Endogenous activation of adenosine A(1) receptors accelerates ischemic suppression of spontaneous electrocortical activity

Cerebral ischemia induces a rapid suppression of spontaneous brain rhythms prior to major alterations in ionic homeostasis. It was found in vitro during ischemia that the rapidly formed adenosine, resulting from the intracellular breakdown of ATP, may inhibit synaptic transmission via the A(1) receptor subtype. The link between endogenous A(1) receptor activation during ischemia and the suppression of spontaneous electrocortical activity has not yet been established in the intact brain. The aim of this study was to investigate in vivo the effects of A(1) receptor antagonism by 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) on the time to electrocortical suppression during global cerebral ischemia. Adult male Wistar rats under chloral hydrate anesthesia were subjected to 1-min transient "four-vessel occlusion" ischemic episodes, separated by 20-min reperfusion. The rats were injected intraperitoneally with either 1.25 mg/kg DPCPX dissolved in 2 ml/kg dimethyl sulfoxide (DMSO) or the same volume of DMSO alone, 15 min before the third ischemic episode. Time to electrocortical suppression was estimated based on the decay of the root mean square of two-channel electrocorticographic recordings. During the first two ischemic episodes, electrocortical suppression appeared after approximately 12 s in both groups. After DMSO administration, ischemic suppression remained unchanged. After DPCPX administration, the time to electrocortical suppression was increased by approximately 10 s, and bursts of activity were recorded during the entire ischemia. These effects disappeared within 15 h after DPCPX administration. Our data provide evidence that during cerebral ischemia endogenous activation of A(1) receptors accelerates the electrical "shut-down" of the whole brain.     

Caffeine reverses antinociception by amitriptyline in wild type mice but not in those lacking adenosine A1 receptors

Amitriptyline is used to treat neuropathic pain in humans. It produces antinociception in several animal models of pain, and this effect is blocked by methylxanthine adenosine receptor antagonists which implicates adenosine it its actions. Here, the antinociceptive effect of amitriptyline, and the ability of caffeine to reverse it, were examined using the formalin test (a model of persistent pain) in wild type mice and mice lacking the adenosine A₁ receptor (A1R). Amitriptyline produced dose-related suppression of flinching in wild type mice following both systemic and intraplantar drug administration; both of these effects were unaltered in A1R −/− mice. Following systemic administration, caffeine reversed the systemic effect of amitriptyline in wild type, but not A1R −/− mice; −/+ mice exhibited an intermediate effect. Intraplantar administration of caffeine also reversed the effect of intraplantar amitriptyline in A1R +/+, but not in −/− or +/− mice. These results indicate that adenosine A₁ receptors are not required in order for amitriptyline to cause antinociception in mice, but they are required to see caffeine reversal of this antinociceptive effect. When A1Rs are present, actions of amitriptyline may, however, partly depend on A1Rs.     

Transient enhancement of inhibitory synaptic transmission in hippocampal CA1 pyramidal neurons after cerebral ischemia

Pyramidal neurons in hippocampal CA1 regions are highly sensitive to cerebral ischemia. Alterations of excitatory and inhibitory synaptic transmission may contribute to the ischemia-induced neuronal degeneration. However, little is known about the changes of GABAergic synaptic transmission in the hippocampus following reperfusion. We examined the GABA_A receptor-mediated inhibitory postsynaptic currents (IPSCs) in CA1 pyramidal neurons 12 and 24 h after transient forebrain ischemia in rats. The amplitudes of evoked inhibitory postsynaptic currents (eIPSCs) were increased significantly 12 h after ischemia and returned to control levels 24 h following reperfusion. The potentiation of eIPSCs was accompanied by an increase of miniature inhibitory postsynaptic current (mIPSC) amplitude, and an enhanced response to exogenous application of GABA, indicating the involvement of postsynaptic mechanisms. Furthermore, there was no obvious change of the paired-pulse ratio (PPR) of eIPSCs and the frequency of mIPSCs, suggesting that the potentiation of eIPSCs might not be due to the increased presynaptic release. Blockade of adenosine A1 receptors led to a decrease of eIPSCs amplitude in post-ischemic neurons but not in control neurons, without affecting the frequency of mIPSCs and the PPR of eIPSCs. Thus, tonic activation of adenosine A1 receptors might, at least in part, contribute to the enhancement of inhibitory synaptic transmission in CA1 neurons after forebrain ischemia. The transient enhancement of inhibitory neurotransmission might temporarily protect CA1 pyramidal neurons, and delay the process of neuronal death after cerebral ischemia.     

