Relative significance of the nitric oxide (NO)/cGMP pathway and K+ channel activation in endothelium‐dependent vasodilation in the femoral artery of developing piglets

Mechanisms mediating endothelium‐dependent vasodilation were investigated in femoral artery rings from <2‐day‐old (newborn) and 2‐week‐old piglets. Based on previous results we hypothesized an age difference in the relative contribution of nitric oxide(NO)‐cyclic 3′,5′‐guanosine monophosphate (cGMP) and K⁺ channel‐activation to acetylcholine (ACh)‐induced vasodilation. Changes in vascular tone were studied in organ baths in the absence or presence of NO synthase(NOS) inhibition or K⁺ channel blockade and the intra‐arterial accumulation of cGMP in response to ACh was measured with radioimmunoassay (RIA). In control experiments, relaxant responses to ACh were equal in the two age groups. In the presence of the NOS‐inhibitors N ^G‐monomethyl‐L ‐arginine acetate (L ‐NMMA; 100 μM ) or N^G‐nitro‐L ‐arginine (L ‐NOARG; 1–100 μM ), however, relaxation was significantly more reduced in femoral artery rings from 2‐week‐old than from newborn, with lower pD₂ values in the older age group. Inhibition of large (BK_Ca) conductance calcium‐sensitive K⁺ channels with tetraethylammonium chloride (TEA; 1 mM ), gave a significant rightward shift in the concentration‐response curves to ACh which was of the same magnitude in both age groups. The ACh‐induced vasodilation was abolished in both age groups by high K⁺ (20 mM ) in combination with L ‐NOARG (100 μM ). The relative increase in cGMP levels after addition of ACh (10 nM ) was significantly larger in rings from newborn compared with 2‐week‐old piglets (12‐ vs. four‐fold). In summary, sensitivity to NOS inhibition increased with age while the effect of K⁺ channel blockade with TEA was the same in femoral artery rings from newborn to 2‐week‐old piglets. Lower sensitivity to NOS inhibition and a larger increase in cGMP in response to ACh could indicate a higher efficacy of the NO/cGMP pathway in this vessel in the newborn piglet.     

Nitric oxide‐induced signalling in rat lacrimal acinar cells

The aim of the present study was to investigate the physiological role of nitric oxide (NO) in mediating secretory processes in rat lacrimal acinar cells. In addition, we wanted to determine whether the acinar cells possess endogenous nitric oxide synthase (NOS) activity by measuring NO production using the fluorescent NO indicator 4,5‐diaminofluorescein (DAF‐2). We initiated investigations by adding NO from an external source by means of the NO‐donor, S‐nitroso‐N‐acetyl‐penicillamine (SNAP). Cellular concentrations of cyclic guanosine 5′‐phosphate (cGMP) ([cGMP]) were measured by radioimmunoassay (RIA), and we found that SNAP induced a fast increase in the [cGMP], amounting to 350% of the [cGMP] in resting cells. Moreover, addition of SNAP and elevating [cGMP] in fura‐2 loaded lacrimal acinar cells, resulted in a cGMP‐dependent protein kinase‐mediated release of Ca²⁺ from intracellular stores, leading to a rise in the intracellular free Ca²⁺ concentration ([Ca²⁺]_i). The Mn²⁺ quenching studies revealed that the Ca²⁺ release was not accompanied by Ca²⁺ influx. Finally, we demonstrate that lacrimal acinar cells possess endogenous NOS activity, which is activated by β‐adrenergic stimulation and not by a rise in [Ca²⁺]_i alone. We show that in rat lacrimal acinar cells, NO and cGMP induce Ca²⁺ release from intracellular stores via G kinase activation. However, the changes in [Ca²⁺]_i are relatively small, suggesting that this pathway plays a modulatory role in Ca²⁺ signalling, thus not by itself causing fast transient increases in [Ca²⁺]_i. In addition, we suggest that endogenously produced NO activated by β‐adrenergic receptor stimulation, plays an important role in signalling to the surrounding tissue.     

