Hyperthermic Responses to Central and Peripheral Injections of Morphine Sulphate in the Cat

Abstract

1 The effect of morphine on body temperature was studied in conscious, unrestrained cats provided with implanted third or lateral cerebral ventricular cannulae, jugular venous catheters and retroperitoneal thermocouples. 2 Intraventricular injections of 2.5-50 pg and intravenous injections of 1-10 mg/kg morphine sulphate produced dose-related hyperthermic responses. Similar mean increases in body temperature after administration of a given dose were elicited in cats which had not previously received morphine and, provided that tolerance was avoided by spacing injections at least 72 h apart, in cats which received a series of injections of morphine. Morphine was at least 850 times more potent when injected into the third ventricle than when given intravenously. Increasing the dose of morphine sulphate injected into the third ventricle to 1250 jig only prolonged the hyperthermia. Morphine did not produce hypothermia at any dose tested. 3 Injection of 10 gg morphine sulphate into the third ventricle produced similar hyperthermias at ambient temperatures (tas) of 4-6, 21-23 and 33-36°C. The increase in body temperature was associated with shivering at the lower tas. At the highest ta, shivering was not evoked, but respiratory rate decreased after morphine if it was initially elevated. These results suggest that morphine increased the level at which body temperature was regulated. 4 Neither metiamide nor indomethacin antagonized morphine so histamine and prostaglandins were apparently not required for the hyperthermic effect.

Modification of thermoregulatory responses in rabbits reared at elevated environmental temperatures.

“…In these animals the first peak was reduced while the second one was absent. If areas under the temperature response curves of control and experimental animals were compared (Clark & Cumby, 1978) they were found to be significantly different (P < 0 00 1). The response of warm -acclimated rabbits to endotoxin is illustrated in Fig.…”

Dose-related thermal antinociceptive effects of intravenous hydromorphone in cats

“…The glucuronide metabolites of both morphine and hydromorphone have been implicated as a cause of these undesirable side effects in rats and humans (van Crugten et al 1997;Smith 2000). In cats, hyperthermia was identified as an adverse side effect of high-dose (1 mg kg )1 ) morphine administration (Clark & Cumby 1978), and a recent retrospective study has implicated hydromorphone use in post-anesthetic hyperthermia (Niedfeldt & Robertson 2006). Because clinical use of opioids such as hydromorphone is often a balance between the dose that produces analgesia and the dose that produces unacceptable side effects (Smith 2000), species-specific experimental dose-effect studies are essential.…”

Efeitos cardiovasculares e analgésicos da administração epidural de ropivacaína isolada ou associada à morfina, em felinos

“…Acredita-se que esse aumento possa estar relacionado com a ropivacaína epidural. Outro fator já muito relatado em felinos é a hipertermia após a administração de opioides, principalmente em doses acima de 1mg kg -1 (CLARK & CUMBY, 1978), o que poderia ter acontecido em resgates sucessivos no decorrer das avaliações. No entanto, destes quatro animais, dois receberam 0,4mg kg -1 totais de morfi na, um recebeu 0,2mg kg -1 e um não recebeu resgate, sugerindo, assim, que a causa pode estar relacionada à ropivacaína epidural.…”