Desensitization of the beta-adrenoceptor of lymphocytes from normal subjects and asthmatic patients in vitro

Tolerance to the protective effect of salmeterol on allergen challenge can be partially restored by the withdrawal of salmeterol regular treatment

STUDY OBJECTIVE

To assess whether the withdrawal of salmeterol treatment for 3 days (72 h) can restore its bronchoprotective ability on specific bronchial provocative test (sBPT) with allergen, which was completely lost after 1 week of regular treatment with salmeterol.

STUDY DESIGN

Single-blind design.

PATIENTS AND METHODS

We investigated 10 nonsmoking subjects (8 men and 2 women; mean +/- SD age, 24 +/- 8 years) with mild intermittent allergic asthma in the stable phase of the disease, who were never previously treated with regular beta(2)-agonists. Subjects with a previous positive early airway response (EAR) to a screening allergen challenge were considered. They underwent sBPT with allergen after a single dose of inhaled salmeterol, 50 microg (T(1)), and then underwent sBPT after 1 week of regular treatment with inhaled salmeterol, 50 microg bid (T(2)); after that, they continued inhaled salmeterol treatment for 4 days, and then changed to inhaled salmeterol with placebo (two puffs bid) for 3 days (72 h) and underwent sBPT with allergen after a single dose of salmeterol, 50 microg (T(3)).

RESULTS

EAR to allergen (DeltaFEV(1) > or = 20% with respect to postdiluent value) was completely abolished by a single dose of salmeterol (T(1); protection index [PI] > or = 50% in all subjects), but it was still present after 1 week of regular treatment with salmeterol (T(2); PI < 50% in all subjects). The maximum FEV(1) percentage fall during sBPT with allergen was significantly lower after withdrawal of regular inhaled salmeterol (T(3)) than after regular treatment with salmeterol (T(2)) (mean, 23% vs 29.5%; range, 4 to 41% vs 18 to 49%, respectively; p < 0.05); a similar result was obtained considering the PI of salmeterol on sBPT with allergen (mean, 44% vs 20%; range, 2 to 86% vs - 11 to 49%, respectively; p < 0.05). However, the maximum FEV(1) percentage fall and PI were significantly different in T(3) than after T(1), and only 4 of 10 patients showed in T(3) a PI > or = 50%.

CONCLUSIONS

The bronchoprotective effect of salmeterol on allergen-induced EAR, completely lost after 1 week of regular treatment with salmeterol, may be partially restored by the withdrawal of salmeterol therapy for 3 days (72 h). However, this withdrawal time period is not sufficient to recover the baseline bronchoprotective efficacy of the first dose of salmeterol.

Tolerance to the protective effect of salmeterol on allergen challenge

Long-term treatment with inhaled beta 2-agonists may be associated with a deterioration in asthma control, potentially due to tolerance. Regular use of short-acting beta 2-agonists has been shown to induce tolerance to allergen or adenosine 5'-monophosphate challenge. The aim of the study was to detect the efficacy of a single dose and a short-term treatment with salmeterol, a long-acting beta 2-agonist, to protect against early asthmatic reaction (EAR) to allergen. Eight subjects with mild allergic asthma underwent two treatment periods in which subjects performed an allergen challenge (specific bronchial provocation test) protected by a single dose (50 micrograms) of salmeterol (Salm-1) followed by a second specific bronchial provocation test after regular treatment with salmeterol for 1 week (Salm-2), or a single dose of placebo (Plac-1) and regular treatment (1 week) with placebo (Plac-2). Each subject performed both treatments in a randomized order. Each time allergen challenge was performed 1 h after last drug inhalation and it was stopped when the same provocative dose of allergen of a previous screening allergen challenge was achieved. The maximum decrease in FEV1 and area under curve in the first hour after allergen inhalation were significantly lower in Salm-1 (max delta FEV1 %, median [range]: 4%[0 to 9]) with respect to Salm-2, Plac-1, Plac-2 (24%[13 to 38], 31%[19 to 50], 30%[6 to 44], respectively, p < 0.001); there was no difference among Salm-2, Plac-1 and Plac-2. In Salm-1, all subjects were protected against EAR, whereas in Salm-2 only 2 subjects showed a partial protection. In conclusion the protective effect of a single dose of salmeterol against allergen-induced EAR was lost after regular treatment with salmeterol for 1 week. The clinical relevance of this mechanism remains to be elucidated.

