Characterization of alpha1-adrenoceptor subtypes mediating vasoconstriction in human umbilical vein. (1/329)

1. The present study attempted to characterize pharmacologically the subtypes of alpha-adrenoceptors mediating contractions in human umbilical vein (HUV). 2. HUV rings were mounted in isolated organ baths and cumulative concentration-response curves were constructed for the alpha-adrenoceptor agonists phenylephrine and adrenaline. Adrenaline was more potent than phenylephrine (pD2=7.29 and 6.04 respectively). 3. Isoproterenol exhibited no agonism on KCl pre-contracted HUV rings. Propranolol (1 microM) and rauwolscine (0.1 microM) did not affect the concentration-response curves to adrenaline. These results demonstrate the lack of involvement of functional beta-or alpha2-adrenoceptors in adrenaline-induced vasoconstriction. 4. The non subtype selective alpha1-adrenoceptor antagonist prazosin was evaluated on phenylephrine and adrenaline concentration-response curves. The effects of the competitive alpha1A and alpha1D-adrenoceptor antagonists, 5-methyl urapidil and BMY 7378 and the irreversible alpha1B selective compound chloroethylclonidine (CEC) were also evaluated on adrenaline concentration-response curves. 5. The potencies of prazosin against responses mediated by adrenaline (pA2= 10.87) and phenylephrine (pA2= 10.70) indicate the involvement of prazosin-sensitive functional alpha1-adrenoceptor subtype in vasoconstriction of the HUV. 6. The potencies of 5-methyl urapidil (pA2 = 6.70) and BMY 7378 (pA2= 7.34) were not consistent with the activation of an alpha1A- or alpha1D-adrenoceptor population. 7. Exposure to a relatively low CEC concentration (3 microM) abolished the maximum response to adrenaline suggesting that this response was mediated by an alpha1B-adrenoceptor subtype. 8. We conclude that HUV express a prazosin-sensitive functional alpha1-adrenoceptor resembling the alpha1B-subtype according with the low pA2 values for both 5-methyl urapidil and BMY 7378 and the high sensitivity to CEC.  (+info)

Sympathovagal balance: how should we measure it? (2/329)

There are complex interactions between the sympathetic and parasympathetic nervous system inputs to the sinus node. The concept of "sympathovagal balance" reflects the autonomic state resulting from the sympathetic and parasympathetic influences. Despite widespread usage of a variety of heart rate (HR) variability parameters as indexes of sympathovagal balance, no index has been validated as a measure of sympathovagal balance. This study evaluated the utility of HR, HR variability, and a new parameter termed the vagal-sympathetic effect (VSE) as indexes of sympathovagal balance. The ideal parameter had to satisfy the following criteria: 1) the index should vary similarly among subjects in response to different autonomic conditions; 2) the variability in the index among subjects exposed to the same autonomic conditions should be small; and 3) the response of the index to various autonomic conditions should reflect the underlying changes in physiological state and have a meaningful interpretation. Volunteers [8 men, 6 women; mean age 28.5 +/- 4.8 (SD) yr] were evaluated for the effects of sympathetic and parasympathetic stimulation and blockade on HR and HR variability. VSE was defined as the ratio of the R-R interval to the intrinsic R-R interval. VSE and R-R interval consistently changed in the expected directions with parasympathetic and sympathetic stimulation and blockade. A general linearized model was used to evaluate the response of each parameter. VSE and R-R interval had r2 values of 0.847 and 0.852, respectively. Natural logarithm of the low-frequency power had an r2 value of 0.781 with lower r2 values for all the other HR variability parameters. The coefficient of variation was also lowest for each condition tested for the VSE and the R-R interval. VSE and R-R interval best satisfy the criteria for the ideal index of sympathovagal balance. Because it is impractical under most conditions to measure the VSE as the index of sympathovagal balance, the most suitable index is the R-R interval.  (+info)

"Uncaging" using optical fibers to deliver UV light directly to the sample. (3/329)

Photolysis or "uncaging" of caged compounds represents a significant tool in cell biology and chemistry. It provides a means for quantitative control of compound delivery with temporal and spatial resolution while observing their consequences for cellular signaling. We discuss the use of ultraviolet-transmitting optical fibers to directly deliver UV energy to the sample, combined with a nitrogen pulsed laser as a source of UV light. In this approach the size of the photolysis area is regulated by the exit aperture of the fiber tip which is controlled by pulling the optical fibers to desirable diameters. A diode (red) laser that is also coupled to the optical fiber aids the location of UV energy delivery through the fiber. We used this method to quantitatively uncage norepinephrine and calcium. The major advantage of this photolysis approach is its independence of microscope objectives and traditional optical pathways. Because the optical pathway of the microscope needs no modification to accommodate this photolysis system, integration with other experimental methods, such as electrochemistry, electrophysiology, confocal microscopy, and wide-field epifluorescence microscopy, is relatively simple.  (+info)

