cyclic-gmp and Hypothermia

Rewarming from accidental hypothermia could be complicated by acute cardiac dysfunction but providing supportive pharmacotherapy at low core temperatures is challenging. Several pharmacological strategies aim to improve cardiovascular function by increasing cAMP in cardiomyocytes as well as cAMP and cGMP levels in vascular smooth muscle, but it is not clear what effects temperature has on cellular elimination of cAMP and cGMP. We therefore studied the effects of differential temperatures from normothermia to deep hypothermia (37 °C-20 °C) on cAMP levels in embryonic H9c2 cardiac cells and elimination of cAMP and cGMP by PDE-enzymes and ABC-transporter proteins. Our experiments showed significant elevation of intracellular cAMP in H9c2-cells at 30 °C but not 20 °C. Elimination of both cAMP and cGMP through ABC transport-proteins and PDE-enzymes showed a temperature dependent reduction. Accordingly, the increased cardiomyocyte cAMP-levels during moderate hypothermia appears an effect of preserved production and reduced elimination at 30 °C. This correlates with earlier in vivo findings of a positive inotropic effect of moderate hypothermia.

Topics: Cryopreservation; Cyclic AMP; Cyclic GMP; Humans; Hypothermia; Myocytes, Cardiac; Rewarming

Rewarming from hypothermia is associated with severe complications, one of which is hypothermia-induced cardiac dysfunction. This condition is characterized by decreased cardiac output accompanied by increased total peripheral resistance. This contributes to mortality rate approaching 40%. Despite this, no pharmacological interventions are recommended for these patients below 30 °C. Raising the intracellular levels of cAMP and/or cGMP, through PDE3- and PDE5-inhibitors respectively, have showed the ability to alleviate hypothermia-induced cardiac dysfunction in vivo. Drugs that raise levels of both cAMP and cGMP could therefore prove beneficial in patients suffering from hypothermia-induced cardiac dysfunction.. The unselective PDE-inhibitor pentoxifylline was investigated to determine its ability to reach the intracellular space, inhibit PDE3 and PDE5 and inhibit cellular efflux of cAMP and cGMP at temperatures 37, 34, 30, 28, 24 and 20 °C. Recombinant human PDE-enzymes and human erythrocytes were used in the experiments. IC. At 20 °C, the IC. This study shows that pentoxifylline has minimal temperature-dependent pharmacodynamic changes, and that it can inhibit elimination of both cAMP and cGMP at low temperatures. This can potentially be effective treatment of hypothermia-induced cardiac dysfunction.. Not applicable.

Topics: Cyclic AMP; Cyclic GMP; Heart Diseases; Humans; Hypothermia; Pentoxifylline

Hypoxia causes a regulated decrease in body temperature (Tb), a response that has been aptly called anapyrexia, but the mechanisms involved are not completely understood. The roles played by nitric oxide (NO) and other neurotransmitters have been documented during hypoxia-induced anapyrexia, but no information exists with respect to hydrogen sulfide (H(2)S), a gaseous molecule endogenously produced by cystathionine β-synthase (CBS). We tested the hypothesis that H(2)S production is enhanced during hypoxia and that the gas acts in the anteroventral preoptic region (AVPO; the most important thermosensitive and thermointegrative region of the CNS) modulating hypoxia-induced anapyrexia. Thus, we assessed CBS and nitric oxide synthase (NOS) activities [by means of H(2)S and nitrite/nitrate (NO(x)) production, respectively] as well as cyclic adenosine 3',5'-monophosphate (cAMP) and cyclic guanosine 3',5'-monophosphate (cGMP) levels in the anteroventral third ventricle region (AV3V; where the AVPO is located) during normoxia and hypoxia. Furthermore, we evaluated the effects of pharmacological modifiers of the H(2)S pathway given i.c.v. or intra-AVPO. I.c.v. or intra-AVPO microinjection of CBS inhibitor caused no change in Tb under normoxia but significantly attenuated hypoxia-induced anapyrexia. During hypoxia there were concurrent increases in H(2)S production, which could be prevented by CBS inhibitor, indicating the endogenous source of the gas. cAMP concentration, but not cGMP and NO(x), correlated with CBS activity. CBS inhibition increased NOS activity, whereas H(2)S donor decreased NO(x) production. In conclusion, hypoxia activates H(2)S endogenous production through the CBS-H(2)S pathway in the AVPO, having a cryogenic effect. Moreover, the present data are consistent with the notion that the two gaseous molecules, H(2)S and NO, play a key role in mediating the drop in Tb caused by hypoxia and that a fine-balanced interplay between NOS-NO and CBS-H(2)S pathways takes place in the AVPO of rats exposed to hypoxia.

Topics: Aminooxyacetic Acid; Analysis of Variance; Animals; Body Temperature; Cyclic AMP; Cyclic GMP; Dose-Response Relationship, Drug; Enzyme Inhibitors; Hydrogen Sulfide; Hypothermia; Hypoxia; Male; Microinjections; Nitrates; Nitric Oxide Synthase; Nitrites; Preoptic Area; Rats; Rats, Wistar; Sulfides; Third Ventricle; Time Factors

Central heme oxigenase-carbon monoxide (HO-CO) pathway has been shown to play a pyretic role in the thermoregulatory response to restraint. However, the specific site in the central nervous system where CO may act modulating this response remains unclear. LC is rich not only in sGC but also in heme oxygenase (HO; the enzyme that catalyses the metabolism of heme to CO, along with biliverdin and free iron). Therefore, the possible role of the HO-CO-cGMP pathway in the restraint-induced-hypothermia by LC neurons was investigated. Body temperature dropped about 0.7 degrees C during restraint. ZnDPBG (a HO inhibitor; 5 nmol, intra-LC) prevented the hypothermic response during restraint. Conversely, induction of the HO pathway in the LC with heme-lysinate (7.6 nmol, intra-LC) intensified the hypothermic response to restraint, and this effect was prevented by pretreatment with ODQ (a sGC inhibitor; given intracerebroventricularly, 1.3 nmol). Taken together, these data suggest that CO in the LC produced by the HO pathway and acting via cGMP is implicated in thermal responses to restraint.

