Modulation of ß-adrenergic receptor in rat lung after gamma irradiation.

OBJECTIVES: To study the effect of γ irradiation on ß-adrenergic receptors of the lung. MATERIALS AND METHODS: Healthy Sprague-Dawley rats were used as an animal model. Cell membrane proteins of lung tissue were harvested after the whole lung received 20 Gy of 60Co γ irradiation. 125I-labeled iodopindolol (125I-IPIN) was used as a ligand of ß-adrenergic receptors. The numbers of the ß-adrenergic receptors were determined by radioligand-receptor binding assay (RBA). Data were compared with irreversible blockage using antagonist bromoacetylalprenololmenthan (BAAM). RESULTS: The post-radiation RBA assay showed that the number of ß-adrenergic receptors in lung tissue decreased at a steady rate. It decreased to 48% of the normal level at the 15th day after irradiation. At 40 days after radiation the level of ß-adrenergic receptors started to increase at a steady rate and reached to the normal level around 70 days after radiation. There were significant differences in receptor synthesis, degradation and regeneration rates between irradiation group and BAMM group. CONCLUSIONS: The whole lung irradiation could severely affect the levels of ß-adrenergic receptors. The potential clinical implications of radiation-induced changes of ß-adrenergic receptors warrant further investigation.

[The role of beta-adrenoreceptors in the mechanism of the hemodynamic action and radiation-protective activity of the copolymer of 2-methyl-5-vinylpyridine with 2-methyl-5-vinylpyridinium-N-oxide]. / Izuchenie roli beta-adrenoretseptorov v mekhanizme gemodinamicheskogo deistviia i protivoluchevoi aktivnosti sopolimera 2-metil-5-vinilpiridina s 2-metil-5-vinilpiridinii-N-oksid.

In experiment on anesthetized dogs and cats in was shown that the new water-soluble copolymer initiated depressive reaction characteristic for beta-adrenomimetics. This effect was levelled with the help of non-selective adrenoblockator--propranololum. In experiment on dogs the preliminary treatment with propranololum decreased the therapeutic antiradiation efficiency of the copolymer from 68.4 to 8.3%.

Changes in cardiac performance and sympathetic stimulation during and after fractionated radiotherapy in a rat model.

The consequences of fractionated irradiation on the number of cardiac alpha- and beta-adrenergic receptors, myocardial norepinephrine concentration and in vitro assessed heart function were studied in Sprague-Dawley rats. Animals were locally irradiated on the thorax with a total dose of 50 Gy, in 5 weeks, using two different fractionation schemes (5 x 2.0 Gy/week and 3 x 3.3 Gy/week). Functional and biochemical assays were performed during treatment and at 6 months after initiation of treatment. During fractionated irradiation, the numbers of alpha- and beta-adrenergic receptors tended to rise. During this period, myocardial norepinephrine concentration remained fairly constant and no decrease in cardiac output was observed. At 6 months, a significant increase of the numbers of alpha- and beta-adrenergic receptors was observed in the 3.3 Gy/fraction group compared to age-matched controls, p = 0.012 and p = 0.02, respectively. At this time point, the myocardial norepinephrine concentration had decreased below control levels (p = 0.008 for the 3.3. Gy/fraction schedule, and p = 0.03 for the 2.0 Gy/fraction schedule). At 6 months, the cardiac output declined to 61% (p = 0.009) and 69% (p = 0.04) of control values for the 3.3 and 2.0 Gy/fraction schedules, respectively. The present data clearly show development of late cardiac sequelae caused by fractionated thorax irradiation with a total dose of 50 Gy. Moreover, this study lends support to the importance of fraction size with regard to the severity of the radiation-induced cardiac damage.

Transcranial magnetic stimulation downregulates beta-adrenoreceptors in rat cortex.

Recently, a method for transcranial magnetic stimulation (TMS) of the brain has been developed. Thus, it is possible to explore neurochemical and behavioral effects of TMS in rats. Repeated TMS (9 days) reduced beta-adrenergic receptor binding in cortex, as does electroconvulsive shock (ECS) and other antidepressant treatments. Thus TMS appears to be a potential antidepressive treatment.

[The intensification of the vasodilator reactions of arterial vessels to stimulation of the beta-adrenergic receptors in the postradiation period]. / Usilenie vazodilatatornykh reaktsii arterial'nykh sosudov na stimuliatsiiu beta-adrenergicheskikh retseptorov v postradiatsionnyi period.

