Reduction In cAMP Content Research Articles

Study on antipyretic effect of Reduning injection on lipopolysaccharide-induced fever rats

To observe the antipyretic effect of Reduning injection (RDN) on lipopolysaccharide (LPS)-induced fever rats and its impact on centric fever medium. Rats were randomly divided into the blank control group, the model group, the Metamizole group, and high and low-dose RDN groups. Except for the blank control group, all of the rats were injected intraperitoneally with LPS (80 microg x kg(-1)) to observe their body temperature changes. The double-antibody sandwich ELSIA method was adopted to determine cAMP content in hypothalamus and MPO in lung tissues of fever peak rats. The high-dose RDN group can obviously reduce the temperature rise in fever rats, and cAMP and MPO content in hypothalamus. RDN showed significant antipyretic effect, which may be related with the reduction of cAMP content in hypothalamus and MPO in lung tissues.

Norepinephrine Inhibits Glucose-Stimulated, Ca2+-Independent Insulin Release Independently from Its Action on Adenylyl Cyclase.

Inhibition of insulin release by norepinephrine has been attributed to activation of ATP-sensitive K+ channels, inactivation of voltage-dependent Ca2+ channels, and inhibition of adenylyl cyclase. However, direct inhibitory action of norepinephrine at a distal site of stimulus-secretion coupling has also been suggested. To obtain more direct evidence for norepinephrine inhibition of insulin release at a distal site, we performed experiments in intact, non-permeabilized beta cells. In rat pancreatic islets, a combination of glucose, phorbol ester and forskolin under stringent Ca2+-free conditions was used as a trigger of insulin exocytosis at a distal site. Norepinephrine inhibited this Ca2+-independent insulin release in a concentration-dependent manner, with an IC50 of 50 nM. The inhibition was complete, reversible, and pertussis toxin-sensitive, and not associated with any reduction of cAMP content in the islet cells. In conclusion, norepinephrine strongly, yet reversibly, inhibits insulin release in intact beta cells at a late step of exocytosis, through pertussis toxin-sensitive, G protein-mediated mechanism(s).

Glucagon-like peptide-1(7-36)amide enhances insulin-stimulated glucose uptake and decreases intracellular cAMP content in isolated rat adipocytes.

We investigated the effect of GLPs on glucose uptake in isolated rat adipocytes. GLP-1(7-36)amide significantly enhanced glucose uptake in the presence of 1 nM insulin. GLP-1(7-36)amide at 15 nM increased glucose uptake maximally by 56.4% as compared with 1 nM insulin alone (P < 0.01). In contrast, with less than 1 nM insulin or without insulin GLP-1(7-36)amide showed no effect on glucose uptake. Full-sequence GLP-1(1-37) at 15 nM in the presence of 1 nM insulin increased glucose uptake by 24.6% as compared with 1 nM insulin alone (P < 0.05). GLP-2 showed no effect on glucose uptake. Further, we examined the effect of GLP-1(7-36)amide on cAMP content in isolated rat adipocytes. Insulin at 1 nM caused a significant decrease of cAMP content. The combination of 15 nM GLP-1(7-36)amide and 1 nM insulin caused a further reduction of cAMP content. These data indicate that GLP-1(7-36)amide possesses augmentative effects on insulin action in isolated rat adipocytes. Furthermore, it is suggested that the stimulatory effect of GLP-1(7-36)amide occurs through the reduction of intracellular cAMP content.

Characterization of a triple opioid system in the human neuroblastoma NMB cell line

The human neuroblastoma NMB cell line was found to contain the three types of opioid receptors (60% δ 25% κ and 15% μ). The opioid receptors were negatively coupled to adenylyl-cyclase. Maximal reduction in cAMP content was achieved by selectively activating single receptor types, indicating the co-presence of the various opioid receptors in the same cells. The opioid receptors in NMB cells were up-regulated following prolonged exposure to the opioid antagonist naloxone and down-regulated following chronic treatment with the opioid agonist etorphine. Down-regulation was time-, dose- and temperature-dependent and was inhibited by colchicine and sodium azide. The NMB culture is presented as an excellent experimental model for studying the selective activation and regulation of the different opioid receptor types when they are co-expressed in the same neuron, as well as for studying interactions between the various opioid receptors.

