Imidazoline 1 receptor activation preserves respiratory drive in spontaneously breathing newborn rats during dexmedetomidine administration

Effect of ambient temperature on dexmedetomidine-induced metabolic and cardiorespiratory suppression in spontaneously breathing newborn rats

Newborn animals are known to increase the ventilation-metabolism ratios in hypoxia, particularly at cold environment by decreasing the thermogenesis. We examined whether ambient temperatures and thermoregulatory suppression due to dexmedetomidine, an α2 adrenoceptor agonist, affect the coupling between ventilation and metabolism in neonatal rats. Wistar rats (3-7 days old) were measured for metabolic and cardiorespiratory indices. Control recordings were made at 34 °C ambient temperature (Ta) and Ta was either kept at 34 °C (Medium), reduced to 27 °C (Low) or increased to 39 °C (High). Once at the desired Ta, the rats were administered normal saline or dexmedetomidine (50 μg∙kg-1) and the indices were again recorded. Control values were comparable between the normal saline and dexmedetomidine groups. Using values relative to the control values in each group, body temperature (Low or High vs. Medium Ta) and heart rate (Low vs. High Ta) were significantly different among the three Ta. At each Ta, the dexmedetomidine group showed significantly lower metabolic rates, minute ventilation, respiratory rate and heart rate, compared to the normal saline group. Despite these changes, the ventilationmetabolism ratios in the dexmedetomidine group were comparable at the Medium and Low Ta, and significantly lower at the High Ta, compared to the normal saline group. Dexmedetomidine plus atipamezole (5 mg∙kg-1, an α2 adrenoceptor antagonist) did not affect the ventilation-metabolism ratios at the Low and High Ta. Although dexmedetomidine suppresses thermoregulatory responses, the coupling of ventilation and metabolic rates can be preserved through α2 adrenoceptor activation at cold, but not at hot, ambient temperature. Our results suggest that α2 adrenoceptor activation impairs control of ventilation at heating or rewarming in newborn rats.

Respiratory sinus arrhythmia in spontaneously breathing, unanesthetized newborn and adult Wistar rats

We examined respiratory sinus arrhythmia (RSA) and possible interaction with respiratory frequency (fR) and heart rate (HR) in spontaneously breathing, unanesthetized newborn Wistar rats (2- to 5-day-old; n = 54) and the adult rats (8-week-old; n = 34). Instantaneous heart rate (inst-HR) was calculated as the reciprocal of the inter-beat-interval. For each breath, RSA was determined as the difference between the maximum and minimum inst-HR value. The absolute RSA or RSA% (RSA per HR) were calculated as the average RSA of 10 consecutive breaths. RSA (or RSA%) in the newborn rats was significantly lower than that in the adult rats. Correlation coefficient between RSA (or RSA%) and 1/fR or HR/fR, but not HR, was significant in newborn rats, whereas only that between RSA (or RSA%) and HR was significant in adult rats. The power spectrum density of heartbeat fluctuation was detectable in both age groups. The present findings suggest that RSA exists and could be influenced by fR, rather than HR, in newborn rats.

Effects of imidazoline agents in a rat conditioned place preference model of addiction

Agmatine (AG), idazoxan (IDZ), and efaroxan (EFR) are imidazoline receptor ligands with beneficial effects in central nervous system disorders. The present study aimed to evaluate the interaction between AG, IDZ, and EFR with an opiate, tramadol (TR), in a conditioned place preference (CPP) paradigm. In the experiment, we used five groups with 8 adult male Wistar rats each. During the condition session, on days 2, 4, 6, and 8, the rats received the drugs (saline, or TR, or IDZ and TR, or EFR and TR, or AG and TR) and were placed in their least preferred compartment. On days 1, 3, 5, and 7, the rats received saline in the preferred compartment. In the preconditioning, the preferred compartment was determined. In the postconditioning, the preference for one of the compartments was reevaluated. TR increased the time spent in the non-preferred compartment. AG decreased time spent in the TR-paired compartment. EFR, more than IDZ, reduced the time spent in the TR-paired compartment, but without statistical significance. AG reversed the TR-induced CPP, while EFR and IDZ only decreased the time spent in the TR-paired compartment, without statistical significance.

