Myocardial beta-receptor and cardiac angiotensin alterations during the acute and chronic phases of viral myocarditis

Recovery from viral myocarditis is usually excellent and complete although it occasionally results in sudden death during its acute stage. While neurohormonal mechanisms play an important role in the adaptation to heart diseases, little is known about the alteration of the neurohormonal system in viral myocarditis. Therefore, we examined the myocardial beta-adrenergic receptor and cardiac angiotensin I and II concentrations in a murine model of viral myocarditis induced by an encephalomyocarditis virus. The down-regulation of the beta 1-adrenergic receptor subtype was observed on day 10. The heart weight, heart weight/body weight ratio and myocardial necrosis were significantly increased at this stage. On day 30, the beta 2-adrenergic receptor subtype was up-regulated without up-regulation of the total beta-adrenergic receptor. Both angiotensin I and II concentrations were significantly increased with myocardial hypertrophy in the left ventricle on day 30. The up-regulation of the total beta-adrenergic receptor and beta 2-subtype was observed on day 120, but neither the angiotensin I nor II concentration was increased. Therefore, the up-regulation of the beta 2-adrenergic receptor density and the temporal increase of the angiotensin I and II concentrations in the murine ventricle during viral myocarditis may play an important role in the pathophysiology of post-viral myocarditis.

Inotropic effect of the cardioprotective agent 2,3-butanedione monoxime in failing and nonfailing human myocardium

The drug 2,3-butanedione monoxime (BDM) was suggested to be a potent cardioprotective agent useful for cardiopreservation. The present study investigated the activity of BDM and its mechanism of action in human myocardium. In electrically driven left ventricular papillary muscle strips and right atrial trabeculae from failing (heart transplants) and nonfailing (donor hearts) human myocardium, isometric force development and the force-frequency relationship were examined. To study the sarcolemmal actions of BDM, competition experiments with 125I-iodocyanopindolol, 3H-ouabain and 3H(+)PN 200-110 were performed. The effect of BDM on the contractile apparatus was tested by investigating its effects on Ca++ sensitivity and on the relaxation parameters of skinned fiber preparations. In papillary muscle strips and in atrial trabeculae, BDM (0.001-30 mM) depressed the isometric force of contraction in a concentration-dependent manner. BDM was more potent in atrial than in ventricular tissue and it shifted the Ca++ concentration-response curve in atrial and ventricular tissue to the right. The potency of BDM to depress force development was significantly lower compared with the L type of Ca++ channel antagonist nifedipine in both atrial and ventricular myocardium. In the presence of 10 mM BDM, the force-frequency relationship becomes positive in failing myocardium but not in the presence of 1 mM BDM, which did not affect the specific binding of 125I-iodocyanopindolol, 3H-ouabain or 3H(+)PN 200-110. This indicated there was no action on beta adrenoceptors, cardiac glycoside receptors and dihydropyridine-type Ca++ channels.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of aging on AV nodal and ventricular beta-adrenergic receptors in the Fischer 344 rat

The effects of aging on atrioventricular (AV) nodal and right and left ventricular beta-adrenergic receptor (beta-AR) characteristics were studied in Fischer 344 rat hearts using quantitative autoradiography. Twenty-micrometer-thick cardiac sections containing the compact AV node from 16 mature (4-6 mo old) rats, 6 middle-aged (12 mo old) rats, and 16 old (24 mo old) rats were incubated with [125I]iodocyanopindolol, [125I]iodocyanopindolol plus atenolol, or ICI 118551. Saturation experiments revealed a significant age-related decrease in AV nodal beta-AR density (mature: 190 +/- 46, middle-aged: 165 +/- 27, old: 133 +/- 34 amol/mm2; P < 0.01), with no change in affinity (mature: 106 +/- 62, middle-aged: 132 +/- 46, old: 128 +/- 66 pM). No age-related changes in AV nodal beta-AR subtype ratio (55% beta 1, 45% beta 2) or estimated compact AV node volume were detected (mature: 66 +/- 17, old: 65 +/- 23 microns 3). No difference in beta-AR density or affinity was detected between mature and old rats in either left (LV) or right (RV) ventricular tissue (LV, mature: 60 +/- 11, middle-aged: 59 +/- 11, old: 62 +/- 11 amol/mm2; RV, mature: 65 +/- 9, middle-aged: 65 +/- 11, old: 58 +/- 10 amol/mm2). beta-AR subtype ratios for the left ventricle (64% beta 1, 36% beta 2) and right ventricle (63% beta 1, 37% beta 2) did not significantly differ between mature and old rats. To summarize, aging from 4 to 24 mo in the Fischer 344 rat is associated with 1) a decrease in AV nodal beta-AR density with no change in affinity; 2) no change in volume of the compact region of the AV node; 3) no change in beta-AR subtype ratio in the AV node, left ventricle, or right ventricle; and 4) no change in either RV or LV beta-AR density.