Influence of short- and long-term inhalation of salbutamol on lung function and beta 2-adrenoceptors of mononuclear blood cells in asthmatic children

Clinical observations have shown that some asthma patients develop tachyphylaxis to beta-sympathomimetic drugs. As down-regulation of the number of beta-adrenoceptors in different human tissues after exposure to catecholamines and beta-adrenergic drugs is well known, we investigated whether a interrelation exists between beta-adrenoceptor down-regulation and clinically detectable beta-adrenergic subsensitivity during beta-sympathomimetic treatment. The following results were obtained: 1. beta 2-Sympathomimetic inhalation treatment with salbutamol in therapeutic doses led to a significant down-regulation of beta 2-adrenoceptors and consecutive cyclic adenosine monophosphate response to isoprenaline. This effect was already detectable after short-term treatment of 3-7 days in 9 asthmatic children. 2. In the long-term study over 6 months, salbutamol inhalation in 12 asthmatic children led to a significant down-regulation of beta-adrenoceptor binding sites on mononuclear blood cells (MNC) from 1539 +/- 91 to 1115 +/- 99 after 14 days, remaining in this range thereafter. 3. The mean airway resistance (Raw) of these 12 patients decreased significantly within 14 days from 8.1 +/- 0.8 to 5.7 +/- 0.5 cm H2O/l/s to remain stable throughout the 6 months of salbutamol treatment. The differences in Raw before and immediately after inhalation of 0.2 mg salbutamol (2 puffs) were unchanged during the study period. It is concluded, that long-term inhalative treatment with salbutamol over a period of 6 months does not result in refractoriness to beta-adrenergic drugs in the airways of asthmatic children, even though a significant down-regulation of beta 2-receptors on peripheral MNC occurs.

Autonomic nervous system abnormalities and asthma

Autonomic nervous system function has been studied both in vitro and in vivo using a variety of methodologies. In asthmatic patients, beta-adrenergic hyporesponsiveness and alpha-adrenergic and cholinergic hyperresponsiveness can be frequently demonstrated. These observations have provided support for the beta blockade theory of asthma, advanced in the late 1960s by Andor Szentivanyi's experiments involving sensitized rodents. However, in addition to asthma, aberrations in autonomic nervous system function have been noted in other individuals including cystic fibrosis patients and their parents, patients with emphysema and bronchitis, and in patients (allergic rhinitis and atopic dermatitis) who have demonstrable IgE antibody responses to a variety of antigens. Thus, although these defects are not specific for asthma, it is noteworthy that these conditions share many clinical features; the ultimate phenotypic expression of these abnormalities may depend on both genetic and environmental factors that have yet to be defined.

Down-regulation of surface beta-adrenoceptors on intact human mononuclear leukocytes. Time-course and isoproterenol concentration dependence

Incubation of human mononuclear leukocytes (MNL) in vitro with isoproterenol resulted in a rapid loss of surface beta-adrenoceptors, determined by radioligand binding at 4 degrees. Isoproterenol concentrations in the range of 10 nM to 100 microM resulted in significant down-regulation of beta-adrenoceptors. At a concentration of 1 microM isoproterenol, the time-dependent loss of surface beta-adrenoceptors closely paralleled the loss in isoproterenol-stimulated adenylate cyclase activity. If receptor number in intact cells was determined at 32 degrees, hardly any loss in receptor number was observed, due to reversal of down-regulation during the incubation period. When beta-adrenoceptor number in broken cell preparations was determined by [125I]cyanopindolol binding at 37 degrees no significant loss was observed, even after 2 hr of isoproterenol treatment, while [3H]CGP-12177 binding resulted in a similar reduction in binding sites as in intact cells. Reversal of loss in surface beta-adrenoceptors was rapid after 1 hr pretreatment with isoproterenol, but followed a biphasic time course after 4 hr pretreatment, with an initial rapid return of about 40% of the down-regulated receptors, followed by a slow, gradual reappearance of receptors. The results indicate that catecholamine exposure leads to a rapid sequestration of MNL surface beta-adrenoceptors away from the cell surface, to a compartment where they are inaccessible to the hydrophilic ligand [3H]CGP-12177 as well as to the lipophilic ligand [125I]cyanopindolol at 4 degrees. Up to 2 hr of isoproterenol treatment does not lead to any breakdown of sequestered beta-adrenoceptors, as they are still recognized by [125I]cyanopindolol binding in broken cell preparations.