Effect of dexmedetomidine on cardiorespiratory regulation in spontaneously breathing adult rats

Purpose

We examined the cardiorespiratory effect of dexmedetomidine, an α2- adrenoceptor/imidazoline 1 (I1) receptor agonist, in spontaneously breathing adult rats.

Methods

Male rats (226−301 g, n = 49) under isoflurane anesthesia had their tail vein cannulated for drug administration and their tail artery cannulated for analysis of mean arterial pressure (MAP), pulse rate (PR), and arterial blood gases (PaO2, PaCO2, pH). After recovery, one set of rats received normal saline for control recording and was then divided into three experimental groups, two receiving dexmedetomidine (5 or 50 μg·kg−1) and one receiving normal saline (n = 7 per group). Another set of rats was divided into four groups receiving dexmedetomidine (50 μg·kg−1) followed 5 min later by 0.5 or 1 mg∙kg−1 atipamezole (selective α2-adrenoceptor antagonist) or efaroxan (α2-adrenoceptor/I1 receptor antagonist) (n = 6 or 8 per group). Recordings were performed 15 min after normal saline or dexmedetomidine administration.

Results

Compared with normal saline, dexmedetomidine (5 and 50 μg·kg−1) decreased respiratory frequency (fR, p = 0.04 and < 0.01, respectively), PR (both p < 0.01), and PaO2 (p = 0.04 and < 0.01), and increased tidal volume (both p = 0.049). Dexmedetomidine at 5 μg·kg−1 did not significantly change minute ventilation (V′E) (p = 0.87) or MAP (p = 0.24), whereas dexmedetomidine at 50 μg·kg−1 significantly decreased V′E (p = 0.03) and increased MAP (p < 0.01). Only dexmedetomidine at 50 μg·kg−1 increased PaCO2 (p < 0.01). Dexmedetomidine (5 and 50 μg·kg−1) significantly increased blood glucose (p < 0.01), and dexmedetomidine at 50 μg·kg−1 increased hemoglobin (p = 0.04). Supplemental atipamezole or efaroxan administration similarly prevented the 50 μg·kg−1 dexmedetomidine-related cardiorespiratory changes.

Principal conclusion

These results suggest that dexmedetomidine-related hypoventilation and hypertension are observed simultaneously and occur predominantly through activation of α2-adrenoceptors, but not I1 receptors, in spontaneously breathing adult rats.

Expression of nischarin, an imidazoline 1 receptor candidate protein, in the ventrolateral medulla of newborn rats

The activation of imidazoline 1 (I₁) receptors is suggested to stimulate the respiratory drive in newborn rats. Here, we immunohistochemically examined whether nischarin, an I₁ receptor candidate protein, is expressed in the ventrolateral medulla, where cardiorespiratory centers are located. Newborn rats (age, 3-5 days) were deeply anesthetized with isoflurane; the brainstem was dissected, sectioned sagittally, and labeled with nischarin. Nischarin-associated signals were observed broadly throughout the newborn rat brainstem, including at motor nuclei (motor trigeminal nucleus and facial nucleus), sensory nuclei (lateral superior olive, medial and spinal vestibular nuclei, cuneate nucleus, spinal trigeminal nucleus, and solitary nucleus), and the rostral and caudal ventrolateral medullar regions. In particular, the rostral ventrolateral medulla included a layer of aggregated nischarin expression along the ventral surface, and the layer was in close contact with GFAP-positive processes. In addition, some Phox2b-positive neurons were positive for nischarin in the region. Our results reveal nischarin expression in the newborn rat brainstem and suggest that I₁ receptor activation at the level of the ventrolateral medulla contributes to central chemoreception and respiratory control in newborn rats.

