Decreased [3H]nitrendipine binding in the brainstem of deoxycorticosterone-NaCl hypertensive rats

Binding studies with the 1,4-dihydropyridine calcium channel antagonist [3H]nitrendipine [( 3H]NTD) were performed in uninephrectomized, deoxycorticosterone (DOCA)-NaCl hypertensive rats and vehicle treated normotensive control littermates. After 6 weeks of treatment, hypertensive (199 mmHg, systolic arterial pressure) DOCA rats showed significantly increased heart, left ventricle, and kidney weight in contrast to normotensive (135 mmHg) controls. [3H]NTD binding in the brainstem was significantly reduced (51 +/- 5 fmol/mg protein) in DOCA-NaCl rats, as compared to controls (116 +/- 24 fmol/mg protein). However, no significant differences were found in the [3H]NTD dissociation constants for DOCA-NaCl (0.43 +/- 0.03 nM) or control rats (0.62 +/- 0.06 nM). Cerebral cortical and left ventricular tissue showed no significant alterations in receptor binding density or affinity. Specific [3H]NTD binding was not significantly altered in other selected brain regions or the atria. These data suggest that alterations in the dihydropyridine binding sites associated with calcium channels in the brainstem may be involved in the etiology of DOCA-NaCl-induced hypertension.     

Central neurotransmitter receptors in hypertensive rats

Muscarinic cholinergic ([³H]QNB), α₁ ? ([³H]WB-4101), and α₂ ? ([³H]clonidine) adrenergic ligand binding was measured in various regions of the brains of adult normotensive, spontaneously hypertensive, and DOCA-salt hypertensive rats. There was a 66% increase in the number of α₁-adrenergic receptors in hypothalamus of the spontaneously hypertensive rats as compared to normotensive controls, with no change in the K_d value. There were no other differences in the spontaneously hypertensive rats and none in the DOCA-salt model. α₁-Adrenergic binding was elevated in hypothalamus of spontaneously hypertensive rats 4–20 weeks of age even though blood pressure in the 4-week old animals was not at hypertensive levels (i.e., <150 mmHg). Treatment of adult spontaneously hypertensive rats with clonidine HCl significantly reduced blood pressure but failed to alter the binding of [³H]WB-4101 in hypothalamus. Thus, it appears that the enhanced number of α₁-adrenergic receptors in hypothalamus of spontaneously hypertensive rats is neither a consequence of the increased blood pressure, nor a phenomenon common to all models of hypertension.     

Hypertensinogenic factors and renal alpha-adrenoceptors in young SHR and WKY rats

The effects of high sodium intake (drinking 1% NaCl), DOCA and DOCA + 1%NaCl for 6 weeks on renal alpha 1- and alpha 2-adrenoceptors and on systolic blood pressure (SBP) were examined in young spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). On normal sodium intake, SHR rats had higher renal alpha 1 (p less than .001) and alpha 2-adrenoceptor densities (p less than .001) and SBP (p less than .001) than WKY rats. Although, WKY rats given either 1% NaCl, DOCA, and DOCA + 1% NaCl developed hypertension after 6 weeks of treatment, only 1% NaCl administration for the same period produced an increase in the alpha 1- and alpha 2-adrenoceptor densities when compared to the control (p less than .01 and p less than .001, respectively). In the SHR rats, to the contrary, ingestion of 1% NaCl and DOCA + 1% NaCl increased the already elevated alpha 2-adrenoceptor density (p less than .001) and SBP even more in this strain after 6 weeks of treatment. Equilibrium dissociation constants (KD), however, were similar for both classes of receptors in experimental and control rats. This study indicates that postweaning exposure of the WKY and SHR rats to a high salt treatment and DOCA can influence the renal alpha-adrenoceptor densities. Although the functional significance of the changes is unclear, it is reasonable to speculate that postweaning exposure to a hypertensinogenic stimuli such as a 1% NaCl and/or DOCA may ultimately interfere with the functional development of the kidney differently in rats genetically predisposed to hypertension (SHR) from normotensive (WKY) rats.     