Transcriptional modulation by n-butyric acid of beta 1-, beta 2-, and beta 3-adrenergic receptor balance in 3T3-F442A adipocytes

3T3-F442A adipocytes, which express major beta 3-adrenergic receptors (beta 3-AR) (90%) and minor beta 1-AR (< 10%) and beta 2-AR (< 1%) populations, were used to investigate regulation by n-butyric acid of beta-AR subtype expression. Following butyrate treatment, EC50 values of beta 1- and beta 2-selective agonists, dobutamine and fenoterol, were decreased, whereas that of the beta 3-selective agonist BRL37344 was increased. Direct binding and competition of (-)-[125I]iodocyanopindolol binding by selective beta 1- and beta 2-AR antagonists, CGP20712A and ICI118551, and by the beta 3-AR agonist, BRL37344, revealed that both beta 1- and beta 2-AR were increased in butyrate-treated adipocytes, whereas beta 3-AR almost totally disappeared. In control adipocytes, beta 1-, beta 2-, and beta 3-AR transcripts (quantitated by a polymerase chain reaction assay) represented 6.5, 0.5, and 93% of total beta-AR mRNA, respectively. In butyrate-exposed cells, proportions of beta-AR proteins and mRNAs were, respectively, 87 and 94% for beta 1 and 9 and 1% for beta 2-AR. beta 3-ARs were barely detectable in binding assays and accounted for 4.5% of beta-AR transcripts. Variations of beta-AR protein and mRNA levels were accompanied by parallel changes in the transcription rates of the corresponding genes. The differential regulation of the three beta-ARs by n-butyric acid, a dietary factor produced from colonic fermentation, may have significant nutritional and energetic consequences.

The high affinity state of the beta 2-adrenergic receptor requires unique interaction between conserved and non-conserved extracellular loop cysteines

A disulfide bond between two extracellular cysteines, conserved in all G-protein-coupled receptors, is believed to be critical for stabilization of the ligand-binding pocket. The beta 2-adrenergic receptor (beta 2-AR) contains two conserved cysteines (Cys106 and Cys184) as well as two other extracellular cysteines (Cys190 and Cys191). The specificity of the interactions between these four cysteines has not yet been clearly established. Mutants encoding alanines for specific extracellular cysteines in the beta 2-AR gene were constructed and expressed in COS-1 and Chinese hamster ovary cells. Ala106, Ala184,190,191, and Ala106,184,190,191 mutants displayed low affinity for the beta-antagonist, 125I-cyanopindolol and insensitivity to dithiothreitol (DTT). The Ala106,191 mutant displayed an intermediate affinity and DTT sensitivity. Mutants Ala184, Ala184,190, and Ala184,191 displayed high affinity and DTT sensitivity, indicating that a solvent-accessible disulfide bond(s) is present in these mutant receptors as in the wild-type beta 2-AR. Additionally, thermal stability studies provided evidence that the extracellular disulfide bonds are essential for stabilization of the high affinity state of the receptor. These studies indicate that the covalent linkage between loops 1 and 2 of the beta 2-AR extracellular domains involves the formation of disulfide bonds, uniquely between Cys106 and Cys191, and Cys184 and Cys190, and is, thus, distinct from that of other G-protein-coupled receptors.

The lymphoblast beta-adrenergic receptor in bipolar depressed patients: effect of chronic incubation with lithium chloride

We have recently reported a study of beta-adrenergic receptor binding characteristics in lymphoblast cell lines derived from patients with bipolar disorder (BD) and healthy, matched control subjects. In the present study we have investigated the effects of incubating cells from the same subjects with lithium chloride (1 mM) for 7 days prior to assay. There was no difference in beta-adrenergic receptor number between control and BD cell lines and incubation with lithium had no effect on receptor number in either group. Exposure of the cells to isoprenaline (1 nM) for 24 h immediately prior to assay caused significantly less down-regulation in BD cells (15 +/- 5%) than control cells (39 +/- 4%), as described previously. Incubation with lithium significantly increased the down-regulation response to isoprenaline in BD cells (39 +/- 6%) but not in control cells (30 +/- 7%). After lithium, the agonist-induced decrease in beta-AR number in BD cells was no longer significantly different from that in control cells. We conclude that lithium selectively enhanced the agonist down-regulation of beta-adrenergic receptors in cells derived from patients with bipolar disorder. The functional significance of this result and the potential biochemical mechanisms responsible for this effect are discussed.