Effect of dexmedetomidine anesthesia on respiratory function in pediatric patients undergoing retinoblastoma resection

The aim of this study was to investigate the effect of dexmedetomidine (Dex) on the respiratory function during anesthesia induction in pediatric patients undergoing retinoblastoma (RB) resection. A total of 87 pediatric patients who underwent RB resection in Yidu Central Hospital of Weifang were recruited into this study. General anesthesia was first induced for all patients, of which 45 were randomly assigned to the experimental group and received Dex through an intravenous infusion pump to maintain general anesthesia. The remaining 42 patients were assigned to the control group and received saline through an intravenous infusion pump. Respiratory function and hemodynamic indexes at five time-points, i.e., before anesthesia induction (T0), 5 min after injection of anesthetic agents (T1), before intubation (T2), 15 min after intubation (T3), and 30 min after extubation (T4), were recorded and compared. Incidence of perioperative cardiac and respiratory adverse events was counted in both groups, and post-anesthesia resuscitation was evaluated and compared. Compared with T0, the respiratory rate (R) of the experimental group was lower at T1-T4, but there was no statistical difference (P<0.05). Compared with T0, the control group had a higher R at T2, lower R at T3 and T4 (P<0.05), and there was no significant difference in R between T0 and T1 (P>0.05). At the same time-point, compared with the experimental group, the R was higher at T2, and lower at T3 and T4 in the control group (P<0.05), and no significant difference was found at T1. Blood oxygen saturation (SpO₂) of the experimental group was slightly lower than that of T0 at T1-T4 (P>0.05). In the control group, the levels of SpO₂ were significantly lower at T1-T4 than those at T0 (P<0.05). Compared with the experimental group at the same time-point, SpO₂ of the control group at T1-T4 decreased significantly (P<0.05). The heart rate (HR) of the experimental and control groups was lower at T1-T4 than that at T0 (P<0.05). The HR of the experimental group was higher than that of the control group at T1-T4 (P<0.05). Mean arterial pressure (MAP) of the experimental and control groups was lower at T1-T4 than that at T0 (P<0.05). MAP of the control group was higher than that of the experimental group at T2 but lower than that at T0 of the control group. MAP of the control group was lower than that of the experimental group at T1-T4. There was no significant difference in incidence of tachycardia, bradycardia, vomiting, hypoxia and laryngism between the two groups (P>0.05). There was no difference in resuscitation and extubation time between the two groups (P>0.05). Finally, agitation of the control group was more severe than that of the experimental group (P<0.05). Therefore, Dex can improve the respiratory function and hemodynamic stability during anesthesia induction in children with RB resection.

Dexmedetomidine protects against lipopolysaccharide-induced early acute kidney injury by inhibiting the iNOS/NO signaling pathway in rats

Increasing evidence has demonstrated that dexmedetomidine (DEX) possesses multiple pharmacological actions. Herein, we explored the protective effect and potential molecular mechanism of DEX on lipopolysaccharide (LPS)-induced early acute kidney injury (AKI) from the perspective of antioxidant stress. We found that DEX (30 μg/kg, i.p.) ameliorated the renal dysfunction and histopathological damage (tubular necrosis, vacuolar degeneration, infiltration of inflammatory cells and cast formation) induced by LPS (10 mg/kg). DEX also attenuated renal oxidative stress remarkably in LPS-induced early AKI, as evidenced by reduction in production of reactive nitrogen species, decreasing malondialdehyde levels, as well as increasing superoxide dismutase activity and glutathione content. DEX prevented activator protein-1 translocation, inhibited phosphorylation of I-kappa B (IκB) and activation of nuclear factor kappa B (NF-κB) in LPS-induced early AKI, as assessed by real-time quantitative polymerase chain reaction and protein levels of c-Jun, c-Fos, IκB and NF-κB. Notably, DEX pretreatment had the same effect as intraperitoneal injection of an inhibitor of inducible nitric oxide synthase inhibitor (1400W; 15 mg/kg), and inhibited the activity of renal inducible nitric oxide synthase (iNOS) and decreased the expression of iNOS mRNA and NO production. However, the protective effect of DEX on LPS-induced early AKI was reversed by the alpha 2 adrenal receptor (α₂-AR) inhibitor atipamezole, whereas the imidazoline receptor inhibitor idazoxan did not. Taken together, DEX protects against LPS-induced early AKI in rats by inhibiting the iNOS/NO signaling pathway, mainly by acting on α₂-ARs instead of IRs.