Role of renal nerves in development of hypertension in DOCA-salt model in rats: a telemetric approach

Centrally mediated hyperactivity of the autonomic nervous system contributes to DOCA hypertension; however, the targeted peripheral vascular bed(s) remain unclear. We propose that if renal sympathetic activity is a factor in the development of DOCA-salt hypertension, then renal denervation (RDNX) should attenuate the hypertensive response. In protocol 1, uninephrectomized RDNX (n = 9) and sham-denervated (n = 6) Sprague-Dawley rats were allowed free access to 0.9% NaCl solution and 0.1% NaCl diet. Mean arterial pressure (MAP) and heart rate were telemetrically recorded for 4 days before and 36 days after DOCA (100 mg/rat) implantation; sodium and water balances were recorded daily. Protocol 2 was similar except that saline intake in sham rats (n = 7) was matched to that observed in RDNX rats of protocol 1 for 30 days; for the last 10 days, the rats were allowed free access to saline. Before DOCA in protocol 1, MAP was lower (P < 0.05) in RDNX rats (99 +/- 1 mmHg) compared with sham rats (111 +/- 3 mmHg); however, heart rate and sodium and water balances were similar between groups. RDNX attenuated the MAP response to DOCA by approximately 50% (DeltaMAP = 22 +/- 3 mmHg, where Delta is change in MAP) when compared with sham rats (DeltaMAP = 38 +/- 6). RDNX rats consumed significantly less saline than sham rats, and cumulative sodium and water balances were reduced by 33% and 23%, respectively. In protocol 2, a similar pattern in MAP elevation was observed in RDNX and saline-restricted, sham-denervated rats even when saline restriction was removed. These results indicate that the renal sympathetic nerves are important in hypertension development but that other factors are also involved.     

Daily sesame oil supplementation attenuates local renin-angiotensin system via inhibiting MAPK activation and oxidative stress in cardiac hypertrophy

The renin-angiotensin system (RAS) is involved in the development of left ventricular hypertrophy (LVH) by which increases cardiac morbidity and mortality. Activation of mitogen-activated protein kinases (MAPKs) and oxidative stress are important in RAS-mediated cardiac hypertrophy. Sesame oil, a potent antioxidant, attenuates hypertension-dependent LVH. We examined the protective role of sesame oil on RAS-mediated MAPK activation and oxidative stress in rats. We induced LVH using a hypertensive model by subcutaneously injecting deoxycorticosterone acetate (DOCA; 15 mg/ml/kg in mineral oil; twice weekly for 5 weeks) and supplementing with 1% sodium chloride drinking water (DOCA/salt) to uninephrectomized rats. Sesame oil was gavaged (0.5 or 1 ml/kg/day for 7 days) after 4 weeks of DOCA/salt treatment. Cardiac histopathology, RAS parameters, expression of MAPKs, reactive oxygen species and lipid peroxidation were assessed 24 h after the last dose of sesame oil. Sesame oil significantly decreased the size of cardiomyocytes and the levels of cardiac renin, angiotensin-converting enzyme and angiotensin II. In addition, sesame oil down-regulated the expression of angiotensin type 1 receptor, JNK and p38 MAPK and apoptosis signal regulating kinase 1, c-Fos and c-Jun in rats receiving DOCA/salt. Furthermore, the induction of nicotinamide adenine dinucleotide phosphate oxidase, superoxide anion and hydroxyl radical and lipid peroxidation by DOCA/salt were inhibited by sesame oil. Sesame oil modulates cardiac RAS to ameliorate LVH by inhibiting MAPK activation and lowering oxidative stress.     

High affinity renal [3H]flunitrazepam binding: Characterization,localization, and alteration in hypertension

The binding of [³H]flunitrazepam was studied in membranes prepared from the kidney and cerebral cortex of unilaterally nephrectomized rats made hypertensive by simultaneous deoxycorticosterone acetate (DOCA) and NaCl administration. A significant 35–43% increase in the number of [³H]flunitrazepam binding sites (Bmax) was found in the renal membranes prepared from the hypertensive rats; there was no change in the density of binding sites in the membranes obtained from the cerebral cortex. The K_d of [³H]flunitrazepam binding did not change either in the renal or in the cerebral membranes (～ 12 nM in the kidney and ～2.0 nM in the brain). Drug specificity studies with renal membranes showed that the inhibition of [³H]flunitrazepam binding by various benzodiazepines did not jibe with their pharmacologic potency as anxiolytic agents. An intrarenal distribution of specific [³H]flunitrazepam binding was found in the bovine kidney; specific binding was greatest in the outer cortex and virtually absent in the medulla, the minor calyx and the renal artery. The evidence that the renal benzodiazepine binding site is of high affinity, is specific, has a unique distribution, and is regulated during hypertension suggests that it may be associated with an important pathophysiologic structure.     