Vesicular GABA release delays the onset of the Purkinje cell terminal depolarization without affecting tissue swelling in cerebellar slices during simulated ischemia

Neurosteroids that can enhance GABA_A receptor sensitivity protect cerebellar Purkinje cells against transient episodes of global brain ischemia, but little is known about how ischemia affects GABAergic transmission onto Purkinje cells. Here we use patch-clamp recording from Purkinje cells in acutely prepared slices of rat cerebellum to determine how ischemia affects GABAergic signaling to Purkinje cells. In voltage-clamped Purkinje cells, exposing slices to solutions designed to simulate brain ischemia caused an early, partial suppression of the frequency of spontaneous inhibitory post synaptic currents (sIPSCs), but after 5–8 min GABA accumulated in the extracellular space around Purkinje cells, generating a large (∼17 nS), sustained GABA_A receptor-mediated conductance. The sustained GABA_A conductance occurred in parallel with an even larger (∼117 nS) glutamate receptor-mediated conductance, but blocking GABA_A receptors did not affect the timing or magnitude of the glutamate conductance, and blocking glutamate receptors did not affect the timing or magnitude of the GABA_A conductance. Despite the lack of interaction between GABA and glutamate, blocking GABA_A receptors significantly accelerated the onset of the Purkinje cell “ischemic” depolarization (ID), as assessed with current-clamp recordings from Purkinje cells or field potential recordings in the dendritic field of the Purkinje cells. The Purkinje cell ID occurred ∼2 min prior to the sustained glutamate release under control conditions and a further 1–2 min earlier when GABA_A receptors were blocked. Tissue swelling, as assessed by monitoring light transmittance through the slice, peaked just after the ID, prior to the sustained glutamate release, but was not affected by blocking GABA_A receptors. These data indicate that ischemia induces the Purkinje cell ID and tissue swelling prior to the sustained glutamate release, and that blocking GABA_A receptors accelerates the onset of the ID without affecting tissue swelling. Taken together these data may explain why Purkinje cells are one of the most ischemia sensitive neurons in the brain despite lacking NMDA receptors, and why neurosteroids that enhance GABA_A receptor function protect Purkinje cells against transient episodes of global brain ischemia.     

Differential novelty detection in rats selectively bred for novelty-seeking behavior

“Novelty-seeking” behavior describes the variability of rats’ locomotor response, namely high and low responders (HR and LR respectively), when exposed to a novel environment. Novelty-seeking in the rat is considered to model “sensation-seeking” in humans, a personality trait related to substance abuse. It is assumed that HR rats and LR rats differ in their emotional reactivity because of the disparate incentive value of contextual stimulus, thus differentially interacting with their environment. However, little is known about how HR and LR rats recognize novelty arising from the environment. The present study evaluates whether phenotype may affect spontaneous, non-spatial novelty discrimination. Selectively bred HR and LR rats were submitted to the novel-object recognition test. The task involved a delay of 3 h after a first encounter with an object (“old”), which had to be discriminated from a second object (“new”). Object discrimination was assessed minute-by-minute during a 3-min choice session. Amnesic effects of scopolamine (0.5 mg/kg, intraperitoneal) were also analyzed. HR-bred rats showed sustained novel-object recognition throughout the 3-min choice session, whereas LR-bred rats began to discriminate between objects only in the last minute. Surprisingly, level of discrimination in scopolamine-treated HR-bred rats was significant during the first minute of the choice test and diminished thereafter, presumably because both objects became equally familiar as they were explored. Additionally, scopolamine induced changes in muscarine M₂ receptor gene expression in a phenotype-dependent manner. Because consistent object discrimination mainly arises during the first minute, these findings may reflect differential novelty detection in HR-bred respect to LR-bred rats.     

腺苷A1受体拮抗剂DPCPX对低氧复氧脑神经元影响的实验研究

目的: 观察腺苷A₁受体拮抗剂DPCPX对低氧复氧(H/R)脑神经元乳酸脱氢酶(LDH)释放量、钙调神经磷酸酶(CaN)、乙酰胆碱酯酶(AChE)活性和细胞外液氨基酸水平的影响。方法: 进行大鼠大脑皮层神经元的体外培养及H/R损伤模型的建立,在低氧同时加入不同浓度DPCPX(终浓度分别为:0、25、50和100 nmol/L)培养8 h、12 h和24 h后复氧24 h,检测LDH释放量的变化,并观察了100 nmol/L DPCPX对12 h低氧的H/R神经元CaN、AChE活性和细胞外液氨基酸水平的影响。结果: 与对照组比较,低氧暴露12 h复氧后100 nmol/L DPCPX组神经元LDH释放量明显增加,CaN和AChE活性显著升高,细胞外液γ－氨基丁酸水平显著降低。结论: DPCPX上调H/R神经元LDH释放量、CaN和AChE活性,降低细胞外液γ-氨基丁酸水平。     

Nitrogen metabolite repression in Aspergillus nidulans: A farewell to tamA?

