic modulation of Ascaris-induced release of histamine. This result supports the conclusion that terbutaline produced its effects by actions mediated by beta-adrenergic receptors on pulmonary mast cells. This experimental approach provides a suitable preparation in which to estimate the effective dose of agonists that modulate antigen-induced mast cell function in vivo.

The effects of frusemide and triamterene on the hypokalaemic and electrocardiographic responses to inhaled terbutaline.

Fifteen normal volunteers were given 5000 micrograms inhaled terbutaline following three separate 4 day oral treatment periods with placebo, frusemide 40 mg, and frusemide 40 mg plus triamterene 50 mg. Serum potassium (K), and electrocardiographic (ECG) responses were measured after 30 min rest and 30 min after inhalation of terbutaline. Frusemide produced significant hypokalaemia compared with placebo (means and 95% CI): 3.58 mmol l-1 (3.5-3.66) vs 3.88 mmol l-1 (3.8-3.96) (P less than 0.001), and this effect was significantly attenuated by the addition of triamterene: 3.80 mmol l-1 (3.72-3.88) (P less than 0.05). Terbutaline alone also caused significant hypokalaemia: from 3.88 mmol l-1 (3.8-3.96) to 3.35 mmol l-1 (3.24-3.46) (P less than 0.001), and a lower absolute level of K was seen when combined with frusemide: 3.13 mmol l-1 (3.02-3.24) (P less than 0.05). The addition of triamterene conferred no significant protection against the combined hypokalaemia: 3.29 mmol l-1 (3.18-3.4). Changes in T wave amplitude during the study periods showed a similar pattern of response to the hypokalaemic effects. These results show that the hypokalaemic response to terbutaline was additive to that of frusemide, and that triamterene attenuated the hypokalaemic response to frusemide, but not terbutaline.

The effect of insulin on skeletal muscle contractions and its relation to the effect produced by BETA-adrenoceptor stimulation.

The soleus, a slow-contracting, and the extensor digitorum longus (EDL), a fast-contracting muscle, from the guinea-pig were prepared for measurement of isometric contractions in vitro. Insulin, 2.5-55 mu/ml, caused a dose-dependent depression of twitches and subtetanic concentrations of the soleus muscle similar to and additive with that produced by the beta 2-adrenoceptor agonist, terbutaline. The effect of terbutaline but not that of insulin was blocked by propranolol. Insulin had no apparent effect on the contractions of the EDL, whereas terbutaline increased the force of contraction. When depressed by KCl, however, insulin partially restored the twitch tension in both muscles. The possible role of effects on the Na+-K+ transport is discussed.

beta-Adrenergic induced synthesis and secretion of phosphatidylcholine by isolated pulmonary alveolar type II cells.

Rat pulmonary alveolar type II cells isolated by trypsinization and discontinuous density gradient ultracentrifugation were maintained in primary culture for 48 hours. The cultured type II cells responded to beta-adrenergic, but not cholinergic, agonists by an increase in the rate of synthesis and also secretion of 3H-phosphatidylcholine. The beta-adrenergic agonists, isoproterenol and terbutaline, 10 microM, caused a 1.7-fold increase in the rate of synthesis of 3H-phosphatidylcholine after a 4-hour incubation. At this time, there was also an increase in the cAMP content of the cultured cells. Terbutaline, 10 microM, caused a 4.9-fold increase in the rate of secretion of 3H-phosphatidylcholine after a 1-hour incubation. The beta-adrenergic effect on both synthesis and secretion by type II cells was blocked by propranolol. 8-Br-cAMP, 100 microM, but not 8-Br-cGMP, mimicked the beta-adrenergic effect on both synthesis and secretion of 3H-phosphatidylcholine. The increased rate of 3H-phosphatidylcholine induced by beta-adrenergic agonists was unaffected by colchicine. These data are consistent with the hypothesis that both synthesis and secretion of pulmonary surfactant are under adrenergic control operating through a beta-receptor and the adenylate cyclase system. These data also suggest that synthesis and secretion of pulmonary surfactant are independent processes. The possibility of other neural or hormonal mechanisms is not excluded.

Effects of terbutaline on human uterine motility at term.

The effects of the selective beta-2-receptor stimulator terbutaline on the activity of gravid, human myometrium were investigated in vitro and in vivo, before and after administration of different beta-receptor blockers. Terbutaline, 0.2-1.0 mu-g/ml, inhibited the spontaneous contractile activity of isolated strips of myometrium. This effect was unaffected by the selective beta-a-receptor blockers practolol, 1 mu-g/ml, and H 93/26, 1 mu-g/ml. However, the non-selective blocker propranolol, 0.1 mu-g/ml, completely inhibited the terbutaline effects. The in vitro effects of terbutaline could be correlated with findings in vivo. Intra-uterine pressure was recorded in 4 pregnant women at term. Infusion of terbutaline, 10-15 mu-g/min, for 20-40 min, effectively inhibited both spontaneous and oxytocin-stimulated uterine activity. There was a moderate increase in maternal heart rate, but no consistent effect on maternal blood pressure. Fetal heart rate was little affected. The uterine effects of terbuline were not influenced by practolol, 5-20 mg i.v., but completely inhibited by propranolol, 1-2 mg i.v. The results suggest that terbutaline inhibits uterine motility by effects on uterine beta-2-receptors and that it can be given in clinically effective doses without adverse circulatory effects on mother or fetus.

Beta-agonist activation of an amiloride-insensitive transport mechanism in rabbit pleura.

The beta-agonist terbutaline increases the net rate of liquid absorption from hydrothoraces with albumin-Ringer solution: since beta-agonists decrease lymphatic drainage, the effect of terbutaline seems due to an increase in solute-coupled liquid absorption, (Zocchi et al. 1994 Respir. Physiol. 97:347-356). In this research we determined in anesthetized rabbits the rate of volume change in albumin-Ringer hydrothoraces of different size with amiloride plus terbutaline, and compared it with that previously obtained in hydrothoraces with amiloride alone. The net rate of liquid absorption was 0.09 ml/h greater (P < 0.01) with amiloride plus terbutaline than with amiloride alone. This indicates that terbutaline activates an amiloride-insensitive mechanism of Na+ transport. The increase in net rate of liquid absorption produced by terbutaline persisted with bumetanide 10(-6) M and SITS 10(-4) M, disappeared almost completely with bumetanide 10(-5) M, and completely with furosemide 10(-3) M. These findings suggest that the mechanism activated by terbutaline, when the amiloride-sensitive mechanisms of the pleura have been blocked, is a Na(+)-K(+)-2 Cl- or Na(+)-Cl- symport little sensitive to bumetanide.