Naloxone produces hypothermia in rats pretreated with beta-endorphin and morphine

Functional effects of systemically administered agonists and antagonists of mu, delta, and kappa opioid receptor subtypes on body temperature in mice

We have investigated the roles of peripheral and central mu, delta, and kappa opioid receptors and their subtypes in opioid-induced hypothermia in mice. Measuring rectal temperature after i.p. injection, opioid agonists [morphine, fentanyl, SNC80 ((+)-4-[(alphaR)-alpha-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)3-methoybenzyl]-N,N-diethylbenzamide), U50,488H ((trans-(dl)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]-benzeneacetamide), and loperamide)] were tested alone or with opioid antagonists [naloxone, beta-funaltrexamine, naloxonazine, naltrindole, 7-benzylidenenaltrexone (BNTX), naltriben, nor-binaltorphimine, 2-(3,4-dichlorophenyl)-N-methyl-N-[(1S)-1-(3-isothiocyanatophenyl)-2-(1-pyrrolidinyl)ethyl]acetamide (DIPPA), and methyl-naltrexone] given 15 min after the agonist. All agonists produced dose-related hypothermia, although at low doses, morphine and U50,488H produced hyperthermia. The effects of morphine and fentanyl were antagonized by naloxone and by the mu(1) antagonist naloxonazine. The delta(2) antagonist naltriben potentiated the hypothermic effect of mu agonists. SNC80-induced hypothermia was blocked by the delta antagonist naltrindole but not by the delta(1) antagonist BNTX. Depending on the dose, the delta(2) antagonist naltriben produced either a potentiation or an attenuation of the effect of SNC80. U50,488H-induced hypothermia was antagonized by the kappa antagonist nor-binaltorphimine but not by acute treatment with the irreversible kappa antagonist DIPPA. The peripherally acting opioid loperamide produced hypothermia that could be blocked by several mu-, delta-, or kappa-selective antagonists as well as the peripherally acting antagonist methyl-naltrexone. Methyl-naltrexone produced a weak potentiation of morphine-, fentanyl-, and U50,488H-induced hypothermia, whereas a significant attenuation of SNC80-induced hypothermia was observed. In conclusion, at high doses, morphine- and fentanyl-induced hypothermia may involve composite action on mu, kappa, and possibly delta opioid receptors after initial activation. In the mediation of delta opioid-induced hypothermia, no clear selectivity between the delta(1) and delta(2) subtypes was defined. The studies provide new evidence that maintenance of the initial effects of agonist/receptor activation vary with the agonist and the receptor. The existence of both central and peripheral components of opioid-induced hypothermia is also emphasized.

Effects of central application of naloxone on the skin temperature response in morphine-dependent rats

This study was designed to identify if the surge in tail skin temperature (TST) observed following systemic administration of naloxone to morphine-dependent rats is mediated by a specific brain locus. Female rats were fitted with cannula located either in the preoptic area-anterior hypothalamus, locus coeruleus, or the frontal cortex. TST was monitored every 5 min for 60 min following central administration of naloxone (1-40 micrograms/0.4 microliters), in morphine-dependent rats. Regardless of the central site of naloxone injection, TST was significantly increased 4-5 degrees C. A threshold dose of 20 micrograms/0.4 microliters (10 micrograms/0.2 microliters, bilaterally) of naloxone was identified to produce this surge in TST in all three brain regions. These results suggest that morphine dependency sensitizes several brain regions to administration of naloxone such that the narcotic antagonist produces a similar change in TST as is observed following its systemic administration. These data further support the use of our morphine-dependent rat model to study the central mechanisms of the menopausal hot flush, and provide additional evidence that the flush response is centrally mediated.

Chronically administered morphine increases dopamine receptor sensitivity in mice

Chronic morphine treatment has been suggested to cause the development of supersensitive dopamine receptors. This increase in sensitivity was detected as a hypersensitivity in direct-acting dopamine agonists and as an increase in the affinity of dopamine receptors. However, these binding studies were performed in animals which had been withdrawn from morphine for a period of 24-48 h prior to killing. In the present study mice were implanted with pellets containing 75 mg of morphine free base. The pellets were left in situ in all experiments. One group of mice exhibited an increased sensitivity to apomorphine 72 h following pellet implantation as evidenced by a decrease in the ED50 of apomorphine for inducing cage climbing behavior. A second matched group of mice was found to have a significant increase in whole brain [3H]spiroperidol binding sites. These results suggest that chronic morphine treatment can cause the development of central supersensitive dopamine receptors. Lithium administered concurrently with the morphine attenuated the increased sensitivity to apomorphine and the increase in the number of [3H]spiroperidol binding sites. Concurrent lithium treatment also facilitated the degree of analgesic tolerance, and naloxone-induced withdrawal hypothermia. The ability of lithium to enhance analgesic tolerance while simultaneously attenuating the increase in dopamine receptors suggests that alterations in dopamine receptors might modify the degree of analgesic tolerance which develops to chronic morphine administration, or might modify the animal's response to thermal stimuli. The mechanism by which lithium enhanced naloxone-induced hypothermia is presently unknown.

