Somatostatin as a mediator of the effect of neurotensin on pentagastrin-stimulated acid secretion in rats

Neurotensin and somatostatin have both been shown to inhibit gastric acid secretion, but no interaction between these peptides has been demonstrated. To determine whether somatostatin might be a mediator of neurotensin's effect on pentagastrin-stimulated gastric acid secretion, we performed the following three experiments. First, we collected 0.2-ml samples of portal venous blood as frequently as every 5 min, and we confirmed a significant release of somatostatin-like immunoreactivity into portal venous blood during neurotensin-induced inhibition of acid secretion. This release of somatostatin-like immunoreactivity and inhibition of acid secretion were only seen in pentobarbital-anesthetized rats, but no sustained release of somatostatin-like immunoreactivity or inhibition of acid secretion occurred in urethane-anesthetized animals. In the second experiment, we analyzed portal plasma by high pressure liquid chromatography, and found that portal somatostatin-like immunoreactivity in blood collected during neurotensin infusion was composed of a single peak corresponding to somatostatin-14. In the third experiment, we found that infusion of antibody to somatostatin prevented neurotensin from inhibiting pentagastrin-stimulated acid secretion. Taken together, these data show that somatostatin, possibly from the stomach itself, is a necessary mediator of neurotensin's inhibitory effect in pentobarbital-anesthetized rats.     

Pentobarbital sodium inhibits calcium uptake in vascular smooth muscle

This report demonstrates that the commonly used anesthetic agent, pentobarbital sodium, in concentrations of 1 · 10^?4 to 2 · 10^?3 M inhibits calcium (Ca²⁺) uptake in both rat aortic and portal venous smooth muscle. The data indicate that total exchangeable Ca²⁺ in portal vein is reduced by about 15% in 1 · 10^?4 M pentobarbital sodium, while the intracellular exchangeable Ca²⁺ is reduced by 24%. On the other hand, in aortic smooth muscle, while 5–20 · 10^?4 M pentobarbital sodium reduces total exchangeable Ca²⁺ by about 15%, intracellular Ca²⁺ is reduced by 22% in 5 · 10^?4 M pentobarbital sodium and by 38% in 2 · 10^?3 M pentobarbital sodium. The present studies thus reveal that concentrations of pentobarbital sodium known to be present during induction of surgical anesthesia can exert significant inhibitory effects on exchangeability and transmembrane movement of Ca²⁺ in at least two different types of blood vessels.     

三种麻醉方法在骨科动物实验中效果比较

目的比较3种麻醉方法在骨科动物实验中的效果,从而得出最佳方法。方法将80只实验动物随机分为3组,A组（速眠新II肌肉注射组）,B组（0.6%戊巴比妥钠静脉注射组）,C组（速眠新II肌肉注射＋0.6%戊巴比妥钠静脉注射联合用药组）,在骨科动物实验中分别进行麻醉、手术,比较3组的麻醉效果,观察其诱导期、麻醉期（麻醉维持时间）、苏醒期、麻醉效果、死亡率等。结果 A组麻醉的诱导期长,效果不好;B组麻醉的诱导期短,但麻醉效果不理想,死亡率高;C组麻醉的诱导期短,麻醉效果好,安全。结论 C组诱导期短,麻醉效果好,安全。无论在实验动物的伦理道德方面,还是在保证动物实验质量方面都是最佳选择。     

Membrane Disordering by Anesthetic Drugs: Relationship to Synaptosomal Sodium and Calcium Fluxes

The effects of membrane perturbants (ethanol, pentobarbital, chloroform, diethylether, phenytoin, cis-vaccenic acid methylester, and cis-vaccenoyl alcohol) on the lipid order of mouse brain synaptic plasma membranes (SPM) were tested by fluorescence polarization using 1,6-diphenyl-1,3,5-hexatriene (DPH) as a probe of the membrane core and 1-[4-(trimethylammonium)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH) as a probe of the membrane surface. The compounds decreased the fluorescence polarization of both probes, indicating that they disordered the membrane lipids. The decrease in polarization was, however, greater for DPH than for TMA-DPH, suggesting a greater effect on the membrane core than on the membrane surface. The voltage-dependent uptake of 24Na and 45Ca was studied in isolated mouse brain synaptosomes as a measure of membrane function. All of the compounds inhibited sodium influx, and their potencies for decreasing sodium uptake and fluorescence polarization of DPH were linearly correlated (r = 0.91). The relationship between changes in sodium influx and TMA-DPH polarization was less consistent (r = 0.66). Synaptosomal calcium uptake was inhibited by most, but not all, of the perturbants, but this inhibition was poorly correlated with changes in fluorescence polarization of DPH (r = 0.36) or TMA-DPH (r = 0.26). These results indicate that the function of synaptic sodium channels is correlated with lipid order in the hydrophobic core of the membrane and that the inhibitory effects of intoxicant-anesthetic drugs on neuronal sodium fluxes may be the result of their capacity to disorder these lipids. In contrast, the effects of drugs on voltage-dependent calcium channels were not clearly related to the capacity of these agents to disorder membrane lipids.     

