We investigated the effect of lipopolysaccharide (LPS) on the induction of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in muscularis resident macrophages of rat intestine in situ. When the tissue was incubated with LPS for 4 h, mRNA levels of iNOS and COX-2 were increased. The majority of iNOS and COX-2 proteins appeared to be localized to the dense network of muscularis resident macrophages immunoreactive to ED2. LPS treatment also increased the production of nitric oxide (NO), PGE(2), and PGI(2). The increased expression of iNOS mRNA by LPS was suppressed by indomethacin but not by N(G)-monomethyl-L-arginine (L-NMMA). The increased expression of COX-2 mRNA by LPS was affected neither by indomethacin nor by L-NMMA. Muscle contractility stimulated by 3 microM carbachol was significantly inhibited in the LPS-treated muscle, which was restored by treatment of the tissue with L-NMMA, aminoguanidine, indomethacin, or NS-398. Together, these findings show that LPS increases iNOS expression and stimulates NO production in muscularis resident macrophages to inhibit smooth muscle contraction. LPS-induced iNOS gene expression may be mediated by autocrine regulation of PGs through the induction of COX-2 gene expression.

In vivo pharmacological effects of ramelteon (TAK-375), a novel, highly MT1/MT2-selective receptor agonist, were studied in rats to determine ramelteon's ability to reentrain the circadian rhythm after an abrupt phase advance. Experiments were also conducted to assess the potential cognitive side effects of ramelteon and its potential to become a drug of abuse. After an abrupt 8-h phase shift, ramelteon (0.1 and 1 mg/kg, p.o.) and melatonin (10 mg/kg, p.o.) accelerated reentrainment of running wheel activity rhythm to the new lightdark cycle. Ramelteon (3-30 mg/kg, p.o.) and melatonin (10-100 mg/kg, p.o.) did not affect learning or memory in rats tested by the water maze task and the delayed match to position task, although diazepam and triazolam impaired both of the tasks. Neither ramelteon (3-30 mg/kg, p.o.) nor melatonin (10-100 mg/kg, p.o.) demonstrated a rewarding property in the conditioned place-preference test, implying that MT1/MT2 receptor agonists have no abuse potential. In contrast, benzodiazepines and morphine showed rewarding properties in this test. The authors' results suggest that ramelteon may be useful for treatment of circadian rhythm sleep disorders without adverse effects typically associated with benzodiazepine use, such as learning and memory impairment, and drug dependence.

A great number of macrophages is found to be evenly distributed in the muscle layer of the gastrointestinal tract. We investigated their effects on smooth muscle contraction and the initiation of immune reactions such as inflammatory responses. Macrophages were demonstrated by the uptake of FITC-dextran and their ultrastructural features were elucidated by electron microscopy. Muscle layers of rats' ilea were incubated with lipopolysaccharide (LPS) for 4-8 h and the force of smooth muscle contraction was measured. The induction effect of inducible nitric oxide synthase (iNOS) on macrophages was then checked by immunohistochemistry. The expression of major histocompatibility complex (MHC) class II was also examined. Macrophages in the muscle layer were confirmed as resident macrophages and were different from a population of dendritic cells. After incubation with LPS, macrophages began to express iNOS and produced NO, and it reduced smooth muscle contraction. iNOS-immunopositive cells increased in a time-dependent manner. Macrophages also began to express MHC class II. The total number of macrophages did not alter after incubation. Results indicate that resident macrophages in the muscle layer induced iNOS as an inflammatory reaction, affected smooth muscle contraction, and initiated immune response in the smooth muscle layer of the gastrointestinal tract, when activated by LPS.

No abstract