Biomedical subjects

R J Summers

Publications and source records attributed to R J Summers.

At least 19 recordsLinked to original sources

PubMed2005

Contrasting roles for beta1, beta2 and beta3-adrenoceptors in memory formation in the chick.

Noradrenaline plays distinct roles in the modulation and consolidation of memory for one-trial, discriminated, avoidance learning in the chick. We have previously shown that activation of beta2-, beta3- and alpha1-adrenoceptors (ARs) by injection into the multimodal forebrain association region (intermediate medial hyperstriatum ventrale [IMHV] or intermediate medial mesopallium [IMM]) is involved in the consolidation of memory 30 min after training and that activation of alpha2-ARs in the caudate putamen plays a role in the reinforcement of memory leading to consolidation in the IMM (IMHV). In this paper we provide evidence that noradrenaline acts at beta1-ARs in the basal ganglia (lobus parolfactorius or medial striatum) in short-term memory processing immediately post-training and demonstrate inhibition of memory by selective AR antagonists at particular times in the sequential memory processing sequence after training. These results support separate roles for beta2- and beta3-ARs in memory consolidation. Our studies suggest that, as a consequence of the learning experience, noradrenaline acts in different brain regions and at different times in memory processing, to enhance memory through distinct populations of ARs.

Adrenergic beta-Agonists↗

PubMed2002

Effects of glucose and 2-deoxyglucose on memory formation in the chick: interaction with beta(3)-adrenoceptor agonists.

Consolidation of a weakly reinforced memory that would otherwise fade after 30 min can be achieved by central or peripheral injection of the selective beta(3)-adrenoceptor agonist CL316243 as well as the beta(2)-adrenoceptor agonist zinterol and the alpha(1)-adrenoceptor antagonist prazosin in the day-old chick. The effect of the beta(3)-adrenoceptor agonist is mimicked by peripheral or central injection of glucose that is effective in enhancing memory from 25 min before to 25 min after training. Glucose uptake into various cell types has been described following activation of beta(3)-adrenoceptors and in this paper we demonstrate that activation of beta(3)-adrenoceptors by CL316243 facilitates the effect of a dose of glucose that does not normally enhance memory, whereas a beta(2)-adrenoceptor agonist and an alpha(1)-adrenoceptor antagonist have no effect. Administration of the glucose uptake inhibitor 2-deoxyglucose prevented the consolidation of strongly reinforced training. The beta(3)-adrenoceptor agonist facilitated the effect of a non-amnestic dose of 2-deoxyglucose to inhibit memory. There are two time periods relative to the learning trial where memory is vulnerable to interference by centrally administered 2-deoxyglucose: one related to short-term memory and one at the time of consolidation into long-term memory. Peripheral injection of 2-deoxyglucose is only effective at the time of consolidation. The action of the beta(3)-adrenoceptor agonist to facilitate the action of 2-deoxyglucose only occurs at the time of consolidation. We suggest that a noradrenergic agonist acting at beta(3)-adrenoceptors enhances memory formation by facilitation of glucose uptake at the time of memory consolidation. This may represent a novel mechanism that would be beneficial for developing compounds for the facilitation of memory in diseases with cognitive deficits.

Adrenergic beta-3 Receptor Agonists↗

PubMed2001

Enhancement of memory consolidation in chicks by beta(3)-adrenoceptor agonists.

The effects of intracranial injection of three beta(3)-adrenoceptor agonists, sodium-4-[-2[-2-hydroxy-2-(-3-chloro-phenyl)ethylamino] propyl]phenoxyacetate (BRL 37344), 2-hydroxy-5(2-((2-hydroxy-3-(4-((1-methyl-4-trifluoromethyl)1H-imidazole-2-yl)-phenoxy)propyl)amino)ethoxy)-benzamide monomethane sulfonate) (+/-)-CGP12177A) and the pro-drug RS-N-(7-carbethoxymethoxyl 1,2,3,4-tetrahydronaphth-2-yl)-2 hydroxy 2-(3-chlorophenyl)ethanamine (SR58611A), were examined on reinforcement of memory in day-old chicks. BRL37344 and CGP12177 facilitated memory, whereas SR58611A had no effect. The dose-response relationships of the beta(3)-adrenoceptor agonists were challenged with the selective beta(3)-adrenoceptor antagonist 3-(2-ethylphenoxy)-1-[(1S)-1,2,3,4-tetrahydronapth-1-ylamino]-2S-2-propanol oxalate (SR59230A) or the beta(2)-adrenoceptor antagonist (-)propranolol. BRL 37344 appeared to act predominantly at beta(3)-adrenoceptors at low doses and at beta(2)-adrenoceptors at higher doses. Facilitation of labile into long-term storage by beta(3)-adrenoceptor agonists appears to be a class action of these drugs.