Changes in body temperature after administration of acetylcholine, histamine, morphine, prostaglandins and related agents: II

This survey continues a second series of compilations of data regarding changes in body temperature induced by drugs and related agents. The information listed includes the species used, the route of administration and dose of drug, the environmental temperature at which experiments were performed, the number of tests, the direction and magnitude of change in body temperature and remarks on the presence of special conditions, such as age or brain lesions. Also indicated is the influence of other drugs, such as antagonists, on the response to the primary agent. Most of the papers were published since 1979, but data from many earlier papers are also tabulated.

Changes in body temperature after administration of amino acids, peptides, dopamine, neuroleptics and related agents: II

This survey begins a second series of compilations of data regarding changes in body temperature induced by drugs and related agents. The information listed includes the species used, the route of administration and dose of drug, the environmental temperature at which experiments were performed, the number of tests, the direction and magnitude of change in body temperature and remarks on the presence of special conditions, such as age or brain lesions. Also indicated is the influence of other drugs, such as antagonists, on the response to the primary agent. Most of the papers were published since 1978, but data from many earlier papers are also tabulated.

Endogenous opioid withdrawal in the Jarisch-Herxheimer reaction

Meptazinol, a partial opioid agonist, diminishes the Jarisch-Herxheimer reaction in relapsing fever whereas naloxone, a pure opioid antagonist, is virtually inert. Because endogenous opioid activity is probably increased in the acute phase, the efficacy of meptazinol is unlikely to be due to agonist activity. However, it is possible that in such a severe reaction there may be an exhaustion of endogenous opioids, giving rise to a naturally occurring quasi-morphine-withdrawal syndrome which responds to meptazinol.

Evidence against involvement of beta-endorphin in thermoregulation in the cat

In the cat naloxone has little, if any, effect on temperature under usual laboratory conditions and does not reduce febrile responses to leukocytic pyrogen. Hence, endogenous opioid peptides that are antagonized by naloxone are not essential for induction of fever or for maintenance of normal temperature in the absence of appreciable thermal stress. The purpose of this study was to assess the contribution of such endogenous opioids to thermoregulation in cats exposed to more severe thermal and non-thermal stresses. Changes in temperature of unanesthetized cats were determined after third cerebral ventricular injections of large doses (100, 250 micrograms) of naloxone or saline vehicle. Naloxone had no appreciable effect on the temperature of cats acutely exposed to hot (34 degrees C) or cold (4 degrees C) environments, either before or after tolerance to morphine had been induced by progressively greater daily or twice-daily intraventricular doses of 10-70 micrograms morphine sulfate. Naloxone also did not significantly affect the temperature of cats subjected to neck-restraint or forced to stand on a small platform if they were to avoid contact with ice water. These results provide no indication that an endogenous opioid peptide, such as beta-endorphin, that is antagonized by naloxone contributes appreciably to thermoregulation in cats. They do not rule out the possibility that endogenous opioids, such as Met-enkephalin, that are not readily antagonized by naloxone are important for normal thermoregulation.

Involvement of both opiate and catecholaminergic receptors in the behavioural excitation provoked by thyrotropin-releasing hormone: comparisons with amphetamine

Following direct administration of thyrotropin-releasing hormone (TRH), but not thyroid-stimulating hormone (TSH) or vehicle solution, into the lateral cerebral ventricle in rats, three main categories of behaviour were provoked: activity of the normal type--stimulation of forward locomotion, head and body rearing (as shown by an enhancement in gross movements); stereotyped activity--increased grooming and head swaying (as shown by an enhancement in fine movements); abnormal behaviour--tail elevation and piloerection (as observed grossly). The behavioural excitation caused by TRH was antagonized by pretreatment of the rats with either a narcotic receptor antagonist, naloxone, an alpha-adrenergic receptor antagonists, yohimbine, or a dopaminergic receptor antagonist, haloperidol, but not with a beta-adrenergic receptor antagonist, propranolol. Intraventricular administration of amphetamine to rats caused stimulation of forward locomotion, head and body rearing, increased grooming and sniffing. Unlike TRH, amphetamine did not produce wet-dog shakes, tail elevation and piloerection. Furthermore, the amphetamine-induced excitation was antagonized by pretreatment with a dopaminergic receptor antagonist, haloperidol, but not with either naloxone, yohimbine or propranolol. The data indicate that both opiate and catecholaminergic receptors are involved in the TRH-induced behavioural excitation, whereas dopaminergic receptors are involved in amphetamine-induced excitement in the rat.