Cardiodepressant mediators are released after myocardial ischaemia: modulation by catecholamines and adenosine

The interaction of recently characterized cardiodepressant mediators with catecholamines and adenosine after myocardial ischaemia was investigated using a model of sequential perfusion of two isolated guinea-pig hearts. Sequential perfusion was initiated after 10, 20, and 30 min (group I, II, and III) of global ischaemia in the first heart. At the onset of sequential perfusion LVdP/dt_max and _min of Heart II decreased by 46 and 44% in group I, by 28 and 34% in group II, and increased by 60 and 24% in group III. Infusion of the β₁-receptor antagonist metoprolol (2.8 μmol L^–1) into Heart II did not modulate contractile changes after 10 min of ischaemia in Heart I, prevented the attenuation of the cardiodepressant effect after 20 min of ischaemia, and completely reversed the positive inotropic effect after 30 min of ischaemia. The A1- and A2-receptor antagonists DPCPX (2 μmol L^–1) and DMPX (20 μmol L^–1) enhanced the positive inotropic and lusitropic effects in Heart II (LVdP/dt_max +154%, LVdP/dt_min +71%) during sequential perfusion after 30 min of ischaemia in Heart I. It is concluded that the effects of cardiodepressant mediators released after myocardial ischaemia are counteracted by a time-dependent release of catecholamines. Endogenous cardiac adenosine, in turn, attenuates the modulatory effects of catecholamines.     

IL‐33‐activated murine mast cells control the dichotomy between RORγt+ and Helios+ Tregs via the MK2/3‐mediated IL‐6 production in vitro

In mast cells, IL‐33 typically induces the activation of NF‐κB, which results in the production of cytokines such as IL‐6 and IL‐2. Here, we demonstrate that the IL‐33‐induced IL‐6 production in murine mast cells and the formation of RORγt⁺ T_regs essentially depends on the MAPKAPs, MK2, and MK3 (MK2/3) downstream of MyD88. In contrast to this, the IL‐33‐induced and MyD88‐dependent IL‐2 production in mast cells contributes to the maintenance of Helios⁺ T_regs. Thereby, the IL‐33‐induced IL‐2 response and, thus, the maintenance of Helios⁺ T_regs are limited by an IL‐6‐mediated autocrine negative feedback stimulation acting on mast cells. Collectively, we present MK2/3 in IL‐33‐activated mast cells as a signaling node, which controls the dichotomy between RORγt⁺ T_reg and Helios⁺ T_reg in vitro.     

Neutrophilic superoxide production can assess pharmacological and pharmacogenetic β‐adrenoreceptor effects

Asthma can be controlled well in most patients by inhaled β‐adrenoreceptor (β₂AR) agonists and steroids. Poor response to β₂AR agonists is difficult to predict, especially in young children and by lung function testing, which may be affected by multiple influences. As an alternative approach, we analyzed ex vivo neutrophilic superoxide inhibition in response to β₂AR stimulation. In 60 healthy volunteers, this assay was unaffected by sex, age, smoking, atopy or asthma status. Furthermore, we assessed effects of genetic variants in β₂AR by sequencing the ADRB2 gene in our cohort and relating genotypes to β₂AR‐mediated neutrophilic superoxide inhibition. Gly16Arg genotypes correlated with minor decrease in overall adrenoresponse in this small study population. Taken together, ex vivo testing of the β₂AR response in human neutrophils represents a robust tool with good signal‐to‐noise ratio at physiological β₂AR agonist concentrations, and this assay may be useful to complement future pharmacogenetic studies in asthma.     

A Fluorescence‐Activated Cell Sorter Analysis of the Relationship Between Protein Kinase G and Endothelial Nitric Oxide Synthase

The process of regulation of NOS after production of nitric oxide is not yet delineated. Protein kinase G may exert a feedback regulation of this enzyme. We used diaminofluorescein assays to detect changes in basal nitric oxide production caused by modulators of protein kinase G activity in freshly isolated ovine lung microvascular endothelial cells. We also used fluorescence activated cell sorter analysis (FACS) to determine molecular and phosphorylation changes caused by PKG activation with 8‐Br‐cGMP. The PKG activator, 8‐Br‐cGMP (100 μM) produced a shift in the basal NO production curve downward. The inhibition began within 5 min and was sustained over 4.5 hr. The two protein kinase G inhibitors 100 μM Rp‐8‐Br‐PET‐cGMPS and 50 nM guanosine 3′‐5′‐cyclic monophosphoro thionate‐8‐Br‐Rp isomer Na salt and the cGMP inhibitor 4 μM Rp‐8‐pCPT‐cGMPS all enhanced NO production as seen by the upward shift in the basal NO curve. Conversely, the PKG activator drug, 100 μM guanosine‐3′‐5′‐cyclic monophosphate‐β‐phenyl‐1NF‐ethano‐8‐bromo sodium salt decreased NO production causing a downward shift in the basal curve. FACS analysis revealed that 5 μM 8‐Br‐cGMP in <5 min caused an increase in N‐terminal labeling of NOS and a decrease in both C‐terminal and serine 1177 labeling of NOS. 8‐Br‐cGMP appeared to increase PKG 1α and to decrease PKG 1β labeling. Changes in other phosphorylation sites were less consistent but overall mean channel fluorescence increased from 19.92 to 217.36 for serine 116 and decreased from 329.27 to 254.03 for threonine 495 phosphorylation. Data indicated that PKG caused both molecular and phosphorylation changes in NOS. Anat Rec 293:1755–1765, 2010. © 2010 Wiley‐Liss, Inc.     

