Effect of Different Formulations of Magnesium Chloride Used As Anesthetic Agents on the Performance of the Isolated Heart of Octopus vulgaris

Abstract

Magnesium chloride (MgCl2) is commonly used as a general anesthetic in cephalopods, but its physiological effects including those at cardiac level are not well-characterized. We used an in vitro isolated perfused systemic heart preparation from the common octopus, Octopus vulgaris, to investigate: (a) if in vivo exposure to MgCl2 formulations had an effect on cardiac function in vitro and, if so, could this impact recovery and (b) direct effects of MgCl2 formulations on cardiac function. In vitro hearts removed from animals exposed in vivo to 3.5% MgCl2 in sea water (20 min) or to a mixture of MgCl2+ ethanol (1.12/1%; 20 min) showed cardiac function (heart rate, stroke volume, cardiac output) comparable to hearts removed from animals killed under hypothermia. However, 3.5% MgCl2 (1:1, sea water: distilled water, 20 min) produced a significant impairment of the Frank-Starling response as did 45 min exposure to the MgCl2+ ethanol mixture. Perfusion of the isolated heart with MgCl2± ethanol formulations produced a concentration-related bradycardia (and arrest), a decreased stroke volume and cardiac output indicating a direct effect on the heart. The cardiac effects of MgCl2 are discussed in relation to the involvement of magnesium, sodium, chloride, and calcium ions, exposure time and osmolality of the formulations and the implications for the use of various formulations of MgCl2 as anesthetics in octopus. Overall, provided that the in vivo exposure to 3.5% MgCl2 in sea water or to a mixture of MgCl2+ ethanol is limited to ~20 min, residual effects on cardiac function are unlikely to impact post-anesthetic recovery.

Short and Long-Term Effects of Anesthesia in Octopus maya (Cephalopoda, Octopodidae) Juveniles

“…Surprisingly, despite the recent increased interest, current information is available only for a few species using a limited variety of substances potentially acting as anesthetic agents: only about 20 substances have been investigated to anesthetize cephalopods (reviewed by Sykes et al, 2012 ; Gleadall, 2013b ; Fiorito et al, 2015 ). Moreover, with few exceptions ( Andrews and Tansey, 1981 ; Pugliese et al, 2016 ; Butler-Struben et al, 2018 ) the majority of anesthetic studies in cephalopods do not explore in-depth the efficacy of the commonly used agents and the physiological effects of anesthesia on the animals. Another limitation is the lack of standardized anesthesia protocols for cephalopods, since distinct methods are described in the literature.…”

The Current State of Cephalopod Science and Perspectives on the Most Critical Challenges Ahead From Three Early-Career Researchers

“…Around 20 substances and/or combinations of anesthetic agents have been tested in a few cephalopod species with some apparent success (for review, see Gleadall, 2013 ; Fiorito et al, 2015 ), but knowledge of their mechanisms of action is very limited. Moreover, descriptions of cephalopod behavior during anesthetic induction and recovery (e.g., Andrews and Tansey, 1981 ; Gonçalves et al, 2012 ; Gleadall, 2013 ; Butler-Struben et al, 2018 ) or of the physiological effects of putative anesthetic agents on the animals ( Pugliese et al, 2016 ; Butler-Struben et al, 2018 ) are relatively few. Variations in the effectiveness of anesthetics in relation to cephalopod age, sex, life stage, body weight, physiological condition and health status, remain largely unexplored, as do the interactions of anesthetics with various parameters, such as temperature, salinity, pH and oxygen level.…”

AJVR Instructions for Authors

“…329,330 A direct addition of magnesium salts to seawater results in a hyperosmotic solution. 331 Magnesium salts may be combined with ethanol for euthanasia of cephalopods. 331 Immersion for at least 15 minutes is recommended for cephalopods, as is an adjunct method like decerebration at least 5 minutes after respiratory arrest or after the animal is insensible.…”

“…331 Magnesium salts may be combined with ethanol for euthanasia of cephalopods. 331 Immersion for at least 15 minutes is recommended for cephalopods, as is an adjunct method like decerebration at least 5 minutes after respiratory arrest or after the animal is insensible. 328,330 At least 30 minutes' immersion is recommended if brain destruction is not an option.…”

“…329 Ethanol may be combined with a magnesium salt solution for euthanasia of cephalopods. 331 Immersion of at least 10 minutes followed by an adjunctive method such as decerebration is recommended. 330 Species susceptibility to the effects of ethanol varies.…”