[Effects of electroacupuncture on beta-endorphin contents in rats]

Effects of electroacupuncture (EA) on pain threshold and beta-endorphin (beta-End) contents in plasma, pituitary (Pit), hypothalamus (Hyp) and cerebrospinal fluid (CSF) were studied in nontreated, dexamethasone (Dex) treated and adrenalectomized (Adrex) male SD rats by the use of specific determination of rat beta-End (combination of HPLC and RIA). EA increased pain threshold and plasma beta-End with no effect on beta-End contents in Pit, Hyp and CSF. Dex did not affect control pain threshold, but tended to reduce EA-induced increase in pain threshold (EA-analgesia, EAA) and EA-induced increase in plasma beta-End. Adrex increased plasma beta-End without change in control pain threshold. Adrex tended to reduce EAA, but a tendency of further increase in plasma beta-End was observed after addition of EA. Adrex increased Pit beta-End, but no further change in Pit beta-End was observed after addition of EA. A positive correlation between plasma beta-End and plasma ACTH was observed in nontreated, Dex treated and Adrex rats. No correlation between plasma beta-End and potency of EAA was observed in nontreated, Dex treated and Adrex rats. The hind-paw pressure test without EA increased plasma beta-End to the same degree as that produced by EA, and it produced no analgesia. These results suggest that Pit beta-End may not be mainly involved in the development of EAA.

Participation of the nucleus reticularis gigantocellularis in the morphine-induced elevation of plasma corticosterone in rats

The effects of morphine, adrenocorticotropic hormone (ACTH) and formalin on plasma corticosterone levels were investigated in the nucleus reticularis gigantocellularis (NRGC)-lesioned rats. ACTH (1.0 U/kg) or formalin (6.4%, 0.2 ml/rat) elevated plasma corticosterone in both sham-lesioned and NRGC-lesioned rats at the same degree, while morphine (10 mg/kg) also elevated plasma corticosterone in sham-lesioned rats, the elevation of which was significantly reduced by NRGC-lesioning. These findings suggest that the NRGC is involved in the corticosterone-increasing effect of morphine, but not involved in the effect of ACTH or formalin.

[Effects of NRGC-lesion on the rates of the development of morphine tolerance and dependence in rats]

The development of tolerance to and dependence on morphine over 1-8 days treatment with morphine were studied with time in rats in which the nucleus reticularis gigantocellularis (NRGC), including the nucleus reticularis paragigantocellularis, were electrically destructed. The NRGC of SD male rats was bilaterally lesioned (DC, 0.5 mA, 40 sec), and morphine analgesia was estimated by the tail flick method. Morphine analgesia in NRGC-destructed rats (D-rat) was reduced to about 50% of that in sham-operated rats (S-rat). The dose of morphine to produce equi-analgesia increased 2-21.8 times during 1-8 days treatment with morphine in S-rat. Throughout this period, ratios of the equi-analgesic dose in D-rat to that in S-rat were almost the same, i.e., the rate of tolerance development to morphine analgesia in D-rat was to the same degree as that in S-rat. Administration of naloxone after 1-6 days treatment with morphine elicited body weight loss and increase in plasma corticosterone (Pcs), degrees of which were dependent on the dose of naloxone or the period of morphine treatment. No difference in these abstinence signs were detected between S- and D-rat, i.e., the rate of development of dependence on morphine in D-rat was to the same degree as that in S-rat. These results suggest that the NRGC participates in the development of morphine analgesia, but does not participate in the development of tolerance to and dependence on morphine.