Adrenergic beta-Agonists↗

PubMed2001

beta(1)- and beta(3)-adrenoceptor mediated smooth muscle relaxation in hypothyroid rat ileum.

The effect of hypothyroidism on gastrointestinal beta(1)- and beta(3)-adrenoceptor function and expression was examined in rat ileal smooth muscle preparations. (-)-Isoprenaline and the selective beta(3) agonist disodium (R,R)-5-[2-[[2-3-chlorophenyl)-2-hydroxyethyl]-amino]propyl]-1,3-benzodioxole-2,2-dicarboxylate (CL 316234) relaxed both control and hypothyroid tissues in a dose-dependent manner. Responses to isoprenaline were reduced in tissues from hypothyroid rats, as was the shift produced with the beta(3)-adrenoceptor antagonist, 3-(2-ethylphenoxy)-1-[(1S)-1,2,3,4-tetrahydronaphth-1-ylamino]-(2S)-2-propanol oxalate (SR 59230A). No change was seen in responses to CL 316243. Experiments with a selective beta(1)-adrenoceptor antagonist produced results suggesting that isoprenaline did not act at this receptor. Messenger RNA levels for both beta(1)- and beta(2)-adrenoceptors were not affected by hypothyroidism. These results show that, unlike in adipose tissues, ileal beta(1)- and beta(3)-adrenoceptors are not directly regulated by thyroid hormone and that beta(3)-adrenoceptor coupling to the relaxation response is reduced in a rat model of hypothyroidism.

Adrenergic beta-Agonists↗

PubMed2001

Synthesis, conformational studies and biological activity of N(alpha)-mono-biotinylated rat relaxin.

Biotin-avidin immobilization can be a useful tool in structure-function studies of hormone receptors. A crucial step is the preparation of a specifically biotinylated hormone that is able to bind to its receptor while leaving the biotin group free for interaction with avidin. The receptor for relaxin, an ovarian peptidic hormone produced during pregnancy, has not yet been isolated. We therefore undertook to prepare a specifically monobiotinylated rat relaxin for use in ligand-searching strategies. Rat relaxin is a convenient analogue because reliable bioassays exist, thus allowing assessment of the effect of N-biotinylation on bioactivity. To help improve the yield of the two-chain, three-disulfide bond rat relaxin, 2-hydroxy-4-methoxybenzyl (Hmb) backbone protection was used during the solid-phase assembly of the B-chain to help prevent any possible chain aggregation. As a final step, while the protected peptide was still on the resin, the biotin label was introduced at the N-terminus of the B-chain using standard coupling protocols. The chain combination with the A-chain was accomplished in reasonable yield. Secondary structural measurements demonstrated that the biotin caused the starting B-chain to adopt a more ordered conformation. The labelled synthetic relaxin exhibited similar circular dichroism spectra to native and synthetic single B-chain peptides. In addition, the biotinylated relaxin showed no significant difference in its chronotropic activity in the rat isolated heart assay compared with the native peptide. Biosensor studies showed that antibody recognition was retained upon attachment of the synthetic relaxin to the streptavidin-derivatized surface.

Animals↗

PubMed2001

beta(1)-Adrenoceptors compensate for beta(3)-adrenoceptors in ileum from beta(3)-adrenoceptor knock-out mice.

