Adenosine inhibits alpha-melanocyte-stimulating hormone release from frog pituitary melanotrophs. Evidence for the involvement of a(1) adenosine receptors negatively coupled to adenylate cyclase

Adenosine is recognized as an important modulator of cell activity. In particular, adenosine regulates the secretion of adrenocorticotropin from anterior pituitary cells. However, the possible role of adenosine on the pars intermedia has never been investigated. In the present study, we have examined the effect of adenosine on α-melanotropin (α-MSH) secretion from the intermediate lobe of the pituitary of the frog (Rana ridibunda), using the perifusion technique. When whole neurointermediate lobes were exposed to graded doses of adenosine (10(-9) to 10(-4) M), a dose-dependent inhibition of a-MSH release was observed. Repeated pulses of adenosine (5 ± 10(-5) M) induced a reproducible inhibition of α-MSH secretion without any desensitization phenomenon. The effect of adenosine was mimicked by the non-selective agonist 5'-N-ethylcarboxamide-adenosine and the highly specific adenosine A, receptor agonist N(6) -[R-phenylisopropyl]-adenosine (R-PIA). In contrast the selective adenosine A(2) receptor agonist, CGS 21680, induced a slight stimulation of α-MSH release. Adenosine-induced inhibition of α-MSH secretion was blocked by the non-selective adenosine antagonist, 8-(p-sulfophenyl)-theophyline. Adenosine and R-PIA also inhibited α-MSH secretion from acutely dispersed pars intermedia cells. Adenosine did not block thyrotropin-releasing hormone-induced α-MSH release from perifused neurointermediate lobes. In contrast, adenosine inhibited both acetylcholine-evoked and muscarine-evoked α-MSH secretion. Finally, R-PIA induced a significant inhibition of basal and forskolin-stimulated cyclic AMP levels in whole neurointermediate lobes. The present results demonstrate that adenosine exerts a direct inhibitory effect on α-MSH release from melanotrope cells through activation of the A(1) receptor subtype, negatively coupled to adenylate cyclase. These data suggest that adenosine may play a physiological role in the regulation of hormone release from the intermediate lobe of the pituitary.     

Factors predicting the acute effect of pamidronate on serum calcium in hypercalcemia of malignancy

Summary In this study we retrospectively reviewed results of the first 9 days of treatment with pamidronate at doses of 30 mg (n=13), 45 mg (n=9), and 90 mg (n=13) in an attempt to see what factors influenced the response of serum calcium to pamidronate.The nadir of serum calcium obtained post treatment was correlated with pretreatment levels of nephrogenous cyclic adenosine monophosphate (NcAMP), the renal tubular threshold for phosphate reabsorption (TmPO4), and the renal tubular threshold for calcium reabsorption (TmCa). Using the post treatment serum calcium levels, patients were divided into good and poor responders depending on whether a normal serum calcium was obtained.Pretreatment NcAMP was significantly correlated with the magnitude of the response of serum calcium (r=0.45, P=0.0001). Pretreatment NcAMP was significantly higher in the poor responders (mean±SEM): 65.0±9.4 nmol/liter GF (poor responders) versus 29.6±6.3 (good responders), P=0.004. NcAMP as a predictor of the acute response of serum calcium showed a sensitivity of 93% and a specificity of 72%. Pretreatment TmPO4 was negatively correlated with the serum calcium response post treatment (r=-0.41, P=0.003). However, though TmPO4 tended to be lower in the poor responders, this was not statistically significant [0.65 mmol/liter GF±0.09 (poor responders) versus 0.76 mmol/liter GF±0.06 (good responders)]. As a predictor of the acute response of serum calcium, TmPO4 was less good with a sensitivity of 70% and specificity of 58%. No significant correlation was present between TmCa and the serum calcium response. A significant negative correlation was evident between NcAMP and TmPO4 (r=-0.35, P=0.003), however, no significant correlation was evident between NcAMP and TmCa or TmPO4 and TmCa.These results suggest that in a hypercalcemic patient where evidence exists for the presence in circulation of a factor with PTH-like activity (i.e., NcAMP is elevated or TmPO4 is low) the response of serum calcium to pamidronate is less good. NcAMP would appear to be a useful predictor of the response of serum calcium, whereas TmPO4 is less discriminating.     