Effects of ethanol on thermoregulation

Clinical reports of accidental hypothermia in alcohol intoxicated individuals exposed to low ambient temperature ( Paton , 1983) have generally been borne out by experimental studies in healthy volunteers. Small doses of ethanol, given to human subjects at normal ambient temperature (Ta), have very little effect on body temperature but a combination of large dose, low Ta and vasodilatation provoked by strenuous exercise, causes a sharp fall in rectal temperature. In experimental animals, the use of relatively larger doses of alcohol and more extreme temperatures, both above and below the thermoneutral zone, has shown that the effect of ethanol is essentially poikilothermic, i.e. an impairment of adaptation to both heat and cold. This effect has been studied in greater detail, in relation to each of the basic thermoregulatory processes. Though small doses of alcohol may increase the metabolic rate under some circumstances, the most common effect at low Ta is inhibition of shivering and therefore reduction of thermogenesis. At the same time it tends to cause increased heat loss by cutaneous vasodilatation. This makes for a greater feeling of comfort in the cold exposed subjects but increases in rate of fall of core temperature. The combination of decreased thermogenesis and increased heat loss, despite falling body temperature, is suggestive of a lowering of the set-point of the thermoregulatory control mechanisms. Consistent with this is a slight increase in ventilatory heat loss after low doses of ethanol but larger doses cause respiratory depression, so that heat loss through the lungs is minor. However, at high Ta ethanol caused hyperthermia in experimental animals and shows enhanced lethality, so that impairment of thermoregulatory effector mechanisms seems to be at least as important as change in set-point. Studies of the effects of ethanol on electrophysiological activity of single neurons in the pre-optic area and anterior hypothalamus (POAH), biochemical activities of neuronal membranes, hypothalamic blood flow, conventional neurotransmitters, amino acid putative neurotransmitters, neuropeptides, prostaglandins and inorganic ions have all failed so far to yield a clear comprehensive picture of the mechanisms by which ethanol affects thermoregulation. In each case, contradictory evidence has been obtained concerning the consequences of ethanol administration, whether by oral, intraperitoneal, intravenous, intracerebroventricular, or direct local (POAH) route.(ABSTRACT TRUNCATED AT 400 WORDS)

An adrenergic link in the hypothalamic pathways which mediates morphine- and beta-endorphin-induced hyperthermia in the rat

The mechanism underlying the hyperthermia induced by intrahypothalamic administration of either morphine or beta-endorphin has been investigated in conscious rats. Direct administration of morphine (1--8 micrograms in 1 microliter) or beta-endorphin (1--3 micrograms in 1 microliter) into the anterior hypothalamus caused hyperthermia in rats at the ambient temperature (8, 22 and 30 degrees C) studied. The hyperthermia in response to opiods was brought about by both increased metabolism and cutaneous vasoconstriction. This hyperthermia, unlike the hypothermia induced by intraventricular administration of opiods was not blocked by naloxone nor did tolerance develop to the response. However, the hypothermia induced by intrahypothalamic administration of opioids was greatly reduced by pretreatment with intrahypothalamic administration of either yohimbine (a blocking agent of alpha-adrenergic receptors) or DL-propranolol (a blocking agent of beta-adrenergic receptors) in the rat. These observations suggest that an adrenergic link occurs in the hypothalamic pathways which mediate morphine- and beta-endorphin-induced hyperthermia in the rat.

Dynorphin (1-13): analgesia, hypothermia, cross-tolerance with morphine and beta-endorphin

Intracerebroventricular administration of 20, 40 and 60 nmol of dynorphin (1-13) produced analgesia, as assessed by flinch/jump response to footshock, and hypothermia in the rat. Rats developed tolerance to both the analgesic and thermic effects of the 20 nmol dose of dynorphin. Dynorphin and beta-endorphin showed cross-tolerance with respect to their analgesic but not their thermic effects. Dynorphin and morphine also produced cross-tolerant analgesic effects. Naloxone (10 mg/kg, IP) completely blocked the barrel rolling produced by 20 nmol dynorphin but did not alter its analgesic or thermic effects.

Peptides and thermoregulation

Several peptides are now known to affect thermoregulation. These include beta-endorphin, bombesin, MIF-I, alpha-MSH, neurotensin, TRH, and DSIP. Some of these have been found to interact with the thermal effects of d-amphetamine, a drug with well established actions on thermoregulation. The effects of morphine on body temperature provide some notable comparisons with beta-endorphin, as do the similarities between the effects of naloxone and MIF-I. In general, it seems that two of the major variables which interact and modify the thermal effects of peptides are ambient temperature and route of administration.