Contributions of adenosine receptor activation to the ocular actions of epinephrine. (4/329)

PURPOSE: Epinephrine is an effective drug for glaucoma treatment. However, the mechanisms responsible for the ocular hypotensive action of this compound are not completely understood. Adenosine is an autacoid released by all cells. This study evaluated the role of adenosine receptor activation in epinephrine-induced changes in ocular function. METHODS: Rabbits were pretreated topically with the moderately selective adenosine A1 antagonist 8-(p-sulfophenyl)theophylline (8-SPT) or the adenosine A2 antagonist 3,7-dimethyl-l-propargylxanthine (DMPX). Epinephrine (500 microg) was then administered, and intraocular pressures (IOPs), pupil diameters (PDs), or total outflow facility was evaluated. In a separate group of animals, epinephrine or vehicle was administered, and aqueous humor samples obtained to evaluate changes in aqueous humor purine levels by means of high-performance liquid chromatography. RESULTS: In control animals, epinephrine produced a biphasic change in IOP: an initial rise in IOP of approximately 1 mm Hg from 1/2 to 1 hour followed by significant reduction in IOP of 8 to 9 mm Hg from 3 to 5 hours postadministration. These animals also exhibited a significant increase in PD of 2 to 3 mm from 1/2 to 2 hours postadministration. Pretreatment with 8-SPT (1000 microg) enhanced the initial rise in IOP, while significantly inhibiting the ocular hypotensive response. Pretreatment with 8-SPT also significantly enhanced the epinephrine-induced increase in PD. Inhibition of the epinephrine-induced reduction in IOP by 8-SPT was dose-related with an IC50 of 446 microg. Administration of 8-SPT alone did not significantly alter IOP or PD. The A2 antagonist DMPX did not alter the epinephrine-induced change in IOP or PD. In rabbits pretreated with 8-SPT, the epinephrine-induced increase in outflow facility was significantly reduced by 60% when compared with those in rabbits treated with epinephrine alone. In vehicle-treated rabbits, aqueous humor adenosine and inosine levels were 2.7 +/- 0.38 and 29 +/- 4.2 ng/100 microl, respectively. Three hours after epinephrine administration, adenosine and inosine levels had significantly increased to 11 +/- 1.6 and 66 +/- 4.4 ng/100 microl, respectively. CONCLUSIONS: These results support the idea that in rabbits epinephrine administration stimulates adenosine release in the anterior segment. This rise in endogenous levels of adenosine then leads to the activation of ocular adenosine receptors and is in part responsible for the ocular hypotensive action of epinephrine.  (+info)

Activation of a thioesterase specific for very-long-chain fatty acids by adrenergic agonists in perfused hearts. (5/329)

We have recently described an acyl-CoA thioesterase specific for very-long-chain fatty acids, named ARTISt, that regulates steroidogenesis through the release of arachidonic acid in adrenal zona fasciculata cells. In this paper we demonstrate the presence of the protein as a 43 kDa band and its mRNA in cardiac tissue. The activity of the protein was measured using an heterologous cell-free assay in which it is recombined with adrenal microsomes and mitochondria to activate mitochondrial steroidogenesis. Isoproterenol and phenylephrine activate the enzyme in a dose-dependent manner (10(-10)-10(-6) M). Both propranolol (10(-5) M) and prazosin (10(-5) M) block the action of isoproterenol and phenylephrine respectively. Antipeptide antibodies against the serine lipase motif of the protein and the Cys residue present in the catalytic domain also block the activity of the protein. Taken together, our results confirm the presence of ARTISt in heart and provide evidence for a catecholamine-activated regulatory pathway of the enzyme in that tissue.  (+info)

Influence of G protein type on agonist efficacy. (6/329)

