Intraperitoneal injection of sodium pentobarbital has the potential to elicit pain in adult rats (Rattus norvegicus)

Abstract

An effective and pain-free killing method is required to achieve the goal of euthanasia, a "good death". Overdose of sodium pentobarbital (PB) by intraperitoneal (IP) injection is a widely accepted technique in laboratory rats, but questions remain regarding pain associated with administration. As PB rapidly causes sedation and loss of consciousness, most studies have relied on indirect evidence of pain. The objective of this study was to assess pain associated with IP PB using an appropriate vehicle control. Adult male and female Sprague Dawley (SD) and female Wistar rats (N = 84) were block randomised by sex and strain to receive one of three treatments: 1) 800 mg/kg PB (pH 11), 2) saline or 3) vehicle controls (pH 11 or 12.5). Behavior (Rat Grimace Scale (RGS), writhing, back arching) was evaluated at baseline, before loss of righting reflex (LORR, PB group), and at 80s, 151s and 10 min post-injection (PI; saline and vehicle control groups). In the PB group, mean time to LORR was 78 ± 7.9 seconds. In the vehicle control groups, RGS scores were increased at 151s PI (SD: p = 0.0002, 95%CI 0.73 to 0.20) from baseline, as was relative frequency of writhing (SD: p < 0.0001; Wistar; p = 0.0004). RGS scores remained elevated 10 mins PI (SD: p = 0.0005, 95%CI 0.71 to 0.18; Wistar: p = 0.0234, 95%CI 0.91 to 0.07) but the relative frequency of writhing did not (p > 0.999). The RGS scores and the relative frequency of writhing remained low in the PB and saline groups (p > 0.05). These results show that, vehicle controls for IP PB result in signs associated with pain, pain may not be experienced following IP PB when LORR occurs quickly, and that the effects of PB limit behavioral pain assessments.

Comparison of the respiratory effects of commonly utilized general anaesthesia regimes in male Sprague-Dawley rats

“…Regarding the choice of anaesthetics, the agents and their respective doses evaluated in the present study were selected based on an extensive literature search and overview of the most commonly applied regimes. Accordingly, some anaesthetic agents were used alone (urethane, pentobarbital and sevoflurane) as they have previously been shown to have appropriate analgesic effects in rodents ( De Wildt et al, 1983 ; Inada et al, 2020 ; Reimer et al, 2020 ). Other agents were used in combinations.…”

Krill oil supplementation reduces the growth of CT-26 orthotopic tumours in Balb/c mice

“…During the study period, food intake was monitored every day and the body weight was measured twice a week. After 21 days of CT-26 cell inoculation or when the tumour size was over 1 cm 3 , animals were culled by overdosing with pentobarbitone (100 mg/kg) [ 27 ]. Kaplan–Meier survival analysis was used to assess the survival rate of animals in each group [ 28 ].…”

Apoptosis inhibition is involved in improvement of sevoflurane‑induced cognitive impairment following normobaric hyperoxia preconditioning in aged rats

“…LORR was assessed by attempting to place the rat in left lateral recumbency, followed by dorsal recumbency. If the rat remained on its back for 10 sec, LORR was considered to be achieved ( 29 ). After successful induction of chloral hydrate, A total of 18 rats from three groups were sacrificed by decapitation.…”