Effects of nitric oxide donors and inhibitors of nitric oxide signalling on endothelin‐ and serotonin‐induced contractions in human placental arteries

In order to explore the role of nitric oxide (NO) in the control of fetoplacental vascular tone in normal pregnancy we have examined the effects of NO donors on uteroplacental arteries pre‐contracted with the vasoconstrictor endothelin‐1 (ET‐1) or serotonin (5‐HT). We have furthermore examined the effects of guanylate cyclase inhibitors on the NO‐induced relaxation. Segments of placental arteries (n=102) obtained from 39 placentas immediately after delivery were mounted in organ baths and superfused with Krebs–Ringer solution at 37 °C. The vessel segments were exposed to drugs for various intervals and the tension was recorded isometrically and registered on a polygraph. Cyclic guanosine monophosphate (cGMP) analysis was performed after extraction of vessel segments using a specific radioimmunoassay. The placental artery segments responded to ET‐1 and 5‐HT with a dose‐dependent vasoconstriction. After pre‐contraction with ET‐1 (10^–7 M ) or 5‐HT (10^–6 M ), the vessels relaxed in response to the NO donors glyceryltrinitrate (GTN) (10^–6 M ) and S‐nitroso‐N‐acetyl‐penicillamine (SNAP) (10^–5 M ). In the presence of the non‐specific guanylate cyclase inhibitor LY 83583 (10^–6 M ), the vessels responded with a small contraction. In the presence of the soluble guanylate cyclase (sGC) inhibitor 1H[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one (ODQ) the non‐treated vessels responded with a relaxation. 1H[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one gave no obvious relaxation in pre‐contracted vessels. Addition of 8‐Br‐cGMP, the cell‐permeant analogue of cGMP, with or without pre‐contraction had no effect on the vessels. Cyclic guanosine monophosphate analysis showed that GTN treatment caused an increase in cGMP after 12 min. Our results indicate that NO acts as a vasodilator in placental vessels. The cGMP‐dependent mechanisms may be involved in NO‐induced relaxation but cGMP‐independent mechanisms appear also to be involved.     

Cerebral blood volume estimation by ferumoxytol‐enhanced steady‐state MRI at 9.4 T reveals microvascular impact of α1‐adrenergic receptor antibodies

Cerebrovascular abnormality is frequently accompanied by cognitive dysfunctions, such as dementia. Antibodies against the α₁‐adrenoceptor (α₁‐AR) can be found in patients with Alzheimer's disease with cerebrovascular disease, and have been shown to affect the larger vessels of the brain in rodents. However, the impact of α₁‐AR antibodies on the cerebral vasculature remains unclear. In the present study, we established a neuroimaging method to measure the relative cerebral blood volume (rCBV) in small rodents with the ultimate goal to detect changes in blood vessel density and/or vessel size induced by α₁‐AR antibodies. For this purpose, mapping of R₂* and R₂ was performed using MRI at 9.4 T, before and after the injection of intravascular iron oxide particles (ferumoxytol). The change in the transverse relaxation rates (ΔR₂*, ΔR₂) showed a significant rCBV decrease in the cerebrum, cortex and hippocampus of rats (except hippocampal ΔR₂), which was more pronounced for ΔR₂* than for ΔR₂. Immunohistological analyses confirmed that the α₁‐AR antibody induced blood vessel deficiencies. Our findings support the hypothesis that α₁‐AR antibodies lead to cerebral vessel damage throughout the brain, which can be monitored by MRI‐derived rCBV, a non‐invasive neuroimaging method. This demonstrates the value of rCBV estimation by ferumoxytol‐enhanced MRI at 9.4 T, and further underlines the significance of this antibody in brain diseases involving vasculature impairments, such as dementia. Copyright © 2014 John Wiley & Sons, Ltd.     