Summary Previous work has established that nitrogen metabolite repression in Aspergillus nidulans is mediated by the positive acting regulatory gene areA. Pateman and Kinghorn (1977) proposed that the gene tamA plays an equally important regulatory role in nitrogen metabolite repression as the result of work with tamA^r-50, an allele leading to inability to utilise nitrogen sources other than ammonium, and tamA^d-1, an allele leading to nitrogen metabolite derepression. Both tamA^r-50 and tamA^d-1 were subsequently lost. We have therefore attempted to reconstruct Pateman and Kinghorn's work with tamA. We propose that tamA^r-50 was in fact a pyroB^– tamA^– double mutation. pyroB^– mutations lead to a block in vitamin B₆ biosynthesis which can be supplemented by extremely high concentrations of ammonium. tamA^– mutations, possibly as the result of a membrane alteration, reduce the concentration of ammonium required to supplement the pyroB^– auxotrophy. There is, however, no evidence that pyroB^– or tamA- mutations, alone or in combination, affect the regulation of the levels of a number of enzymes subject to nitrogen metabolite repression. Reversion of pyroB^– strains constitutes a powerful positive selection technique for obtaining a wide variety of mutations in glnA, the probable structural gene for glutamine synthetase. We suggest that the nitrogen metabolite derepressed phenotype attributed to tamA^d-1 might have resulted from an extremely leaky glnA^– mutation.     

Novel 8-(furan-2-yl)-3-benzyl thiazolo [5,4-e][1,2,4] triazolo [1,5-c] pyrimidine-2(3H)-thione as selective adenosine A2A receptor antagonist

Adenosine A_2A receptor (A_2AR) antagonists have emerged as potential drug candidates to alleviate progression and symptoms of Parkinson's disease (PD), and reduce the dopaminergic side effects. The synthesis of novel compound 8-(furan-2-yl)-3-benzyl thiazolo [5,4-e][1,2,4] triazolo [1,5-c] pyrimidine-2-(3H)-thione (BTTP) was carried out to evaluate the potential of BTTP as A_2AR antagonist using SCH58261, a standard A_2AR antagonist. The strong interaction of BTTP with A_2AR (ΔG = −12.46 kcal/mol and K_i = 0.6 nM) in silico analysis was confirmed by radioligand receptor binding studies showing high affinity (K_i = 0.004 nM) and selectivity with A_2AR (A_2A/A₁ = 1155-fold). The effect of CGS21680 (selective A_2AR agonist) induced cAMP concentration (0.1 pmol/ml) in HEK293 cells was antagonized with BTTP (0.065 pmol/ml) and SCH58261 (0.075 pmol/ml). Furthermore, BTTP pre-treated (5, 10 and 20 mg/kg) haloperidol-induced mice demonstrated significant attenuation in catalepsy and akinesia. BTTP induced elevation in the striatal dopamine concentration (2.90 μM/mg of tissue) was comparable to SCH58261 (2.92 μM/mg of tissue) at the dose of 10 mg/kg. The results firmly articulate that BTTP possesses potential A_2AR antagonist activity and can be further explored for the treatment of PD.     

The role of neuronal GABAA receptor subunit mutations in idiopathic generalized epilepsies

Rare GABA_A receptor γ2 and α1 subunit mutations of pathogenic effect have been described segregating in families with “monogenic” epilepsies. We now report globally on the genetic variation contained within all 16 neuronal GABA_A receptor subunit genes from the one patient cohort. The cohort consists of GEFS⁺, FS, and IGE subgroups as either sporadic cases or index cases from small families, with one index case from one large IGE family. The rarity of mutations and coding variation in general across all of the subunits suggests a low tolerance for mutations affecting GABA mediated neuronal inhibition. Characterization of the broader channelopathy load associated with susceptibility to these common epilepsies mostly with complex genetics will need to be expanded beyond the family of GABA_A receptor subunits to all families of neuronal ion channels and their interacting molecules by systematic mutation detection associated with functional investigation of their naturally occurring genetic variations.     

