Beta-adrenoceptor function in white blood cells from newborn infants: no relation to plasma catecholamine levels

The role of neutrophils in neuro-immune modulation

Neutrophils are peripheral immune cells that represent the first recruited innate immune defense against infections and tissue injury. However, these cells can also induce overzealous responses and cause tissue damage. Although the role of neutrophils activating the immune system is well established, only recently their critical implications in neuro-immune interactions are becoming more relevant. Here, we review several aspects of neutrophils in the bidirectional regulation between the nervous and immune systems. First, the role of neutrophils as a diffuse source of acetylcholine and catecholamines is controversial as well as the effects of these neurotransmitters in neutrophil's functions. Second, neutrophils contribute for the activation and sensitization of sensory neurons, and thereby, in events of nociception and pain. In addition, nociceptor activation promotes an axon reflex triggering a local release of neural mediators and provoking neutrophil activation. Third, the recruitment of neutrophils in inflammatory responses in the nervous system suggests these immune cells as innovative targets in the treatment of central infectious, neurological and neurodegenerative disorders. Multidisciplinary studies involving immunologists and neuroscientists are required to define the role of the neurons-neutrophils communication in the pathophysiology of infectious, inflammatory, and neurological disorders.

Adrenergic modulation of migration, CD11b and CD18 expression, ROS and interleukin-8 production by human polymorphonuclear leukocytes

OBJECTIVES

Adrenergic modulation of immunity has been extensively characterized, however, few information exist regarding polymorphonuclear leukocytes (PMN), despite their key role in immunity and inflammation. We investigated the effect of adrenergic agents on human PMN migration, CD11b and CD18 expression, reactive oxygen species (ROS) and interleukin (IL)-8 production, and on adrenoceptor (AR) expression.

METHODS

Migration was measured by the Boyden chamber assay, CD11b/CD18 expression was assessed by flow cytometry, intracellular ROS were detected by spectrofluorimetry, and IL-8 was quantitated by standard ELISA assay. AR mRNA levels were measured by real-time PCR and PMN morphology was studied by scanning electron microscopy.

RESULTS

Adrenaline(A), noradrenaline and the β-AR agonist isoprenaline reduced N-formyl-Met-Leu-Phe (fMLP)-induced migration, CD11b/CD18 expression, and ROS production, without affecting IL-8. The effect of A on CD11b was antagonized by yohimbine and propranolol, and increased by prazosin. The effect on ROS production was completely abolished by propranolol. PMN expressed α(1A)-, α(1B)-, α(1D)-, α(2A)-, α(2C)-, β(1)-, β(2)-, and β(3)-AR mRNA. A prevented fMLP-induced morphological changes of PMN.

CONCLUSIONS

Adrenergic agents reduced PMN responses mainly through β-AR, although α-AR may contribute at least to CD11b expression. AR-operated pathways in PMN should be investigated in disease conditions and in the response to therapeutic agents.

Adrenergic modulation of immune cells: an update

Sympathoadrenergic pathways are crucial to the communication between the nervous system and the immune system. The present review addresses emerging issues in the adrenergic modulation of immune cells, including: the specific pattern of adrenoceptor expression on immune cells and their role and changes upon cell differentiation and activation; the production and utilization of noradrenaline and adrenaline by immune cells themselves; the dysregulation of adrenergic immune mechanisms in disease and their potential as novel therapeutic targets. A wide array of sympathoadrenergic therapeutics is currently used for non-immune indications, and could represent an attractive source of non-conventional immunomodulating agents.

The distribution of major lymphocyte subsets in cord blood is associated with its pH

OBJECTIVES

To assess in venous cord blood the distribution of major lymphocyte subsets according to pH and medications used during labor.

DESIGN AND METHODS

Venous cord blood was sampled immediately after labor from 70 newborns (35 males and 35 females) delivered vaginally. Lymphocytes were immunophenotyped by flow cytometry and pH was measured using the AVL 900 automated blood gas analysis system. Data on birth weight, gestational age at delivery, length of labor, presence of stained amniotic fluid, medications used during labor, maternal risk factors, age and parity were collected.