Topics: Animals; Behavior, Animal; Body Temperature; Carbon Monoxide; Cyclic GMP; Deuteroporphyrins; Enzyme Inhibitors; Heme; Heme Oxygenase (Decyclizing); Hypothermia; Locus Coeruleus; Lysine; Male; Microinjections; Rats; Rats, Wistar; Restraint, Physical

Topics: Anesthetics, Intravenous; Animals; Cerebellum; Cyclic GMP; Hypothermia; Ketamine; Mice; Nitric Oxide; Nitric Oxide Synthase; Pentobarbital; Proto-Oncogene Proteins c-fos; Riluzole; Signal Transduction; Thiazoles

In in vitro studies, SR 48692, a nonpeptide neurotensin receptor antagonist, inhibited the binding of [3H] or [125I]neurotensin to membrane preparations from 10-day-old mouse brains and from HT-29 cells with Ki values of 3.9 and 8.6 nM, respectively. SR 48692 also antagonized the neurotensin-induced mobilization of intracellular calcium in HT-29 cells, in agreement with previous findings. In rat cerebellar slices SR 48692 blocked the increase in cyclic GMP levels evoked by neurotensin in a dose-dependent manner. In vivo, SR 48692 antagonized the increase in rat brain mesolimbic dopamine turnover induced by the systemically active neurotensin peptide, EI [(N-Me)Arg-Lys-Pro-Trp-tert-Leu-Leu]. No effects on dopamine turnover of either EI or SR 48692 were observed in the striatum. SR 48692 did not antagonize the EI-induced decreases in mouse body temperature and spontaneous locomotor activity (LMA) or the decreases in LMA induced by ICV-administered neurotensin. Although other explanations are possible, these findings support the hypothesis that a subtype of the NT receptor may mediate the locomotor and hypothermic actions of this peptide and that it is different from the NT receptor that is involved in dopamine turnover.

Topics: Animals; Brain Chemistry; Calcium; Carcinoma; Cells, Cultured; Colonic Neoplasms; Cyclic GMP; Dopamine; Humans; Hypothermia; Locomotion; Male; Membranes; Mice; Neurotensin; Oligopeptides; Psychotropic Drugs; Pyrazoles; Quinolines; Radioligand Assay; Rats

Hypothermia has previously been demonstrated to induce supersensitivity (defined as a decrease in the ED50) of guinea pig left atria to the negative inotropic effect of carbachol. In the present investigation, the dissociation constant (pKA or -log KA) for carbachol, determined using benzilylcholine mustard, was found to be significantly increased at 25 degrees C compared to 37 degrees C. However, the increase in pD2 (-log ED50) for carbachol at 25 degrees C was much less than would be predicted from the increase in pKA. Increasing the extracellular Ca2+ concentration or the frequency of stimulation, both of which, like hypothermia, are believed to increase Ca2+ influx into cardiac cells, resulted in a decrease in sensitivity to carbachol. Carbachol had no significant effect on cAMP or cGMP levels at either 37 degrees C or at 25 degrees C. These results suggest that the hypothermia-induced increase in sensitivity of left atria to carbachol can be explained by an increase in the affinity of the muscarinic receptor for this agonist. However, the expression of this increased affinity appears to be limited. This may be due to a concurrent decrease in the efficacy of the carbachol muscarinic receptor complex.

Topics: Animals; Calcium; Carbachol; Cyclic AMP; Cyclic GMP; Female; Guinea Pigs; Heart Atria; Hypothermia; In Vitro Techniques; Male; Myocardial Contraction; Receptors, Muscarinic

Sodium nitroprusside (NP) was found to decrease the tissue lactate level under conditions of high (HiOxSa) and low (hypoxia) oxygen saturation in spontaneously beating rat atria. Nitroprusside also increased the level of cyclic GMP (cGMP) in a dose-dependent manner in both states. The time course and dose dependence of these effects suggest that cGMP might be responsible for the decreased tissue level of lactate demonstrated. The findings suggest that cGMP might inhibit lactate production in HiOxSa and antagonize the hypoxia-induced acceleration of anaerobic metabolism. It is proposed that a state of low-rate glycolysis results from this inhibitory effect of cGMP. Furthermore, the possible role of cGMP as a feed-back regulator of the redox state is discussed in the light of these findings.

Topics: Animals; Cyclic GMP; Dose-Response Relationship, Drug; Ferricyanides; Glycolysis; Hypothermia; Hypoxia; In Vitro Techniques; Lactates; Lactic Acid; Male; Myocardial Contraction; Myocardium; Nitroprusside; Rats; Rats, Inbred Strains

Topics: Animals; Body Temperature; Body Temperature Regulation; Cats; Cyclic GMP; Dibutyryl Cyclic GMP; Fever; Hypothermia; Injections, Intraventricular; Time Factors