Peptide and non-peptide opioid-induced hyperthermia in rabbits

Effect of dermorphin on thermoregulation in rats at selected ambient temperatures

Intraperitoneal administration of dermorphin caused dose-dependent changes in rats core temperature and tail skin temperature (indicative of compensatory thermoregulatory vasoreactions in rats). The character of these changes depended strongly on the environmental temperature at which the inversion of the dermorphin-induced thermoregulatory effect was observed. In the cold environment (4-7 degrees C) dermorphin caused a significant, stable, dose-dependent hypothermia. In the thermoneutral environment (27-28 degrees C) dermorphin also caused hypothermia, but this effect was less pronounced. In the hot environment (31-32 degrees C) dermorphin caused hyperthermia. Dermorphin-induced changes in tail skin temperature indicate that dermorphin suppresses the thermoregulatory peripheral compensatory vasomotor reactions. Pretreatment with naloxone attenuated dermorphin-induced effects on core temperature and partially enhanced vasomotor effects of dermorphin. The data obtained indicate that dermorphin affects the core temperature regulation via mu-opiate receptors, whereas vasomotor effects of the peptide are probably mediated via naloxone-insensitive receptors.

The effect of neurotensin, TRH and the delta-opioid receptor antagonist ICI 174864 on alcohol-induced narcosis in rats

The effects of microinjections of thyrotropin-releasing hormone (TRH), neurotensin and ICI 174864 into the nucleus accumbens, nucleus caudatus, septum and mesencephalic periaqueductal grey were studied on ethanol-induced narcosis in the rat. Levels of narcosis were assessed by alterations in ethanol-induced hypothermia and sleep time. Ethanol produces a 2 degree C fall in body temperature over the first hour which then recovered over the next 2 h. Sedation was produced to the extent that the righting reflex was lost for between 80 and 90 min. In the nucleus caudatus all 3 peptides were ineffective at altering narcosis. In the periaqueductal grey, septum and accumbens, TRH (5 micrograms) and ICI 174864 (1 microgram) microinjections significantly reduced the sleep time by between 50 and 70%. ICI 174864 was approximately 10 times more potent that TRH at reducing the sleep time. In addition, both these peptides significantly accelerated the recovery from the ethanol-induced hypothermia in the periaqueductal grey, septum and accumbens. ICI 174864 prevented the ethanol-induced fall in body temperature. Neurotensin (5 micrograms) significantly increased the sleep time by up to 50% and potentiated the ethanol-induced hypothermia. These results suggest that the administration of TRH or the blockade of delta-opioid receptors, resulting in an inhibition of endogenous enkephalin transmission, may significantly inhibit ethanol narcosis in the rat. Opposing this, the application of neurotensin appears to potentiate ethanol narcosis. These results also indicate that endogenous enkephalin release plays an important role in ethanol narcosis.

Changes in body temperature after administration of antipyretics, LSD, delta 9-THC and related agents: II

Antipyretics, in particular acetaminophen, aspirin and ibuprofen, constitute the single most important class of drugs used therapeutically for an effect on body temperature. Hallucinogens exert prominent actions on the central nervous system, and it is not surprising that, like so many other centrally-acting agents, they too often affect temperature. This compilation primarily covers the considerable amount of data published from 1981 through 1985 on the interactions of these drugs and thermoregulation, but data from many earlier papers not included in a previous compilation are also tabulated. The effects of agents not classically considered as antipyretics on temperatures of febrile subjects are also covered. 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 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.

Seasonal difference in thermoregulatory responses to opiates in a mammalian hibernator

Accumulated evidence suggests that increased endogenous opioid activities may facilitate the onset of hibernation. The present study investigated the change in thermoregulatory responses following ICV infusion of morphine or [D-Ala2]-Met enkephalinamide (EK) in unanesthetized, unrestrained Columbian ground squirrels (Spermophilus columbianus) during its annual hibernation cycle. In the nonhibernating phase, low doses of either morphine (less than 160 micrograms) or EK (less than 400 micrograms) elicited a dose-related hyperthermia and an increase in heat production, whereas a higher dose of opiates caused hypothermia and a decrease in metabolic rate. Naloxone (5 mg/kg, SC) pretreatment reduced or reversed both the hyper- and hypothermic responses to opiates. Lower ambient temperature (5 degrees C) enhanced the hypothermic response and attenuated the hyperthermic response. In the hibernating phase, euthermic ground squirrels exhibited a reduced responsiveness to exogenous opiates: the hyperthermic response to low dose of morphine (10 micrograms) was significantly reduced and hyperthermia, rather than hypothermia was observed at the highest dose of morphine (160 micrograms). The reduced responsiveness to opiates observed during the hibernating phase seems to suggest a reduction in opiate receptor efficacy which is in agreement with the contention that an increase in endogenous opioid activities may be incumbent with the commencement of hibernation.

Changes in body temperature after administration of adrenergic and serotonergic agents and related drugs including antidepressants: 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 from 1980 to 1984 but data from many earlier papers are also tabulated.