It was shown with endothelium-containing and endothelium-denuded aorta segments that external gamma-irradiation of rats (6.0 Gy) results in intensification of vasodilatation reactions on beta-adrenoceptor stimulation by isoprenaline with maximum in 30th day of post-radiation period. This post-radiation alteration is not related with endothelium-derived relaxing factor.

Modification of the beta-adrenergic sensitivity of rat submandibular gland by constant light.

Rats exposed for 2, 5, 10, 20, 35 and 50 days to constant light (CL) showed beta-adrenergic desensitization of the submandibular gland as indicated by dose-response curves to 1.5, 2.0, 3.0, 10.0, 30.0 and 50.0 micrograms/kg isoproterenol. The phenomenon, evident with 1.5, 2.0 and 50.0 micrograms/kg after 2 days at CL, was more intense as time of exposure increased to reach values of about 50% those for controls after 20 days. After 35 and 50 days, desensitization showed some reversion, but the secretory responses were still lower than for controls maintained under a typical photoperiod. In the groups of rats exposed to CL for 20 days, gland wet and dry weights were higher (10%) than those of controls. These changes probably indicate an adaptation of the sympathetic control of salivary secretion induced by environmental illumination.

[Modifying effect of incorporated 137Cs on the mechanism of adrenergic control of myocardial contraction]. / Modifitsiruiushchee vliianie inkorporirovannogo 137Cs na mekhanizmy adrenergicheskogo kontrolia sokratitel'noi funktsii miokarda.

Incorporated 137Cs (absorbed dose of 0.26 Gy) causes decrease of myocardial's contractile function and inotropic response to beta-adrenagonists effect, isoproterenol-stimulated adenylate cyclase activity and beta-adrenoreceptors affinity. Adrenergic effects, mediated by alpha-adrenergic structures on heart contractile function, on the contrary, become stronger, that is due to the increase of the receptors' density on sarcolemma surface.

Noradrenergic innervation and receptor responses of cardiovascular tissues from young and aged rats after acute microwave exposure.

Young and senescent rats were exposed to 2,450 GHz microwaves for 45' and the effects of this treatment on the noradrenergic pattern and beta-cardiac and alpha-aortic receptorial functions were evaluated. In young animals, an increase in noradrenergic innervation was observed, while no functional modification was shown. In aged rats the increase in fluorescent fibers was almost the same as that observed in young rats, but significant variations in functional responses were found. Both at atrial and ventricular levels responses to the beta-agonist isoprenaline were unmodified in their affinity indices, but showed a marked decrease in the maximal responses; by contrast the activity of noradrenaline on the aortic alpha-adrenoceptors showed a great increase in maximal response without changes in the pD2 values. These results suggest that the predominant effect of microwave exposure consists in an increase in the noradrenergic pattern, and this effect is not related to the functional modifications.

[Modification of adrenergic regulation of heart function under effect of radio-ecological factors within 10-kilometer zone of the accident at Chernobyl nuclear plant]. / Modifikatsiia adrenergicheskoi reguliatsii funktsii serdtsa pod vliianiem radioékologicheskikh uslovii v 10-kilometrovoi zone avarii na ChaES.

Rats kept within the ten-kilometer zone of Chernobyl disaster over a period of 30 days exhibited a decreased heart function response to beta-adrenoreceptor stimulus, reduced density of the receptor structures in cardiomyocytes and their affinity to specific agonists. The number of beta-adrenoreceptors in myocardium cells was restored in 6 months, but their affinity and heart function response to the effect of beta-adrenoagonists remained decreased. No significant changes were observed in regulation influenced indirectly via alpha-adrenoreceptors.

A method for evaluating the effects of ligands upon Gs protein-coupled receptors using a recombinant melanophore-based bioassay.

As an increasing number of medically important receptors that couple to stimulatory guanine nucleotide (Gs) proteins are isolated and cloned, there is an equally escalating need for methods to rapidly and reproducibly evaluate potential ligands for their properties as agonists or antagonists. Recently, a bioassay that can quickly and accurately determine the effects of numerous chemicals on a beta 1-like adrenergic receptor (AR) endogenous to melanophores derived from Xenopus laevis was developed. Here, the general utility of the melanophore-based pigment dispersion assay is demonstrated by employing it to evaluate the effects of drugs on a human beta 2 AR. Melanophores were both transiently and stably transfected with a plasmid encoding a beta 2 AR. Stimulation of recombinant cells expressing the beta 2 AR, but not wild-type cells, with beta 2-selective agonists induced pigment dispersion and concomitant elevations in intracellular cAMP. Using a microtiter plate reader, it was straightforward to construct reproducible dose-response curves and rapidly determine rank-order potency and EC50 and IC50 values for agonists and antagonists, respectively. The demonstration of functional expression of a human beta 2 AR in the melanophore-based bioassay suggests that the system may be used for the rapid pharmacological characterization of ligands upon any specific Gs-linked receptor for which a cDNA clone is available.