1α,25‐dihydroxyvitamin D3 acts via transforming growth factor‐β to up‐regulate expression of immunosuppressive CD73 on human CD4+ Foxp3– T cells

Vitamin D deficiency is associated with increased incidence and severity of various immune‐mediated diseases. Active vitamin D (1α,25‐dihydroxyvitamin D3; 1,25(OH)₂D3) up‐regulates CD4⁺ T‐cell expression of the purine ectonucleotidase CD39, a molecule that is associated with the generation of anti‐inflammatory adenosine. Here we aimed to investigate the direct impact of 1,25(OH)₂D3 on expression of the downstream ecto‐5′‐nucleotidase CD73 by human CD4 T cells, and components of the transforming growth factor‐β (TGF‐β) pathway, which have been implicated in the modulation of CD73 by murine T cells. At 10^?8 to 10^?7 m , 1,25(OH)₂D3 significantly increased expression of CD73 on peripheral human CD4⁺ T cells. Although 1,25(OH)₂D3 did not affect the mRNA expression of latent TGF‐β₁, 1,25(OH)₂D3 did up‐regulate expression of TGF‐β‐associated molecules [latency‐associated peptide (LAP), glycophorin A repetitions predominant (GARP), GP96, neuropilin‐1, thrombospondin‐1 and α_v integrin] which is likely to have contributed to the observed enhancement in TGF‐β bioactivity. CD73 was highly co‐expressed with LAP and GARP following 1,25(OH)₂D3 treatment, but unexpectedly, each of these cell surface molecules was expressed primarily on CD4⁺ Foxp3^– T cells, rather than CD4⁺ Foxp3⁺ T cells. Notably, neutralization of TGF‐β significantly impaired 1,25(OH)₂D3‐mediated induction of CD73. Collectively, we show that 1,25(OH)₂D3 enhances expression of CD73 on CD4⁺ Foxp3^– T cells in a process that is at least partially TGF‐β‐dependent. These data reveal an additional contributing mechanism by which vitamin D may be protective in immune‐mediated disease.     

β3‐AR and the vertebrate heart: a comparative view

Recent cardiovascular research showed that, together with β₁‐ and β₂‐adrenergic receptors (ARs), β₃‐ARs contribute to the catecholamine (CA)‐dependent control of the heart. β₃‐ARs structure, function and ligands were investigated in mammals because of their applicative potential in human cardiovascular diseases. Only recently, the concept of a β₃‐AR‐dependent cardiac modulation was extended to non‐mammalian vertebrates, although information is still scarce and fragmentary. β₃‐ARs were structurally described in fish, showing a closer relationship to mammalian β₁‐AR than β₂‐AR. Functional β₃‐ARs are present in the cardiac tissue of teleosts and amphibians. As in mammals, activation of these receptors elicits a negative modulation of the inotropic performance through the involvement of the endothelium endocardium (EE), G_i/0 proteins and the nitric oxide (NO) signalling. This review aims to comparatively analyse data from literature on β₃‐ARs in mammals, with those on teleosts and amphibians. The purpose is to highlight aspects of uniformity and diversity of β₃‐ARs structure, ligands activity, function and signalling cascades throughout vertebrates. This may provide new perspectives aimed to clarify the biological relevance of β₃‐ARs in the context of the nervous and humoral control of the heart and its functional plasticity.     

Reactivities of ω‐Unsaturated Methacrylate Oligomers toward tert‐Butoxy Radicals: Investigation of the Effect of Degree of Polymerization and Ester Alkyl Group

The reactivities of ω‐unsaturated methacrylate oligomers (RMA‐n; n = 2–5) toward tert‐butoxy radicals (t‐BuO^·) as a model of the addition step in addition‐fragmentation chain transfer (AFCT) have been investigated by the nitroxide trapping technique in combination with HPLC and electrospray ionization mass spectrometry. The ratio of the rate coefficients for the addition of ω‐unsaturated methyl methacrylate oligomers (MMA‐n) to t‐BuO^· to the β‐fragmentation of t‐BuO^· (k_add/k_β), where k_β can be treated as a constant, has been shown to decrease with increasing n due to increased steric hindrance of the α‐substituents. However, the value of k_add/k_β reaches a constant value at n = 3–4, and the greatest extent of suppression of the addition rate compared with MMA is less than a factor of four. Comparison of the values of k_add/k_β for ω‐unsaturated cyclohexyl methacrylate oligomers (CHMA‐n; n = 2 and 3) with MMA‐n revealed that the extent of suppression increased with increasing n without regard to the ester alkyl group. Hydrogen abstraction by t‐BuO^· from RMA‐n appears to occur mainly at the ester alkyl groups, and the extent is much greater from CHMA‐n than from MMA‐n.