Synergistic Regulation of Cytosolic Ca2+ Concentration by Adenosine and alpha1-Adrenergic Agonists in Mouse Striatal Astrocytes

Adenosine has a broad array of actions on neurons but astrocytes also possess adenosine receptors. We have previously shown that adenosine, by acting on astrocytes in the striatum, can modulate neuronal responses mediated by receptors coupled to phospholipase C through an astrocyto - neuronal interaction. In addition, adenosine was found to potentiate the alpha1-adrenergic production of inositol phosphates in astrocytes. The mechanism involved in this potentiation was further investigated by examining the effects of adenosine and alpha1-adrenergic receptor agonists on cytosolic Ca2+ in cultured striatal astrocytes from the embryonic mouse in primary culture. When used alone, methoxamine, a selective agonist of alpha-adrenergic receptors or 2-chloroadenosine, a stable analogue of adenosine, induced a transitory increase in cytosolic Ca2+, but their combined addition led to a sustained increase in cytosolic Ca2+, which seems to be due to a Ca2+ influx, because it was not observed in the absence of external Ca2+. Voltage independent Ca2+ channels contribute to this process and different blockers of voltage-operated calcium channels, such as dihydropyridines, phenylalkylamines, La3+ or Co2+ were ineffective in suppressing the sustained cytosolic Ca2+ elevation. Three observations suggest the implication of arachidonic acid in the observed potentiation: (i) arachidonic acid induced a sustained elevation of cytosolic Ca2+ similar to that evoked by the coapplication of methoxamine and 2-chloroadenosine; (ii) the addition of arachidonic acid during the calcic plateau produced by the combined application of the agonists did not increase further cytosolic Ca2+ levels; (iii) in the presence of methoxamine, 2-chloroadenosine induced a release of arachidonic acid. The stimulation of phospholipase C and the resulting activation of protein kinase C induced by methoxamine seem to be required for the potentiating effect of 2-chloroadenosine on cytosolic Ca2+. In fact, the direct activation of protein kinase C by an exogenous diacylglycerol analogue mimicked the effect of methoxamine because, in this condition, 2-chloroadenosine alone evoked a sustained elevation of cytosolic Ca2+. Therefore, methoxamine, through the successive activation of phospholipase C and protein kinase C, could allow a lipase, probably phospholipase A2, to be stimulated by 2-chloroadenosine. Arachidonic acid has already been shown to trigger the opening of K+ channels and the formation of inositol phosphates in other cell types. Therefore, in striatal astrocytes, 2-chloroadenosine, through an arachidonic acid-mediated hyperpolarization, could increase the Ca2+ driving force and thus improve Ca2+ influx through inositol phosphate-gated channels. This hypothesis is further supported by the suppressing effect of a 50 mM KCI-induced depolarization on the long lasting elevation of cytosolic Ca2+ seen in the combined presence of 2-chloroadenosine and methoxamine.     

Distribution and metabolic fate of adenosine nucleotides in the membrane of storage vesicles from bovine adrenal medulla