RESULTS

The percentage of T lymphocytes decreased while the percentage of NK lymphocytes increased with decreasing pH over the whole range of pH values. The proportions of T and NK lymphocytes were associated with the administration of neuroplegics, spasmolytics or dihydroergotoxin in the first stage of labor.

CONCLUSIONS

Cord blood pH and labor-associated variables should be taken into account to adequately interpret the profile of major lymphocyte subsets as a marker of the effect of different prenatal factors on the immune system of neonates.

Ontogeny of G-protein expression: control by beta-adrenoceptors

Cardiac cell homeostasis is maintained in the face of excessive beta-adrenoceptor stimulation through the process of desensitization. Desensitization is not an inherent property of these cells but rather is acquired during development; neonates given beta-agonists actually show heterologous sensitization, involving changes in the expression and catalytic activity of adenylyl cyclase (AC) as well as an increased receptor/G-protein coupling. The current study examines the role of specific G-protein components, G(s)alpha and G(i)alpha, in the ontogeny of beta-adrenoceptor responses and in the transition from agonist-induced sensitization to desensitization. Between postnatal days (PN) 6 and 15 there was a significant decrease in the 52 kDa isoform of G(s)alpha with no accompanying change of the 45 kDa form; over the same period, G(i)alpha3 also declined substantially. In contrast, the 45 kDa isoform of G(s)alpha and G(i)alpha1,2 remained fairly constant over the same period and fluoride-stimulated AC activity increased. Treatment with isoproterenol on PN2-5 did not result in any significant changes in G(s)alpha expression but robustly decreased G(i)alpha1,2. These changes were accompanied by heterologous sensitization of AC activity at the level of AC itself, evidenced by equivalent increases in the enzymatic response to fluoride and forskolin-Mn2+. Isoproterenol given to older animals (PN11-14) also caused specific loss of G(i) protein, in this case targeting G(i)alpha3, whereas G(s)alpha again was unchanged; in contrast to the younger group, the older animals displayed heterologous desensitization of AC at the level of G-protein function (specific loss of the fluoride response). These results indicate that the normal ontogenetic increase of cardiac beta-adrenoceptor coupling to AC is not dependent on the absolute amount of G-proteins, nor on the relative balance of stimulatory (G(s)) and inhibitory (G(i)) subunits. However, the ability of receptor stimulation to downregulate G(i)alpha1,2, an event which is specific to immature cardiac cells, is likely to be an important component of the resistance of the fetal/neonatal heart to agonist-induced desensitization and hypertrophy. The maintenance of cardiac beta-adrenoceptor signaling in the face of intense stimulation is likely to play an important role in the physiologic adaptations necessary to the perinatal transition.

Ontogeny of beta-adrenoceptor/adenylyl cyclase desensitization mechanisms: the role of neonatal innervation

The ability of adrenergic stimulation to elicit desensitization of the beta-receptor/adenylyl cyclase signaling cascade is not an inherent property of cells but rather is acquired during the period in which sympathetic innervation develops. This study examines whether innervation provides the signal that enables target cardiac and hepatic cells to learn to desensitize their responses. Neonatal rats were sympathectomized with 6-OHDA on postnatal day 1 and were treated at various ages with a regimen of isoproterenol known to elicit desensitization in adults. In control rats, desensitization first appeared between days 6 and 15. Desensitization was heterologous, involving changes in the efficiency of G-protein coupling, as there were parallel decreases in isoproterenol-stimulated adenylyl cyclase activity, basal activity and fluoride-stimulated activity (maximal G-protein activation) without changes in forskolin-Mn2+-stimulated activity (total cyclase catalytic activity). The lesioned animals showed a delay in the onset of desensitization as isoproterenol did not evoke decreased responsiveness until day 25 in the heart; the liver did not display agonist-induced desensitization even at day 25. The effects of lesioning on development of desensitization were entirely separable from those on regulation of beta-receptors themselves: agonist-induced decreases in receptor binding appeared by day 15 in both control and lesioned animals. Uniquely in the youngest animals (6 days old), isoproterenol treatment produced heterologous sensitization of adenylyl cyclase responses rather than desensitization, with a parallel increase in basal, isoproterenol-, fluoride- and forskolin-Mn2+-stimulated activity; the latter indicates induction of total catalytic activity as the primary mechanism of sensitization. The lesioned neonates did not show sensitization, despite the fact that during this period, sympathetic pathways are not functionally competent. Our results indicate that innervation provides a timing signal for the onset of desensitization capabilities of sympathetic target cells, but is not absolutely required for the cells to learn how to desensitize. Prior to the onset of desensitization, agonists induce sensitization that may be important in preserving physiological responsiveness during ontogenetic surges of adrenergic activity. The absence of sensitization in lesioned animals implies that, before physiological function is completely established, early pioneer synapses provide a trophic signal that enables cells to increase their sensitivity to stimulation during the perinatal transition period.