Effect of 5,7-dihydroxytryptamine, ovariectomy and gonadal steroids on serotonin receptor binding in rat brain

Quantitative autoradiography was used to assess alterations in serotonin (5-HT) receptor binding in the hypothalamus and hippocampus following denervation with 5,7-dihydroxytryptamine (5,7-DHT), ovariectomy (OVX) and gonadal steroid manipulation. Seven days after 5,7-DHT injection, 5-HT1a receptor density was significantly increased in the ventromedial hypothalamic nucleus (VMN) of intact but not OVX female rats. Under these conditions 5-HT1b receptor density was unchanged in any brain region examined and 5-HT transporter binding was decreased in all 5,7-DHT injected animals. In addition, there was a significant interaction between OVX and 5,7-DHT for both the 5-HT1a receptor and the 5-HT transporter in the VMN, such that OVX inhibited the 5,7-DHT-induced increase in 5-HT1a receptors and attenuated the 5,7-DHT-induced decrease in 5-HT transporter binding. In a separate experiment the effect of gonadal steroid manipulation on 5-HT receptor binding was assessed. In female OVX rats, 5-HT1a receptor density was unchanged by estrogen or estrogen and progesterone administration. In male rats, castration significantly decreased 5-HT1a receptor density in the medial preoptic area. Estrogen and progesterone administration to female OVX rats increased the density of 5-HT1b receptors in the VMN, as compared to estrogen alone. The relationship of these results to the role of 5-HT in mediating lordosis behavior is discussed.

A single point mutation increases the affinity of serotonin 5-HT1D alpha, 5-HT1D beta, 5-HT1E and 5-HT1F receptors for beta-adrenergic antagonists

The serotonin 5-HT1B and 5-HT1A receptors bind certain beta-adrenergic antagonists, such as propranolol and pindolol, with high affinity. Other 5-HT1 receptors that display very low affinity for beta-adrenergic antagonists, have either a threonine (T) (5-HT1D alpha, 5-HT1D beta and 5-HT1E) or an alanine (A) (5-HT1F) residue in the homologous position in the seventh transmembrane domain. In the case of the human 5-HT1D beta receptor, replacement of this T with asparagine (N), dramatically increases its ability to bind beta-adrenergic antagonists. To assess whether other 5-HT1 receptors would behave similarly, we have used site-directed mutagenesis to replace the T or A in 5-HT1D alpha, 5-HT1E and 5-HT1F receptors with N. Both the wild-type and mutant genes were expressed transiently in COS-7 cells and radioligand binding studies were performed by using [3H]5-HT and [125I]iodocyanopindolol. Using [3H]5-HT, we found that the affinities of all the mutant receptors for propranolol and pindolol were significantly increased by 100-1000 fold, 5-HT1D alpha and 5-HT1F receptors showing the highest and the 5-HT1E receptor displaying the lowest affinity. On the other hand, the affinities for 5-HT were essentially unchanged as compared to the wild-type receptors. All mutant receptors bound [125I]iodocyanopindolol with high affinity, KD values ranging between 0.04 nM (mutant 5-HT1D alpha) and 0.57 nM (mutant 5-HT1E), whereas the wild-type receptors failed to show any specific binding with this radioligand in the same concentration range used for the mutant receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Classical and atypical binding sites for beta-adrenoceptor ligands and activation of adenylyl cyclase in bovine skeletal muscle and adipose tissue membranes