1. This study examines beta(1)-, beta(2)- and beta(3)-adrenoceptor (AR)-mediated responses, mRNA levels and radioligand binding in ileum from beta(3)-AR knock-out (-/-) (KO) and wild type (+/+) (FVB) mice. 2. In KO and FVB mice, SR59230A (100 nM) (beta(3)-AR antagonist) antagonized responses to (-)-isoprenaline in both KO and FVB mice. (-)-Isoprenaline mediated relaxation of ileum was antagonized weakly by ICI118551 (100 nM) (beta(2)-AR antagonist). Responses to (-)-isoprenaline were more strongly antagonized by CGP20712A (100 nM) (beta(1)-AR antagonist), propranolol (1 microM) (beta(1)-/beta(2)-AR antagonist), carvedilol (100 nM) (non-specific beta-AR antagonist), and CGP12177A (100 nM) (beta(1)-/beta(2)-AR antagonist) in ileum from KO than in FVB mice. 3. Responses to CL316243 (beta(3)-AR agonist) in ileum from FVB mice were antagonized by SR59230A (100 nM) but not by propranolol (1 microM) or carvedilol (100 nM). CL316243 was ineffective in relaxing ileum from KO mice. 4. CGP12177A had no agonist actions in ileum from either KO or FVB mice. 5. beta(1)-AR mRNA levels were increased 3 fold in ileum from KO compared to FVB mice. This was associated with an increased maximum number of beta(1)-/beta(2)-AR binding sites (B(max)). beta(2)-AR mRNA levels were unaffected while no beta(3)-AR mRNA was detected in KO mice. 6. In mouse ileum, beta(3)-ARs and to a lesser extent beta(1)-ARs are the predominant adrenoceptor subtypes mediating relaxation in ileum from FVB mice. In KO mice beta(1)-ARs functionally compensate for the lack of beta(3)-ARs, and this is associated with increased beta(1)-AR mRNA and levels of binding.

Adrenergic beta-Agonists↗

PubMed2001

Stimulation of alpha1-adrenoceptors inhibits memory consolidation in the chick.

Investigation of the effects of the different adrenoceptor (AR) subtypes in memory formation may reveal discrete actions of noradrenaline in memory modulation and storage mediated through particular AR subtypes. Noradrenaline injected intracerebrally in the chick produced biphasic effects on memory consolidation with enhancement at low doses and inhibition at high doses. We have previously shown that the enhancement by the lower doses of noradrenaline is attributable to actions at beta2- and beta3-adrenoceptors, whereas the inhibitory effect of higher doses is attributable to alpha1-adrenoceptors. The present studies show that the inhibition of memory by high doses of noradrenaline is mimicked by the alpha1-AR agonist methoxamine, and the dose-response curve is shifted to the right by pretreatment with the alpha1-AR antagonist prazosin. alpha1-ARs may play a critical role in memory formation in highly stressful situations, when noradrenaline levels are high in particular brain regions. It is not known where the alpha1-ARs responsible for the effect on memory are localized. alpha1-ARs are found on neurons and astrocytes and in the cerebral vasculature and therefore the action of high doses of noradrenaline via alpha1-AR agonists could be via an action at any of these sites. Activation of alpha1-adrenoceptors in the intermediate hyperstriatum ventrale in the chick forebrain by the alpha1 adrenoceptor agonist methoxamine inhibits the consolidation of memory. Because the same effect is produced by high levels of noradrenaline, it is likely that stimulation of alpha1-ARs is the mechanism underlying this effect.

Adrenergic alpha-1 Receptor Agonists↗

PubMed2001

The effects of human GH and its lipolytic fragment (AOD9604) on lipid metabolism following chronic treatment in obese mice and beta(3)-AR knock-out mice.

Both human GH (hGH) and a lipolytic fragment (AOD9604) synthesized from its C-terminus are capable of inducing weight loss and increasing lipolytic sensitivity following long-term treatment in mice. One mechanism by which this may occur is through an interaction with the beta-adrenergic pathway, particularly with the beta(3)-adrenergic receptors (beta(3)-AR). Here we describe how hGH and AOD9604 can reduce body weight and body fat in obese mice following 14 d of chronic ip administration. These results correlate with increases in the level of expression of beta(3)-AR RNA, the major lipolytic receptor found in fat cells. Importantly, both hGH and AOD9604 are capable of increasing the repressed levels of beta(3)-AR RNA in obese mice to levels comparable with those in lean mice. The importance of beta(3)-AR was verified when long-term treatment with hGH and AOD9604 in beta(3)-AR knock-out mice failed to produce the change in body weight and increase in lipolysis that was observed in wild-type control mice. However, in an acute experiment, AOD9604 was capable of increasing energy expenditure and fat oxidation in the beta(3)-AR knock-out mice. In conclusion, this study demonstrates that the lipolytic actions of both hGH and AOD9604 are not mediated directly through the beta(3)-AR although both compounds increase beta(3)-AR expression, which may subsequently contribute to enhanced lipolytic sensitivity.