Hypothalamic opioids and the acute-phase glycoprotein response in guinea pigs

Endogenous opioids (EO) probably do not modulate endotoxin (LPS)- or interleukin 1 (IL1)-induced fever because naloxone does not prevent its development. Yet, increases in CSF and hypothalamic levels of beta-endorphin have been reported during LPS-and IL1-induced fevers. Since IL1 also reduces the specific binding of opioids to their receptors in guinea pig brain, the opioids could be involved in modulating nonfebrile effects of IL1. To determine whether EO might have a role in the IL1-induced acute-phase glycoprotein response of guinea pigs, (1) naloxone (5 and 10 mg/kg, SC) was injected prior to LPS (S. enteritidis 2 micrograms/kg, IV; N = 5), and (2) morphine (MOR, 10 micrograms/microliter), [D-ala2]-met-enkephalinamide (DAME, 5 micrograms/microliter), or dynorphin A (DYN, 5 micrograms/microliter) was injected into the preoptic area (1 microliter, bilaterally; N = 8/treatment) or into the 3rd ventricle (N = 4/treatment); pyrogen-free saline was the control injection. Measurements were: core temperature (Tco) and, as indices of acute-phase glycoproteins, plasma levels of copper (Cu) and N-acetylneuraminic acid (NANA). Naloxone did not prevent the fever or the increases in plasma Cu and NANA levels evoked by LPS. The intracerebral administration of opioid agonists by either route induced variable rises in Tco, each with a different pattern, but no increases in plasma Cu and NANA levels. Thus, EO do not participate in the central modulation of acute-phase glycoprotein synthesis, but may have a role in influencing other nonthermal IL1 effects in the CNS.

Changes in body temperature and metabolic rate following microinjection of Met-enkephalinamide in the preoptic/anterior hypothalamus of rats

The effects of Met-enkephalinamide (MET-ENKamide) on brain temperature (Tb) and metabolic rate (MR) were assessed following direct administration into the preoptic/anterior hypothalamus (PO/AH) of freely moving rats. Bilateral microinjections of saline or MET-ENKamide (1-25 micrograms/microliter) were delivered through cannula guide tubes previously implanted in nine animals. Thiorphan, an enkephalinase inhibitor, was microinjected into the PO/AH of two of the animals. All injections were made remotely at an ambient temperature of 22 +/- 1 degree C in a volume of 1 microliter. Measurements of Tb (via a brain-dwelling thermistor) and MR were recorded continuously. The ability of naloxone to antagonize the effects of MET-ENKamide was investigated by fashioning a double-barreled injection cannula to fit within each guide tube; 1 microliter of saline or naloxone (1-10 micrograms) was delivered bilaterally into the PO/AH followed by 1 microliter of MET-ENKamide (25 micrograms) 5-10 min later. PO/AH administration of MET-ENKamide (1-25 micrograms) produced dose-dependent increases in Tb preceded by dose-dependent increases in MR, with a characteristic time course of approximately 30 min. Naloxone antagonized the rise in Tb and MR, either partially or completely, depending on dose. When administered alone, naloxone had no effect on Tb or MR. Microinjection of thiorphan (10 micrograms) into the PO/AH evoked increases in Tb and MR that were similar to those responses induced by MET-ENKamide. These results support a role for endogenous Met-enkephalin in the regulation of Tb in the rat.

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 opiates: 1983

This paper is the sixth in an annual series of reviews of research involving the endogenous opiates, each installment being restricted to work published during the previous year. Although the early articles in the series attempted to be comprehensive and cover the complete range of research with the opiate peptides, in the last two years we have limited our coverage to non-analgesic and behavioral work due to the enormous number of articles published in the field. The specific areas discussed here include stress, tolerance and dependence, consummatory responses, other gastrointestinal functions, interactions with alcohol, mental illness, learning and memory, cardiovascular responses, respiratory effects, thermoregulation, neurological disorders, activity, and miscellaneous other topics. As in previous years, we have attempted to present a relatively complete review of the subjects covered only for the previous year and generally have not tried to evaluate their contributions relative to those of past years.

Role of beta-endorphin in the control of body temperature in the rabbit

There is evidence of release of the opioid peptide beta-endorphin (beta-E) in the hypothalamus during development of fever and stress-induced hyperthermia. In the unanesthetized rabbit, microinjection of beta-E in the preoptic/anterior hypothalamus (POAH) results in peripheral vasoconstriction, inhibition of evaporative heat loss, and a prolonged elevation of body temperature. These reactions are magnified with increases in ambient temperature. Injections of beta-E nearly abolish vasodilation to back heating and also postural enhancement of heat dissipation ( sprawling , limb extension) in a hot environment. beta-E has also been found to reduce the thermal sensitivity of single POAH neurons to ambient heating. However, POAH beta-E injections do not alter metabolic rate at ambient temperatures from 2 to 27 degrees C, and to this extent beta-E-induced hyperthermia is distinct from fever. It is suggested that beta-E reduces sensitivity of POAH neurons to high ambient temperature and that this reduction leads to increased peripheral vasoconstriction, inhibition of evaporative heat loss, and modification of behavioral thermoregulation resulting in a regulated-type elevation in body temperature. A general neural model is proposed to explain the thermoregulatory effects of beta-E in the rabbit.

Hyperthermic effects of centrally injected (D-ala2, N-Me-Phe4, Met-(O)5-ol)-enkephalin (FK 33-824) in rabbits and guinea-pigs

Intracerebroventricular administration of (D-ala2, N-Me-Phe4, Met-(O)5-ol)-enkephalin (FK 33-824) induced dose-related hyperthermia in rabbits and guinea-pigs. Prostaglandins (PG) and norepinephrine (NE) were not involved in the hyperthermia induced by FK 33-824 because a cyclooxygenase inhibitor, indomethacin, and an alpha-adrenoceptor antagonist, phenoxybenzamine, had no antagonistic effects. Likewise, cAMP was not required since a phosphodiesterase inhibitor, theophylline, did not accentuate the hyperthermia due to FK 33-824. It is suggested that mu receptors were involved in the induction of hyperthermia by FK 33-824 in rabbits and guinea-pigs since naloxone attenuated it. These results indicate that FK 33-824-induced hyperthermia is not mediated by PG, NE and cAMP, but rather that mu receptors are involved in the induction of hyperthermia by FK 33-824.