Characterization of Urothelial Inclusions in Male Wistar Han Rats Treated Orally With the Novel α2A-Adrenoceptor Agonist Tasipimidine

Intracellular inclusions were observed in urinary bladder epithelium of male Wistar rats, following oral treatment with high doses of the α_2A-adrenoceptor agonist tasipimidine for 28 days. No cell death or inflammation was associated with the brightly eosinophilic inclusions. Electron microscopy (EM) studies showed that the inclusions represented intact or fragmented red blood cells (RBC) resulting from erythrophagocytosis, further supported by the presence of iron in urothelial cells. In addition, scattered iron-positive macrophages were observed in the submucosa and muscle layer, indicating microvascular leakage, as no major hemorrhage was evident. Despite the presence of inclusions, the urothelium showed normal uroplakin III distribution, normal cell turnover, and an absence of α-2u-globulin. It is, therefore, concluded that the inclusions were not associated with urothelial damage or increased renewal of the epithelium. This finding shows also that urothelial cells have the capability to phagocytize and break down RBCs originating from submucosal microvascular leakage. Similar changes were not observed in tasipimidine-treated beagle dogs (28 days), suggesting these findings were rat specific. The leakage of RBCs into the urothelium is suggested to be a consequence of exaggerated pharmacology leading to vasoconstriction of submucosal blood vessels in combination with transient increased bladder distension and pressure.

Pharmacokinetics and sedative effects of alfaxalone with or without dexmedetomidine in rabbits

This study aimed to investigate the specific pharmacokinetic profile and effects of alfaxalone after intravenous (IV) and intramuscular (IM) administration to rabbits and evaluate the potential interaction with dexmedetomidine. The study design was a blinded, randomized crossover with a washout period of 2 weeks. Five New Zealand white rabbits were used. Each animal received single IV and IM injections of alfaxalone at a single dose of 5 mg/kg, and single IV and IM injections of alfaxalone (5 mg/kg) combined with dexmedetomidine (100 μg/kg) administered intramuscularly. Blood samples were collected at predetermined times and analysed by high-performance liquid chromatography. The plasma concentration-time curves were analysed by non-compartmental analysis. Sedation/anaesthesia scores were evaluated by a modified numerical rating scale. At pre-determined time points heart and respiratory rates were measured. Times to sternal recumbency and standing position during the recovery were recorded. Concentrations of alfaxalone alone were very similar (slighty smaller) to concentrations when alfaxalone was combined with dexmedetomidine, after both routes of administration. Dexmedetomidine enhanced and increase the duration of the sedative effects of alfaxalone. In conclusion, alfaxalone administered in rabbits provides rapid and smooth onset of sedation. After IV and IM injections of alfaxalone combined with dexmedetomidine, a longer MRT and a deeper and extended sedation have been obtained compared to alfaxalone alone. Consequently, alfaxalone alone or in combination with dexmedetomidine could be useful to achieve respectively moderate to deep sedation in rabbits.

Are the pharmacology and physiology of α₂ adrenoceptors determined by α₂-heteroreceptors and autoreceptors respectively?

α(2)-Adrenoceptors are important mediators of physiological responses to the endogenous catecholamines noradrenaline and adrenaline. In addition, α(2)-adrenoceptors are pharmacological targets for the treatment of hypertension, sympathetic overactivity and glaucoma. α(2)-Adrenoceptors are also targeted to induce sedation and analgesia in anaesthesia and intensive care. α(2)-Adrenoceptors were first described as presynaptic receptors inhibiting the release of various transmitters from neurons in the central and peripheral nervous systems. In addition to these presynaptic neuronal receptors, α(2)-adrenoceptors were also identified in many non-neuronal cell types of the body. Gene-targeting in mice provided a comprehensive assignment of the physiological and pharmacological functions of these receptors to specific α(2A)-, α(2B) - and α(2C)-adrenoceptor subtypes. However, the specific cell types and signalling pathways involved in these subtype-specific α(2)-adrenoceptor functions were largely unexplored until recently. This review summarizes recent findings from transgenic mouse models, which were generated to define the role of α(2)-adrenoceptors in adrenergic neurons, that is, α(2)-autoreceptors, versus α(2)-adrenoceptors in non-adrenergic neurons, termed α(2)-heteroreceptors. α(2)-Autoreceptors are primarily required to limit release of noradrenaline from sympathetic nerves and adrenaline from adrenal chromaffin cells at rest. These receptors are desensitized upon chronic activation as it may for instance occur due to enhanced sympathetic activity during chronic heart failure. In contrast, pharmacological effects of acutely administered α(2)-adrenoceptor agonist drugs essentially require α(2)-heteroreceptors in non-adrenergic neurons, including analgesia, sedation, hypothermia and anaesthetic-sparing as well as bradycardia and hypotension. Thus a clear picture has emerged of the significance of auto- versus heteroreceptors in mediating the physiological functions of α(2)-adrenoceptors and the pharmacological functions of α(2)-adrenoceptor agonist drugs respectively.

Hypertensive crisis from chronic intoxication with nasal decongestant and cough medications

Cardiac hypertensive structural changes, catecholamine-related cardiomyopathy, and congestive heart failure (CHF) have been encountered in pheochromocytoma, as a result of prolonged exposure to high concentrations of endogenous catecholamines. A 34-year-old man presented with severe hypertension, cardiomegaly, and CHF, presumably as a result of continuous alpha-adrenergic intoxication with oxymetazoline hydrochloride, phenylephrine hydrochloride, and ephedrine hydrochloride, consumed in massive doses by an overuse of nasal decongestants and cough syrup (daily doses of 20, 100, and 300 mg, respectively). Coadministered chlorpromazine hydrochloride and trimeprazine tartrate may have also contributed to the clinical presentation through their anticholinergic and antihistaminic properties. The possibility of an overuse of these over-the-counter drugs should be considered in the differential diagnosis of hypertensive emergencies, especially with the simultaneous use of anticholinergic and antihistamine medications, beta-blocking agents, or monoamine oxidase inhibitors.

Assessment of the sedative effects of dexmedetomidine, an alpha 2-adrenoceptor agonist, with analysis of saccadic eye movements

Single intravenous doses (0.5 microgram/kg and 1.0 microgram kg) of dexmedetomidine (4(5)-(1-(2,3-dimethylphenyl)ethyl)imidazole), a selective alpha 2-adrenoceptor agonist, and saline placebo were administered to six healthy volunteers (4 males and 2 females) in a double-blind, placebo-controlled cross-over study. The effects on vigilance were assessed using both subjective estimation (visual analogue scale, VAS) and objective tests (critical flicker fusion frequency, CFF; the Maddox wing; saccadic eye movement analysis). Dose-dependent subjective sedation was seen in VAS measurements, and impairment of vigilance was observed in CFF, Maddox wing and peak saccadic velocity, while saccade latency was not influenced by dexmedetomidine. The changes in vigilance were concurrent with moderate reductions in blood pressure and heart rate. CFF, the Maddox wing and peak saccadic velocity all proved sensitive in the assessment of sedation induced by dexmedetomidine.