Terbutaline-induced desensitization of human lymphocyte beta 2-adrenoceptors. Accelerated restoration of beta-adrenoceptor responsiveness by prednisone and ketotifen

We investigated, in 36 healthy volunteers, the effects of prednisone and ketotifen on recovery of lymphocyte beta 2-adrenoceptor density (determined by (-)-125iodocyanopindolol binding) and responsiveness (assessed by lymphocyte cyclic AMP [cAMP] responses to 10 microM (-)-isoprenaline) after desensitization by the beta 2-agonist terbutaline. Terbutaline (3 X 5 mg/d) decreased lymphocyte beta 2-adrenoceptor density by approximately 40-50%; concomitantly, lymphocyte cAMP responses to 10 microM (-)-isoprenaline were significantly reduced. After withdrawal of terbutaline beta 2-adrenoceptor, density and responsiveness gradually increased, reaching predrug levels after 4 d. Prednisone (1 X 100 mg orally) accelerated beta 2-adrenoceptor recovery; only 8-10 h after administration of the steroid beta 2-adrenoceptor density and cAMP responses to (-)-isoprenaline had reached values not significantly different from pretreatment levels. Similar effects were obtained with ketotifen (2 mg; thereafter 2 X 1 mg/d for 4 d): 24 h after application of the drug beta 2-adrenoceptor density and cAMP responses to (-)-isoprenaline had reached pretreatment levels. Furthermore, ketotifen simultaneously applied with terbutaline completely prevented terbutaline-induced decrease in lymphocyte beta 2-adrenoceptor density and responsiveness. Prednisone (1 X 100 mg orally) or ketotifen (2 mg; thereafter 2 X 1 mg/d for 2 d) had no significant influence on lymphocyte beta 2-adrenoceptor density in healthy volunteers not pretreated with terbutaline, but shifted the ratio high-to-low affinity state of the lymphocyte beta 2-adrenoceptor toward high affinity state. We conclude that glucocorticoids as well as ketotifen can accelerate recovery of density and responsiveness of lymphocyte beta 2-adrenoceptors desensitized by long-term treatment with beta 2-agonists. Such an effect may have clinical implications for preventing tachyphylaxis of asthmatic patients against therapy with beta 2-agonists.

Effect of exercise on isoprenaline-induced lymphocyte cAMP production in atopic asthmatics and atopic and non-atopic, non-asthmatic subjects

The effect of exercise on isoprenaline-induced cyclic adenosine monophosphate (cAMP) production was studied in peripheral-blood lymphocytes obtained from ten patients with atopic asthma, seven subjects who were atopic but did not have asthma and eight non-atopic, non-asthmatic control subjects. The asthma in the atopic subjects was mild only requiring intermittent treatment with inhaled beta adrenoceptor agonists, none of which were taken in the 48 hr prior to the study. Exercise consisted of a standardized 6-min run on a treadmill sufficient to raise the subject's pulse rate to greater than 160 bpm and respiratory function was measured before and at 5, 10, 15, 20, 30 and 60 min after the test. Blood samples were taken 5 min before and at 10 and 60 min after exercise, lymphocytes were separated by density gradient centrifugation and cAMP measured by a competitive radioimmunoassay. Exercise led to a significant decrease (27%) in the forced expiratory volume in 1 sec (FEV1) in the ten atopic asthmatic subjects but no change (less than 3%) in the non-atopic and atopic non-asthmatics. There was no significant difference in the unstimulated cAMP levels before exercise in the three groups, but stimulation with isoprenaline caused a significantly greater rise in cAMP in the non-atopic, non-asthmatic subjects when compared to both the atopic asthmatics and the atopic subjects without asthma. Exercise led to a significant elevation of cAMP in all three groups of subjects, but the same differences between the groups remained.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro effects of aqueous cotton dust extract on leucocyte cyclic adenosine monophosphate levels

