Reciprocal inhibition versus unloading response during stretch reflex in humans.

Rotation of an upper limb joint produces excitatory stretch reflex peaks M1 and M2 in the stretched muscles and simultaneous decrease in electromyographic (EMG) activity in the shortened muscles. The objective of this study was to examine whether the decreased activity in the antagonists (rINHIB) is purely from unloading of the spindles or receives active inhibition involving inhibitory interneurons. If rINHIB is due only to unloading, then the termination of rINHIB should vary with the duration of perturbation used to elicit stretch reflex, namely shorter stretches should result in shorter values of decreased periods of EMG. To examine this question, rectangular pulses, ranging in duration from 25 to 150 ms, were used to stretch wrist flexors or extensors with a torque motor. These rectangular pulses resulted in joint rotations which peaked at times (T(peak)) ranging from approximately 75-160 ms. As shown by previous authors, when the duration of rotation was shortened, the magnitude of M1 did not change, while the magnitude of M2 decreased. However, termination time of rINHIB in the shortened muscles did not change with change in T(peak), implying thereby that unloading of spindles of the antagonist muscles is not the only mechanism for the reduction in activity and that inhibitory reflex pathways most likely contribute. Possible sources of inhibition are discussed for the short- and long-latency inhibition.

Proprioceptive reaction times and long-latency reflexes in humans.

The stretch of upper limb muscles results in two electromyographic (EMG) peaks, M1 and M2. The amplitude of M2 peak can generally be modified by giving prior instruction to the subject on how to react to the applied perturbation. The unresolved question is whether the amplitude modulation results from change in the gain of the reflex pathway contributing to M2, or by superposition of reaction time (RT) activity. The following study attempted to resolve this question by examining the overlap between proprioceptive RT and M2 activities. Subject's right wrist flexors were stretched, and he/she was instructed either (1) not to intervene (passive task) or (2) to react as fast as possible by simultaneously flexing both wrists (active or compensate task). Under passive and active conditions, M1 and M2 were observed from EMG of right wrist flexors, and during the active condition, RT activities were additionally observed from both sides. The onset and offset of M2 (M1(onset), M2(offset)) were measured from the passive averages, while the RT was measured from the averaged EMG response of the left wrist flexors. For between-subject correlations, the data were divided into two sets: (1) subjects with RT shorter than M2(offset) (fast group) and (2) subjects with RT more than 10 ms longer than their M2(offset) (slow group). Modulation during M2 period was large for the fast group, and it was almost zero for the slow group. These results indicate that the superimposition of RT activity mainly contributes to the instruction-dependent modulation of M2 peak.

Recovery of human motoneurons during rotation.

During prolonged contractions, few studies have reported rotation among low threshold motoneurons. The question arises whether a motoneuron stops firing due to an increase in firing threshold or whether it is due to regional switching of activity among muscle fascicles. We postulated that if the rest period resulted from an increase in firing threshold, a progressive recovery in the excitability of the motoneuron would be observed during the rest period. The excitability of soleus or tibialis anterior motoneurons was tested during the rest periods. The results showed that a previously tonic motoneuron that had dropped off during rotation, rarely responded to Ia or TMS inputs in the initial parts of the rest period; however, its response probability increased significantly in the second half. Based on these data, we suggest that the observed rotation is due to changes in firing thresholds of motoneurons during prolonged firing.

What's related? Generalizing approaches to related articles in medicine.

INTRODUCTION: We did formative evaluations of several variations to the computation of related articles for non-bibliographic resources in the medical domain. METHODS: A binary model and several variations of the vector space model were used to measure similarity between documents. Two corpora were studied, using a human expert as the gold standard. RESULTS: Variations in term weights and stopword choices made little difference to performance. Performance was worse when documents were characterized by title words alone or by MeSH terms extracted from document references. DISCUSSION: Further studies are needed to evaluate these methods in medical information retrieval systems.

Suppression of human inflammatory cell function by subtype-selective PDE4 inhibitors correlates with inhibition of PDE4A and PDE4B.

