CRF-evoked bradycardia in urethane-anesthetized rats is blocked by naloxone

CRF, injected IV at a dose of 6 nmol/kg, produced a fall in blood pressure and in heart rate in urethane-anesthetized rats. The CRF-bradycardia was not obtained in hypophysectomized animals, in animals pretreated with dexamethasone, or in animals pretreated with the narcotic antagonist, naloxone (1 mg/kg, IV). By contrast, the hypotensive effects of CRF were not affected by these procedures. Vagotomy or pretreatment with a low dose of N-methylnaloxone did not affect the CRF-bradycardia, indicating that the slowing of the heart was not due to parasympathetic stimulation or due to a peripherally mediated opioid chemoreflex. The results suggested that the CRF-bradycardia was mediated by the release of opioid peptides from the pituitary.     

Kinetics and Physical Parameters of Rat Brain Opioid Receptors Solubilized by Digitonin and CHAPS

Rat brain opioid receptors were solubilized with digitonin and a zwitterionic detergent, 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate (CHAPS). The yield of solubilization was 70-75% with digitonin and 30-35% with CHAPS. Kinetic and equilibrium studies performed from digitonin extracts resulted in KD values comparable with those of the membrane fractions. Two [3H]naloxone binding sites were obtained in the extracts similarly to membrane fractions. The rank order potency of drugs used in the competition experiments did not change during solubilization. The distributions of mu, delta, and kappa opioid receptor binding sites were similar in membrane and digitonin-solubilized fractions (48-50% mu, 35-37% kappa, and 13-17% delta subtypes). The hydrodynamic properties of digitonin- and CHAPS-solubilized preparations were studied by sucrose density gradient centrifugation and Sepharose-6B chromatography. In all cases, two receptor populations were identified with the following parameters: sedimentation coefficients for the digitonin extracts were 9.2S and 13.2S and for CHAPS extract 8S and 15.6S; the Stokes radii were 45 A and 65A for the digitonin extract and 31A and 76A for the CHAPS-solubilized preparation.     

Effect of opiate-active substances on pancreatic polypeptide levels in dogs

The present study examines the effect of orally and intravenously administered opiate-active substances on peripheral vein plasma pancreatic polypeptide (PP) levels in conscious dogs. The intragastric instillation of digested gluten stimulated postprandial PP levels significantly which was reduced by the specific opiate-receptor antagonist naloxone. Naloxone had no effect when added to undigested gluten. Similarly, naloxone reduced significantly the postprandial PP response to a test meal of casopeptone which contains the opiate-active β-casomorphins. The addition of synthetic β-casomorphins to a liver extract/sucrose test meal significantly augmented the rise of postprandial PP levels which was also blocked by naloxone. The intravenous infusion of morphine, leu-enkephalin, D-ala²-D-leu⁵-enkephalin, β-casomorphin-5 and β-casomorphin-4 elicited a dose-dependent and naloxone reversible effect on basal PP levels. During a background infusion of glucose and amino acids the same opiate-active substances had either none or a stimulatory effect on PP release in these dogs. The addition of naloxone abolished the stimulatory effect in response to β-casomorphin-5 and β-casomorphin-4 and resulted in an inhibition of PP levels during the infusion of morphine and leu-enkephalin. This latter inhibitory effect was no longer observed when the dose of naloxone was increased ten- and fifty-fold, respectively. The present data suggest that orally ingested opiate-active substances participate in the stimulation of postprandial PP release in dogs via specific opiate-receptor mediated mechanisms. The effect of intravenously administered opiate-active substances on PP levels depends on the metabolic state with regard to the level of circulating nutrients. It is suggested that PP release is stimulated via μ-opiate receptors and inhibited via δ-opiate receptors. An increase of circulating nutrients would “activate” μ-receptor sites which are masked in the basal state when exogenous opiates are administered. However, with regard to endogenous opiates an increase of circulating nutrients, mainly carbohydrates, activates inhibitory effects of endogenous opiates suggesting that exogenous and endogenous opiates act at different target sites.     

大鼠扣带回前部对外侧缰核单位放电的抑制作用

电刺激扣带回前部,对75％的外侧缰核痛兴奋神经元(pain-excitative neuron of lateral habenular nucleus,LHPE)和75％的痛抑制神经元(pain-inhibitive neuron of lateral habenular nucleus,LHPI)的自发放电均产生抑制作用,并取消躯体和内脏伤害性刺激对外侧缰核(lateral habenular nucleus,LHN)单位放电的影响。扣带回内微量注射吗啡可以抑制LHPE的自发放电,并取消伤害性刺激对LHPE的增频效应。注射纳洛酮则使LHPE的自发放电增多,加强伤害性刺激对LHPE的增频作用,并可拮抗电针对LHPE伤害性刺激反应的抑制作用。     

侧脑室注射纳络酮对幼龄家兔迷走—加压反应的影响

以４－３０日龄健康家兔为实验材料,研究了给幼兔单侧侧脑室注射纳络酮对迷走加压反应的。结果显示,纳络酮对４－１５日龄幼兔的迷走－加压反应无影响,对２０日龄左右幼兔的迷走－加压反应出现部份阻断效应,但与注药前相比无显著差异,对２５,３０日龄幼兔的迷走－加压反应阻断作用明显,与注药前相比有显著差异。     

Ceruletide increases threshold and tolerance to experimentally induced pain in healthy man