Aqueous cotton dust extracts (ACDE) stimulated production of cyclic adenosine monophosphate (cAMP) in normal human peripheral blood mononuclear leucocytes (MNL). This response was not due to prostaglandin production by monocytes or platelets in the cell preparation nor to stimulation of the beta-adrenergic or H2 receptors; however, desensitization experiments indicated that the response may be receptor mediated. The possible involvement of such receptor desensitization in byssinosis pathogenesis is discussed.

Impaired lymphocyte cyclic adenosine monophosphate responses in atopic eczema

Peripheral blood lymphocyte cyclic AMP responses to isoprenaline, prostaglandin E2 and histamine were examined in patients with atopic eczema, in the presence and absence of a potent phosphodiesterase inhibitor (PDEI). Basal cyclic AMP levels were not significantly different in atopic and control groups. In the presence of the PDEI, there were impaired cyclic AMP responses to both isoprenaline and prostaglandin E2 in the atopic group. Differences between atopic and control cyclic AMP responses were exaggerated by the omission of the PDEI, when impaired responses to all agonists were observed in lymphocytes from atopic subjects. These results imply that, in atopic eczema, lymphocytes exhibit impaired responses not only at the beta-adrenoceptor site but at unrelated sites of adenylate cyclase activation, and these observations are consistent with increased leukocyte phosphodiesterase activity.

In vitro desensitization of beta adrenergic receptors in human neutrophils. Attenuation by corticosteroids

The receptor alterations involved in catecholamine-induced desensitization of adenylate cyclase in human neutrophils have been investigated as has the ability of hydrocortisone to modify such alterations. Incubation of human neutrophils with isoproterenol for 3 h in vitro resulted in an 86% reduction in the ability of isoproterenol to stimulate cyclic AMP accumulation in the cells. Two types of receptor alterations were documented. There was a 40% reduction in the number of beta adrenergic receptors (42 vs. 25 fmol/mg protein, P < 0.005) present after desensitization as assessed by [(3)H]dihydroalprenolol ([(3)H]DHA) binding. In addition the receptors appeared to be relatively uncoupled from adenylate cyclase. This uncoupling was assessed by examining the ability of the agonist isoproterenol to stabilize a high-affinity form of the receptor, detected by computer modelling of competition curves for [(3)H]DHA binding. Desensitized receptors were characterized by rightward-shifted agonist competition curves. When hydrocortisone was added to the desensitizing incubations (combined treatment) there was a statistically significant attenuation in the desensitization process as assessed by the ability of isoproterenol to increase cyclic AMP levels in the cells. Although combined treatment did not prevent the decline in receptor number, it did attenuate the uncoupling of the receptors. Combined treatment resulted in competition curves intermediate between the control and the rightward-shifted desensitization curves. Prednisolone was similar to hydrocortisone in attenuating isoproterenol-induced uncoupling. Thus, steroids appeared to attenuate agonist-induced desensitization of the beta adrenergic receptor-adenylate cyclase system by dampening the ability of agonists to uncouple receptors without modifying their ability to promote down-regulation of beta adrenergic receptors.

Lymphocyte beta-adrenergic refractoriness induced by theophylline or metaproterenol in healthy and asthmatic subjects

Beta-adrenergic refractoriness was assessed in human lymphocytes following in vivo administration of the beta-adrenergic agonist, metaproterenol, the phosphodiesterase inhibitor, theophylline, or both concomitantly, to normal and asthmatic subjects. In normal subjects both beta-adrenergic receptor number and isoproterenol stimulated cAMP response decreases during therapy with metaproterenol (59 +/- 3; 51 +/- 16% of control, respectively), theophylline (76 +/- 6; 78 +/- 16), or concomitant metaproterenol and theophylline (47 +/- 4; 69 +/- 13). The asthmatic subjects were of two types; one type responding to metaproterenol or theophylline therapy by down regulation of receptor number to zero or near zero values, and a second group of asthmatics insensitive to down regulation of receptor number. The results suggest that the induction of the refractory state is different between asthmatics and non-asthmatics, and that there may be a role for cAMP in the development of beta-adrenergic refractoriness, in vivo.