1. The radioligand [125I]-iodocyanopindolol ([125I]-ICYP) was used under standard ligand binding conditions, to detect beta 1- and beta 2-adrenoceptors in membrane preparations from bovine skeletal muscle and adipose tissue. High concentrations of [125I]-ICYP were also used, to identify an 'atypical' binding site in skeletal muscle. Finally, adenosine 3':5'-cyclic monophosphate (cyclic AMP) production was measured in the same membrane preparations, to determine the relationship between the beta-adrenoceptor sub-types present and the production of this second-messenger. 2. According to the results of radioligand binding studies, both skeletal muscle and adipose tissue membranes have beta 2-adrenoceptors, characterized by a high affinity for the beta 2-selective antagonist, ICI 118551 (pK 8.3 and 8.6 respectively); and a low affinity for the beta 1-selective antagonist CGP 20712A (pK 5.2 in both tissues). Antagonism of (-)-isoprenaline-stimulated cyclic AMP production by low concentrations of ICI 118551, yielded pseudo pA2 values in muscle and adipose tissue of 7.6 and 8.7 respectively, confirming that beta 2-adrenoceptors in these tissues are linked to the production of the second-messenger. 3. Although beta 1-adrenoceptors could not be detected in either skeletal muscle or adipose tissue membranes by use of ligand binding techniques, high pseudo pA2 values were obtained (8.0 and 8.2 respectively), when CGP 20712A was used to block the stimulation of cyclic AMP production by (-)-isoprenaline. This finding is consistent with the presence in both tissues of a population of beta 1-adrenoceptors which is small, but efficiently coupled to the second-messenger. 4.In addition to identifying standard beta 1- and beta 2-adrenoceptors, it was also established that skeletal muscle membranes have an 'atypical' binding site which has a relatively low affinity for [125]-ICYP(pK8.84), but which exists in abundance. At high concentrations of radioligand, the 'atypical' site accounted for 89% of the total [125I]-ICYP binding sites present.5. The results of second-messenger studies do not support the hypothesis that skeletal muscle or adipose tissue membranes contain functional beta 3-adrenoceptors: based on the failure of a beta 3-adrenoceptor-selective agonist (BRL 37344) to stimulate cyclic AMP production, the absence of a biphasic response to (-)-isoprenaline, and the observation that cyclic AMP production was not resistant to blockade by either ICI 118551 or CGP20712A.6. It is concluded that data from radioligand binding studies do not accurately reflect the contribution made by beta 1- and beta 2-adrenoceptors to cyclic AMP production in bovine skeletal muscle and adipose tissue membranes. Furthermore, the 'atypical' [125I]-ICYP binding site identified in bovine skeletal muscle does not represent a functional bovine beta 3-adrenoceptor.

Predominance of beta 3-adrenergic component in catecholamine activation of lipolysis in garden dormouse adipocytes

The beta 3-adrenoceptor (AR) agonists are potent activators of lipolysis in white adipose tissue. beta-AR agonists were tested here on the lipolytic activity of a hibernator, the garden dormouse (Eliomys quercinus L.). All the agonists exhibited full intrinsic activity; the most potent was the beta 3-AR agonist BRL-37344 [half-maximal effective concentration (EC50) = 0.8 nM]. The beta-antagonist idocyanopindolol (ICYP) also stimulated lipolysis of white adipocytes with the same potency and intrinsic activity as BRL-37344. The blockade of lipolytic effects of epinephrine or norepinephrine was similar to that of BRL-37344: the beta 1- and the beta 2-antagonists were quite ineffective. Total blockade occurred only with 100 microM bupranolol whatever the beta-agonist tested. This argues for the presence of a beta 3-component in the adrenergic-induced lipolysis. (-)-[125I]ICYP and (-)-[3H]CGP-12177 both labeled two populations of binding sites. On adipocyte membranes, binding of 0.6 nM (-)-[3H]CGP-12177 was inhibited with the following order of potency: isoproterenol > BRL-37344 > epinephrine. This order was modified at 20 nM, arguing for the beta-atypical nature of the low-affinity sites. Thus garden dormouse adipocytes possess beta 3-ARs, which are involved to an important degree in the adrenergic activation of lipolysis.

Ontogeny of [125I]iodocyanopindolol-labelled 5-hydroxytryptamine1B-binding sites in the rat CNS

Little is known about the ontogeny of the 5-hydroxytryptamine1B (5-HT1B) receptor, a putative terminal autoreceptor in the CNS. To learn more about the regional development of 5-HT1B sites and how early these sites may become functional, we studied [125I]iodocyanopindolol ([125I]ICYP)-labelled central 5-HT1B sites in developing postnatal rat brain and spinal cord. Significant ontogenic changes in Bmax were found in neocortex, hippocampus, striatum and brainstem. Maximum binding-site density was reached by 21 days in hippocampus and cortex, but not until 28 days in striatum. The rank order of binding site density changed with rat age, but Bmax was consistently high in brainstem and low in cerebellum. The percent increases in Bmax also varied with brain region, ranging from a 2-fold increase in brainstem up to 8-fold increases in cortex and striatum. In competition studies, the Ki for 5-HT and for RU 24969 was the same in 5-day-old and adult rat brain. These data indicate regional differences in the ontogeny of 5-HT1B-binding sites and suggest that 5-HT1B receptors are functional early in the postnatal period.