Previous studies suggested that ceruletide might be endowed with analgesic and sedative properties. To investigate the effects of ceruletide on experimentally induced pain and on central nervous functions, two studies, each involving 24 healthy subjects, were carried out in random double-blind fashion. Every subject participated in three experiments one week apart. In study 1, 120 and 60 ng/kg/hr ceruletide IV increased threshold and tolerance to electrically and threshold to thermally induced cutaneous pain significantly more than saline (p<0.001), the higher dose being slightly more active. Only mild sedative effects occurred. Study 2 compared the effects of 60 and 6 ng/kg/hr ceruletide IV to those of 0.4 mg/kg/hr pentazocine IV and investigated whether these effects were naloxone reversible. Both ceruletide doses, 60 ng/kg/hr slightly more than 6 ng/kg/hr, elevated threshold and tolerance to electrically induced and threshold to thermally induced pain markedly, pentazocine acted stronger and longer than ceruletide (p<0.001). Naloxone reversed the effects of pentazocine but not of ceruletide. Conclusion: ceruletide (1) exerts potent naloxone resistant analgesic effects, which, however, are inferior to those of pentazocine, and (2) produces only mild sedation.     

Modulation of spontaneous seizures in the mongolian gerbil: effects of beta-endorphin

Intraventricular injection of beta-endorphin (0.1-3 micrograms) into gerbils from the UCLA seizure sensitive strain reduced the incidence and severity of spontaneous epileptiform seizures, both the motor manifestations and the preceding high voltage focal spiking and accompanying seizure activity in the cortical EEG. This "'anticonvulsant" effect of beta-endorphin was prevented by prior administration of naloxone (1 mg . kg-1 IP). These findings suggest that the endogenous opioid peptide may be involved in the normal suppression of the epileptic diathesis in these animals during the interictal periods.     

Neuropeptides and thermoregulation: the interactions of bombesin, neurotensin, TRH, somatostatin, naloxone and prostaglandins

In this study we have examined the interactions of bombesin (1 microgram ICV), neurotensin (1 microgram ICV), TRH (10 micrograms ICV), somatostatin (10 micrograms ICV), PGE2 (10 micrograms ICV) and naloxone (10 mg/kg SC) on thermoregulation in the rat at room temperature (20 +/- 1 degree C). Given alone, bombesin, neurotensin, somatostatin and naloxone all produced hypothermia (bombesin greater than neurotensin greater than somatostatin congruent to naloxone). PGE2 was hyperthermic, and TRH had no effect. Bombesin and PGE2 neutralized one another's effects. Neurotensin had no effect on PGE2-induced hyperthermia. Naloxone enhanced the hypothermic effect of bombesin and somatostatin enhanced the rate of onset of hypothermia after bombesin. TRH had no effect on bombesin-induced hypothermia. TRH, somatostatin and naloxone had no effect on neurotensin-induced hypothermia. TRH antagonized the hypothermia due to naloxone and somatostatin.     

Demonstration and Characterization of Opiate Inhibition of the Striatal Adenylate Cyclase

Abstract: The conditions in which Leu⁵-enkephalin inhibition of striatal adenylate cyclase was observed were defined. It was determined that enkephalin inhibition was dependent on GTP. The apparent K_m for GTP in opiate inhibition was determined to be 0.5 and 2 μM when 0.1 mM- and 0.5 mM-ATP were used as substrate. ITP, but not CTP or UTP, could substitute for GTP in the reaction. Though the addition of monovalent cations—Na⁺,K⁺, Li⁺, Cs⁺, and choline⁺—stimulated striatal adenylate cyclase activity, enkephalin inhibition of striatal adenylate cyclase did not require Na⁺ when theophylline was used as the phosphodiesterase inhibitor. Under optimal conditions, i.e., 20 μM-GTP and 100 mM-Na⁺, Leu⁵-enkephalin inhibited the striatal adenylate cyclase activity by 23–27%. When the enkephalin regulation of the cyclase activity was further characterized, it was observed that Leu⁵-enkephalin inhibited the rate of the enzymatic reaction. Kinetic analysis revealed that the opioid peptide decreases V_max values but not the K_m values for the substrates Mg²⁺ and Mg-ATP. Agents such as MnCl₂, NaF, and guanyl-5′-ylimido-diphosphate, which directly activated the adenylate cyclase, antagonized the opiate inhibition. Levorphanol and (–)naloxone were more potent than dextrorphan and (+)naloxone in inhibiting adenylate cyclase and in reversing the enkephalin inhibition, respectively. There were differences in the potencies of various opiate peptides in their inhibition of striatal adenylate cyclase activity, with Met⁵- > Leu⁵-enkephalin > β-endorphin. The opiate receptor through which the enkephalin inhibition was observed is most likely δ in nature, since in the presence of either Na⁺ or K⁺, the magnitude of the alkaloid inhibition was reduced, whereas the peptide inhibition was either potentiated or not affected.     

纳洛酮和大豆黄酮对泌乳早期大鼠血浆LH的影响

32只泌乳期大鼠分成4组,第I组为对照组,第Ⅱ组为纳洛酮组,第Ⅲ组为大豆黄酮组,第Ⅳ组为大豆黄酮及纳洛酮组。结果是,泌乳第12天,与对照组相比,第Ⅱ组与第Ⅳ组血浆LH水平显著提高,第Ⅲ组差异不明显。