An agonist at a specific G protein-coupled receptor may exhibit a range of efficacies for any given response in a cell-specific manner. We report that the relationship between different states of agonism is regulated by the type of G protein expressed in the cell. In NIH-3T3 alpha(2)-adrenergic receptor (AR) transfectants, the alpha(2)-AR agonists clonidine, oxymetazoline, UK-14304, and epinephrine increased [(35)S]guanosine-5'-O-(3-thio)triphosphate binding in a dose-dependent manner from a basal value of 101.2 +/- 6. 5 fmol/mg to a maximal response (100 microM) of 196.6 +/- 9.8, 182.3 +/- 2, 328.1 +/- 11.2, and 340.6 +/- 3 fmol/mg, respectively. Thus, clonidine and oxymetazoline behaved as partial agonists. Receptor-mediated activation of G proteins in membrane preparations was blocked by cell pretreatment with pertussis toxin, indicating receptor coupling to the subgroup of pertussis toxin-sensitive G protein (Gialpha2,3) expressed in NIH-3T3 cells. Ectopic expression of Goalpha1 but not Gialpha1 increased the relative efficacy of clonidine and oxymetazoline such that the two ligands now behaved as close to full agonists in this assay system. The relationship between full and partial agonists in the different genetic backgrounds was not altered by progressive reduction in the amount of G protein available for coupling to receptor. The increased efficacy observed for clonidine in the Goalpha1 transfectants was not due to changes in the relative affinities or amounts of high-affinity, Gpp(NH)p-sensitive binding of agonist. These data suggest that there is little difference in the ability of clonidine to interact with or stabilize alpha(2)-AR-Gialpha2/Gialpha3 versus alpha(2)-AR-Goalpha1 complexes, but that the subsequent step of signal transfer from receptor to G protein is more readily achieved for the clonidine/alpha(2)-AR/Goalpha1 complex. Such observations have important implications for receptor theory and drug development.  (+info)

Differential effects of epinephrine and norepinephrine on cAMP response and g(i3)alpha protein expression in cultured sympathetic neurons. (7/329)

The effect of 24-h pretreatment with epinephrine (EPI) or norepinephrine (NE) on alpha(2)- and beta-adrenoceptor agonist-induced, cAMP responses and G(i3)alpha-protein expression was studied in primary cultures of rat superior cervical ganglionic (SCG) neurons. SCG neurons, 10 to 12 days in culture, accumulated cAMP when stimulated with the beta-adrenoceptor agonist isoproterenol and the preferential beta(2)-adrenoceptor antagonist ICI 118,551 blocked this response. Similarly, the preferential alpha(2)-adrenoceptor agonist UK14,304 inhibited forskolin-stimulated cAMP accumulation, implying that cultured SCG neurons possess functional alpha(2)- and beta(2)-adrenoceptors. A 24-h treatment of SCG neurons with EPI or NE induced desensitization of the cAMP response to the beta-adrenoceptor agonist isoproterenol. Simultaneously, EPI treatment increased the maximal inhibitory cAMP response to the alpha(2)-adrenoceptor agonist UK14,304 and NE was without effect. Immunoblotting analyses of G(i3)alpha subunits revealed that 24-h EPI but not NE treatment induces a 3- to 4-fold increase in the expression of G(i3)alpha subunits. Furthermore, EPI-induced up-regulation of alpha-subunit expression can be blocked by the preferential beta(2)-adrenoceptor antagonist ICI 118,551 but not by the preferential beta(1)-adrenoceptor antagonist CGP 20712A. Our results suggest that changes in alpha(2)-adrenoceptor responsiveness induced by EPI may involve activation of beta(2)-adrenoceptors that influence the expression of inhibitory G proteins. Thus, primary cultures of sympathetic neurons by possessing functional alpha(2)- and beta-adrenoceptors may be a suitable model system to study the signaling mechanisms of "cross talk" between these adrenoceptor subtypes, which are known to play a central role in cardiovascular function.  (+info)

Mental well-being in alcohol withdrawal: relationship to alpha2-adrenoceptor function. (8/329)

The possible relationship between postsynaptic alpha2-adrenoceptor function, as assessed by the growth hormone (GH) response to clonidine (CLON) and aspects of mental well-being by self-report of mood using the Swedish Mood Adjective Check List, was investigated in alcohol-dependent patients in the early withdrawal period. Patients had blunted GH responses to CLON and worse mental well-being than control subjects immediately after the end of alcohol intake. No relation was found between mental well-being and postsynaptic alpha2-adrenoceptor function. After 1 week, the GH responses to CLON remained blunted, whereas the state of mental well-being had improved to levels similar to those of control subjects. The results further support a downregulated alpha2-adrenoceptor function during 1 week of alcohol withdrawal. Furthermore, even if subsensitive postsynaptic alpha2-adrenoceptor function was not generally related to state of mood, patients with the lowest postsynaptic alpha2-adrenoceptor function reported the highest levels in the dimensions pleasantness/unpleasantness and activation/deactivation when sober.  (+info)

• 1
• 2
• 3
• 4
• 5
• 6
• 7
• 8
• 9
• 10