     

Expansion of the CD4−, CD8− γδ T cell subset in the spleens of mice during non-lethal blood-stage malaria

Splenic γδ T cells (CD4^?, CD8^?) increased more that 10-fold upon resolution of either Plasmodium chabaudi adami or P. c. chabaudi infections in C57BL/6 mice compared to controls. Similarly, a 10- to 20-fold expansion of the γδ T cell population was observed in β₂-microglobulin deficient (β²-m^0.0) mice that had resolved P. c. adami, P. c. chabaudi or P. yoelii yoelii infections. In contrast, increases in the number of splenic αβ T cells in these infected mice were only two to three-fold indicating a differential expansion of the γδ T cell subset during malaria. Because nucleated cells of β₂-m^0/0 mice lack surface expression of major histocompatibility complex class I and class Ib glycoproteins, our findings suggest that antigen presentation by these glycoproteins is not necessary for the increasing number of γδ T cells. Our observation that after resolution of P. c. adami malaria, C57BL/6 mice depleted of CD8⁺ cells by monoclonal antibody treatment had lower numbers of γδ T. cells than untreated controls suggests that the demonstrated lack of CD8⁺ cells in β₂-m^0/0 mice does not contribute to the expansion of the γδ T cell population during non-lethal malaria.     

Polymerization of 1,3‐Pentadiene Initiated by Aluminium Trichloride in Nonpolar Solvent: Pseudo‐Control is Explained by Continuous Grafting

Summary: The cationic polymerization of 1,3‐pentadiene initiated by AlCl₃ was studied in nonpolar solvent. It was previously shown that at room temperature the active species were long‐lived and that the number‐average molar mass of the polymer chains was increasing with the polymerization yield. In order to explain this apparent control, the macromolecules were labeled with a transfer agent, triphenylamine (NPh₃). The latter binds to active species by electrophilic aromatic substitution. The labeling of the polymer chains indicated that at 20 °C the polymer chains mainly contained one NPh₃ molecule per macromolecule while the NPh₃ content was higher for the high molar mass chains due to a “grafting from” polymer transfer mechanism. Thus, the pseudo‐control was assigned to the branching reactions. The labeling process by NPh₃ also succeeded at ?10 °C. Whereas at ?10 °C a dialkylation of NPh₃ was observed, a trialkylation at 20 °C was obtained. The analysis of the polymer microstructure at both temperatures highlighted an interaction between the active centers and NPh₃. This paper also describes a process to synthesize tri‐arm stars polymers by cationic polymerization.

RI SEC chromatograms of soluble polymers synthesized at 20 °C in the presence of NPh₃ with increasing reaction times (r = [NPh₃]/[AlCl₃] = 1); (a) t = 0.25 h, (b) t = 0.5 h, (c) t = 1 h, (d) t = 2 h, (e) t = 18 h, (f) t = 48 h; [AlCl₃] = 2.3 × 10^?2 mol · L^?1, [1,3‐pentadiene] = 1.6 mol · L^?1, pentane.     

Nitric oxide inhibits arginine-vasotocin-induced increase of water osmotic permeability in frog urinary bladder

The present study addressed the question of whether nitric oxide (NO) participates in regulation of osmotic water permeability in the urinary bladder of the frog Rana temporaria L. Experiments were carried out on isolated, paired hemi-bladders filled with amphibian Ringer solution diluted 1:10 with distilled water. Sodium nitroprusside (SNP, 125–250 µM), an NO donor, markedly attenuated the increase of osmotic water flow elicited by arginine-vasotocin (AVT) (AVT 10^–10 M: 2.20±0.26; AVT plus 200 µM SNP: 1.21±0.15 µl/min cm², n=20, P<0.001). This effect of SNP was apparent only in the presence of 50 µM zaprinast, an inhibitor of the cGMP-specific phosphodiesterase-5 (PDE5). In the presence of zaprinast, SNP elevated cGMP production significantly both in control and AVT-stimulated urinary bladders, but had no effect on the level of cAMP (AVT 5×10^–10 M: 7.6±0.6; AVT plus SNP 200 µM: 7.5±0.4 pmol/mg protein, n=8, N.S.). 1H-[1,2,4]-oxadiazole-[4,3-a]-quinoxalin-1-one (ODQ, 25–100 µM), an inhibitor of soluble guanylate cyclase, enhanced the AVT-induced water flow, decreased the SNP-stimulated increase of cGMP in the bladder tissue and almost abolished the inhibitory effect of SNP on the AVT-induced hydroosmotic response. 8-(p-Chlorophenylthio)-cGMP (8-pCPT-cGMP, 25 or 50 µM), a membrane-permeable cGMP analogue specific for cGMP-dependent protein kinase (PKG), inhibited, whereas 2 µM KT-5823, an inhibitor of PKG, significantly stimulated the increase of water flow induced by AVT. The inhibitory effect of SNP on AVT-induced water flow was almost completely reversed by KT-5823, but not by 50–100 µM erythro-9-[2-hydroxy-3-nonyl]adenine (EHNA), an inhibitor of cGMP-activated PDE2. Immunohistochemistry of urinary bladder slices with antibodies against different types of NO synthase (NOS) revealed a positive immunostaining for neuronal NOS (nNOS) in the mucosal epithelium. These results suggest that in the frog urinary bladder endogenous NO is involved in regulation of water osmotic permeability. NO inhibits the AVT-induced increase of water flow at least partly by activation of PKG, which interferes with the hydroosmotic effect of AVT probably at (a) post-cAMP step(s).     