ETA receptor-mediated role of endothelin in the kidney of doca-salt hypertensive rats

Renal effects of FR139317, an endothelin ET_A receptor antagonist, were examined using anesthetized normotensive and deoxycorticosterone acetate (DOCA)-salt hypertensive rats. The intravenous bolus injection of FR139317 (10 mg/kg) produced a slight decrease in mean blood pressure (MAP; −13%) in the control rats and this hypotension was accompanied by a moderate renal vasodilation (renal vascular resistance: RVR; −12%). In the DOCA-salt hypertensive rat, FR139317 had a more pronounced hypotensive effect (MAP; −26%) accompanied by a potent renal vasodilation (RVR; −33%). FR 139317 significantly increased renal blood flow only in the DOCAsalt rats. In contrast, FR139317 produced a significant decrease in urine flow and urinary sodium excretion only in control rats. Northern blot analysis revealed that the renal prepro endothelin-1 (ET-1) mRNA level was significantly increased in DOCA-salt hypertensive rats. Thus, it seems likely that endogenous ET-1 is responsible for the maintenance of DOCA-salt-induced hypertension. We also suggest that at least in part, ET-1 and £ta receptors are involved in renal hemodynamic abnormalities in DOCA-salt-induced hypertension. The augmentation of renal ET-1 production may possibly have a function in the development and maintenance of DOCA-salt-induced hypertension.     

Characterization of postsynaptic β-adrenergic receptors and presynaptic muscarinic cholinergic receptors in the rat spleen

The β-adrenergic and muscarinic cholinergic receptors in the splenic homogenates of control and 6-hydroxydopamine (6-OHDA) treated rats were characterized. The specific binding of [³H]dihydroalprenolol (DHA) and [³H]quinuclidinyl benzilate (QNB) in the rat spleen were saturable and of high affinity and showed pharmacological specificity of splenic β-adrenergic and muscarinic cholinergic receptors. Following 6-OHDA treatment, the Bmax value for specific [³H](-)DHA binding to the rat spleen was significantly increased by 26 percent and 22 percent compared to control at 2 and 3 weeks without a change in the Kd. In contrast, there was a 38 percent decrease in the Bmax for [³H](-)QNB in the 6-OHDA treated rat spleen at 2 and 3 weeks respectively without a change in the Kd. The Bmax value at 5 weeks was significantly greater than that at 2 or 3 weeks. The splenic norepinephrine (NE) concentration was markedly reduced by the 6-OHDA treatment at 1 to 3 weeks, while there was a significant recovery in the splenic NE concentration at 5 weeks. Thus, our results strongly suggest that we are biochemically localizing muscarinic cholinergic receptors on the sympathetic nerves of the rat spleen and that the β-adrenergic receptors of the spleen are localized postsynaptically.     

Alterations of cardiac and lymphocyte β- adrenoceptors in rat with chronic heart failure

The alterations of cardiac and lymphocyte β-adrenoceptors were observed in the rats with chronic heart failure produced by constriction of both abdominal aorta and renal artery. The results showed that β₁-adrenoceptor density and mRNA levels were increased, whereas these levels remained unchanged for β₂. The concentrationcontractile response curve for isoproterenol was shifted m the right in cardiac atrium, whereas the concentration-CAMP accumulation response curve for isoproterenol in myocardium was not changed. The number of β-adrenoceptom in blood lymphocyte was markedly reduced. Thus in the heart-failure rats the density of cardiac β-adrenoceptor was increased accompanying reduced β-adrenoceptormediated positive inotropic response, suggesting a post adenylate cyclase dysfunction or impaired contractile components. In contrast, the alteration of β-adrenoceptor in lymphocyte is consistent with the reduced β-adrenoceptor-mediated inotropic response in heart.     