Circulating noradrenaline and beta-adrenergic receptors in children with congestive heart failure

This study was designed to investigate changes in plasma catecholamine concentrations and the number of beta-adrenoceptors (beta-AR) of circulating lymphocyte in 94 noncyanotic congenital heart patients. In 43 patients with congestive heart failure, beta-AR density was significantly lower (p < 0.001) and plasma noradrenergic levels were significantly higher (p < 0.001) compared with corresponding values in 51 patients without heart failure. A significant negative correlation between lymphocyte beta-AR density and plasma noradrenergic levels was observed (r = -0.61, p < 0.001). The degree of left-to-right shunt and pulmonary pressure was correlated directly with noradrenaline level and inversely with lymphocyte beta-AR density. Both plasma noradrenaline level and lymphocyte beta-AR density return to normal in children with heart failure after surgical repair. Our results support the idea that changes in noradrenaline level and lymphocyte beta-adrenoceptor density occur concurrently with the presence and severity of heart failure in children.

Single umbilical artery ligation-induced fetal growth retardation: effect on postnatal adaptation

To assess whether prolonged intrauterine stress and resultant fetal growth retardation result in depletion of adrenal catecholamines and alter the adrenergic signal transduction system, we studied newborn sheep after single umbilical artery ligation (SUAL)-induced growth retardation. The animals were delivered at term, and postnatal cardiovascular, pulmonary, endocrine, and metabolic responses were measured. We also evaluated the status of myocardial and pulmonary beta-adrenergic receptor number and function. SUAL caused significant growth retardation but relative preservation of brain and adrenal gland weight and adrenal catecholamine content. Blood pressure, plasma free fatty acid, and glucose responses at birth were blunted in SUAL animals. The plasma epinephrine (Epi) and norepinephrine levels were comparable in both groups for the first 2 h of age. By 4 h, both plasma concentration and plasma appearance rate of Epi were reduced to 40% of control in SUAL animals (P less than 0.05). Neither beta-receptor density, affinity, nor adenylate cyclase activity were altered by SUAL in either cardiac or pulmonary membranes. These results suggest that, rather than overt depletion, there is relative sparing of initial adrenal medullary function that later waned. This response and preservation of the beta-adrenergic signal transduction system may represent partial compensation for the physiological stress induced by SUAL.

Beta-adrenoceptor responsiveness in intact leukocytes from adults and newborn infants; effect of phosphodiesterase inhibitors

Intact mononuclear and polymorphonuclear leukocytes from adults and newborn infants were used to estimate the beta 2-adrenoceptor responsiveness in vitro. The accumulation of cAMP in response to receptor stimulation by isoprenaline was used as a measure of the receptor responsiveness. The relevance of the method is dependent on the activity of the cAMP phosphodiesterase inside the cells. The xanthine derivatives, theophylline (4 mmol l-1) and 3-isobutyl-l-methyl-xanthine (0.1-2.5 mmol l-1), were used to inhibit the cAMP phosphodiesterase activity. It appears that 3-isobutyl-l-methyl-xanthine at 2.5 mmol l-1 inhibits the phosphodiesterase activity almost completely. By use of this concentration no age-dependent changes in the isoprenaline-stimulated cAMP accumulation in mononuclear and polymorphonuclear leukocytes from adults and newborn infants could be demonstrated.