Two Mouse Lines Selected for Differential Sensitivities to β-Carboline-Induced Seizures Are Also differentially Sensitive to Various Pharmacological Effects of Other GABAA Receptor Ligands

Two mouse lines were selectively bred according to their sensitivity (BS line) or resistance (BR line) to seizures induced by a single i.p. injection of methyl -carboline-3-carboxylate (-CCM), an inverse agonist of the GABA_A receptor benzodiazepine site. Our aim was to characterize both lines' sensitivities to various physiological effects of other ligands of the GABA_A receptor. We measured diazepam-induced anxiolysis with the elevated plus-maze test, diazepam-induced sedation by recording the vigilance states, and picrotoxin- and pentylenetetrazol-induced seizures after i.p. injections. Results presented here show that the differential sensitivities of BS and BR lines to -CCM can be extended to diazepam, picrotoxin, and pentylenetetrazol, suggesting a genetic selection of a general sensitivity and resistance to several ligands of the GABA_A receptor.Personnalité et conduites adaptatives,     

Role of apoptosis inducing factor (AIF) for hippocampal neuronal cell death following global cerebral ischemia in mice

The molecular mechanisms of neuronal cell death following circulatory arrest are still not fully understood. In the current study we investigated the role of apoptosis-inducing factor (AIF), a major caspase-independent mitochondrial cell death protein, for neuronal cell death following global cerebral ischemia (GCI). C57/Bl6 or low AIF expressing Harlequin mutant mice (AIF^low) and their wild-type littermates were subjected to 10 min of GCI. DNA damage, nuclear pathology, and localization of AIF were investigated 6, 24, and 72 h after GCI by TUNEL and DAPI staining, and immunohistochemistry, respectively. Cell death of hippocampal CA1 neurons following GCI was associated with nuclear translocation of AIF, nuclear pyknosis, and DNA fragmentation, i.e. ∼80% of all TUNEL-positive neurons had nuclear AIF staining. In AIF^low mice neuronal cell loss was reduced by 60% (p < 0.02). The current experiments suggest that AIF-mediated signaling represents a novel mechanism of neuronal cell death following GCI.     

Caffeine reverses antinociception by oxcarbazepine by inhibition of adenosine A1 receptors: Insights using knockout mice

Oxcarbazepine is an anticonvulsant drug that has been explored as a novel therapeutic agent to treat neuropathic pain in humans. It produces antinociception in several preclinical models of pain, and these actions are blocked by methylxanthine adenosine receptor antagonists which implicates adenosine it its actions. In this study, the antinociceptive effect of oxcarbazepine, and the ability of caffeine to reverse its actions, were examined using the formalin test (2%) in wild-type mice and in mice lacking adenosine A₁ receptors by way of further exploring the involvement of adenosine in its actions. Oxcarbazepine produced dose-related suppression of formalin-evoked flinching responses in wild-type mice following both systemic and intraplantar administration, and this action was reversed by systemic and intraplantar administration of caffeine, respectively. The ability of oxcarbazepine to inhibit flinching after systemic and intraplantar administration was unaltered in homozygous (−/−) and heterozygous (+/−) adenosine A₁ receptor knockout mice. However, caffeine no longer reversed this antinociception. Our results indicate that, while adenosine A₁ receptors are not required for oxcarbazepine to produce antinociception in knockout mice, such receptors are essential in order to see caffeine reversal of this antinociceptive effect.     

Carotid chemoreceptor “resetting” revisited

Carotid body (CB) chemoreceptors transduce low arterial O₂ tension into increased action potential activity on the carotid sinus nerves, which contributes to resting ventilatory drive, increased ventilatory drive in response to hypoxia, arousal responses to hypoxia during sleep, upper airway muscle activity, blood pressure control and sympathetic tone. Their sensitivity to O₂ is low in the newborn and increases during the days or weeks after birth to reach adult levels. This postnatal functional maturation of the CB O₂ response has been termed “resetting” and it occurs in every mammalian species studied to date. The O₂ environment appears to play a key role; the fetus develops in a low O₂ environment throughout gestation and initiation of CB “resetting” after birth is modulated by the large increase in arterial oxygen tension occurring at birth. Although numerous studies have reported age-related changes in various components of the O₂ transduction cascade, how the O₂ environment shapes normal CB prenatal development and postnatal “resetting” remains unknown. Viewing CB “resetting” as environment-driven (developmental) phenotypic plasticity raises important mechanistic questions that have received little attention. This review examines what is known (and not known) about mechanisms of CB functional maturation, with a focus on the role of the O₂ environment.     