Agonist Binding to α2-Adrenoceptors Is Elevated in the Locus Coeruleus from Victims of Suicide

Abstract: The binding of an agonist, p-[¹²⁵I]iodoclonidine, and an antagonist, [³H]yohimbine, to α₂-adrenoceptors was measured autoradiographically in the locus coeruleus from 10 pairs of antidepressant-free victims of suicide and age-matched controls. Agonist binding to α₂-adrenoceptors was significantly greater in the locus coeruleus from victims of suicide compared with control subjects. In contrast, antagonist binding to α₂-adrenoceptors in the locus coeruleus did not differ significantly between control and suicide subjects. HPLC analysis of norepinephrine in tissue sections of the locus coeruleus did not reveal any differences between control subjects and suicide victims, suggesting that differences in agonist binding are not a result of differences in retention of the endogenous agonist norepinephrine in tissue sections. The increase in agonist binding to α₂-adrenoceptors in the locus coeruleus of victims of suicide links an altered expression of the high-affinity state of autoinhibitory α₂-adrenoceptors with suicide.     

Renal atrial natriuretic peptide receptors binding properties and function are resistant to DOCA-salt-induced hypertension in rats

Atrial natriuretic peptide receptor types A (NPR-A) and C (NPR-C) binding properties and functional characteristics in renal glomeruli have been investigated in deoxycorticosterone acetate (DOCA)-treated hypertensive Wistar-Kyoto (WKY) rats and their respective controls. We found that DOCA administration had no significant effect on the maximum binding capacity or the affinity of renal NPR-A and NPR-C. NPR-C is involved in the regulation of cAMP production. Our results indicate that the cAMP production by NPR-C is not altered in DOCA-induced hypertension, since ANP(1-28), CNP(1-22) and C-ANP, which specifically bind to NPR-C, show a similar inhibitory effect on cAMP production stimulated by the physiological agonist histamine in glomeruli from DOCA-treated rats and controls. Finally, we have found that DOCA-induced hypertension does not modify NPR-A or NPR-C expression in rat glomerular membranes. These findings indicate that NPR-A and NPR-C binding properties and NPR-C-mediated inhibition of cAMP generation remain unaltered in DOCA-treated rats.     

Vascular responses to sodium arachidonate in experimental hypertension

This study characterizes vascular responsiveness to sodium arachidonate (C 20:4) in four models of hypertension [deoxycorticosterone acetate (DOCA) hypertensive rats, two kidney-one clip (2K-1C) renal hypertensive rats, spontaneously hypertensive rats (SHR), and psychosocial hypertensive mice]. Isolated arterial strips (aorta, mesenteric artery, tail artery) were equilibrated under optimal resting tension in physiological salt solution for measurement of isometric force generation. Dose-response curves to arachidonate (10(-10) to 10(-4) g/ml) in arteries from DOCA and 2K-1C hypertensive rats were shifted to the left compared to those in arteries from control rats. In arteries from SHR and psychosocial hypertensive mice, the dose-response relationships were unchanged compared to normotensive values. Arteries from DOCA hypertensive and 2K-1C hypertensive rats developed greater maximal contractile responses to arachidonate than controls; maximal responses in arteries from SHR and psychosocial hypertensive mice were unchanged compared to normotensive values. Contractions to arachidonate were inhibited by indomethacin (0.5 and 5 micrograms/ml) and by aspirin (5 and 50 micrograms/ml). The fatty acid, oleate (C 18:1), had no effect on the contractile state of the arteries, whereas prostaglandin F2 alpha caused contraction. These results indicate altered responsiveness to exogenous arachidonate in arteries from DOCA and 2K-1C hypertensive rats, but not in arteries from SHR and psychosocial hypertensive mice.     