1. Of the four major phosphodiesterase 4 (PDE4) subtypes, PDE4A, PDE4B and PDE4D are widely expressed in human inflammatory cells, including monocytes and T lymphocytes. We explored the functional role of these subtypes using ten subtype-selective PDE4 inhibitors, each belonging to one of two classes: (i) dual PDE4A/PDE4B inhibitors or (ii) PDE4D inhibitors. 2. These compounds were evaluated for their ability to inhibit antigen-stimulated T-cell proliferation and bacterial lipopolysaccharide (LPS)-stimulated tumour necrosis factor alpha (TNFalpha) release from peripheral blood monocytes. 3. All compounds inhibited T-cell proliferation in a concentration-dependent manner; with IC50 values distributed over an approximately 50 fold range. These compounds also inhibited TNFalpha release concentration-dependently, with a wider ( approximately 1000 fold) range of IC50 values. 4. In both sets of experiments, mean IC50 values were significantly correlated with compound potency against the catalytic activity of recombinant human PDE4A or PDE4B when analysed by either linear regression of log IC50 values or by Spearman's rank-order correlation. The correlation between inhibition of inflammatory cell function and inhibition of recombinant PDE4D catalytic activity was not significant in either analysis. 5. These results suggest that PDE4A and/or PDE4B may play the major role in regulating these two inflammatory cell functions but do not rule out PDE4D as an important mediator of other activities in mononuclear leukocytes and other immune and inflammatory cells. Much more work is needed to establish the functional roles of the PDE4 subtypes across a broader range of cellular functions and cell types.

Expression and cellular localization of the CC chemokines PARC and ELC in human atherosclerotic plaques.

Local immune responses are thought to play an important role in the development of atherosclerosis. Histological studies have shown that human atherosclerotic lesions contain T lymphocytes throughout all stages of development, many of which are in an activated state. A number of novel CC chemokines have been described recently, which are potent chemoattractants for lymphocytes: PARC (pulmonary and activation-regulated chemokine), ELC (EBI1-ligand chemokine), LARC (liver and activation-regulated chemokine), and SLC (secondary lymphoid-tissue chemokine). Using reverse transcriptase-polymerase chain reaction and in situ hybridization, we have found gene expression for PARC and ELC but not for LARC or SLC in human atherosclerotic plaques. Immunohistochemical staining of serial plaque sections with specific cell markers revealed highly different expression patterns of PARC and ELC. PARC mRNA was restricted to CD68+ macrophages (n = 14 of 18), whereas ELC mRNA was widely expressed by macrophages and intimal smooth muscle cells (SMC) in nearly all of the lesions examined (n = 12 of 14). ELC mRNA was also found to be expressed in the medial SMC wall of highly calcified plaques (n = 4). Very low levels of ELC mRNA expression could also be detected in normal mammary arteries but no mRNA expression for PARC was detected in these vessels (n = 4). In vitro, ELC mRNA was found to be up-regulated in aortic SMC stimulated with tumor necrosis factor-a and interferon-gamma but not in SMC stimulated with serum. Both PARC and ELC mRNA were expressed by monocyte-derived macrophages but not monocytes. The expression patterns of PARC and ELC mRNA in human atherosclerotic lesions suggest a potential role for these two recently described CC chemokines in attracting T lymphocytes into atherosclerotic lesions.

1,4-Cyclohexanecarboxylates: potent and selective inhibitors of phosophodiesterase 4 for the treatment of asthma.

Evaluation of a variety of PDE4 inhibitors in a series of cellular and in vivo assays suggested a strategy to improve the therapeutic index of PDE4 inhibitors by increasing their selectivity for the ability to inhibit PDE4 catalytic activity versus the ability to compete for high affinity [3H]rolipram-binding sites in the central nervous system. Use of this strategy led ultimately to the identification of cis-4-cyano-4-[3-(cyclopentyloxy)-4-methoxyphenyl]cyclohexane-1-carboxyl ic acid (1, SB 207499, Ariflo), a potent second-generation inhibitor of PDE4 with a decreased potential for side effects versus the archetypic first generation inhibitor, (R)-rolipram.

Prolonged beta adrenoceptor stimulation up-regulates cAMP phosphodiesterase activity in human monocytes by increasing mRNA and protein for phosphodiesterases 4A and 4B.