[The effect of the lateral hypothalamic area on the pulmonary surfactant system]. / Vliianie lateral'nogo gipotalamicheskogo polia na surfaktantnuiu sistemu legkikh.

The level of lipids, lipase activity and lungs' blood capacity were studied on 62 rats. Dispersal cobalt was infused into the hypothalamic lateral area of rats with adrenalectomy or injected with droperidol, obsidan, reserpine. Their effect upon the hypothalamus involved a decrease in surfactant phospholipids and lung's blood capacity. Possible adrenergic mechanisms of affecting the lung surfactant system are discussed.

Time dependent changes in myocardial norepinephrine concentration and adrenergic receptor density following X-irradiation of the rat heart.

The hearts of 9 to 12-weeks-old Sprague-Dawley rats were locally irradiated with a single dose of 20 Gy. The effects on myocardial norepinephrine concentrations and on alpha-adrenergic and beta-adrenergic receptor densities was examined up to 16 months post-treatment. Myocardial norepinephrine concentrations were reduced (to 50% of control values between 8 and 16 months) after irradiation. Receptor binding studies using radioactive ligands demonstrated that alpha-adrenergic receptor density was increased to maximally 210% of control values and that beta-adrenergic receptor density was increased to maximally 150% of control values, both measured at 8 months posttreatment. The affinities of both receptor types were not changed after irradiation. An inverse correlation was found between the myocardial norepinephrine concentration and the alpha-adrenergic receptor density. Myocardial norepinephrine concentration was not correlated to the beta-adrenergic receptor density. The changes in myocardial norepinephrine concentration and receptor density observed after irradiation suggest that even 16 months after irradiation overt cardiac failure was not occurring as the radiation-induced alterations differ considerably from those reported for failing hearts.

[Adrenergic control of myocardial contractile function in rats with incorporated 137Cs]. / Adrenergicheskii kontrol' sokratitel'noi funktsii miokarda krys s inkorporirovannym 137Cs.

It was shown on isolated myocardium preparations that internal gamma irradiation of rats with 137Cs (1.6 MBq/kg) decreased the contractile function of ventricles and had no essential effect on the auricle contractility. The inotropic response of myocardium to activation of alpha-adrenergic receptors decreased, and of beta-adrenergic receptors decreased.

[Post-radiation changes in cardiac contractility and responses mediated by beta adrenergic receptors in mature and old age]. / Postradiatsionnye izmeneniia sokratitel'noi aktivnosti i oposreduemogo beta-adrenergicheskimi retseptorami funktsional'nogo otveta serdtsa v zrelom i starom vozraste.

Experiments were performed on isolated perfused hearts of rats of the middle and old age. The animals were irradiated with 60Co gamma-rays at a dose of 1 Gy and a dose rate of 2.7 x 10(-4) Gy/s. This exposure enhanced pacemaking activity and attenuated contractile activity of rat hearts. The biomechanical changes were most distinct in adult rats. It can be assumed that the mechanisms responsible for heart contraction and relaxation as well as for their self-regulation are more resistant to ionizing radiation in old-aged animals. Post-radiation changes of neurohormonal regulation show different age-related features. In adult rats, the exposure caused only a decline of the chronotropic response to stimulation of beta-adrenoreceptors whereas in old animals it produced a decline of inotropic and coronary responses. It is postulated that mechanisms underlying adrenergic effects at the level of the receptor apparatus of coronary vessels and cardiomyocytes experience greater changes in old-aged animals exposed to irradiation.

Increased number of cardiac adrenergic receptors following local heart irradiation.

The effect of local X irradiation on cardiac alpha and beta receptors was studied in Wistar rats. Animals were given local heart irradiation with single doses of 15 or 20 Gy and were examined after a range of latency times of 7 to 400 days. Using the radioactive ligands [3H]CGP-12177 and [3H]prazosin, the maximal binding capacity was determined from saturation experiments. At 7 days after 20 Gy the maximal binding capacity of both alpha and beta receptors was reduced to below the level of untreated control animals. Subsequently it rose continually to a maximum of 160% of the control level for beta receptors and 130% for alpha receptors at 400 days postirradiation. The antagonist affinity as judged from the dissociation constant for [3H]CGP 12177 and [3H]prazosin did not change significantly. A similar effect was observed after 15 Gy. An increase in adrenergic receptors may represent an important pathogenetic link between early morphological and late functional changes in the pathogenesis of radiation-induced heart disease.