Effect of morphine and acetylcholine on contractile activity and cyclic AMP in guinea-pig ileum

Neither acute nor prolonged exposure to morphine altered cAMP content or spontaneous movements of longitudinal muscle-myenteric plexus strips of the guinea-pig ileum. By contrast, exogenous acetylcholine or electrical stimulation of the strips elicited both a decrease of cAMP concentration and a twitch response. Atropine blocked the effects of stimulation on these parameters. Addition of morphine to electrically stimulated strips inhibited the twitch response but did not affect cAMP levels. Incubation with morphine led to the development of tolerance to the inhibitory effect on twitch activity and prevented the fall in cAMP normally elicited by electrical stimulation. These results suggest that muscarinic activation is associated with a reduction of cAMP content, an effect which would be impaired in opiate-tolerant tissues.

Effects of adenosine analogues on contractile response and CAMP content in guinea-pig isolated ventricular myocytes

In the present study the effects of adenosine analogues were investigated on cAMP content and contractile response in guinea-pig ventricular myocytes. The adenosine analogues (-)-N6-phenylisopropyladenosine (R-PIA), 5'-N-ethylcarboxamideadenosine (NECA) and (+)-N6-phenylisopropyladenosine (S-PIA) in the presence of 0.01 mumol/l isoprenaline reduced contractile response concentration-dependently. R-PIA and NECA were about equipotent (IC25: 0.01 mumol/l and 0.039 mumol/l respectively), while S-PIA was less potent (IC25: 0.6 mumol/l). Isoprenaline stimulated cAMP content was reduced by R-PIA (IC25: 0.004 mumol/l) and with lower potency by S-PIA (IC25: 0.15 mumol/l), but the extent of reduction of cAMP by R-PIA and S-PIA (to 55% and 64% respectively) was less than the reduction of contractile response (to 26% and 55% respectively). This suggests that the effects of R- and S-PIA on contractile response are only in part due to a reduction in cAMP content. In addition, NECA did not decrease cAMP content but decreased contractile response to the same extent as R-PIA. Similar results were obtained in the presence of the phosphodiesterase inhibitor Ro 20-1724. Time course studies revealed that the effects of R-PIA (1 mumol/l) on cAMP content and contractile response coincided reaching steady state after 5 min and remained stable thereafter. The effects of NECA (1 mumol/l) on contractility also reached steady state within 5 min, whereas it did not change cAMP content. It is concluded that the reduction of contractility by adenosine analogues in the presence of isoprenaline can only in part be explained by a reduction of cAMP content.(ABSTRACT TRUNCATED AT 250 WORDS)

Bactericidal defect of neutrophils in a guinea pig model of thermal injury is related to elevation of intracellular cyclic-3',5'-adenosine monophosphate.

PG of the E series inhibit major effector functions of polymorphonuclear leukocytes (PMN) by elevating intracellular cAMP. The present study investigated the involvement of this mechanism in the bactericidal defect of PMN induced by thermal injury in a guinea pig model. Peripheral and peritoneal exudate PMN harvested from thermally injured guinea pigs at 1 or 2 days postburn had decreased bactericidal activity against Pseudomonas aeruginosa and a marked increase in cAMP content. Production of PGE1 by these cells in the absence of exogenous PMN activators was also increased. Treatment of PMN in vitro or in vivo with nonsteroidal anti-inflammatory drugs (indomethacin, ibuprofen, and piroxicam) restored bactericidal activity to normal and concomitantly reduced cAMP content and PGE1 production. A concomitant reduction in cAMP content and PGE1 production was also observed as bactericidal activity of PMN returned to normal under natural conditions during 4 to 7 days postburn. The enhancement of PMN bactericidal activity mediated by NSAID was fully counteracted by purified PGE1, theophylline, and by cAMP itself. These results suggest that the bactericidal defect of PMN induced by thermal injury is related to elevation of cAMP and that PGE1 plays a significant role in this phenomenon.