Adipose Tissue↗

PubMed2000

Intracerebroventricular administration of the beta(3)-adrenoceptor agonist CL 316243 causes Fos immunoreactivity in discrete regions of rat hypothalamus.

Intracerebroventricular (i.c.v.) administration of the beta(3)-AR agonist BRL37344 causes dose dependent decreases in food intake in rats suggesting a role for beta(3)-AR in the central control of feeding. We have conducted experiments investigating the effects of i.c.v. administration of the selective beta(3)-AR agonist CL316243 on Fos expression to determine whether beta(3)-AR stimulation affects neurones within specific brain nuclei. Significantly higher numbers of Fos positive cells were found in the rats treated i.c.v. with CL316243 compared with control rats in the paraventricular hypothalamus, lateral hypothalamic area, ventromedial hypothalamic nucleus and dorsal hypothalamic area. Pre-treatment with the selective beta(3)-AR antagonist SR59230A resulted in a significant decrease in the number of Fos positive cells in all those areas compared with rats treated with CL316243 alone. These experiments demonstrate that i.c.v. administration of selective beta(3)-AR agonist causes neuronal activation in hypothalamic areas important in the central regulation of appetite via a beta(3)-AR mediated effect.

Adrenergic beta-Agonists↗

PubMed2000

Novel strategy for the synthesis of template-assembled analogues of rat relaxin.

The 'template-assembled synthetic protein' (TASP) concept provides a simple and elegant approach for the preparation of analogues that retain key structural elements. We have synthesized TASP molecules containing the putative active site of relaxin, a peptide that has similar structural features to insulin but a markedly different biological role. Two types of chemoselective thiol ligation strategies (thioether and thiazolidine) were used and compared. The synthetic pendant peptides contain an essential region for bioactivity that is located in the alpha-helical region of the relaxin B-chain. Depending on whether the thioether or the thiazolidine chemistry was used to attach the peptides to the template, the reacting amino acid was placed either at the C-terminus or N-terminus, respectively, thus allowing the choice of orientation relative to the carrier molecule. The template molecule consists of a decapeptide with two proline-glycine turns and four evenly spaced lysine residues that were functionalized with the appropriate chemical moiety. This allowed reaction with the appropriately derivatized peptides in solution. To improve the template ligation step using the thioether approach, a pendant peptide C-terminal cysteamine residue was used to reduce potential steric hindrance during conjugation. The design of the peptides as well as the synthetic strategy resulted in the acquisition of mimetics showing weak non-competitive and weak competitive antagonist properties.

Animals↗

PubMed2000

Separate roles for beta2- and beta3-adrenoceptors in memory consolidation.

Consolidation of a labile memory which would not normally be stored can be achieved by intracerebral administration of noradrenaline. In a series of experiments using discriminated, one trial passive avoidance learning with the day-old chick, the effect of noradrenaline has been shown to be due to actions at different subtypes of adrenoceptors. The effect of noradrenaline is dose-dependent, with a moderate dose producing memory consolidation. However, higher doses of noradrenaline (0.3-10 nmol/hemisphere) prevent consolidation, an effect not seen with isoprenaline suggesting that these doses stimulate alpha-adrenoceptors. The promotion of memory consolidation by noradrenaline or isoprenaline at low doses was attributable to beta3-adrenoceptors and at medium doses to beta2-adrenoceptors. At higher doses of noradrenaline, there was alpha1-adrenoceptor-mediated inhibition of memory consolidation. Consolidation can also be achieved by administration of either beta2- or beta3-adrenoceptor agonists at specific times after training. Although these two adrenoceptors both promoted memory consolidation, there was a differential action on the stages of memory formation. The dose-response curve to the beta3- and the beta2-agonists was shifted by the appropriate antagonist but not by the antagonist at the other beta-adrenoceptor. Although beta1-adrenoceptors are present in chick brain, they do not seem to have a role in memory formation. These results explain why noradrenaline, acting at different adrenoceptors, can have different effects on memory formation with memory being either consolidated or inhibited depending on the dose. The findings also demonstrate a role in memory formation for beta3-adrenoceptors found in the brain. Agonists acting specifically at beta2- or beta3-adrenoceptors may be of value in diseases involving cognitive impairment.