Beta-adrenergic receptors on murine lymphocytes: density varies with cell maturity and lymphocyte subtype and is decreased after antigen administration.

beta-Adrenergic receptors were assayed on intact, viable, murine splenocytes and thymocytes using the labeled adrenergic antagonists [3H]-dihydroalprenolol l-[ring propyl-3H(N)] ([3H]DHA) and 4-(3-t-butylamino-2-hydroxypropoxy)-[5,7-3H]benzimidazol-2-one ([3H]CGP 12177). The sites detected by [3H]DHA did not always possess the characteristics of beta-adrenergic receptors and were demonstrated to be stereospecific only after the addition of the binding assay. Populations of cells from C57Bl/6 inbred and CF1 outbred mice were compared. Purified T cells from C57Bl/6 mice had fewer receptors than did either whole spleen or B cells. Thymocytes from either strain had significantly fewer receptors than did the other lymphocyte populations. However, mature medullary thymocytes purified from C57Bl/6 mice had higher numbers of receptors per cell which were comparable to those of the splenic T cell. Radiation-resistant splenocytes recovered from CF1 mice 24 hr after 700 rad of irradiation possessed greatly increased numbers of receptors per cell. Immunization with sheep red blood cells caused a significant reduction in the density of receptors on splenocytes from C57Bl/6 mice. The wide variations observed in the density of beta-adrenergic receptors, possibly related to cell maturity or state of activation, seem to provide opportunities for differential modulation of cell functions by either endogenous or exogenous adrenergic agents.

Effects of UVB irradiation on epidermal adenylate cyclase responses in vitro: its relation to sunburn cell formation.

UVB irradiation augmented the beta-adrenergic adenylate cyclase response of pig skin epidermis in vitro. The effect was observed 2-4 h following the irradiation and lasted at least for 48 h. There was no significant difference in cyclic AMP phosphodiesterase activity between control and UVB-irradiated epidermis at lower irradiation dose (150 mJ/cm2), which is the dose of the most marked beta-adrenergic augmentation effect. The augmentation effect was specific to the beta-adrenergic system; adenosine and histamine adenylate cyclase responses were unchanged or decreased depending on the irradiation dose. Histologically, marked sunburn-cell formation was observed following the UVB irradiation. It has been suggested that oxygen intermediates generated by ultraviolet radiation participate in sunburn-cell formation. The addition of superoxide dismutase (SOD) in the incubation medium significantly inhibited sunburn-cell formation. On the other hand, the beta-adrenergic augmentation effect was not affected by the addition of SOD. Other scavengers of oxygen intermediates (catalase, catalase + SOD, xanthine, or mannitol) did not inhibit the UVB-induced beta-adrenergic augmentation effect. Further, superoxide-anion generating systems (hypoxanthine-xanthine oxidase system and acetaldehyde-xanthine oxidase system) revealed no stimulatory effect on the beta-adrenergic response of epidermis. These results indicate that (a) the UVB-induced beta-adrenergic augmentation effect is inherent to skin and does not depend on systemic factors such as inflammatory infiltrates following UVB irradiation; (b) in contrast to sunburn-cell formation, induction of the beta-adrenergic adenylate cyclase response is not directly associated with oxygen intermediates generated by UVB irradiation.

Molecular size of alpha 1- and beta-adrenoceptors in rat brain cortex as determined by a radiation inactivation method.

Frozen whole rat cerebral cortex was exposed to 10 MeV electrons from a linear accelerator. Based on the theory of target size analysis, the in situ molecular weight of alpha 1-adrenoceptors (labelled by [3H]prazosin) and beta-adrenoceptors (labelled by [3H]dihydroalprenolol) was 57 800 daltons and 42 600 daltons, respectively.

[Mechanisms of the disorder of the hormonal regulation of plasma membrane adenylate cyclase in the rat liver during early ontogeny under in vitro irradiation]. / Mekhanizmy narusheniia gormonal'noi reguliatsii adenilattsiklazy plazmaticheskikh membran pecheni krysy v khode rannego ontogeneza v usloviiakh oblucheniia in vitro.

Possible reasons for the previously detected inhibitory effect of gamma-radiation (100-1000 Gy in vitro) on isoproterenol-stimulated activity of adenylate cyclase (AC) of the liver plasma membranes of a 20-day-old rat fetus were investigated. It was discovered that the number of beta-adrenergic receptors was reduced. Analysis of basal and fluorine-stimulated activities of AC attests to the radiation-induced damage to catalytic and N-regulatory proteins. The radiation-induced derangement of membrane lipids, where AC functions, is shown.