Human peripheral blood monocytes were treated for 4 h with a combination of the beta-agonist salbutamol (3 microM) and the low-Km cAMP-specific phosphodiesterase (PDE4) inhibitor rolipram (30 microM) to produce a prolonged elevation of cAMP and consequent increase in PDE activity. After this treatment, isozyme-selective PDE inhibitors were used to characterize the cAMP PDE profiles of high-speed supernatants before and after DEAE-Sepharose column chromatography. These experiments, in which total soluble PDE activity was increased by 58%, showed that the increased PDE activity is due to up-regulation of PDE4 and that at least two of the four subtypes are up-regulated. Experiments in whole cells demonstrated that this relatively modest increase in PDE4 activity has significant functional consequences, reducing cAMP accumulation in response to both PGE2 and lower, though not maximal, concentrations of rolipram. Further characterization of PDE4 subtype expression in control and treated monocytes, using polymerase chain reaction and Western blotting with subtype-specific peptide antibodies, showed that resting monocytes express both mRNA and protein for PDE4A, PDE4B and PDE4D. The amount of message for PDE4A and PDE4B appeared to increase upon up-regulation, whereas mRNA for PDE4D was not detected in treated cells. Western blots showed increases in the amount of protein for both PDE4A and PDE4B after treatment. We conclude that the PDE4 subtypes are differentially regulated upon prolonged exposure to elevated cAMP, with the consequence that the PDE4 profiles of control and treated cells differ not only in total activity but also in the relative proportions of the subtypes represented.

Salbutamol up-regulates PDE4 activity and induces a heterologous desensitization of U937 cells to prostaglandin E2. Implications for the therapeutic use of beta-adrenoceptor agonists.

Previous studies with U937 cells, a human monocyte cell line, have shown that the activity of cyclic nucleotide phosphodiesterase 4 (PDE4) is increased by agents that elevate cyclic AMP content. The present experiments were conducted to determine 1) whether an increase in PDE4 steady-state message and/or protein accompanies the up-regulation of PDE4 activity and 2) whether the up-regulation changes the functional responses of U937 cells to activators of adenylyl cyclase. To up-regulate PDE4 activity, U937 cells were treated for 4 h with a combination of 1 microM salbutamol, a beta-adrenoceptor agonist, and 30 microM rolipram, a PDE4 inhibitor. Cells were washed extensively to remove drugs and used immediately in various experimental protocols. Reverse transcriptase-polymerase chain reactions conducted with primers specific for the four PDE4 subtypes suggested that pretreatment with salbutamol and rolipram increased steady-state mRNA levels of PDE4A and PDE4B, but not PDE4C or PDE4D. Immunoblot analyses using two rabbit polyclonal antibodies, one directed against human recombinant PDE4A and PDE4D and a second directed against human recombinant PDE4B, revealed bands of immunoreactivity corresponding to approximately 125 kDa (PDE4A) and approximately 70 kDa (PDE4B), respectively, that increased in intensity after cells were treated with salbutamol and rolipram. As demonstrated in both time course and concentration-response studies with prostaglandin E2 (PGE2), an agent that activates adenylyl cyclase by a non-beta-adrenoceptor-mediated mechanism, cAMP accumulation was substantially decreased in cells in which PDE4 activity had been up-regulated. The difference in PGE2-stimulated cAMP accumulation between control and PDE4 up-regulated cells was greatly reduced in the presence of rolipram, consistent with the notion that an increase in PDE4 activity was responsible for the heterologous desensitization. Functionally, up-regulation of PDE4 markedly decreased the ability of PGE2 to inhibit LTD4-induced Ca2+ mobilization in intact cells. A hypothetical implication of these results is that increasing PDE4 activity in vivo by administering beta-adrenoceptor agonists could exacerbate inflammatory processes by decreasing the activity of endogenous anti-inflammatory agents such as PGE2.

The ability of phosphodiesterase IV inhibitors to suppress superoxide production in guinea pig eosinophils is correlated with inhibition of phosphodiesterase IV catalytic activity.