Adrenergic beta-Agonists↗

PubMed2000

beta(3)-adrenoceptor regulation and relaxation responses in mouse ileum.

1. This study examines the relationship between beta(3a)- and beta(3b)-adrenoceptor (AR) mRNA levels, beta(3)-AR binding and changes in ileum responses in mice treated with the beta(3)-AR agonist (R, R)-5-[2[[2-(3-chlorophenyl)-2-hydroxyethyl]-amino]-propyl]1, 3-benzodioxole-2,2-dicarboxylate (CL316243), or the beta(3)-AR antagonist 3-(2-ethylphenoxy)-1-[(1S)-1,2,3, 4-tetrahydronapth-1-ylamino]-2S-2-propanol oxalate (SR59230A), or dexamethasone or forskolin. 2. Levels of beta(3a)- and beta(3b)-AR mRNA and the maximum number of binding sites (B(max)) in ileum were unaffected following CL316243 treatment, although responses to CL316243 were reduced by 50% following 4 and 24 h treatment, indicating another desensitization mechanism not involving changes in receptor expression or number. beta(3a)-AR mRNA levels were reduced in both brown (BAT) and white adipose tissue (WAT) but beta(3b)-AR mRNA levels were significantly reduced only in WAT. Levels of beta(3a)- and beta(3b)-mRNA returned towards normal with continued treatment. 3. SR59230A treatment markedly increased beta(3)-AR mRN levels in ileum and BAT but not in WAT. The increase in beta(3)-AR mRNA levels in ileum was associated with increased B(max) levels in binding analysis and increased responses to CL316243, suggesting these as the cause of sensitization. 4. Treatment with forskolin (4 h) or dexamethasone (4 h) significantly reduced beta(3a)-AR mRNA levels in BAT and WAT but did not alter levels in ileum. Responses to CL316243 in ileum were unaffected by either treatment. 5. In summary, the beta(3)-AR is differently regulated in adipose tissue and ileum: Treatment with SR59230A increased beta(3)-AR number, mRNA and responsiveness in ileum, whereas treatment with CL316243 reduced responses without affecting beta(3)-AR number or mRNA levels.

Adipose Tissue↗

PubMed2000

Human sensitivity to phase perturbations in natural images: a statistical framework.

Fourier-phase information is important in determining the appearance of natural scenes, but the structure of natural-image phase spectra is highly complex and difficult to relate directly to human perceptual processes. This problem is addressed by extending previous investigations of human visual sensitivity to the randomisation and quantisation of Fourier phase in natural images. The salience of the image changes induced by these physical processes is shown to depend critically on the nature of the original phase spectrum of each image, and the processes of randomisation and quantisation are shown to be perceptually equivalent provided that they shift image phase components by the same average amount. These results are explained by assuming that the visual system is sensitive to those phase-domain image changes which also alter certain global higher-order image statistics. This assumption may be used to place constraints on the likely nature of cortical processing: mechanisms which correlate the outputs of a bank of relative-phase-sensitive units are found to be consistent with the patterns of sensitivity reported here.

Discrimination, Psychological↗

PubMed1999

The role of the sympathetic nervous system in the regulation of leptin synthesis in C57BL/6 mice.

The objectives of this study were to determine whether leptin synthesis is regulated by the sympathetic nervous system and if so whether beta-adrenergic receptors mediate this effect. We show that sympathetic blockade by reserpine increases leptin mRNA levels in brown but not white adipose tissue, while acute cold-exposure decreases leptin expression 10-fold in brown adipose tissue and 2-fold in white adipose tissue. The cold-induced reduction in leptin mRNA can be prevented by a combination of propranolol and SR 59230A but not by either antagonist alone, indicating that beta3-adrenergic receptors and classical beta1/beta2-adrenergic receptors both mediate responses to sympathetic stimulation. Circulating leptin levels reflect synthesis in white adipose tissue but not in brown adipose tissue.