Anesthetic Barbiturates Enhance Gsα-Dependent Cyclic AMP Production in S49 Mouse Lymphoma Cells

Abstract: Cyclic AMP (cAMP) regulates many important physiological processes. Barbiturates influence cAMP regulation, possibly through effects on G proteins. This study used intact S49 mouse lymphoma cells to characterize the role of G proteins in the effect of barbiturates on cAMP regulation. cAMP accumulation was determined in intact S49 WT (wild-type) and S49 cyc^? cells (the G_sα-deficient mutant) by measuring the conversion of [³H]-ATP to [³H]cAMP in cells preloaded with [³H]adenine. Pentobarbital enhanced cAMP accumulation in WT cells in the absence (basal) or presence of isoproterenol but had no effect on the EC₅₀ for isoproterenol. This effect was dose dependent with a 50–60% enhancement at 2 mM pentobarbital. Pentobarbital did not affect forskolin-stimulated cAMP accumulation in WT cells. In cyc^? cells, basal and forskolin-stimulated cAMP accumulation were stimulated only at the highest concentration of pentobarbital used (2 mM). Pentobarbital did not affect the inhibition of cAMP accumulation by somatostatin in WT cells, and pertussis toxin treatment of WT cells did not affect the action of pentobarbital on cAMP accumulation. Pentobarbital did not affect isoproterenol-stimulated adenylyl cyclase activity in whole-cell homogenates or membranes prepared from WT cells. The S-(?)-isomer of pentobarbital enhanced isoproterenol-stimulated cAMP accumulation more than the R-(+)-isomer. Phenobarbital and barbituric acid did not enhance isoproterenol-stimulated cAMP accumulation, whereas the anesthetic barbiturates hexobarbital, pentobarbital, and thiopental all enhanced activity. These results suggest that pentobarbital enhances cAMP accumulation in intact WT cells by a mechanism that is dependent on G_sα but independent of G_i. The properties of barbiturates that are responsible for the enhancement of cAMP accumulation may be related to the properties that are responsible for producing sedation and anesthesia.     

Kainate-enhanced release of D-[3H]aspartate from cerebral cortex and striatum: reversal by baclofen and pentobarbital

A study was made of the actions of the excitant neurotoxin, kainic acid, on the uptake and the release of D-[2,3-3H]aspartate (D-ASP) in slices of guinea pig cerebral neocortex and striatum. The slices took up D-ASP, reaching concentrations of the amino acid in the tissue which were 14-23 times that in the medium. Subsequently, electrical stimulation of the slices evoked a Ca2+-dependent release of a portion of the D-ASP. Kainic acid (10(-5)-10(-3) M) produced a dose-dependent inhibition of D-ASP uptake. The electrically evoked release of D-ASP was increased 1.6-2.0 fold by 10(-5) and 10(-4)M kainic acid. The kainate-enlarged release was Ca2+-dependent. Dihydrokainic acid, an analogue of kainic acid with little excitatory or toxic action, did not increase D-ASP release but depressed D-ASP uptake. Attempts were made to block the action of kainic acid with baclofen and pentobarbital, compounds which depress the electrically evoked release of L-glutamate (L-GLU) and L-aspartate (L-ASP). Baclofen (4 X 10(-6)M), an antispastic drug, and pentobarbital (10(-4)M), an anesthetic agent, each inhibited the electrically evoked release of D-ASP and prevented the enhancement of the release above control levels usually produced by 10(-4)M kainic acid. It is proposed that 10(-5) and 10(-4)M kainic acid may enhance the synaptic release of L-GLU and L-ASP from neurons which use these amino acids as transmitters. This action is prevented by baclofen and pentobarbital. In view of the possibility that cell death in Huntington's disease could involve excessive depolarization of striatal and other cells by glutamate, baclofen might be effective in delaying the loss of neurons associated with this condition.     