Interactions between response to inhaled prostaglandin E2 and chronic beta-adrenergic agonist treatment

Cumulative inhalation dose-response curves for the response to prostaglandin E2 (PGE2) have been constructed in normal subjects and patients with mild, stable asthma. In normal subjects cumulative inhalation dose-response curves were also constructed for salbutamol. In normal subjects dose-related bronchodilatation occurred in response to both PGE2 and salbutamol, although both the within-subject and the between-subject variation was significantly greater with salbutamol. Most asthmatic subjects gave a biphasic response to PGE2 on at least one occasion, PGE2 being a bronchoconstrictor above a certain level of specific airways conductance (sGaw) and a bronchodilator below. Chronic treatment with inhaled salbutamol (400 micrograms four times a day) had no effect on the normal subjects' response to salbutamol but there was a significant shift of the PGE2 dose-response curve to the left, indicating increased bronchodilatation (p less than 0.02). Stabilisation of the asthmatics' dose-response curve in the direction of bronchodilatation also occurred and was more pronounced (p less than 0.005). In the normal subjects PGE2 may be concerned in the control of airway smooth-muscle tone and in limiting bronchoconstriction induced by mediators such as histamine, and chronic salbutamol treatment may be important in enhancing these effects of PGE2. 80 mg oral propranolol given one and a half hours before had no effect on PGE2-induced bronchodilatation; but the question whether chronic treatment with beta-blockers has any effect needs investigation.

Airway response to salbutamol: effect of regular salbutamol inhalations in normal, atopic, and asthmatic subjects

This study was designed to determine whether resistance to the airway effects of the beta-agonist, salbutamol, would develop in three groups of subjects while taking large doses of inhaled salbutamol. Six normal non-atopic, six atopic non-asthmatic, and eight atopic asthmatic subjects were studied by an identical technique. The development of resistance was assessed from salbutamol dose-response studies in which the airway response was measured as specific airway conductance (sGaw). Further evidence was sought in the atopic and asthmatic subjects by measuring the airway response to a standard histamine inhalation challenge and the protective effect of 100 micrograms salbutamol on this challenge, and by six-hourly peak flow recordings. Subjects were assessed before and during four weeks in which they took inhaled salbutamol regularly in doses increasing to 500 microgram quid in week 4. Normal subjects showed a progressive reduction in the bronchodilator (sGaw) response to salbutamol during the four weeks, indicating the progressive development of resistance. The atopic subjects, both asthmatic and non-asthmatic, showed no reduction in the response to salbutamol during the four weeks, nor any change in the response to histamine challenge or in regular peak flow readings. These results demonstrate that asthmatic patients do not develop bronchial beta-adrenoceptor resistance easily and suggests that they and atopic non-asthmatic subjects are less susceptible to its development than normal subjects.

Heterologous desensitization of leukocytes: a possible mechanism of beta adrenergic blockade in atopic dermatitis

Studies of mononuclear leukocytes from patients with atopic dermatitis showed depressed cyclic AMP (cAMP) responses after exposure to isoproterenol, histamine, and prostaglandin E1. Because plasma and tissue histamine levels are elevated in atopic dermatitis, we questioned whether histamine or other mediators might be responsible for cAMP abnormalities. We found that exposure of normal cells to low (10(-6)M) concentrations of histamine, isoproterenol, or prostaglandin E desensitized the cells to subsequent stimulatory concentrations of any of the agonists. This heterologous desensitization occurred within 15 min and persisted for days, with gradual recovery of cAMP responses roughly paralleling those of cells from patients with atopic dermatitis. These findings provide a possible explanation for Szentivanyi's beta adrenergic blockade theory and the depressed leukocyte cAMP response to multiple agonists in atopy.