Adipose Tissue↗

PubMed1999

Desensitization of cardiac beta-adrenoceptor signaling with heart failure produced by myocardial infarction in the rat. Evidence for the role of Gi but not Gs or phosphorylating proteins.

This study examined mechanisms of beta-adrenergic (AR) desensitization in a myocardial infarction (MI) model of heart failure in the rat. Inotropic responses to isoproterenol (non-selective beta-AR agonist) and RO 363 (selective beta1-AR agonist), in left atria and left papillary muscle, were reduced by up to 65%, while chronotropic responses in right atria were unaffected. beta1- and beta2-AR density did not change after MI, suggesting that changes in beta-AR responsiveness are due to changes occurring downstream of the receptor. Inotropic and chronotropic responses to forskolin were not altered in right and left atria and left papillary muscle after MI, suggesting changes at the level of the G-proteins. Pertussis toxin treatment of animals restored inotropic responses to isoproterenol in left atria and left papillary muscle to levels seen in the sham group, indicating that inactivation of Gi-proteins improves inotropic function in MI rats, and that beta-ARs couple to Gi in cardiac failure. Expression of G-protein receptor kinase 2 (GRK2), beta-arrestin1 and the regulatory subunits of cAMPdPK (RI alpha and RII alpha), showed no change after MI. However the expression of Gi alpha2 was significantly increased in left ventricle (sham 0.888+/-0.140, MI 1. 759+/-0.352 P=0.026), right ventricle (sham 0.031+/-0.004, MI 0. 037+/-0.002 P=0.006) and atria (sham 0.107+/-0.006, MI 0.138+/-0.006 P=0.004), with no changes observed in the expression of Gs alpha. These results suggest that increases in Gi play an important role in the decreased beta-AR responsiveness in the rat model of MI.

Adrenergic beta-Agonists↗

PubMed1999

Solid-phase synthesis of ovine Leydig cell insulin-like peptide--a putative ovine relaxin?

The primary structure of ovine Leydig cell insulin-like peptide (Ley I-L) was recently deduced from the corresponding cDNA sequence. It consists of two peptide chains and three disulphide bonds in an arrangement similar to both relaxin and insulin. As in relaxin B-chain, an Arg-X-X-X-Arg sequence exists within the Ley I-L B-chain although it is located four residues towards the C-terminus from the corresponding position within relaxin. This sequence of amino acids is known to be essential for relaxin biological activity and its presence in Ley I-L suggested that the peptide might possess a relaxin-like function. Ovine Ley I-L was assembled by Fmoc-solid-phase synthesis of the separate chains followed by their combination in solution at high pH. The purity and identity of the chain-combined peptide was confirmed by chemical characterization including mass spectrometry. At physiological concentrations, the peptide was shown not to possess relaxin-like activity in the rat isolated atrial chronotropic and inotropic assay. This strongly suggests that Ley I-L is not a relaxin in the sheep. In order to explore further a possible structural relationship between Ley I-L and relaxin, we prepared a synthetic analogue of ovine Ley I-L containing a single replacement of B-chain residue 12, His, with Arg. This was found to possess significant relaxin-like chronotropic and inotropic activity demonstrating that the tertiary structure of Ley I-L is similar to that of relaxin and highlighting the key requirement for the five-residue sequence, Arg-X-X-X-Arg, to be present in position B12-16 for characteristic relaxin activity.

Amino Acid Sequence↗

PubMed1999

Quantitative autoradiographic studies of relaxin binding in rat atria, uterus and cerebral cortex: characterization and effects of oestrogen treatment.

