Hypothermic effects of alkylxanthines: evidence for a calcium-independent phosphodiesterase action

Inhibition of type 4 cAMP-phosphodiesterases (PDE4s) in mice induces hypothermia via effects on behavioral and central autonomous thermoregulation

Inhibitors of Type 4 cAMP-phosphodiesterases (PDE4s) exert a number of promising therapeutic benefits, including potent anti-inflammatory, memory- and cognition-enhancing, metabolic, and antineoplastic effects. We report here that treatment with a number of distinct PDE4 inhibitors, including Rolipram, Piclamilast, Roflumilast and RS25344, but not treatment with the PDE3-selective inhibitor Cilostamide, induces a rapid (10-30 min), substantial (-5 °C) and long-lasting (up to 5 h) decrease in core body temperature of C57BL/6 mice; thus, identifying a critical role of PDE4 also in the regulation of body temperature. As little as 0.04 mg/kg of the archetypal PDE4 inhibitor Rolipram induces hypothermia. As similar or higher doses of Rolipram were used in a majority of published animal studies, most of the reported findings are likely paralleled by, or potentially impacted by hypothermia induced by these drugs. We further show that PDE4 inhibition affects central body temperature regulation and acts by lowering the cold-defense balance point of behavioral (including posture and locomotion) and autonomous (including cutaneous tail vasodilation) cold-defense mechanisms. In line with the idea of an effect on central body temperature regulation, hypothermia is induced by moderate doses of various brain-penetrant PDE4 inhibitors, but not by similar doses of YM976, a PDE4 inhibitor that does not efficiently cross the blood-brain barrier. Finally, to begin delineating the mechanism of drug-induced hypothermia, we show that blockade of D2/3-type dopaminergic, but not β-adrenergic, H1-histaminergic or opiate receptors, can alleviate PDE4 inhibitor-induced hypothermia. We thus propose that increased D2/3-type dopaminergic signaling, triggered by PDE4 inhibitor-induced and cAMP-mediated dopamine release in the thermoregulatory centers of the hypothalamus, is a significant contributor to PDE4 inhibitor-induced hypothermia.

Low, but not high, dose caffeine is a readily available probe for adenosine actions

Caffeine is very widely used and knowledge of its mode of action can be used to gain an understanding of basal physiological regulation. This review makes the point that caffeine is - in low doses - an antagonist of adenosine acting at A₁, A_2A and A_2B receptors. We use published and unpublished data to make the point that high dose effects of caffeine are not only qualitatively different but have a different underlying mechanism. Therefore one must be careful in only using epidemiological or experimental data where rather low doses of caffeine are used to draw conclusions about the physiology and pathophysiology of adenosine.

Effects of paraxanthine and caffeine on sleep, locomotor activity, and body temperature in orexin/ataxin-3 transgenic narcoleptic mice

STUDY OBJECTIVE

Caffeine, an adenosine A1 and A2a receptor antagonist, is a widely consumed stimulant and also used for the treatment of hypersomnia; however, the wake-promoting potency of caffeine is often not strong enough, and high doses may induce side effects. Caffeine is metabolized to paraxanthine, theobromine, and theophylline. Paraxanthine is a central nervous stimulant and exhibits higher potency at A1 and A2 receptors, but has lower toxicity and lesser anxiogenic effects than caffeine.

DESIGN

We evaluated the wake-promoting efficacy of paraxanthine, caffeine, and a reference wake-promoting compound, modafinil, in a mice model of narcolepsy, a prototypical disease model of hypersomnia. Orexin/ataxin-3 transgenic (TG) and wild-type (WT) mice were subjected to oral administration (at ZT 2 and ZT14) of 3 doses of paraxanthine, caffeine, modafinil, or vehicle.