Beta-adrenoceptor agonists and hypoxia in sheep fetuses

Sheep fetuses, near term, were studied to test the influence of a tocolytic beta agonist, terbutaline, on fetal responses to hypoxia. After fetal exteriorization the drug was administered intravenously to the mother in three different doses: The max group comprised 11 ewes receiving 67-134 micrograms min-1. Seven ewes were given 30 micrograms min-1 and eight ewes were infused with 10 micrograms min-1. Seventeen fetuses served as controls. Hypoxia was induced by intermittent complete occlusions of the maternal abdominal aorta. Maternal terbutaline levels were high (range 50-748 nmol l-1) in the max group and the 30-micrograms group, whereas those in the 10-micrograms group were in the clinical range (range 11-58 nmol l-1). Fetuses in the max and 30-micrograms groups reacted to moderate hypoxia with excessive responses of heart rate, blood pressure myocardial contractility and ST waveform changes and a 50% mortality rate during severe hypoxia as compared with 12% in the control animals. Ten micrograms min-1 did not decrease the survival but caused an increase in myocardial workload and a negative energy balance during severe hypoxia.

Density and agonist-promoted high and low affinity states of the beta-adrenoceptor on human B- and T-cells

beta-Adrenoceptor binding on peripheral blood mononuclear cells (PBMC) of healthy adult volunteers was investigated using the radioligand 125iodo-cyanopindolol (ICYP). Saturation binding studies were performed with nine different concentrations of ICYP. Receptor density and affinity were calculated by Scatchard plots. Resolution of beta-adrenoceptors into those with high and low affinity state of the beta-adrenoceptor was obtained from inhibition curves with salbutamol using Hofstee plots. Receptor density on enriched B-cells ('B-cells') was two-fold higher than on enriched T-cells ('T-cells') (P less than 0.025). Affinity (KD values) of beta-adrenoceptors did not differ for B- and T-cells. However, when two distinct binding states for beta-adrenoceptor agonists were identified using salbutamol displacement curves, beta-adrenoceptors on T-cells presented more receptors in a high affinity state than those on B-cells (P less than 0.01). Since the ability of an agonist to activate adenylate cyclase is closely correlated with the ratio of low to high affinity states formed in the presence of the agonist, increased intrinsic activity for the beta-adrenoceptor agonist on T-cells may be postulated. In conclusion, determination of the B/T ratio is a prerequisite for interpretation of beta-adrenoceptor changes on peripheral lymphocytes in various diseases.

Beta-adrenergic receptors of lymphocytes in children with allergic respiratory diseases

The beta-adrenergic receptor binding sites on peripheral lymphocytes in children with bronchial asthma (n = 16) and seasonal allergic rhinitis (n = 8) were examined in comparison with normal controls (n = 18) by means of 124I-cyanopindolol. The number of beta-adrenergic receptors was significantly lower in the asthmatic group (858 +/- 460/lymphocyte) than in the controls (1564 +/- 983/lymphocyte). The value (1891 +/- 1502/lymphocyte in children with allergic rhinitis was slightly higher than that in healthy controls. Of the 24 patients suffering from allergic diseases of the lower or upper airways, the bronchial histamine provocation test was performed in 21; 16 gave positive results, while 5 were negative. No difference in beta-adrenergic receptor count was found between the histamine-positive and negative patients. Neither was there any correlation between the number of beta-adrenergic receptors and the high (16/24) and low (8/24) serum IgE concentrations found in allergic patients. The significant decrease in beta-adrenergic receptor count in asthmatic children lends support to Szentiványi's concept. Further qualitative and quantitative analysis of lymphocyte beta-adrenergic receptors may provide an individual approach to the treatment of bronchial asthma with beta-sympathomimetic drugs.