Induction of bronchial hypersensitivity: evidence for a role for prostaglandins

Bronchial hyper-responsiveness is a particular feature of asthma, but also occurs in normal subjects after a viral upper respiratory tract infection or ozone inhalation. Such stimuli would be expected to result in the release of chemical mediators of inflammation. In this study, the effects of one of these, prostaglandin F2 alpha (PGF2 alpha), on the response of normal subjects to inhaled histamine has been investigated. Nine normal volunteers took 10 inhalations of increasing concentrations of PGF2 alpha at 15-minute intervals from a Wright's nebuliser under standard conditions until a change in sGaw could be detected. The next lowest serial dilution of PGF2 alpha was subsequently inhaled by each subject every 15 min for 90 min to ensure the absence of a cumulative effect. Inhalation dose-response curves to histamine diphosphate were constructed on two separate occasions using the same standardised technique. Doses were administered every 15 min and sGaw determined five minutes after each. On one occasion each dose of histamine was immediately preceded by the non-active test dose of PGF2 alpha and on the second by saline as placebo. The study was performed double-blind and in random order. After pretreatment with PGF2 alpha the histamine dose-response curve was significantly shifted to the left in a parallel fashion (p less than 0.001). There was a significant decrease in the doses of histamine required to cause a 20% fall in sGaw (p less than 0.0015) but no significant change in the slopes of the dose-response regression lines, indicating that bronchial muscle sensitivity rather than reactivity had been predominantly affected.

Adrenoceptors: molecular nature and role in atopic diseases

Since Szentivanyi proposed the idea that asthma and other atopic diseases are due to a beta adrenergic defect there has been much interest in the role of the adrenergic receptors in allergy. The radioactive ligand binding techniques developed within the last few years have greatly increased our knowledge concerning the molecular nature of the adrenoceptors and the events following receptor stimulation. The adrenoceptors have shown to be very dynamic structures. Their number and affinity may be altered due to various physiological and pharmacological stimuli. Their role in the pathogenesis of atopic diseases has not been definitely settled, but there seem to be a true beta adrenergic hyporesponsiveness and alpha hyperresponsiveness in asthma. This article briefly describes the radioligand binding technique and summarizes our present knowledge of the nature of the alpha and beta adrenoceptors and their possible role in atopic diseases.

Regulation of human leukocyte beta receptors by endogenous catecholamines: relationship of leukocyte beta receptor density to the cardiac sensitivity to isoproterenol

High levels of beta receptor agonist have previously been shown to down-regulate beta receptor density on circulating leukocytes in man; however, the factors controlling receptor density under physiological conditions have not previously been defined. To determine whether beta receptor density is normally down-regulated by circulating, physiological levels of catecholamines we have examined the relationship between receptor density and catecholamine levels. Urinary epinephrine and norepinephrine were significantly reciprocally correlated to lymphocyte receptor density. A similar relationship existed between beta receptor density and supine plasma epinephrine, norepinephrine, upright epinephrine, and norepinephrine levels. Change in sodium intake from 10 to 400 meq/d caused a 52% increase in lymphocyte and a 48% increase in polymorphonuclear beta receptor density. The changes in receptor density were accompanied by an increase in the sensitivity to isoproterenol measured as a fall in the dose of isoproterenol required to raise the heart rate by 25 beats per minute. Beta receptor density on both lymphocyte and polymorphonuclear cells was significantly correlated to the cardiac sensitivity to isoproterenol. Propranolol administration resulted in an increase in the density of beta receptors on lymphocyte and polymorphonuclear cells that correlated with the subject's pretreatment catecholamine levels. These findings, therefore, suggest that physiological levels of catecholamines normally down-regulate beta receptors in man and that blockade of this down-regulation by propranolol allows receptor density to increase.