Lidocaine increases the number of beta-adrenoceptors in neonatal rat cardiocytes in culture

Some physiological functions of the heart are modulated through cardiac beta-adrenoceptors. In acute myocardial infarction, ventricular arrhythmias occur frequently and class I antiarrhythmic drugs such as lidocaine are often administered continuously over long period. The aim of this study was to investigate the effects of long-term treatment with lidocaine on cardiac beta-adrenoceptors. Ventricular cardiocytes from 2-day-old Wistar rat were cultured in the presence or absence of lidocaine, and beta-adrenoceptors of the membrane fraction of the cells were measured with a binding assay using [125I]-iodocyanopindolol ([125I]CYP) as a radioligand. When the cells were cultured in the presence of lidocaine at clinical or toxic concentrations, the binding of [125I]CYP to the cells increased in a concentration (10(-5) mol/l-10(-3) mol/l)--and time (12-72 h)--dependent manner. The effect was due to an increase in maximum binding and was not due to a change in the dissociation constant for the ligand. The stimulation of adenylyl cyclase activity in the cell membrane by 1 mumol/l isoproterenol increased in lidocaine-treated cells. The increased number of receptors returned to the control level when the cells were cultured without lidocaine for a further 24 h. These results indicate that lidocaine up-regulates cardiac beta-adrenoceptors at both clinical or toxic doses during the period of treatment. Other antiarrhythmic drugs such as disopyramide (Ia), mexiletine (Ib) and flecainide (Ic) also increased the number of beta-receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

A highly conserved tyrosine residue in G protein-coupled receptors is required for agonist-mediated beta 2-adrenergic receptor sequestration

An aromatic residue, tyrosine 326 in the prototypical human beta 2-adrenergic receptor, exists in a highly conserved sequence motif in virtually all members of the G protein-coupled receptor family. The potential role of this conserved aromatic amino acid residue in the cellular processes of sequestration (a rapid internalization of the surface receptor) and down-regulation (a slower loss of total cellular receptors) associated with agonist-mediated desensitization of the beta 2-adrenergic receptor was assessed by replacing tyrosine residue 326 with an alanine residue (beta 2AR-Y326A). This mutation completely abolishes agonist-mediated receptor sequestration without affecting the ability of the receptor to activate maximally adenylyl cyclase, to undergo rapid desensitization, and to down-regulate in response to agonist. The only other major change associated with the mutated receptor is a complete loss of the ability to resensitize following rapid desensitization. These results imply that this tyrosine residue, which is part of a highly conserved sequence motif in G protein-coupled receptors, may be responsible for their agonist-mediated sequestration and that sequestration and down-regulation of the receptor are dissociable phenomena. The lack of resensitization in the sequestration-defective beta 2-adrenergic receptor mutant strongly suggests that the sequestration pathway is an important mechanism by which cells re-establish the normal responsiveness of G protein-coupled receptors following the removal of agonist.

Catecholamine stimulated lipolysis in differentiated human preadipocytes in a serum-free, defined medium

Adipocyte precursors from the stromal vascular fraction of human adipose tissue were allowed to differentiate in serum-free defined medium, whereafter their catecholamine stimulated lipolytic response was compared to that of mature isolated human adipocytes. Seventy-five to ninety percent of the fibroblast-like cells accumulated lipid droplets and glycerol-3-phosphate dehydrogenase activities of 1,000-2,800 mU/mg protein were measured in cell homogenates of differentiated cells. Lipolysis could be stimulated by both isoproterenol and norepinephrine in both differentiated preadipocytes as well as mature adipocytes. The results obtained with beta-adrenergic agents suggested the presence of a higher affinity receptor in differentiated preadipocytes as compared to mature adipocytes. Mature adipocytes responded well to beta-adrenergic agents, but no antilipolytic alpha 2-adrenergic response was observed in the differentiated preadipocytes. The presence of Gi proteins in the differentiated preadipocytes was suggested by the antilipolytic effect of adenosine as well as the lipolytic activity generated by pertussis toxin. In conclusion, our medium supported the differentiation of a very high percentage of human preadipocytes which developed a sensitive beta-adrenergic lipolytic response but which lacked an alpha 2-adrenergic antilipolytic response.

Receptor-G-protein coupling in desensitization-resistant mutant adrenal cells

Mutant isolates from the Y1 mouse adrenocortical tumor cell line (designated Y1DR) were previously shown to resist homologous desensitization of adenylyl cyclase via endogenous ACTH receptors or transfected beta 2-adrenergic receptors. To further localize the site of the DR mutation, we examined the agonist-binding properties of the transfected beta 2-adrenergic receptor in parental Y1 cells and the DR mutant before and after desensitization with the beta-adrenergic agonist isoproterenol. Binding studies were carried out using [125I]iodocyanopindolol as the labeled ligand and isoproterenol as the competing agonist. We found that the DR mutant has a greater number of high affinity receptors in the basal state than does the Y1 parent (70-80% vs. < or = 50%) and that treatment of membranes from parent or mutant cells with guanyl-5'-yl imidodiphosphate and NaCl converts all of the high affinity sites to low affinity sites. After desensitization with isoproterenol, only low affinity binding sites are detected in parental Y1 cells, whereas the DR mutants retain an appreciable number of high affinity receptors. These results indicate that the DR mutant may resist desensitization by affecting agonist-induced uncoupling of receptors from their guanyl nucleotide-binding regulatory G-proteins.