Summary The reactions of adenosine ¹⁴C- and ³²P-labelled ATP with isolated membranes from catecholamine storage vesicles of the bovine adrenal medulla were studied. In presence of Mg²⁺ about twice as much of ³²P-radioactivity combined with the membrane as ¹⁴C-adenosine compounds at 31°C and also at 0°C, while in the absence of Mg²⁺ the amounts of ¹⁴C and ³²P incorporated were similar for both substances. Autoradiography of the SDS-polyacrylamide gel after electrophoresis of the ³²P-ATP-treated membrane protein showed two distinct zones corresponding to protein bands. Sonication released twice as much ³²P-ATP as ¹⁴C-ATP from the space within the membrane particles indicating that at least half of the ATP present in this space did not contain its original terminal phosphate group. About 40–45% of the ³²P-radioactivity was incorporated in the membrane lipids, whereas only small amounts of ¹⁴C-radioactivity were extracted with the lipids. About 1/3 of the incorporated ¹⁴C-radioactivity was not extractable with acids. The same amount remained in the ³²P-ATP treated preparation acid-stably bound after extraction of the lipids and thus must be firmly bound ATP. When the reaction of the membrane preparation with labelled ATP was performed at 0°C the fractions of the acid-stably bound ³²P- and ¹⁴C-radioactivity increased. About 1 nmole/mg of protein (10–15%) of the bound ³²P-radioactivity was exchangeable against unlabelled ATP, while only a very small fraction (<0.5 nmole/mg protein) of the ¹⁴C-radioactivity was exchanged against unlabelled ATP. Preincubation of the membrane particles with ATP-Mg²⁺ at 0°C induced 30% inhibition of the ATPase activity and abolition of the net uptake of catecholamines. Different K _m values obtained from initial velocity studies of ATPase activity and the overall-incorporation of ³²P-radioactivity indicated that a direct correlation between these processes did not exist. Different strong inhibitory effects exerted by ADP on the ATPase activity and net uptake of catecholamine at the one hand and the overall ³²P- and ¹⁴C-incorporation at the other hand supported that view. It is concluded that only small fractions of the observed ³²P-and ¹⁴C-incorporation can be involved in the ATP-hydrolyzing reaction.     

Synthesis of [18F]‐labeled adenosine analogues as potential PET imaging agents

The syntheses of adenosine analogues, 2′‐deoxy‐2′‐[¹⁸F]fluoro‐9‐β‐D ‐arabinofuranosyladenine ([¹⁸F]‐FAA) and 3′‐deoxy‐3′‐[¹⁸F]fluoro‐9‐β‐D ‐xylofuranosyladenine ([¹⁸F]‐FXA) are reported. Adenosine ( 1 ) was converted to its methoxytrityl derivatives 2 and 3 as a mixture. After separation, these derivatives were converted to their respective triflates 4 and 5 . Each triflate was reacted with tetrabutylammonium[¹⁸F]fluoride to produce 6b or 7b , which by acidic hydrolysis yielded compounds 8b and 9b . Crude preparations were purified by HPLC to obtain the desired pure products. The radiochemical yields were 10‐18% decay corrected (d. c.) for 8b and 30‐40% (d. c.) for 9b in 4 and 3 runs, respectively. Radiochemical purity was >99% and specific activity was >74 GBq/μmol at the end of synthesis (EOS). The synthesis time was 90‐95 min from the end of bombardment (EOB). Copyright © 2003 John Wiley & Sons, Ltd.     

吡啶-2,6(1H,3H)二酮生物碱对ADP、AA、Collagen诱导的兔血小板聚集的影响

目的观察吡啶－２，６（１Ｈ，３Ｈ）二酮生物碱（ＳＨ１）对ＡＤＰ、ＡＡ、Ｃｏｌｌａｇｅｎ诱导的兔血小板聚集的影响。方法用比浊法测定了ＳＨ１体外对兔血小板聚集的影响。结果ＳＨ１对３种诱导剂的最大抑制率分别为６２．１６％、４５．２５％、５３．６７％。大剂量组明显加快ＡＤＰ诱导的兔血小板聚集后的解聚速度。ＳＨ１显著延长Ｃｏｌａｇｅｎ的诱导起聚时间。结论ＳＨ１０．８～４．０ｍｍｏｌＬ－１范围内明显抑制ＡＡ、ＡＤＰ、Ｃｏｌａ－ｇｅｎ诱导的兔血小板聚集。其抑制作用有明显的量效关系。其机制待进一步研究。     