Effects of pentobarbital tolerance to and dependence on GABAB receptor binding

Effects of pentobarbital pellet implantation on [³H]baclofen binding in the frontal cortex of cerebellum of rat brains were examined. In the frontal cortex, pentobarbital tolerance caused an increase in the number of binding sites (B_max) without changing their affinity (K_D). Twenty-four hours after withdrawal of the pentobarbital pellets, there was a significant increase in the K_D and B_max values. Cerebellar binding, in contrast, was not significantly changed in any of the treatment groups. Addition of 1 mM of pentobarbital directly to binding assays using cortical membrane produced as increase in K_D without a change in B_max.In vitro, pentobarbital affected neither the K_D nor the B_max in the cerebellar [³H]baclofen binding. These results suggest that like the GABA_A receptor, [³H]baclofen binding to the GABA_B receptor in rat frontal cortex was affected by pentobarbital tolerance and dependence, and that there are regional differences in the properties of the GABA_B receptor.     

地西泮和戊巴比妥钠对两种小鼠镇静催眠作用强度的观察

目的：观察地西泮和戊巴比妥纳对不同种属小鼠自主活动和睡眠效应的影响,为筛选影响中枢神经系统功能的药物提供可参考的选择动物的依据。方法：分别取昆明种和ICR小鼠各40只,设对照组和地西泮给药组,每组20只,给药组ig地西泮4mg／kg,对照组给生理盐水,连续3天,末次给药后45分钟测定小鼠自主活动。另取两种小鼠各20只,分别ip戊巴比妥钠50mg／kg,观察两种小鼠的睡眠情况,记录潜伏期和睡眠时间。结果：ICR小鼠ig地西泮后,表现明显的镇静作用,自主活动的次数和对照组比较明显减少,P〈0．01;而昆明种小鼠给相同剂量的地西泮,小鼠自主活动的次数减少不明显,P〉0．05。昆明种和ICR小鼠同样ip阈上剂量的戊巴比妥钠,两者在睡眠潜伏期上无明显差异,但在睡眠时间上,则ICR小鼠的睡眠时间明显长于昆明种小鼠,P〈0．01。结论：ICR小鼠对中枢抑制药的反应性更好,适合于这类药物的筛选,尤其对作用相对较弱的中药制剂,可能提高筛选的阳性率。     

Changes in [3H]Forskolin Binding to Adenylate Cyclase and [3H]Phorbol Dibutyrate Binding to Protein Kinase C in Pentobarbital Tolerant/Dependent Rats

These studies were designed to examine the effect of chronic administration of pentobarbital on activity of adenylate cyclase (AC) and protein kinase C (PKC) in the rat brain by autoradiography. Recently, it has been suggested that the phosphorylation of specific proteins may be involved in the development of physical dependence. An experimental model of barbiturate tolerance and dependence was developed using i.c.v. infusion of pentobarbital (300 g/ 10 l/hr for 7 days) by osmotic minipumps and abrupt withdrawal from pentobarbital. The levels of [³H]forskolin binding were elevated (28–67%) in cortex, thalamus, dentate gyrus, hippocampal CA3 and cerebellum of the pentobarbital withdrawal animals, while these changes were not observed in tolerant rats. The levels of [³H]phorbol dibutyrate binding were highly elevated (38–65%) in the region of cortex, caudate putamen, septum, thalamus, dentate gyrus, and cerebellum of rats withdrawal from pentobarbital. These results show that the levels of AC and PKC were significantly elevated in pentobarbital withdrawal rats, and suggest that the levels of AC and PKC are altered in a region-specific manner during pentobarbital withdrawal.     

In Situ Hybridization Evidence of Differential Modulation by Pentobarbital of GABAA Receptor α1- and β3-Subunit mRNAs

Abstract: Tolerance to and withdrawal from pentobarbital were induced in rats by continuous intracerebroventricular infusion via subcutaneously implanted osmotic minipumps. In situ hybridization of GABA_A receptor α₁- and β₃-subunit mRNA was conducted using synthetic 3'- end ³⁵S-dATP-labeled oligodeoxynucleotide probes. Results were quantified by film densitometry. In animals that were tolerant to pentobarbital, levels of α₁-subunit mRNA were decreased in hippocampus, superior colliculus, and inferior colliculus, but levels of β₃-subunit mRNA were not affected. Dramatically increased levels of GABA_A receptor subunit mRNA were observed in animals 24 h after withdrawal from chronic pentobarbital treatment. These increases occurred in cerebral cortex and cerebellum for the α₁ subunit and in cerebral cortex only for the β₃-subunit. These data provide further support to the structural and pharmacological GABA_A receptor heterogeneity in discrete brain areas. The observed changes of subunit expression may underlie, at least in part, the receptor up- and down-regulation observed in receptor ligand binding studies.