Increase in stimulatory G protein and glucagon-responsive adenylate cyclase activity in rat liver following partial hepatectomy

Hepatocytes from partially hepatectomized rat livers show enhanced glucagon-sensitive adenylate cyclase activity. Bmax and Kd values of glucagon receptors (GR), measured by [125I]glucagon binding to liver plasma membranes, remained unchanged following partial hepatectomy. The amount of stimulatory G proteins (Gs), quantified by cholera toxin catalyzed ADP-ribosylation, increased in parallel with an increment in glucagon-responsive adenylate cyclase activity. It is proposed that an increment of Gs is one of the factors responsible for enhancement of glucagon-sensitive adenylate cyclase activity following partial hepatectomy.

Development and regulation of beta adrenergic receptors in kitten visual cortex: an immunocytochemical and autoradiographic study

The developmental pattern and laminar distribution of beta 1 and beta 2 adrenergic receptor subtypes were studied in cat visual cortex with autoradiography using [125I]iodocyanopindolol as a ligand and also with immunocytochemistry using a monoclonal antibody directed against beta adrenergic receptors. In the primary visual cortex of adult cats, the laminar distributions of both beta 1 and beta 2 adrenergic receptors revealed by autoradiography were very similar, with concentrations in layers I, II, III and VI. In young kittens (postnatal days 1 and 10), fewer beta adrenergic receptors were present, and they were concentrated in the deep cortical layers (V-VI) and subcortical white matter. Between postnatal days 15 and 40, beta adrenergic receptors increased in density more quickly in the superficial layers than they did in the deep and middle cortical layers. By postnatal day 40, the adult pattern was achieved, with two bands of intense binding in the superficial and deep cortical layers and a lower density in layer IV. Immunocytochemical techniques applied to adult cat cortex showed that beta adrenergic receptor-like immunoreactivity was found in different populations of neurons and glial cells. The immunoreactive neural cells were most dense in layers II, III and VI. About 50% of these immunoreactive neural cells were glial cells, primarily astrocytes. Immunoreactive pyramidal cells were mostly located in layers III and V. In layer IV, many stellate cells were stained. Immunoreactive astrocytes in the subplate and white matter progressively increased in number during development until adulthood. The pattern of laminar distribution and the developmental process was not affected by interrupting noradrenergic innervation from locus coeruleus either before or after the critical period. However, when visual input was interrupted by lesions of the lateral geniculate nucleus in young kittens (postnatal day 10), the density of both beta adrenergic receptor subtypes decreased significantly in the deep cortical layers. Lateral geniculate nucleus lesions in adult cats resulted in a pronounced decrease in beta adrenergic receptor density in layer IV.

Changes in cardiac beta-adrenoceptors in human heart diseases: relationship to the degree of heart failure and further evidence for etiology-related regulation of beta 1 and beta 2 subtypes

Radioligand binding studies were performed to investigate total beta-adrenoceptor density (Bmax) and beta 1 and beta 2 subtype distribution in left ventricular biopsies obtained from 8 prospective transplant donors serving as controls and from 143 patients with different degrees of heart failure (NYHA class II to IV) undergoing aortic or mitral valve surgery due to aortic or mitral stenosis, aortic or mitral regurgitation, as well as combined aortic or mitral valve lesions (stenosis and regurgitation). In 13 other patients, heart failure was due to hypertrophic obstructive cardiomyopathy (N = 6, NYHA III), tetralogy of Fallot (N = 4, NYHA III), or Becker's muscular dystrophy (N = 3, NYHA IV). Bmax was assessed by (-)-(125I)-iodocyanopindolol used as radioligand. Competition experiments with the highly selective beta 1-adrenoceptor antagonist CGP 20712A were performed for determination of beta 1- and beta 2-adrenoceptor subtypes. In biopsies taken from transplant donors, the Bmax was found to be 70.1 +/- 5.8 fmol/mg protein. In all groups investigated the extent of total beta-adrenoceptor downregulation was related to the degree of heart failure. The decrease in Bmax was found to be about 20% (NYHA II), 45% (NYHA III), and 60% (NYHA IV) when compared with controls. There was no significant difference in the reduction of total beta-adrenoceptor density between isolated aortic or mitral valve diseases and combined valve lesions. Independent of the degree of heart failure, selective downregulation of the beta 1 subtype was found in patients with isolated or combined aortic valve diseases, hypertrophic obstructive cardiomyopathy, and Becker's muscular dystrophy.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of parameters of in vitro lymphocyte beta 2-adrenoceptor function in normal and asthmatic subjects