RESULTS

Paraxanthine, caffeine, and modafinil significantly promoted wakefulness in both WT and narcoleptic TG mice and proportionally reduced NREM and REM sleep in both genotypes. The wake-promoting potency of 100 mg/kg p.o. of paraxanthine during the light period administration roughly corresponds to that of 200 mg/kg p.o. of modafinil. The wake-promoting potency of paraxanthine is greater and longer lasting than that of the equimolar concentration of caffeine, when the drugs were administered during the light period. The wake-promotion by paraxanthine, caffeine, and modafinil are associated with an increase in locomotor activity and body temperature. However, the higher doses of caffeine and modafinil, but not paraxanthine, induced hypothermia and reduced locomotor activity, thereby confirming the lower toxicity of paraxanthine. Behavioral evaluations of anxiety levels in WT mice revealed that paraxanthine induced less anxiety than caffeine did.

CONCLUSIONS

Because it is also reported to provide neuroprotection, paraxanthine may be a better wake-promoting agent for hypersomnia associated with neurodegenerative diseases.

Oseltamivir, an anti-influenza virus drug, produces hypothermia in mice

Oseltamivir phosphate (Tamiflu), an anti-influenza virus drug, is hydrolyzed by carboxylesterase to an active metabolite. The metabolite inhibits the influenza virus-specific neuraminidase. In this study, the effects of oseltamivir on normal core body temperature were studied in mice. Oseltamivir (30-300 mg/kg, intraperitoneally (i.p.) and 100-1000 mg/kg, orally (p.o.)) dose-dependently lowered the body temperature. The effects of oseltamivir (p.o.) continued longer than those of oseltamivir (i.p.), and approximately triple doses of oral oseltamivir were needed to produce the same peak effects as intraperitoneal oseltamivir. The non-steroidal anti-inflammatory drug diclofenac (1-30 mg/kg, i.p.) did not affect body temperature, and (at 30 and 60 mg/kg, s.c.) did not interact with the hypothermic effects of oseltamivir (100 mg/kg, i.p.). Zanamivir, which also inhibits neuraminidase, did not produce hypothermia at doses of 100 and 300 mg/kg, i.p. Clopidogrel (100, 300 mg/kg, i.p.), which is metabolized by the same carboxylesterase, tended to decrease the hypothermic effects of oseltamivir (100 mg/kg, i.p.). These results suggest that the hypothermic effects of oseltamivir are due to its hydrolytic metabolite, and that the hypothermia observed in mice has some relationship to the antipyretic effects and severe hypothermia (adverse event) observed in influenza patients after taking oseltamivir.

Sex differences in mouse heart rate and body temperature and in their regulation by adenosine A1 receptors

AIM

To examine cardiac function, body temperature and locomotor behaviour in the awake adenosine A(1) receptor knock out mouse of both sexes.

METHODS

Male and female A(1)R (+/+) and (-/-) mice, instrumented with telemetric devices, were recorded during basal conditions and after drug administration.

RESULTS

Female mice had higher heart rate, body temperature and locomotion, both during daytime and during the night. Awake A(1)R (-/-) mice had a slightly elevated heart rate, and this was more clear-cut in males. Heart rate was also higher in Langendorff-perfused denervated A(1)R (-/-) hearts. Body temperature was higher in A(1)R (-/-) males and females; locomotor activity was higher in A(1)R (-/-) females, but not in males. The adenosine receptor agonist R-PIA (0.2 mg kg(-1)) decreased heart rate and body temperature, but less in A(1)R (-/-) animals than in A(1)R (+/+) mice (P < 0.001 in both parameters). The unselective adenosine receptor antagonist caffeine had a minor stimulatory effect on heart rate in lower doses, but depressed it at a dose of 75 mg kg(-1). Body temperature was increased after a low dose (7.5 mg kg(-1)) of caffeine in both sexes and genotypes, and markedly reduced after a high dose (75 mg kg(-1)) of caffeine. An intermediary dose of caffeine 30 mg kg(-1) increased or decreased body temperature depending on genotype and sex. Locomotor responses to caffeine were variable depending both on genotype and sex.

CONCLUSION

Thus, the adenosine A(1) receptor is involved in the regulation of heart rate, body temperature and locomotor activity, but the magnitude of the involvement is different in males and females.

