Calcium fluxes in isolated acinar cells from rat parotid. Effect of adrenergic and cholinergic stimulation.
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Rat parotid acinar cells dispersed by a combination of enzymatic treatments remain sensitive to adrenergic and cholinergic agonists. Previous studies have implicated Ca2+ in both adrenergic and cholinergic responses. This paper describes the effects of adrenergic and cholinergic stimulation upon 45Ca2+ fluxes in isolated parotid acinar cells. Suspensions of dispersed cells took up 45Ca2+ from the medium. The net rate of isotope influx was increased by the adrenergic agonists epinephrine, norepinephrine, isoproterenol, and phenylephrine, and by the cholinergic agonists acetylcholine and carbamylcholine. In 1 mM Ca2+, epinephrine was capable of increasing the 45Ca2+ influx in 40 min to three times that of resting cells. Isoproterenol, a beta-adrenergic agonist, was only half as effective as epinephrine in stimulating maximal calcium uptake although it was equally effective in stimulating maximal amylase release in the same cells. Experiments with the alpha-adrenergic antagonist phentolamine, the beta-adrenergic antagonist propranolol, and the cholinergic antagonist atropine confirmed that alpha- and beta-adrenergic and cholinergic stimulation each had a direct stimulatory effect on 45Ca2+ uptake. N6,O2'-Dibutyryl adenosine 3':5'-monophosphate also caused some stimulation of net calcium uptake. Direct measurement of Ca2+ efflux indicated that the increased calcium uptake in the presence of epinephrine was not the indirect result of a decrease in efflux. The rates of both basal and epinephrine-stimulated calcium uptake increased with increasing calcium concentration in the medium. Epinephrine had little effect on the rate of calcium uptake at 0.15 mM Ca2+. Although the energy poison NaCN had little effect on the basal rate of calcium uptake, the stimulable component of calcium uptake was inhibited by NaCN at all calcium concentrations tested (0.2 to 4.1 mM). (+info)
The effect of autonomic blockers on heart rate: a comparison between two ethnic groups.
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The influence of autonomic blockers on the heart rate of ten Bushmen and eight White volunteers was studied. There were significant differences in heart rate response to atropine alone between the White's and Bushmen. However, after prior beta-adrenoceptor blockade, these differences were no longer significant. It is postulated that a varying pharmacogenetic sensitivity to autonomic blockers may result from inequality of vagal or sympathetic tone. (+info)
Autonomic drugs and the accommodative system in rhesus monkeys.
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Intraoperative floppy iris syndrome: pathophysiology, prevention, and treatment.
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PURPOSE: To extend upon previous reports, observations, and discussions of intraoperative floppy iris syndrome (IFIS) with the goal of providing new insight into the syndrome's pathophysiology, prevention, and treatment. METHODS: Following a review of IFIS and its relationship to autonomic pharmacology, evidence for anatomic changes following exposure of humans and other animals to autonomic drugs is described. The clinical implications for these findings are discussed as they relate to the treatment and prevention of this syndrome. RESULTS: IFIS has been associated with the use of adrenergic antagonists even after they have been discontinued years prior to surgery. Some investigators believe that this persistence of IFIS reflects anatomic structural change. Evidence from laboratory experiments and human clinical studies using topically applied and systemic autonomic drugs supports the possibility of anatomic changes coexisting with IFIS observed during cataract surgery. CONCLUSIONS: IFIS is a relatively rare syndrome, often associated with the use of systemic alpha-blockers and conditions that influence dilator muscle tone. Laboratory and clinical evidence supports the possibility of anatomic changes following the use of autonomic drugs. The persistence of IFIS years after cessation of treatment with alpha-blockers suggests that the potential risks of discontinuing these drugs prior to cataract surgery outweigh potential benefits. (+info)
The effects of cocaine on intracellular Ca2+ handling and myofilament Ca2+ responsiveness of ferret ventricular myocardium.
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1. When ferret right ventricular papillary muscles were stimulated with threshold punctate pulses (0.33 Hz; 30 degrees C), cocaine, 10(-5) M, increased peak tension development from 815 +/- 120 to 1125 +/- 180 mg (P less than 0.05) and increased the rate of relaxation from peak tension (time to 80% decline from peak tension decreased from 155 +/- 11 to 144 +/- 11 ms; P less than 0.05). These changes in the twitch were associated with comparable changes in the amplitude and time course of the calcium transient measured with aequorin (amplitude increased from 62 +/- 4 to 90 +/- 7% (P less than 0.05) of maximal values; time to 80% decline from peak amplitude decreased from 84 +/- 8 to 64 +/- 3 ms; P less than 0.05). These effects were markedly attenuated in the presence of the beta-adrenoceptor-blocking agent, propranolol, 6 x 10(-7) M, or by maximization of catecholamine release from the adrenergic nerve endings with field pulses of suprathreshold strength, indicating that catecholamine release from the adrenergic nerve endings is responsible for the positive inotropic and lusitropic responses to low and moderate doses of cocaine (i.e., less than or equal to 10(-5) M). 2. High doses of cocaine (i.e., greater than 10(-5) M) produced negative inotropic and lusitropic effects that were associated with a decreased amplitude and prolonged duration of the calcium transient. 3. In aequorin-loaded intact fibres, cocaine 10(-5) M did not affect the force-calcium relationship unless catecholamines were present. Cocaine, 10(-5) M, significantly shifted the force-calcium relationship of saponin-skinned muscles (pCa50 = 6.14 +/- 0.05 versus 5.92 +/- 0.07; P less than 0.05), indicating reduced responsiveness of the myofilaments to calcium. F. (maximal Ca2+-activated force) was reduced to 58% of control in the presence of 10- M cocaine, while the slope of the calcium-force curve remained unchanged. These data indicate that cocaine may also decrease myofilament calcium sensitivity and maximal calciumactivated force, via mechanisms independent of catecholamines, when cellular diffusion barriers are eliminated. (+info)
A catecholamine transporter from the human parasite Schistosoma mansoni with low affinity for psychostimulants.
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Effect of losartan, an angiotensin II type 1 receptor antagonist on cardiac autonomic functions of rats during acute and chronic inhibition of nitric oxide synthesis.
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We studied the effect of losartan on baroreflex sensitivity (BRS) and heart rate variability (HRV) of adult Wistar rats during acute and chronic inhibition of nitric oxide synthesis by N(G)-nitro-L-arginine methyl ester (L-NAME). Chronic L-NAME administration (50 mg/kg per day for 7 days, orally through gavage) increased mean arterial pressure (MAP), heart rate but significantly decreased BRS. In addition, a significant fall of standard deviation of normal RR intervals, total spectral power, high frequency spectral power and a rise of low frequency to high frequency (LF: HF) ratio was seen. Acute L-NAME administration (30 mg/kg, i.v. bolus dose) also raised MAP and impaired HRV but it was associated with augmented BRS for bradycardia reflex. Losartan treatment (10 mg/kg, i.v.) in both acute and chronic L-NAME treated rats, decreased MAP but the difference was not significant. On the other hand, losartan administration normalized depressed BRS for bradycardia reflex and significantly reduced LF to HF ratio in chronic L-NAME treated rats. But this improvement was not observed in acute L-NAME group. These results indicate importance of mechanisms other than renin-angiotensin system in the pressor response of both acute as well as chronic L-NAME. However, autonomic dysregulation especially following chronic L-NAME appears to be partly angiotensin dependent. (+info)