There is conflicting data in the literature as to whether subsensitivity of in-vivo beta 2-adrenoceptor (beta 2-AR) responses in patients with asthma is due to an endogenous defect of beta 2-AR or an effect of exogenous beta 2-agonist therapy. The purpose of the study was to compare in-vitro parameters of lymphocyte beta 2-AR function in eight age and sex matched normal [FEV1, 98 (2)% predicted] volunteers and asthmatic [FEV1, 60 (5)% predicted] subjects. The asthmatic group were washed out for 4 weeks by substituting inhaled beta 2-agonist therapy with ipratropium bromide, in order to exclude possible exogenous effects of beta 2-agonist exposure. Receptor binding affinity (Kd) and density (Bmax) were evaluated using (-)125I-iodocyanopindolol and maximal cAMP response (Emax) was assayed following stimulation with isoprenaline (10(-4) M). No significant differences were found between the normal and asthmatic group for Kd (pmol.l-1): 9.65 vs 10.2, Bmax (fmol/10(6) cells): 1.9 vs 1.6, or Emax (pmol/10(6) cells): 4.24 vs 4.85. Thus, parameters of beta 2-AR function are unaltered in asthmatic patients who have not been exposed to beta 2-agonists, suggesting that asthma is not associated with an endogenous defect of beta 2-AR.

Characterization of cardiac beta-adrenergic receptors in the guinea pig heart: application to study of beta-adrenergic receptors in shock models

The myocardial response to catecholamines is significantly diminished in many types of shock or heart failure. The guinea pig heart is an ideal model for the study of shock, as it is relatively inexpensive, and the cardiovascular system of the guinea pig most closely resembles that of the human. Using this model, we have developed techniques to characterize and quantitate changes in beta-adrenergic receptors (beta AR) in the guinea pig heart after burn injury. Preliminary experiments were performed to determine the optimum binding conditions, e.g., incubation time and conditions, protein concentrations, rinsing, etc. Additional experiments were conducted using agonists and antagonists to characterize the rank order of potency and stereospecificity of the beta AR. Crude membrane preparations (50 micrograms/250 microliters) from sham-burned and burned hearts were incubated with 8-10 concentrations of 125I-cyanopindolol (10-450 pM) at 37 degrees C for 1 hr. Under these conditions, binding assays were linear with respect to protein concentration and time. Alprenolol (10 microM) was used to determine nonspecific binding. The membrane preparations used in this study bound both agonists and antagonists with a rank order of potency and stereospecificity characteristic of a beta-adrenergic receptor. Finally, agonist competition curves were performed with isoproterenol in the presence and absence of Gpp(NH)p to determine receptor regulation by the Gs protein. Analysis using computer-assisted techniques suggests that the fraction of high-affinity beta-receptors is significantly reduced after burn injury (41.2 +/- 4.7%) compared to sham-burned controls (54 +/- 2%, P < or = 0.023).(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo EEDQ dose-dependently inactivates rat brain 5-HT receptors but not 5-HT uptake sites

The present study investigates the inactivation and recovery of brain serotonin (5-HT) recognition sites by EEDQ (N-ethoxycarbonyl-2-ethoxy-1,2,-dihydroquinoline). Adult male Sprague-Dawley rats were given a single s.c. injection of vehicle (1:1 EtOH/H2O) or EEDQ (1-20 mg kg-1) and sacrificed at 4 h and 7 days (10 mg kg-1 dose) post-injection. EEDQ dose-dependently reduced the Bmax of 5-HT1A(3H-DPAT),5-HT1B(125I-CYP),5-HT2(3H-ketanserin) and 5-HT2/1C(125I-DOI) receptors in cortical homogenates. In contrast, EEDQ was without effect on the 5-HT transporter recognition site (3H-paroxetine). No significant changes in affinity were observed for 5-HT1B, 5-HT2 or 5-HT2/1C receptors. The rank order of sensitivity to EEDQ inactivation was: 5-HT1A > 5-HT1B > 5-HT2 approximately 5-HT2/1C >>> 5-HT uptake sites. This study demonstrates: (1) differential EEDQ inactivation and recovery of 5-HT receptors and (2) lack of EEDQ inactivation of the 5-HT transporter.