Correlations between central hypotensive and peripheral hypertensive effects of structurally dissimilar alpha-adrenoceptor agonists

The possible similarity between peripheral (vascular) and central α-adrenoceptors was investigated. For 12 structurally dissimilar α-adrenoceptor agonists, including clonidine, a correlation study is described between the adrenergic effects mediated by both types of α-adrenoceptors, i.e. hypotensive and hypertensive efficacies. Hypotensive activity was quantified by means of a pC₂₅, calculated from log dose-response curves determined after intravenous administration to anaesthetized, normotensive rats. Accordingly, hypertensive potency was expressed as a pC₆₀, established in pithed, normotensive rats. Apparent partition coefficients (log P′) were measured between octanol and buffer (pH=7.4; 37°C) to account for the difference in accessibility to both classes of α-adrenoceptors. A most significant, positive relationship was derived between pC₂₅ and a linear combination of pC₆₀ and log P′. This finding indicates a resemblance among the central and peripheral α-adrenoceptors excited by the drugs. The results are discussed and explained in the light of the recent identification of distinct populations of postsynaptic α₁- as well as α₂-adrenoceptors in peripheral vascular smooth muscle, both involved in drug-induced vasoconstriction.     

An analysis of the DOCA-salt model of hypertension in HO-1-/- mice and the Gunn rat

Heme oxygenase-1 (HO-1) is induced in the vasculature in the DOCA-salt model of hypertension in rats. Whereas the HO system and its products may exert vasodilator effects, recent studies have suggested that the HO system may predispose to hypertension. The present study examined the effects of selected components of the HO system, specifically, the HO-1 isozyme and the product bilirubin in the DOCA-salt model of systemic hypertension; the experimental approach employed mutant rodent models, namely, the HO-1(-/-) mouse and the hyperbilirubinemic Gunn rat. DOCA-salt induced HO-1 protein in the aorta in HO-1(+/+) mice and provoked a significant rise in systolic arterial pressure in HO-1(-/-) mice but not in HO-1(+/+) mice; this effect could not be ascribed to impaired urinary sodium excretion or impaired glomerular filtration rate in the DOCA-salt-treated HO-1(-/-) mice. The administration of DOCA salt to uninephrectomized rats significantly increased systolic arterial pressure in wild-type rats, an effect that was attenuated in the mutant Gunn rat; this reduction in systemic hypertension in the DOCA-salt-treated Gunn rat was not due to a greater induction of HO-1 in the vasculature or to a more avid urinary sodium excretion. DOCA-salt impaired endothelium-dependent and endothelium-independent vasorelaxation in wild-type rats but not in Gunn rats; prior exposure to bilirubin repaired the defect in endothelium-dependent vasorelaxation in aortic rings in DOCA-salt-treated rats. DOCA salt stimulated vascular production of superoxide anion in wild-type but not in Gunn rats. We suggest that HO-1 and the product bilirubin may exert a countervailing effect in the DOCA-salt model of systemic hypertension.     

Pharmacological evaluation of ocular β-adrenoceptors in rabbit by tissue segment binding method

AimsThis study evaluates ocular (iris, ciliary body and ciliary process) and nonocular (atria and lung) β-adrenoceptors in rabbit to characterize the plasma membrane β-adrenoceptors and binding affinities of β-adrenoceptor antagonists.Main methodsThe tissue segment binding method with a hydrophilic radioligand (?)-4-[3-t-butylamino-2-hydroxypropoxy]-[5,7-³H]benzimidazol-2-one ([³H]-CGP12177) was employed.Key findingsSpecific and saturable binding of [³H]-CGP12177 to intact tissue segments was detected by using (±)-propranolol to define nonspecific binding, showing a single population of plasma membrane binding sites with high affinity. Competition experiments with selective β₁- and β₂-adrenoceptor antagonists revealed a single population of β₂-adrenoceptors in ocular tissues and of β₁-adrenoceptors in atria, but mixed populations of β₁- and β₂-adrenoceptors in 70% and 30%, respectively, in lung. A competition curve for timolol was biphasic in lung and its binding affinity for β₂-adrenoceptors was approximately 158-fold higher than for β₁-adrenoceptors, indicating the β₂-selectivity of timolol. In contrast, competition curves for stereoisomers of befunolol, carteolol, and propranolol were monophasic in all tissues. The (?)-enantiomers of these antagonists were more potent than corresponding (+)-enantiomers in displacing from [³H]-CGP12177 binding, and the isomeric potency ratios of befunolol and carteolol were less than those of propranolol.SignificanceThis study with tissue segment binding method suggests that the binding affinity of (?)-enantiomers of β-adrenoceptor antagonists for plasma membrane β-adrenoceptors (β₁-adrenoceptors of atria, β₂-adrenoceptors of ocular tissues, and mixed β₁-/β₂-adrenoceptors of lung) is higher than that of corresponding (+)-enantiomers and their stereoselectivity is different between β-adrenoceptor antagonists.     