Elevation of cyclic AMP (cAMP) content inhibits eosinophil function. Because phosphodiesterase IV (PDE IV) appears to be the major PDE isozyme present in eosinophils, inhibitors of this isozyme should suppress eosinophil activation. Previous studies on PDE IV have revealed that this enzyme possesses both cAMP catalytic activity that is inhibitable by rolipram, a prototypical PDE IV inhibitor, and a high-affinity binding site for rolipram. The function of this high-affinity rolipram binding site relative to the inhibitory action of compounds is not clear because the rank order potency of PDE IV inhibitors for competing with [3H]-rolipram binding is distinct from that for inhibiting cAMP hydrolysis. Consequently, the present experiments were carried out to fulfill the following objectives: 1) to determine whether PDE IV inhibitors suppress eosinophil function and, if so, 2) to establish a correlation between this functional activity and inhibition of PDE IV catalytic activity or interaction with the high-affinity rolipram binding site. Various PDE inhibitors produced approximately 60% maximal inhibition of formylmethionine-leucine-phenylalanine-induced superoxide anion production, so that IC30 concentrations were used as a basis to compare the potency of various PDE inhibitors. Selective PDE IV inhibitors were the most potent compounds tested. PDE inhibitors selective for other isozymes were devoid of activity or considerably less potent.(ABSTRACT TRUNCATED AT 250 WORDS)

Initial biochemical and functional characterization of cyclic nucleotide phosphodiesterase isozymes in canine colonic smooth muscle.

Cyclic nucleotides mediate relaxation of gastrointestinal smooth muscle. The intracellular concentration of these second messengers is determined by a balance between their synthesis and metabolism. Because cyclic nucleotide phosphodiesterase enzymes (PDE) are the sole enzymes responsible for their degradation, it is essential to determine the role of the various PDE isozymes in regulating cyclic nucleotide content of gastrointestinal smooth muscle. To examine the role of different PDE isozymes in colonic smooth muscle motility, soluble PDE activity was measured in fractions obtained from homogenates of canine colon using DEAE sepharose chromatography. PDE activity was determined using [3H]cyclic AMP (cAMP) (1 microM) or [3H]cyclic GMP (cGMP) (1 microM) as a substrate. Results indicated that colonic smooth muscle contains at least two forms of PDE with a high affinity for cGMP. One form was stimulated by calmodulin (type I) and the other was inhibited by low concentrations of zaprinast (type V). In addition, colonic smooth muscle contains at least two isozymes that prefer cAMP as a substrate. One form was inhibited by SB 94120 and cGMP (type III) and the other by rolipram (type IV). An additional peak of PDE activity was identified. The hydrolysis of cAMP by this peak was greatly enhanced by the presence of cGMP, suggesting that this activity belonged to type II or cGMP-stimulated PDE. The functional role of these isozymes was evaluated by determining the ability of selective PDE inhibitors to antagonize a carbachol (0.3 microM)-induced contraction of isolated circular colonic muscle strips in the presence of forskolin (0.2 microM). Concentration-dependent decreases in contractile activity were observed with the following potency order: rolipram > Ro 20-1724 > isobutyl methylxanthine > SB 94120 > zaprinast. These results demonstrate that colonic smooth muscle contains several PDE isozymes and that selective inhibition of PDE isozymes can increase cyclic nucleotide content and antagonize contractile responses. Functionally, PDE IV appears to be very important in reducing contractile activity, suggesting that selective PDE IV inhibitors might be useful in the treatment of gut hypermotility disorders.

5-Hydroxytryptamine (5-HT) and SK&F 103829 contract canine lower esophageal sphincter smooth muscle by stimulating 5-HT2 receptors.

Addition of 5-HT or SK&F 103829 (2,3,4,5 tetrahydro-8[methyl-sulfonyl]-1 H-3-benzazepin-7-ol hydrobromide) contracts isolated strips of canine lower esophageal sphincter (LES) circular smooth muscle. 5-HT acts directly on the smooth muscle, since pretreatment with the neurotoxin TTX does not inhibit this contraction. Depletion of extracellular calcium or pretreatment with nifedipine inhibited the contraction to both 5-HT and SK&F 103829. Therefore, in this smooth muscle, the contraction produced by both 5-HT and SK&F 103829 requires extracellular calcium and is sensitive to inhibition by a voltage-dependent Ca2+ channel antagonist. In addition, with respect to 5-HT, SK&F 103829 appeared to act as a partial agonist. Receptor alkylation studies using phenoxybenzamine demonstrated no receptor reserve for the contractile response to 5-HT. Nonsurmountable antagonism of the contraction induced by 5-HT and SK&F 103289 was observed with several 5-HT2 antagonists, i.e., methysergide, ketanserin, cyproheptadine, and LY 53857. Using a method established for pseudoirreversible antagonism, the Ki values for these 5-HT2 receptor antagonists were estimated. Results suggested that both 5-HT and SK&F 103829 contract the canine LES by interacting at the same receptor site and that this receptor site has characteristics of the 5-HT2 receptor. Finally, neither bulbocapnine, domperidone, nor prazosin significantly alters the response to 5-HT or SK&F 103829. Thus, isolated strips of canine LES contain a contractile 5-HT2 receptor, and SK&F 103829 behaves as a partial agonist at this site.