The binding characteristics of the relaxin receptor in rat atria, uterus and cortex were studied using a [33P]-labelled human gene 2 relaxin (B33) and quantitative receptor autoradiography. The binding kinetics of [33P]-human gene 2 relaxin (B33) were investigated in slide-mounted rat atrial sections. The binding achieved equilibrium after 60 min incubation at room temperature (23+/-1 degrees C) and dissociated slowly. The association and dissociation rate constants were 4.31+/-0.34x10(8) M(-1) x min(-1) and 1.55+/-0.38x10(-3) min(-1) respectively. Thus, the kinetic dissociation constant was 3.46+/-0.59 pM. Binding was saturable to a single population of non-interacting sites throughout atria, in uterine myometrium and the 5th layer of cerebral cortex. The binding affinities (pK(D)) of [33P]-human gene 2 relaxin (B33) were 8.92+/-0.09 in atrial myocardium and 8.79+/-0.04 in cerebral cortex of male rats, and 8.79+/-0.10 in uterine myometrium. Receptor densities in the cerebral cortex and atria were higher than in uterine myometrium, indicating that relaxin also has important roles in non-reproductive tissues. In male rats, treatment with 17beta-oestradiol (20 microg in 0.1 ml sesame oil s.c., 18-24 h) significantly decreased the density of relaxin receptors in atria and cerebral cortex. Identical treatment in female rats had no significant effect in atria and cerebral cortex, but it significantly increased the density of relaxin receptors in uterine myometrium. Relaxin binding was competitively displaced by porcine and rat native relaxins. Porcine native relaxin binds to the relaxin receptor in male rat atria (8.90+/-0.02), and cerebral cortex (8.90+/-0.03) and uterine myometrium (8.89+/-0.03) with affinities not significantly different from human gene 2 (B33) relaxin. Nevertheless, rat relaxin binds to the receptors with affinities (8.35+/-0.09 in atria, 8.22+/-0.07 in cerebral cortex and 8.48+/-0.06 in uterine myometrium) significantly less than human gene 2 (B33) and porcine relaxins. Quantitative receptor autoradiography is the method of choice for measurement of affinities and densities of relaxin receptor in atria, uterine myometrium and cerebral cortex. High densities were found in all these tissues. 17beta-oestradiol treatment produced complex effects where it increased the densities of relaxin receptors in uterus but decreased those in atria and cerebral cortex of the male rats, and had no effect on the atria and cerebral cortex of the female rats.

Animals↗

PubMed1999

Characterization of beta-adrenoceptor mediated smooth muscle relaxation and the detection of mRNA for beta1-, beta2- and beta3-adrenoceptors in rat ileum.

1. Functional and molecular approaches were used to characterize the beta-AR subtypes mediating relaxation of rat ileal smooth muscle. 2. In functional studies, (-)-isoprenaline relaxation was unchanged by CGP20712A (beta1-AR antagonist) or ICI118551 (beta2-AR antagonist) but shifted by propranolol (pKB=6.69). (+/-)-Cyanopindolol, CGP12177 and ICID7114 did not cause relaxation but antagonized (-)-isoprenaline relaxation. 3. BRL37344 (beta3-AR agonist) caused biphasic relaxation. The high affinity component was shifted with low affinity by propranolol, (+/-)-cyanopindolol, tertatolol and alprenolol. CL316243 (beta3-AR agonist) relaxation was unaffected by CGP20712A or ICI118551 but blocked by SR58894A (beta3-AR antagonist; pA2 = 7.80). Enhanced relaxation after exposure to forskolin and pertussis toxin showed that beta3-AR relaxation can be altered by manipulation of components of the adenylate cyclase signalling pathway. 4. The beta-AR agonist RO363 relaxed the ileum (pEC50=6.18) and was blocked by CGP20712A. Relaxation by the beta2-AR agonist zinterol (pEC50=5.71) was blocked by SR58894A but not by ICI118551. 5. In rat ileum, beta1-, beta2- and beta3-AR mRNA was detected. Comparison of tissues showed that beta3-AR mRNA expression was greatest in WAT>colon=ileum >cerebral cortex>soleus; beta1-AR mRNA was most abundant in cerebral cortex > WAT > ileum = colon > soleus; beta2-AR mRNA was expressed in soleus > WAT > ileum = colon > cerebral cortex. 6. These results show that beta3-ARs are the predominant beta-AR subtype mediating rat ileal relaxation while beta1-ARs may produce a small relaxation. The beta2-AR agonist zinterol produces relaxation through beta3-ARs and there was no evidence for the involvement of beta2-ARs in relaxation despite the detection of beta2-AR mRNA.

Adenylate Cyclase Toxin↗