Effect of Noradrenergic Lesions on Subtypes of α2-Adrenoceptors in Rat Brain

Abstract: The binding of [³H]rauwolscine to α_2A- (also referred to as α_2D-) and α_2C-adrenoceptors in homogenates of rat cerebral cortex was measured by exploiting the selectivity of oxymetazoline for α_2A-adrenoceptors. Inhibition of [³H]rauwolscine binding by oxymetazoline was modeled best assuming binding to two sites (p < 0.001). Competition curves for oxymetazoline were shifted rightward by the addition of GTP (250 µM) but were still fit best by a two-site model (p < 0.001). A concentration of oxymetazoline was calculated that would optimally antagonize [³H]rauwolscine binding (with GTP present) to oxymetazoline-sensitive α_2A-adrenoceptors, minimally inhibiting binding to α_2C-adrenoceptors. Subsequently, [³H]rauwolscine binding to α_2A- and α_2C-adrenoceptors in cortex was examined 3 weeks after destruction of noradrenergic terminals. Binding to α_2C-adrenoceptors was increased significantly after treatment with 6-hydroxydopamine (6-OHDA) compared with vehicle-treated controls, whereas binding to α_2A-adrenoceptors was unchanged. Pretreatment of rats with desipramine before 6-hydroxydopamine, to protect noradrenergic neurons, resulted in no changes in binding to either α_2A- or α_2C-adrenoceptors. Thus, α_2C-adrenoceptors are regulated by changes in synaptic availability of norepinephrine. α_2A-Adrenoceptors are either not regulated by synaptic norepinephrine or are located both post- and presynaptically so that up-regulation of postsynaptic α_2A-adrenoceptors is offset by a loss of presynaptic α_2A-adrenoceptors.     

Endogenous and Exogenous Regulation of Human α- and β-Adrenergic Receptors

Abstract

Regulation of human β2-adrenergic receptors in lymphocytes (determined by (±)-125 iodocyanopindolol (ICYP) binding) and α₂-adrenergic receptors in platelets (determined by ³H-yohimbine binding) was studied. While α₂-adrenergic receptor number did not change with age, a significant negative correlation between the number of α₂-adrenergic receptors and age was found; plasma catecholamines, on the contrary, were elevated in the elderly.In healthy women during normal menstrual cycle the number of α₂-adrenergic receptors decreased with increasing plasma estradiol levels.Incubation of lymphocyte membranes with isoprenaline (100 μM) and of platelet membranes with clonidine (1-100 μM) led to a reduction of the number of β₂- and α₂-receptors, respectively, without changes in the K_D-values. Treatment of hypertensive patients with clonidine (3x150 μg/die) for 7 days reduced the number of α₂-adrenergic receptors in platelets. In platelet membranes from such treated patients inhibition of ³H-yohimbine binding by clonidine and adrenaline was not affected by 10-⁴MGTP. It is concluded, that human α- and β-adrenergic receptors undergo regulatory mechanisms similar to those recently described for adrenergic receptors in a variety of animal models.     

Guanine nucleotide regulatory protein alterations in young Milan hypertensive strain rats

Vascular smooth muscle cell membranes from prehypertensive rats of the Milan hypertensive strain (MHS) were used to examine adenylyl cyclase activity and its regulation by guanine nucleotide regulatory proteins (G-proteins). Basal adenylyl cyclase activity was similar in MHS and Milan normontensive strain (MNS) membranes. Forsokolin (10^?4 M) produced a significantly greater stimulatory response in MHS membranes, but this was not observed with NaF (10^?2 M). Isoporterenol (10^?4 M) caused a significantly decreased stimulation of adenylyl cyclase activity in MHS membranes, while prostaglandin E₁ (10^?5 M) produced similar responses in the two strains. G_i function and GTP responses, as observed by biphasic effects of GTP on isoproterenol-stimulated membranes, were similar in both strains. The levels of G_i2α and G_qα/G₁₁α were similar in the two strains, while the levels of G_sα (44 and 42 kDa forms) and the β-subunit were significantly reduced by ～20% in MHS membranes. The α-subunit of G_i3 was dramatically reduced by ～80% in MHS membranes. The affinities of β-adrenergic receptors for the antagonist, cyanophindolol, were similar in the two strains; however, the number of β-adrenoceptors was substantially reduced in MHS membranes. These findings may be of relevance to altered vascular reactivity and transmembrane ion distribution observed in the MHS.     