Inhibition of neuronally induced relaxation of canine lower esophageal sphincter by opioid peptides.

Opioid peptides have profound effects on gut motility. To assess their actions on enteric neurons regulating sphincteric smooth muscle, the ability of several opioid agonists to antagonize the neuronally induced relaxation of canine lower esophageal sphincter smooth muscle was examined. Opioid peptides selective for mu (FK 33-824) or delta [( D-Pen2,D-Pen5]enkephalin) receptors produced a concentration dependent inhibition of electrical field stimulation (EFS)-induced relaxation. In contrast, neither kappa (ketocycloclazine) or sigma (SK & F 10047) opioid agonists were potent inhibitors of EFS-induced relaxation. This inhibition was relatively selective for opioid agonists since BHT 933 (alpha 2 adrenoceptor agonist) and SK & F 89124 (D2 dopamine agonist) did not inhibit EFS-induced relaxation. Furthermore, naloxone antagonized the effects of both FK 33-824 and DPDPE. These functional data suggest that opioid receptors are present on sphincteric intrinsic inhibitory neurons and that stimulation of these neuronal receptors can regulate lower esophageal sphincter relaxation.

Fuel-stimulated insulin secretion by clonal hamster beta-cell line HIT T-15.

Insulin secretion by monolayer cultures of HIT T-15 cells was measured in response to various fuel molecules (glucose, dihydroxyacetone, lactate, glutamine, alpha-ketoisocaproic acid, alpha-ketoisovaleric acid) and a nonmetabolized glucose analogue (3-O-methylglucose). HIT cells secreted insulin in response to fuel molecules, but 3-O-methylglucose was ineffective. Stimulation of insulin release by fuels was increased by isobutylmethylxanthine and blocked by antimycin A. Iodoacetate selectively inhibited glucose-stimulated insulin release but had little effect on alpha-ketoisocaproic acid-stimulated insulin secretion. These results indicate that HIT cells retain the capacity of normal beta-cells to act as fuel sensors. Thus, HIT cells may provide a well-defined and relatively abundant tissue source in studies of stimulus-secretion coupling in beta-cells stimulated by fuels.

Glucose transport by radiation-induced insulinoma and clonal pancreatic beta-cells.

Sugar uptake was measured in dispersed cells prepared from radiation-induced insulinomas transplantable in NEDH rats and in three clonal beta-cell lines maintained in continuous culture (RIN m5F, RIN 1046, HIT). Uptake of D-glucose and 3-O-methyl-D-glucose by insulinoma cells was rapid so that the intracellular concentration of D-hexoses approximated the concentration in the incubation medium by 15-30 s. L-Glucose was taken up only slowly. 3-O-methyl-D-glucose uptake by RIN m5F, RIN 1046, and HIT cells was slow; with 1 mM 3-O-methylglucose in the medium, equilibrium was attained at 20 min, but with 10 mM 3-O-methylglucose, equilibrium was not attained even at 20 min. In HIT cells incubated with D-glucose for 30 min, the intracellular concentration of glucose was less than the medium glucose concentration, indicating glucose transport is a nonequilibrium reaction in this cell line. These data indicate that radiation-induced insulinoma cells retain the capacity of normal beta-cells to transport sugar at high rates. RIN m5F, RIN 1046, and HIT cells transport sugar slowly, however, and thus differ from normal beta-cells. In RIN m5F, RIN 1046, and HIT cells, unlike in normal beta-cells, glucose transport may be the site regulating glucose metabolism.