Hathaipat Rattanathanya (Research Institute of Wildlife Ecology, Department of Interdisciplinary Life Sciences, Departments, University of Veterinary Medicine Vienna) Hathaipat Rattanathanya Anna Binetti (Clinical Centre for Small Animal Health and Research, Clinical Department for Small Animals and Horses, Departments, University of Veterinary Medicine Vienna) Anna Binetti Friederike Pohlin (Research Institute of Wildlife Ecology, Department of Interdisciplinary Life Sciences, Departments, University of Veterinary Medicine Vienna) Friederike Pohlin Susana C.M. Ferreira (Research Institute of Wildlife Ecology, Department of Interdisciplinary Life Sciences, Departments, University of Veterinary Medicine Vienna) Susana C.M. Ferreira Christina Braun (Clinical Centre for Small Animal Health and Research, Clinical Department for Small Animals and Horses, Departments, University of Veterinary Medicine Vienna) Christina Braun Johannes Schramel (Clinical Centre for Small Animal Health and Research, Clinical Department for Small Animals and Horses, Departments, University of Veterinary Medicine Vienna) Johannes Schramel Leith C.R. Meyer Leith C.R. Meyer Anna Haw (Research Institute of Wildlife Ecology, Department of Interdisciplinary Life Sciences, Departments, University of Veterinary Medicine Vienna) Anna Haw Marja Raekallio Marja Raekallio Stefan Böhmdorfer Stefan Böhmdorfer Szilvia Kalogeropoulu (Research Institute of Wildlife Ecology, Department of Interdisciplinary Life Sciences, Departments, University of Veterinary Medicine Vienna) Szilvia Kalogeropoulu Martina Mosing (Clinical Centre for Small Animal Health and Research, Clinical Department for Small Animals and Horses, Departments, University of Veterinary Medicine Vienna) Martina Mosing Gabrielle Stalder (Research Institute of Wildlife Ecology, Department of Interdisciplinary Life Sciences, Departments, University of Veterinary Medicine Vienna) Gabrielle Stalder Springer 2026 Background Etorphine, a highly potent opioid widely used in wildlife immobilisation, is known to cause cardiorespiratory compromise. This study aimed to investigate the effects of a serotonergic agonist, BIMU-8 and an alpha-2 adrenoreceptor antagonist, vatinoxan on pulmonary hypertension and cardiovascular function in etorphine-immobilised sheep, as a model for wild ungulates. Six sheep were immobilised three times in a randomised, prospective, controlled crossover design using intramuscular etorphine (0.05 mg·kg−1). Seven minutes later, sheep received intravenous BIMU-8 (1.5 mg·kg−1), vatinoxan (0.15 mg·kg−1), or sterile water (control). Respiratory rate, pulmonary arterial, systemic arterial and central venous pressures, electrocardiography, heart rate, and cardiac output were recorded. Data were collected at resting state, six minutes post-etorphine, and at six-minute intervals post-treatment. Naltrexone was administered 19 minutes post-treatment to reverse immobilisation. Linear mixed-effects models were used for statistical analysis. Results Etorphine induced bradypnea, pulmonary hypertension, dysrhythmias, and tachycardia in sheep. BIMU-8 significantly reduced mean pulmonary arterial pressure (F2,91 = 4.17, p = 0.02) and mean arterial pressure (F2,89 = 6.01, p < 0.01) but was associated with severe tachydysrhythmia. Vatinoxan decreased respiratory rate (F2,91 = 4.13, p < 0.01), increased cardiac output (F2,91 = 10.88, p < 0.01), and reduced body temperature (F6,85 = 2.2, p = 0.05), while having no effect on pulmonary or systemic arterial pressures. Conclusion BIMU-8 reduces etorphine-induced pulmonary and systemic hypertension, but causes tachydysrhythmias, requiring further evaluation. Vatinoxan improves cardiac output, without alleviating pulmonary hypertension in etorphine-immobilised sheep. PDFDocument eng 2026-08-21T08:32:38.058946666Z 2026 BIMU-8 Etorphine Opioid Vatinoxan Pulmonary Hypertension Cardiovascular 1891996 b application/pdf http://creativecommons.org/licenses/by/4.0/