Differential response of two models of genetically modified mice fed with high fat and cholesterol diets: relationship to the study of non-alcoholic steatohepatitis

Thyroid hormone deficiency has been reported to decrease expression and function of both β₁- and β₂-adrenoceptor in different tissues including heart. The purpose of this study was to examine the possible contribution of β₃-adrenoceptors to cardiac dysfunction in hypothyroidism. In addition, effect of this pathology on β₁- and β₂-adrenoceptor was investigated. Hypothyroidism was induced by adding methimazole (300 mg/l) to drinking water of rats for 8 weeks. Cardiac hemodynamic parameters were measured in anesthetised rats in vivo. Responses to β-adrenoceptor agonists were examined in rat papillary muscle in vitro. We also studied the effect of hypotyroidism on mRNA expression of β-adrenoceptors, Giα, GRK, and eNOS in rat heart. All of the hemodynamic parameters (systolic, diastolic and mean arterial pressure, left ventricular pressure, heart rate, +dp/dt, and ?dp/dt) were significantly reduced by the methimazole treatment. The negative inotropic effect elicited by BRL 37344 (a β₃-adrenoceptor preferential agonist) and positive inotropic effects produced by isoprenaline and noradrenaline, respectively, were significantly decreased in papillary muscle of hypothyroid rats as compared to those of controls. On the other hand, hypothyroidism resulted in increased cardiac β₂- and β₃-adrenoceptor, Giα₂, Giα₃, GRK3, and eNOS mRNA expressions. However, β₁-adrenoceptor and GRK2 mRNA expressions were not changed significantly in this pathology. These results show that mRNA expression of β₃-adrenoceptors as well as the signalling pathway components mediated through β₃-adrenoceptors are significantly increased in hypothyroid rat heart. Since we could not correlate these alternates with the decreased negative inotropic response mediated by this receptor subtype, it is not clear whether these changes are important for hypothyroid induced reduction in cardiac function.     

Selective Increase of α2A-Adrenoceptor Agonist Binding Sites in Brains of Depressed Suicide Victims

Abstract: The α_2A- and α_2C-adrenoceptor subtypes were evaluated in postmortem brains from suicides with depression (n = 22), suicides with other diagnoses (n = 12), and controls (n = 26). Membrane assays with the antagonist [³H]RX821002 (2-[³H]methoxyidazoxan) suggested the presence of α_2A-adrenoceptors in the frontal cortex and both α_2C-adrenoceptors and α_2A-adrenoceptors in the caudate. The proportions in caudate were similar in controls (α_2A, 86%; α_2C, 14%), depressed suicides (α_2A, 91%; α_2C, 9%), and suicides with other diagnoses (α_2A, 88%; α_2C, 12%). Autoradiography of [³H]RX821002 binding under α_2B/C-adrenoceptor-masking conditions confirmed the similar densities of α_2A-adrenoceptors in the cortex, hippocampus, and striatum from controls and suicides. In the frontal cortex of depressed suicides, competition of [³H]RX821002 binding by (?)-adrenaline revealed a greater proportion (61 ± 9%) of α_2A-adrenoceptors in the high-affinity conformation for agonists than in controls (39 ± 5%). Simultaneous analysis with the agonists [³H]clonidine and [³H]UK14304 and the antagonist [³H]RX821002 in the same depressed suicides confirmed the enhanced α_2A-adrenoceptor density when evaluated by agonist, but not by antagonist, radioligands. The results indicate that depression is associated with a selective increase in the high-affinity conformation of the brain α_2A-adrenoceptors.