高效液相色谱法测定地黄中腺苷含量

目的:建立地黄中腺苷含量的测定方法,测定不同品种地黄中腺苷的含量。方法:采用高效液相色谱法测定地黄中腺苷含量。以KYWG-C₁₈为固定相,6%乙腈为流动相,检测波长为260nm。结果:腺苷在0.002mg/ml～0.01mg/ml线性良好。回归方程为Y=1.7742×10-4+8.9021×10-7X,r=0.9995。平均回收率为94.1%。RSD=1.86%(n=5)。结论:本法简便、快速、结果可靠。     

实验性脑损伤后脑组织内腺苷、肌苷含量的变化及其意义

研究大鼠急性脑损伤后腺苷含量变化及其生代代谢。方法：采用大鼠液压脑损伤模型,用高效液相色谱法测定大鼠脑损伤前后脑皮质内腺苷和肌苷含量。结果：大鼠脑损伤后１０ｍｉｎ,伤侧大脑皮质内腺苷含量即明显升高,与对伤后３０ｍｉｎ升至最高值,伤后２ｈ腺苷含量恢复正常水平。结论腺苷参与继发性脑损伤后的病理生理过程。     

Marked enhancement of anti-allodynic effect by combined intrathecal administration of the adenosine A1-receptor agonist R-phenylisopropyladenosine and morphine in a rat model of central pain

BACKGROUND: There is often no satisfactory treatment for chronic pain after spinal cord injury. We have previously reported that intrathecal (i.t.) administration of the adenosine A1-receptor agonist R-phenylisopropyl-adenosine (R-PIA) or the opioid morphine has anti-allodynic effects in a model of presumed chronic central pain after photochemically induced spinal cord injury in rats. In the present study, we set out to investigate the possible interaction between i.t. R-PIA and morphine in spinally injured rats. METHODS: Sprague-Dawley rats displaying allodynia-like behaviors to mechanical and cold stimuli after photochemically induced spinal cord injury with minor motor deficits were used. R-PIA and morphine, either alone or in combination, were administered i.t. through an implanted catheter to lumbar spinal cord. RESULTS: Cumulative doses of R-PIA or morphine dose-dependently reduced the mechanical allodynia-like behavior, with a threshold of 1 nmol and 1.5 nmol, respectively. When co-administrated, R-PIA and morphine produced marked suppression of mechanical allodynia at doses of 5 pmol and 7.5 pmol, respectively. The effect of i.t. co-administration of R-PIA and morphine on cold allodynia was comparable to i.t. R-PIA alone. The combination of R-PIA and morphine did not increase adverse effects such as motor deficits in comparison to either drug alone. CONCLUSION: These results demonstrate a supra-additive interaction between the adenosine A1-receptor agonist R-PIA and morphine to reduce mechanical allodynia-like behavior in rats with chronic spinal cord injury. The combination of R-PIA and morphine administered spinally may be superior to R-PIA or morphine alone for treating such pain.     

肺结核患者外周血腺苷脱氨酶活性与淋巴细胞的相关性研究

目的探讨肺结核患者外周血淋巴细胞内腺苷脱氨酶(ADA)活性和全血淋巴细胞绝对值的相关性。方法用全自动生化分析仪及全血细胞计数仪分别测定肺结核患者外周血的ADA活性和淋巴细胞绝对值、比值。结果肺结核活动期组与非活动期组外周血ADA活性均显著高于正常人组(P<0.05),肺结核活动期组与非活动期组患者外周血ADA活性与淋巴细胞绝对值的相关系数分别为0.191和0.154,P>0.05。结论肺结核患者淋巴细胞内ADA活性升高,淋巴细胞绝对值及比值减低,肺结核患者淋巴细胞内ADA活性升高与淋巴细胞绝对值无明显相关。