R-苯异丙基腺苷介导的心肌延迟预适应与核因子-κB的关系

目的:进一步验证腺苷A₁受体激动剂R-苯异丙基腺苷(R-PIA)能否使大鼠心脏产生延迟药理性预适应,以及核因子-kappaB和Mn-SOD在其发生机制中的作用。方法:雄性Wistar大鼠,随机分为3组(n=12):生理盐水组、R-PIA组、R-PIA+DPCPX(特异性腺苷A₁受体阻滞剂)组。各组4只大鼠在用药24h,杀鼠获取左室心肌样品,待测心肌NF-κB结合活性(EMSA法)及Mn-SOD含量(ELISA法)。其余8只大鼠在给药24h,开胸结扎左冠状动脉前降支30min、再灌注120min,摘取心脏,用于梗塞范围测定(TTC染色法)。结果:R-PIA组心肌梗塞范围显著小于生理盐水组(P＜0.01),而R-PIA+DPCPX组与生理盐水组比较无显著性差异(P＞0.05)。R-PIA组心肌NF-κB结合活性与生理盐水组比较明显增强,其Mn-SOD的含量也显著高于生理盐水组(P＜0.01)。R-PIA+DPCPX组心肌NF-κB结合活性和Mn-SOD含量与生理盐水组比较无显著差异(P＞0.05)。结论:本研究提示R-PIA药理性延迟预适应与心肌NF-κB激活、Mn-SOD表达增加之间具有一定的关联性。     

Negative crosstalk between M1 and M2 muscarinic autoreceptors involves endogenous adenosine activating A1 receptors at the rat motor endplate

At the rat motor nerve terminals, activation of muscarinic M₁ receptors negatively modulates the activity of inhibitory muscarinic M₂ receptors. The present work was designed to investigate if the negative crosstalk between muscarinic M₁ and M₂ autoreceptors involved endogenous adenosine tonically activating A₁ receptors on phrenic motor nerve terminals. The experiments were performed on rat phrenic nerve-hemidiaphragm preparations loaded with [³H]-choline (2.5 μCi/ml). Selective activation of muscarinic M₁ and adenosine A₁ receptors with 4-(N-[3-clorophenyl]-carbamoyloxy)-2-butyryltrimethylammonium (McN-A-343, 3 μM) and R-N⁶-phenylisopropyladenosine (R-PIA, 100 nM), respectively, significantly attenuated inhibition of evoked [³H]-ACh release induced by muscarinic M₂ receptor activation with oxotremorine (10 μM). Attenuation of the inhibitory effect of oxotremorine (10 μM) by R-PIA (100 nM) was detected even in the presence of pirenzepine (1 nM) blocking M₁ autoreceptors, suggesting that suppression of M₂-inhibiton by A₁ receptor activation is independent on muscarinic M₁ receptor activity. Conversely, the negative crosstalk between M₁ and M₂ autoreceptors seems to involve endogenous adenosine tonically activating A₁ receptors. This was suggested, since attenuation of the inhibitory effect of oxotremorine (10 μM) by McN-A-343 (3 μM) was suppressed by the A₁ receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (2.5 nM), and by reducing extracellular adenosine with adenosine deaminase (0.5 U/mL) or with the adenosine transport blocker, S-(p-nitrobenzyl)-6-thioinosine (NBTI, 10 μM). The results suggest that the negative crosstalk between muscarinic M₁ and M₂ autoreceptors involves endogenous adenosine outflow via NBTI-sensitive (es) nucleoside transport system channelling to the activation of presynaptic inhibitory A₁ receptors at the rat motor endplate.     

Anaerobic threshold and maximal steady-state blood lactate in prepubertal boys

Summary To elucidate further the special nature of anaerobic threshold in children, 11 boys, mean age 12.1 years (range 11.4–12.5 years), were investigated during treadmill running. Oxygen uptake, including maximal oxygen uptake (VO_2max), ventilation and the ventilatory anaerobic threshold were determined during incremental exercise, with determination of maximal blood lactate following exercise. Within 2 weeks following this test four runs of 16-min duration were performed at a constant speed, starting with a speed corresponding to about 75% ofVO_2max and increasing it during the next run by 0.5 or 1.0 km·h^–1 according to the blood lactate concentrations in the previous run, in order to determine maximal steady-state blood lactate concentration. Blood lactate was determined at the end of every 4-min period. Anaerobic threshold was calculated from the increase in concentration of blood lactate obtained at the end of the runs at constant speed. The mean maximal steady-state blood lactate concentration was 5.0 mmol · 1^–1 corresponding to 88% of the aerobic power, whereas the mean value of the conventional anaerobic threshold was only 2.6 mmol · 1^–1, which corresponded to 78% of theVO_2max. The correlations between the parameters of anaerobic threshold, ventilatory anaerobic threshold and maximal steady-state blood lactate were only poor. Our results demonstrated that, in the children tested, the point at which a steeper increase in lactate concentrations during progressive work occurred did not correspond to the true anaerobic threshold, i.e. the exercise intensity above which a continuous increase in lactate concentration occurs at a constant exercise intensity.     