[The role of the pituitary in the development of electroacupuncture analgesia in rats]

In order to investigate the involvement of pituitary beta-endorphin in electroacupuncture analgesia (EAA), the effects of hypophysectomy, dexamethasone (Dex) and adrenalectomy on the analgesia and the increase in plasma corticosterone (Cort) and ACTH levels produced by electroacupuncture (EA) were studied in male SD rats. In saline-treated and Dex-treated rats, plasma Cort levels were correlated with plasma ACTH levels. In non-treated rats, the time course of EA-induced increase in pain threshold was similar to that of EA-induced elevation of plasma Cort levels. In the hypophysectomized rats, EAA was significantly reduced and the EA-induced increase in plasma Cort was also abolished. Single administration of a large dose of Dex tended to reduce EAA and significantly reduced the EA-induced increase in plasma Cort and ACTH. Further suppression of pituitary functions by 4 days-treatment with Dex resulted in further reduction of EAA and the EA-induced increase in plasma Cort and ACTH. On the other hand, hind-paw pressure test without EA produced an increase in plasma Cort and ACTH to the same extent as that produced by EA and produced no analgesia. In the adrenalectomized rats, EAA was reduced, and the plasma ACTH level, which was sixteen times higher than that of nonoperated rats, was further elevated 2-fold higher by EA. No correlation between plasma ACTH levels and the increase in pain thresholds was observed in individual rats of the saline-treated and Dex-treated groups. Control pain thresholds were not influenced by hypophysectomy, Dex or adrenalectomy. These results suggest that pituitary beta-endorphin may not be mainly involved in EAA.

[Effects of human calcitonin on the response to noxious stimuli and morphine-antinociception]

Effects of human calcitonin (HCT) on the responses of mice and rats to noxious stimuli of various types and morphine-antinociception in the mice tail-pinch method were studied as compared with procine calcitonin (PCT). I.c.v. administration of HCT (0.007-0.071 mg/mouse) delayed response time to tail-pinch stimuli and suppressed acetic acid writhing dose-relatedly. PCT (0.5-3 U/mouse, i.c.v.) exerted a dose-related antinociceptive effect in the tail-pinch and acetic acid writhing methods. The antinociceptive effect was also produced by s.c. administration of HCT (0.071-7.1 mg/kg) and PCT (10-1000 U/kg) in the tail-pinch and writhing methods, while the antinociceptive effect was not detected by the tail-flick method following i.c.v. and s.c. administration of HCT and PCT. Increase in response threshold in the hind paw pressure test was produced by 0.071-7.1 mg/kg, s.c. of HCT and 10-1000 U/kg, s.c. of PCT in rats. Inhibition of writhing due to i.c.v. administration of HCT and PCT was not antagonized by naloxone. Pre-drug control response time to tail-pinch stimuli tended to be shortened after 7-14 days of s.c. treatment with CT, especially with PCT. Pretreatment with HCT and PCT exerted no obvious influence on their acute effects. Morphine-antinociception in the tail-pinch method tended to be potentiated by single s.c. dose of HCT and to be decreased by 14 days chronic s.c. treatment with HCT. The role of calcium in HCT action was discussed.

[A specific and quantitative determination of rat beta-endorphin. Combination of HPLC and RIA]

A specific and quantitative method for the determination of rat beta-endorphin by the combination of HPLC and RIA was developed. Rabbit antiserum against camel beta-endorphin (c beta-E) was raised and used for RIA at the final concentration of 1:10000. The quantitative range estimated from the displacement curve was 0.1-2.0 ng. Cross-reactivities with Met-Enk, Leu-Enk, alpha-MSH, alpha-endorphin, ACTH and human beta-E were less than 0.1, less than 0.1, less than 0.1, less than 0.1, 2 and 100%, respectively. These peptides were separated from each other by reversed phase HPLC with UV254 nm detection, and the minimum detectable dose of c beta-E was found to be 1 microgram. beta-E-like immunoreactivity (beta-ELIR) in the HPLC effluent was determined by RIA. The HPLC-RIA chromatogram of authentic c beta-E exhibited a single peak which coincided with the peak of c beta-E detected by UV, and 80% of the injected c beta-E (1-100 ng) was detected in the c beta-E fraction. The HPLC-RIA chromatogram of rat pituitary, hypothalamus, cerebrospinal fluid and plasma revealed the presence of 1-3 peaks, one of which was observed at the position of c beta-E. The HPLC elution of rat pituitary resolved the material into two peaks of biological activity, one of which coincided with the peak of beta-ELIR at the position of c beta-E. The HPLC-RIA chromatogram of the c beta-E fraction from pituitary obtained by gel-chromatography exhibited three peaks, one of which coincided with c beta-E. These results suggest that beta-ELIR in the c beta-E fraction of the HPLC elution may reflect rat beta-E accurately.

