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31.01.2022: Chemical immobilisation is often required for the management, conservation and veterinary care of captive and free-ranging wildlife species.For many wild animal species, this requires the use of highly potent anaesthetics or much higher doses than compared to domestic animals. However, the use of such potent anaesthetics, or high doses, is also associated with undesirable side effects, such as respiratory depression in the case of highly potent opioids, or pronounced cardiovascular side effects such as increased blood pressure or reduced heart rate in the case of high doses of specific sedatives. Two recent studies by the Research Institute of Wildlife Ecology at Vetmeduni now show how these side effects can be significantly minimised through the simultaneous administration of substances that act specifically on the signalling pathway of cells. The researchers see this as an important step towards improving animal welfare during anaesthesia.

Opioid-induced respiratory compromise remains a significant challenge in etorphine-immobilised wildlife. Selective serotonergic agonists are a potential option for preventing or treating such respiratory depression, as demonstrated in a recently published study by Vetmeduni in cooperation with the University of Pretoria, South Africa and the University of Natural Resources and Applied Life Sciences (BOKU), Vienna. The key finding of the study: BIMU-8, a selective 5-hydroxytryptamine receptor 4 (5-HT4) agonist, significantly reduces opioid-induced respiratory compromise in etorphine-immobilised goats (Capra aegagrus hircus).

BIMU-8: a promising drug candidate alleviating etorphine-induced respiratory compromise

The intravenous injection of BIMU-8 attenuated etorphine-induced respiratory compromise in the study animals, as indicated by improvements in respiratory rate, peripheral arterial blood oxygen saturation (SpO2), partial pressure of arterial oxygen (PaO2) and the alveolar-arterial oxygen partial pressure gradient (P(A-a)O2). A simultaneous increase in heart rate and temporary decrease in arterial blood pressure caused by BIMU-8 are to be investigated in future studies.

“Without antagonising immobilisation, BIMU-8 attenuated etorphine-induced respiratory depression and improved pulmonary gas exchange, which restored blood oxygenation and prevented hypercapnia (elevated carbon dioxide levels in the blood) from occurring. These effects indicate that BIMU-8 may be a good drug candidate for the treatment or prevention of etorphine-induced respiratory compromise in immobilised wild animals,” says the study’s first author, Gabrielle Stalder, from the Research Institute of Wildlife Ecology at Vetmeduni.

Vatinoxan reduces cardiovascular side effects associated with medetomidine-tiletamine-zolazepam

Another international study led by the University of Veterinary Medicine Vienna in cooperation with the University of Pretoria and the University of Helsinki investigated how anaesthesia, with a combination of the sedative medetomidine and the anaesthetic tiletamine/zolazepam, can be improved. This combination is commonly used to anaesthetise non-domestic mammals. However, the use of medetomidine is associated with pronounced cardiovascular side effects, such as decreased heart rate, elevated blood pressure and reduced cardiac output. The researchers investigated the effects of the peripherally acting alpha-2-adrenoceptor antagonist vatinoxan on cardiovascular properties in wild boar (Sus scrofa) anaesthetised with the medetomidine-tiletamine-zolazepam (MTZ) combination.

Improved wildlife anaesthesia

According to the study’s last author, Gabrielle Stalder, vatinoxan reduced side effects of the cardiovascular active sedative medetomidine, especially hypertension, in MTZ-immobilised wild boar: “Intravenous administration of vatinoxan significantly reduced systemic and pulmonary artery hypertension induced by medetomidine in wild boar.” Vatinoxan also effectively reversed slow heart rates in MTZ-anaesthetised wild boar, although this effect was short-lived.

Stalder sees the results of both studies as encouraging: “Our data show that both BIMU-8 and vatinoxan have the potential to significantly improve the welfare of animals during wildlife anaesthesia events.”

The article “Investigation of cardiorespiratory effects of the selective 5-HT4 agonist BIMU-8 in etorphine-immobilised goats (Capra aegagrus hircus) in a randomized, blinded and controlled trial” by Nadine Tod, Gabrielle Stalder, Hanna Rauch, Stefan Böhmdorfer, Anna Haw, Hanno Gerritsmann, Johanna Painer and Leith Meyer was published in Veterinary Record.

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The article “Cardiovascular effects of intravenous vatinoxan in wild boars (Sus scrofa) anaesthetised with intramuscular medetomidine-tiletamine-zolazepam” by Joy Einwaller, Leith C. R. Meyer, Ulrike Auer, Marja Raekallio, Julia Nowack, Anna Haw, Sebastian Vetter, Johanna Painer and Gabrielle Stalder was also published in Veterinary Record.

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