Autoradiographic analysis of serotonin receptors and transporter in kindled rat brain

While serotonin (5-HT) has been shown to be anticonvulsant in several types of experimentally induced seizures, 5-HT receptor binding has not been investigated in the kindling model of epilepsy. The present study examined the effects of amygdala kindling on two 5-HT receptor subtypes and on the 5-HT transporter in rat brain. Kindling induced a persistent bilateral increase in 5-HT1A binding in the dentate gyrus, while 5-HT1B receptors increased only in a delayed fashion. Binding to the 5-HT transporter was transiently decreased in dentate gyrus. In cerebral cortex, binding of the three ligands was unchanged. Alterations in 5-HT receptors and the 5-HT transporter may endogenously modulate kindled seizures. Additionally, autoradiography of adenosine A1 receptors revealed no change for these receptors in any brain region.

3,5,3'-L-triiodothyronine regulation of beta-adrenergic receptor density and adenylyl cyclase activity in synaptosomal membranes of aged rats

To determine the effect of aging on T3 up-regulation of beta-adrenergic receptor activity of purified synaptosomal membranes (SPM), beta-adrenergic receptor density (Bmax) and adenylyl cyclase (AC) activity were measured in young (6 months old) and aged (26 months old) male F-344 rats at baseline and after treatment with triiodothyronine (T3), 15 micrograms/100 g, intraperitoneally for 10 days. The Bmax (fmol/mg protein) as measured by 125I-iodocyanopindolol binding was reduced in aged rats (70.8 +/- 4.1) compared to young rats (93.5 +/- 11.2). T3 treatment resulted in a significant increase in Bmax of young rats but not in aged rats (P < 0.05). The AC activity (pmol cAMP/mg) in response to prostaglandin E1 (PGE1) was reduced in aged rats compared to young rats (67.8 +/- 2.9 vs 108.3 +/- 18.6; P < 0.01). The sodium fluoride (NaF) stimulated AC activity was not altered with age. A net isoproterenol stimulated AC activity could not be demonstrated in any age group. T3 treatment did not alter AC activity of SPM. It is concluded that aging is associated with reduced responsiveness to T3-stimulated up-regulation of beta-adrenergic receptor number in synaptosomal membranes.

Role of adrenergic tone in mechanical and functional properties of carotid artery during aging

The present study was designed to assess the role of the adrenergic tone in the regulation of carotid arterial compliance during aging. An experimental model of in situ isolated carotid arteries has been used to evaluate the elastic properties of the arterial wall in young (3-mo-old) and older (18-mo-old) Wistar rats. Binding experiments were performed in the same strain of rats to evaluate alpha 1- and beta-adrenoceptor affinity and density. In a third set of experiments, structural parameter of the carotid artery in younger and older rats was evaluated. Arterial distensibility (compliance per unit of volume) was significantly lower in older rats. This was associated with a significant thickness of the media (45.6 +/- 2.8 vs. 57.5 +/- 5.7 microns, P < 0.01) and increased collagen content in older rats (4,420 +/- 310 vs. 7,320 +/- 850 microns 2/mm, P < 0.001). However, carotid arterial compliance was not altered in older rats because of the significant increase in cross-sectional area with aging. Aging did not affect alpha 1-adrenoceptor affinity and density, whereas it decreased beta-density without changing their affinity. Pharmacological stimulation of alpha 1-adrenoceptor with phenylephrine (10(-5) M) decreased compliance in older but not in younger animals. Blockade of these receptors with prazosin or labetalol increased compliance in younger and had no effect on older rats. beta-receptor stimulation with isoproterenol or blockade with propranolol had no effect in any of the studied groups. We suggest that with aging there is an increased vasoconstricting effect of alpha-agonists and a decreased vasodilatative action of alpha-blockade.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of agonist-induced internalization and down-regulation of beta-adrenergic receptors in isolated rat lung and heart preparations

Using isolated lung and heart preparations from male Sprague-Dawley rats, this study characterizes whether the beta-adrenergic receptor (BAR) agonist isoproterenol (ISO) can induce internalization and down-regulation of BAR in these tissues. The results showed that ISO-induced BAR internalization was time- and concentration-dependent in the lung preparations. When the lung and heart preparations were compared, however, the same ISO (10 microM, 30 min) treatment only induced BAR internalization in the lung but not in the heart preparations. Pretreatment of hypertonic sucrose medium (0.45-0.6 M) for 30 min inhibited about 50% of ISO-induced BAR internalization in the lung preparations. Treatment of either ISO (10 microM) or terbutaline (10 microM) for 3 hr or 12 hr did not significantly decrease the number of BAR in both tissue preparations. However, ISO (10 microM, 12 hr) increased the KD value of the radioligand [125I]-iodocyanopindolol for BAR in the heart homogenates. This ISO-induced KD change was not observed in the presence of cycloheximide (20 micrograms/ml), a protein synthesis inhibitor. In the presence of cycloheximide (20 micrograms/ml), ISO also did not decrease the BAR number in either tissue preparation.