Effect of α‐, β‐ and γ‐Cyclodextrins on the Inverse Temperature Transition of the Bioelastic Thermo‐Responsive Polymer Poly(VPGVG)

The influence of α‐, β‐ and γ‐cyclodextrins (CDs) on water solutions of the elastin‐like thermo‐responsive poly(VPGVG) has been studied in this work. All the three CDs were able to increase the temperature at which the inverse temperature transition of this polymer takes place (T_t). This shift was dose‐dependent and β‐CD showed the highest power to shift T_t, being γ‐cyclodextrin the weaker. However, the low solubility of β‐CD limited the maximum T_t shift achieved and, for this reason, the maximum shift in T_t was obtained by α‐CD. The results showed in this work has been tentatively explained by the formation of inclusion compounds between the apolar side chain of some of the amino acids present in the polymer and the corresponding CD as the cause behind the observed T_t shifts. Furthermore, and as a peculiarity of special interest, the shift to higher values in T_t caused by CDs was obtained without the typical reduction in the latent heat showed by other additions or chemical modifications of the polymer chain that also shift T_t to higher values, as reported in the literature.     

Effects of subacute treatment with toluene on cerebrocortical α- and β-adrenergic receptors in the rat. Evidence for an increased number and a reduced affinity of β-adrenergic receptors

Subacute treatment with toluene (80–1500 p.p.m.) produces a dose-dependent reduction of affinity and increase in density of the β-adrenergic antagonist [³H]dihydroalprenolol binding sites in the frontoparietal cortex of the male rat, while the binding characteristics of a,-adrenergic ([³H]WB 4101) and α₂^-adrenergic ([³H]p-aminoclonidine) binding sites in the same region is unaffected by this treatment as evaluated in vitro. Therefore, it is suggested that the cortical β-adrenergic receptors are particularly vulnerable to the action of toluene in vivo. It is speculated that as a result cortical β-adrenergic neurotransmission may be altered following exposure to low concentrations of toluene, possibly related to the physico-chemical properties of toluene, leading to changes in membrane fluidity.     

Additive hypothermic effects of the 5‐HT1A receptor agonist 8‐OH‐DPAT and the dopamine D2/3 receptor agonist 7‐OH‐DPAT in the rat

The objective of this study was to examine possible interactions between serotonergic and dopaminergic agents lowering core temperature via stimulation of 5‐HT_1A and dopamine (DA) D₂ receptors, respectively. The effects of the 5‐HT_1A receptor agonist (±)‐8‐hydroxy‐2‐(di‐n‐propylamino)tetralin HBr (8‐OH‐DPAT) and the DA D_2/3 receptor agonist 7‐OH‐DPAT on core temperature was monitored in adult male Wistar rats, approximately 300 g body weight. The temperature probe was connected to a PC‐assisted temperature instrument, and an automated printer device was activated when the temperature reading had stabilized (±0.1 °C) for 10 s. As expected, 7‐OH‐DPAT [0.5 and 2.0 μmol kg^–1 subcutaneous (s.c.)] as well as 8‐OH‐DPAT (0.15–2.4 μmol kg^–1 s.c.), produced a dose‐dependent hypothermia. When combined, there were additive effects of the two compounds, although the effects of 7‐OH‐DPAT were attenuated by 8‐OH‐DPAT at the higher doses (0.6–2.4 μmol kg^–1), in all probability because of emerging DA D₂ receptor blocking properties of the latter compound.