Role of nitric oxide in systemic effect of theophylline on mouse body temperature

In the present study, the interaction of nitric oxide synthase (NOS) inhibitors, L-NAME (N(G)-nitro-L-arginine methyl ester HCl) and L-NA (N(omega)-nitro-L-arginine), and its precursor, L-arginine (2-(S)-2-amino-5-[(aminoiminomethyl)amino] pentatonic acid), with theophylline on mouse body temperature was studied. Intraperitoneal (i.p.) injection of different doses of theophylline altered body temperature. Lower doses of theophylline (12.5 and 25 mg/kg) increased, but a higher dose (100 mg/kg) reduced, the animals' body temperature. The combination of L-arginine (20 and 40 mg/kg) with the highest dose of theophylline potentiated the hypothermic effect induced by the latter drug, while L-arginine by itself did not alter body temperature. L-NAME (10-80 mg/kg) or L-NA (10 mg/kg) plus a lower dose of theophylline (12.5 mg/kg) reduced the theophylline-induced hyperthermic response. L-NA (1, 5, and 10 mg/kg) in combination with the high dose of theophylline (100 mg/kg) also induced greater hypothermia. Both L-NAME and L-NA by themselves reduced body temperature. It is concluded that nitric oxide (NO) may be involved in the effects of theophylline on body temperature in mice.

On the mechanisms by which theophylline changes core body temperature in mice

In the present work, the effects of neurotransmitter antagonists on theophylline-induced changes in body temperature were investigated. Intraperitoneal (i.p.) administration of a low dose of theophylline (25 mg/kg) induced slight hyperthermia, while high doses (75 and 100 mg/kg) induced hypothermia. The hypothermic effect of theophylline was decreased by pretreatment of animals with the dopamine D2 receptor antagonists sulpiride (15 and 30 mg/kg i.p.) and pimozide (0.125 and 0.25 mg/kg i.p.), the muscarinic receptor antagonist atropine (2.5 and 5 mg/kg i.p.) and the 5-HT receptor antagonist metergoline (0.25 mg/kg i.p.). However, the dopamine D1 receptor antagonist SCH 23390 (0.05 and 0.5 mg/kg i.p.), the alpha-adrenoceptor antagonist phenoxybenzamine (2.5 and 5 mg/kg i.p.) and the beta-adrenoceptor antagonist propranolol (5 and 10 mg/kg i.p.) did not after the theophylline response. In reserpinized mice, theophylline caused a dose-dependent rise in body temperature. The response was blocked in animals pretreated with phenoxybenzamine, propranolol and atropine. Single treatment of animals with either SCH 23390 or sulpiride, and also with a combination of the two drugs, decreased the hyperthermia induced by theophylline in reserpinized mice. Pimozide or metergoline did not have any effect in this respect. These data suggest that the hypothermic response to theophylline may be mediated through dopaminergic, cholinergic and serotonergic mechanisms. The hyperthermic action of theophylline in reserpinized animals may be mediated through dopaminergic, cholinergic and adrenergic systems. Overall it seems likely that theophylline interacts with modulatory mechanisms involved in thermoregulation.

Opioid receptor mediation of the hypothermic response to caffeine

Caffeine and other methylxanthines induce a dose-dependent reduction in core body temperature in mice. These experiments investigated the effects of neurotransmitter and neuromodulator antagonists on caffeine-induced hypothermia. Pretreatment with the alpha 2-adrenoceptor antagonist, atipamezole; the beta-adrenoceptor antagonist, propranolol; the dopamine antagonist, haloperidol; or the benzodiazepine receptor antagonist, flumazenil had no intrinsic effects on core body temperature nor did they interact significantly with the hypothermic effects of caffeine. The alpha 1-adrenoceptor antagonist, prazosin and the 5-HT receptor antagonist, metergoline significantly enhanced the hypothermic effects of caffeine, probably involving a combined effect with their intrinsic hypothermic actions. Pretreatment with the opiate receptor antagonist, naloxone (3 mg/kg i.p.), had no intrinsic effect on core body temperature but attenuated the hypothermic effect of caffeine reflected in a parallel shift to the right in the caffeine dose-effect curve. The naloxone-induced attenuation of the hypothermic effects of caffeine was also seen to be dose-dependent. The results reveal that opiate receptors (but not adrenoceptors, 5-HT, dopamine or benzodiazepine receptors) may play a role in modulating the hypothermic action of caffeine and possibly other methylxanthines.