The plant hormone zeatin riboside inhibits T lymphocyte activity via adenosine A2A receptor activation

Cytokinins are plant hormones that play an integral role in multiple aspects of plant growth and development. The biological functions of cytokinins in mammalian systems are, however, largely uncharacterized. The naturally occurring cytokinin zeatin riboside has recently been demonstrated to activate the mammalian adenosine A_2A receptor, which is broadly expressed by various cell types including immune system cells, with the activation of the A_2AR playing a role in the regulation of cells involved in both innate and adaptive immunity. We show for the first time that zeatin riboside modulates mammalian immune system activity via an A_2AR-dependent mechanism. Specifically, zeatin riboside treatment induces the production of cyclic adenosine monophosphate (cAMP) by T lymphocytes and inhibits the production by CD3⁺CD4⁺ T cells of interferon (IFN)-γ, IL-2, tumor-necrosis factor (TNF)-α, IL-4 and IL-13, and the production by CD3⁺CD8⁺ T cells of IFN-γ, IL-2 and TNF-α. Additionally, the upregulation of CD25, CD69 and CD40L by activated T lymphocytes is modulated by zeatin riboside. Zeatin riboside treatment also potently inhibits thioglycollate-induced peritoneal leukocytosis. The immunomodulatory activities of zeatin riboside are blocked by co-treatment with the selective A_2AR antagonist ZM241385. These data suggest that zeatin riboside possesses therapeutic potential as a mammalian immunomodulatory agent.     

Physical activity decreases the number of β-adrenergic receptors on human lymphocytes

Summary On intact human lymphocytes a specific binding site (BS) for¹²⁵I-Cyanopindolol (¹²⁵I-CYP), a derivative of the -blocking drug pindolol, was characterized. Inhibition of binding for catecholamines in the following order of potency: l-isoprenaline > l-adrenaline > l-noradrenaline proves the BS as a ₂-receptor subtype. In 77 healthy persons (36 females, 41 males) the number of BS amounted to 2,639±125 BS/cell without any significant correlation to age (17–86 years) or sex. The dissociation constant (K_D) indicating the affinity of iodocyanopindolol to the BS on intact lymphocytes was K _d =1.9±1.1×10^–10 M. A change of the number of -adrenergic receptors on intact human lymphocytes has been measured previously in asthmatics and in the myocardium of patients with congestive heart failure. We investigated a possible change in the -receptors on lymphocytes by physical and mental activity (stress) in physicians going about their daily routine work. Persons left alone in a hospital room reading or sleeping were defined as inactive controls. The number of BS on intact lymphocytes was significantly higher in inactive persons at 8 a.m. (2,230±482 BS) compared to active persons (1,743±285 BS;P<0.05) and at 1 p.m. (2,394±253 BS vs 1,733±556;P<0.05) but not different at 6 p.m. (1,634±578 BS vs 1,768±588 BS;P<0.1). The K _d remained unchanged under all conditions. The serum noradrenaline and adrenaline levels were also measured during the day. The serum adrenaline levels were higher in the active group than in the inactive group at 8 a.m. (46±11 pg/ml vs 22±8 pg/ml;P<0.01) and at 1 p.m. (36±13 pg/ml vs 13±5 pg/ml;P<0.01) but not at 6 p.m. (37±28 pg/ml vs 13±6 pg/ml;P<0.1). Our data clearly show higher serum adrenaline levels but fewer BS on intact human lymphocytes in active persons than in inactive persons at 8 a.m. and 1 p.m. The high catecholamine serum levels may cause a down-regulation of the number of -receptors in the active persons.Abbreviations ¹²⁵I-CYP ¹²⁵Iodocyanopindolol - BS binding site - K _d dissociation constant - cAMP cyclic adenosine monophosphate With support of Deutsche Forschungsgemeinschaft Kr 679/3-I