[Morphine tolerance and dependence liability in NRGC-destructed rats]

The nucleus reticularis gigantocellularis (NRGC), including the nucleus reticularis paragigantocellularis (NRPG), of male Sprague Dawley rats was destructed bilaterally by DC 0.5 mA for 40 sec (D-rats). Morphine analgesia estimated by the tail pinch method in 4 and 10 days morphine treated sham operated rats (S-rats), of which the test doses were 40 and 80 mg/kg, respectively, was equal to or smaller than the analgesia by 5 mg/kg in non-treated S-rats. Morphine analgesia at 5 mg/kg in non-treated D-rats was weaker than that in S-rats. Morphine analgesia in 4 and 10 days morphine treated D-rats, of which the test doses were 40 and 80 mg/kg, respectively, was stronger than the analgesia by 5 mg/kg but weaker than that by 20 mg/kg in non-treated D-rats. These results indicate development of morphine tolerance in S- and D-rats. Reverse of diurnal variation in body weight and disappearance of diurnal variation in body temperature and in plasma corticosterone concentration (Pcs) were observed similarly in S- and D-rats during morphine treatment. Body weight loss, increase in Pcs and plasma ACTH concentration, and increase in adrenal weight were elicited by morphine withdrawal in both morphine treated S- and D-rats. These signs during morphine treatment and after morphine abstinence indicate the development of morphine dependence in D-rats. These results suggest that the NRGC participates in development of morphine analgesia, but does not participate in development of morphine tolerance and dependence.

Intercellular junctions in odontoblasts of the rat incisor studied with freeze-fracture

The morphology and distribution of various types of intercellular junctions were investigated in young odontoblasts. Gap junctions were found between odontoblasts as well as between odontoblasts and fibroblasts in the dental pulp. The junctions between odontoblasts were larger and more numerous than those between odontoblast and fibroblast, suggesting that the former may play an important role in regulating cellular activity and the latter may provide a pathway of low electrical resistance between odontoblast and nerve fibres. Irregularly-shaped gap junctions appeared as small aggregations of particles associated with a particle-free area and may indicate that the junction might not yet have been completely assembled. Tight junctions were observed at the distal ends of the young odontoblasts, arranged to form small maculae or faciae occludentes rather than belt-like zonulae. It is therefore not likely that the junction contributes to barrier function in the young odontoblasts. Although structures resembling typical desmosome were recognizable, this type of junction in odontoblasts is properly termed a desmosome-like junction from its morphological peculiarities.

[Effect of destruction of nucleus reticularis gigantocellularis of rat medulla oblongata on morphine analgesia]

It was confirmed that the nucleus reticularis gigantocellularis (NRGC), including the nucleus reticularis paragigantocellularis (NRPG), was a highly sensitive site in the production of morphine analgesia by the micro-injection technique (ED50 = 8.5 ng/rat). The NRGC of SD male rats (280-350 g) was bilaterally lesioned by direct current (0.5 mA for 40 sec). The body weight was decreased by NRGC destruction, while no abnormality in motor activity was observed in NRGC-destructed rats. The size of lesion was decreased in relation to the days after operation. The size of the destructed area immediately after operation was about 30% of the NRGC area. Morphine analgesia was estimated by tail pinch and hind paw pressure tests. No change in control pain threshold was produced by NRGC lesioning. Morphine analgesia due to 5, 10 and 15 mg/kg s.c. were depressed almost equally be NRGC lesioning, and depression % was 60-70%. Time course of the morphine effect in NRGC-destructed rats was similar to that in sham operated rats. The degree of depression of morphine analgesia by NRGC lesioning was dependent on the extent of NRGC lesioning, i.e., the more the destructed area of NRGC was extended, the more the morphine analgesia was depressed. Reduction of morphine analgesia in rats in which the position of destruction had deviated from the NRGC was smaller than that in rats in which the destruction was exactly at the NRGC. These results suggest that the NRGC, including the NRPG, plays an important role in morphine analgesia.