The beta-adrenoreceptor in human lymphocytes

The beta-adrenoreceptors of human lymphocytes were investigated by binding assays using a radiolabelled beta-adrenoreceptor agonist, 3H-hydroxybenzylisoproterenol, in an intact cell system. Intact human lymphocytes had binding sites for the ligand, which seemed to represent physiological beta-adrenoreceptors. Thus, assay of binding of the beta-adrenergic agonist, 3H-HBI, by intact lymphocytes can be used to study beta-adrenoreceptors in human tissue and to elucidate possible beta-adrenoreceptor disorders in human diseases.

Tachyphylaxis to beta-adrenoceptor agonists in human bronchial smooth muscle: studies in vitro

In studies on human isolated peripheral airway smooth muscle; 1 A concentration dependent beta-adrenoceptor tachyphylaxis was observed to isoprenaline. 2 Cross desensitization to other beta-adrenoceptor agonists was demonstrated. 3 The desensitization was reversible with time. Hydrocortisone appeared to accelerate the recovery from the desensitized state. Low concentration isoprenaline (10(-9) mol l-1) prevented recovery whereas cyclohexamide 1.8 x 10(-4) mol l-1 had no noticeable effect on recovery. Continued occupancy of the receptor appears to prevent recovery. The recovery from the desensitized state does not apparently require synthesis of new proteins. 4 Bronchial wall cyclic AMP response to isoprenaline was attenuated after isoprenaline induced desensitization whereas total phosphodiesterase activity of bronchial wall was not altered by desensitization. Thus by exclusion the adenylate cyclase receptor complex may be altered in human peripheral airway smooth muscle beta-adrenoceptor tachyphylaxis.

Effects of ethanol on human lymphocyte levels of cyclic AMP. In vitro: Potentiation of the response to isoproterenol, prostaglandin E2 or adenosine stimulation

The effects of ethanol, acetone and dimethylsulfoxide (DMSO) were tested on the accumulation of cyclic AMP in human peripheral blood lymphocytes in vitro. Isoproterenol (1.0X10(-8) - 1.0X10(-4)M), PGE2 (3X10(-8)-3X10(-6)M), adenosine (10(-7) - 10(-4)M) and phenylisopropyladenosine (10(-8) - 10(-4)M) caused a dose dependent increase in cyclic AMP accumulation. Over the entire range of concentration of stimulating drugs, ethanol caused an enhanced accumulation of cyclic AMP. At temperatures between 15 degrees and 30 degrees the effect of ethanol rose with increasing concentration from 0.2-6%. At 37 degrees and 40 degrees, 6% ethanol had less stimulatory effect than 2% ethanol. The effect of ethanol was shared by acetone and to a minor extent by DMSO, and was present also when phosphodiesterase was inhibited by isobutylmethylxanthine. It is suggested that ethanol enhances adenylate cyclase activity as a consequence of altered cell membrane fluidity. Since the effects on cyclic AMP accumulation can be observed already at rather low concentration of the solvents they may be of toxicological significance.

Desensitization of the beta-adrenoceptor of lymphocytes from normal subjects and patients with phaeochromocytoma: studies in vivo

1 Following the observation that lymphocyte beta-adrenoceptor responsiveness was not depressed in asthmatics treated only with non-adrenergic drugs we have explored the effects of prolonged exposure to beta-adrenoceptor agonists in normal subjects. 2 Treatment with oral salbutamol (12-16 mg/kg/day for 10 days), or with inhaled salbutamol (3000 microgram/day for 8-10 days) resulted in a significant reduction in lymphocyte beta-adrenoceptor responsiveness. 3 A 48 h infusion of isoxsuprine (10 mg/h) resulted in a marked depression of lymphocyte beta-adrenoceptor responsiveness (P less than 0.001). 4 Prolonged elevation of endogenous catecholamines caused by phaeochromocytoma was also associated with a marked depression of lymphocyte beta-adrenoceptor responsiveness (P less than 0.001). 5 There was no evidence that an increase in phosphodiesterase activity could explain the reduced cyclic AMP response. 6 It is concluded that diminished beta-adrenoceptor response occurs as a response to prolonged exposure to beta-adrenoceptor agonists. It is likely that the diminished response seen in asthmatic subjects can be explained on a similar basis and does not indicate an inherent cellular defect. 7 The possible clinical significance of such changes in asthmatics are discussed.