Relationship between calcium, cyclic AMP, ATP, and intracellular pH and the capacity of hamster spermatozoa to express hyperactivated motility

Capacitation of hamster caudal spermatozoa at a density of 1 x 10(6)/ml is associated with a progressive rise in cAMP levels that precedes the onset of hyperactivated motility. This increase is not expressed by caput spermatozoa incubated under identical conditions. Both the incidence of hyperactivation and the rise in cAMP levels are severely attenuated in the absence of exogenous calcium. Neither factor is restored to control levels by the addition of the phosphodiesterase inhibitor IBMX, although in the presence of exogenous calcium, this reagent increased cAMP levels, stimulated percentage motility and advanced the appearance of hyperactivation. Treatment of spermatozoa at a density of 1 x 10(6)/ml with the calmodulin antagonist, calmidazolium (CZ), caused severe disruption of sperm motility and abolished hyperactivation, while causing only a slight reduction in cAMP content. Addition of IBMX in the presence of CZ elevated cAMP content to levels higher than normally observed during capacitation but did not restore either coordinated or hyperactivated motility. To determine both the mechanisms responsible for this elevation of cAMP content and the changes that occur during epididymal maturation to facilitate the expression of this increase, the free cytosolic calcium concentration, ATP levels, and intracellular pH of caput and caudal cells were compared. The calcium content of caudal spermatozoa rose significantly at a time when cAMP levels were increasing, while ATP content and intracellular pH fell. However, the inability of caput spermatozoa to express a rise in cAMP content was not due to deficiencies in any of these factors. These results indicate a positive role for the cAMP rise in the expression of hyperactivated motility and that the fundamental control mechanism governing both these events may be the influx of calcium that accompanies capacitation in this species.

Cell cycle traverse and macromolecular synthesis in BHK fibroblasts as affected by insulin

Insulin produced a 10-fold activation of cAMP phosphodiesterase activity and a 3-fold reduction in cAMP content in serum-deprived, growth-arrested BHK fibroblasts. Insulin did not promote growth of these cells, as judged by measurement of cell number, but it did promote reentry of cells into the cell cycle and progression into S phase, as determined by rates of macromolecular synthesis, and autoradiographic and microfluorometric analyses. Insulin stimulation of macromolecular synthesis can be blocked by the addition of a phosphodiesterase inhibitor, suggesting that these effects of insulin on the cell cycle may be mediated through its activation of cAMP phosphodiesterase.

The influence of plasma proteins on human platelet metabolism.

Abstract This study, which focuses on certain essential parameters of platelet metabolic activity—oxygen consumption, lactate production and cyclic AMP (cAMP) content—indicates that platelet metabolism is significantly influenced by the plasma protein environment. Thus, platelet oxygen consumption in platelet-rich plasma was 88 per cent higher than oxygen consumption of washed platelets. Oxygen consumption of washed platelets could be restored to values comparable to those obtained for platelet-rich plasma by the addition to the washed platelet suspensions of either autologous plasma, purified albumin or purified IgG immunoglobulin. In contrast, the addition of fibrinogen and purified IgA myeloma protein from a patient with bleeding diathesis and platelet dysfunction had no effect on oxygen consumption of washed platelets. Platelet lactate production was identical in platelet-rich plasma and washed platelet suspensions. The addition to washed platelets of autologous plasma, albumin or gamma globulin did not affect lactate production; however, when either fibrinogen or the purified IgA myeloma protein were added to suspensions of washed platelets, lactate production increased significantly over the values observed in either platelet-rich plasma or washed platelets. cAMP levels were considerably lower in washed platelets than in platelets in platelet-rich plasma. When gamma globulin and albumin were added to suspensions of washed platelets, cAMP levels further decreased; and this reduction in cAMP content was progressive with time. In contrast, the addition of fibrinogen to suspensions of washed platelets caused no change in platelet cAMP content. Thus, different plasma proteins affected different parameters of platelet metabolism in different ways. Although an understanding of the mechanisms whereby plasma proteins affect platelet membrane function and metabolic activity is lacking, our experiments underscore the need for a concise definition of the plasma protein environment in the assessment of human platelet metabolism.