Highly selective inhibitors of thromboxane synthetase. 1. Imidazole derivatives

The structure--activity relationships of imidazole derivatives as inhibitors of thromboxane (TX) synthetase were investigated. Introduction of various substituents (e.g., one or two methyl groups, a halogen atom, a methylidene group, unsaturated bonds, or a phenylene group) into the alpha position or other positions in the carboxy-bearing side chain of 1-(7-carboxyheptyl)imidazole (15) was found to increase the inhibitory potency. The length of the side chains with the phenylene group was optimum for the inhibitory potency on TX synthetase in the region of 8.5-9.0 A. Among the tested imidazole derivatives, 1-(7-carboxy-7-methyl-2-octynyl)imidazole (47), 4-[3-(1-imidazolyl)-propyl]benzoic acid (50), and (E)-4-(1-imidazolylmethyl)cinnamic acid (54) and its alpha-methyl analogue (57) showed the highest potency with an IC50 in the range of 10(-8) to 10(-9) M. Inhibition by these derivatives was highly selective for the TX synthetase, since other enzymes such as fatty acid cyclo-oxygenase and prostacyclin synthetase were not affected.

Highly selective inhibitors of thromboxane synthetase. 2. Pyridine derivatives

The enzyme thromboxane (TX) synthetase is inhibited by pyridine. The beta-substituted pyridine derivatives showed higher inhibitory potency than the gamma-substituted ones having the same side chain. Among the beta-substituted derivatives containing the omega-carboxyalkyl group, the compounds with 6-8 carbon atoms in the side chain were especially effective. The derivatives holding the phenylene group in the side chain exhibited much higher inhibitory activity than those of the alkylene type. Among them, (E)-3-[4-(3-pyridylmethyl)phenyl]-2-methylacrylic acid hydrochloride (5a) had the highest potency (IC50 = 3 x 10(-9) M). The beta-substituted pyridine derivatives and 1-substituted imidazole derivatives which had the same side chain showed almost the same potency. The beta-substituted pyridine derivatives do not inhibit arachidonic acid cyclooxygenase or prostaglandin I2 synthetase, two other enzymes of the arachidonic cascade.

Change of polyamine content in mouse skin by leupeptin, a protease inhibitor, during early stage of tumorigenesis

The effect of a microbial protease inhibitor, leupeptin, on the content of polyamine in the mouse skin was examined during the early stage of tumorigenesis induced by a single application of 7,12-dimethylbenz[a]anthracene (DMBA) and repeated application of croton oil thereafter. Polyamine content in the skin was measured at 3, 5, 7, and 9 weeks during tumorigenesis. The mice with no visible tumor were selected for measurement of polyamine content at 9 weeks. Mice were left untreated for at least 1 week before measurement of polyamine. Polyamine in the skin was extracted with ice-cold 0.4N HClO4 and separated into putrescine, spermidine, and spermine fractions through CM-cellulose column. Polyamine concentration was determined by fluorometry with fluorescamine. Group A mice painted with croton oil 3 times a week did not develop tumors. Group B mice painted with a single DMBA developed skin tumors, and group C mice painted with a single DMBA and croton oil 3 times a week showed higher development of skin tumors than group B. Group D mice treated as group C and then painted with leupeptin about 2 hr after croton oil treatment. Animals in groups B, C, and D had higher spermidine content as group A at 3 and 5 weeks. Content of spermidine in group B decreased at 7 and 9 weeks compared with group C which had a high content throughout the time tested. Leupeptin treatment in group D inhibited spermidine content in the skin after 7 weeks without affecting until 5 weeks.