We tested the hypothesis that dexmedetomidine (Dex) has greater alpha(2)- vs. alpha(1) selectivity than clonidine and causes more alpha(2)-selective vasoconstriction in the human forearm. After local beta-adrenergic blockade with propranolol, forearm blood flow (plethysmography) responses to brachial artery administration of Dex, clonidine, and phenylephrine (alpha(1)-agonist) were determined i...

1. The effects of clonidine and adrenaline on adenosine 5'-triphosphate (ATP)-sensitive K+ channels were studied in pancreatic beta-cells from normal mice. 2. When perifused with a medium containing 1 mM glucose, many of the ATP-sensitive K+ channels in the beta-cell membrane are open. Under these conditions, clonidine (5-100 microM) reversibly decreased 86Rb efflux from the islets, whereas adr...

Clonidine-induced changes in the serotonergic neuronal activity of the central nervous system were estimated by measuring the concentrations of serotonin (5-HT) and its major metabolite, 5-hydroxyindole-3-acetic acid (5-HIAA), in the cerebrospinal fluid (CSF) of anesthetized rats. Clonidine (30 and 300 micrograms/kg, i.v.) led to 74% and 60% reductions in the concentration of 5-HT in the CSF 60...

The relaxant effect of clonidine and the possible involvement of imidazoline I1 receptors in bovine tracheal smooth muscle (BTSM) were examined. Clonidine caused concentration-dependent significant relaxation in BTSM precontracted with 0.1 or 1 microM carbachol (CCh) but not in 72.7 mM KCl-induced contraction. The relaxation in CCh-contracted BTSM was inhibited by yohimbine (1 microM) and idazo...

The effects of Hypericum perforatum (St John's wort) on morphine withdrawal syndrome and comparison with clonidine have been investigated in morphine-dependent rats. Adult male Wistar rats were subjects. The frequencies of withdrawal behavioral signs (rearing, teeth chattering and jumping) induced by naloxone challenge were demonstrated in morphine dependent rats receiving Hypericum perforatum ...

A single dose of clonidine developed tolerance to its analgesic effect. The tolerance reached its peak acutely on the 2nd day and lasted more than 5 days. Neither the analgesic effect nor the development of tolerance was modified by the pretreatment with naloxone. On the 2nd day, clonidine tolerant animals were also tolerant to morphine, but morphine tolerant animals, after a single dose of mor...

In order to assess the effect of spinal clonidine on tourniquet pain, 30 patients scheduled to undergo orthopaedic surgery under spinal anaesthesia were allocated randomly to two groups. Patients in group I (n = 15) received 0.5% isobaric bupivacaine 15 mg plus isotonic saline 1 ml. Patients in group II (n = 15) received 0.5% bupivacaine 15 mg plus clonidine 1 ml (150 micrograms). Sensory block...

In addition to its centrally mediated hypotensive action, clonidine causes a decrease in intraocular pressure associated with a long-lasting mydriasis. The present study was conducted to determine to what extent this drug-induced pupillary dilation is of central or peripheral origin. Pupil size was observed in cats anesthetized with pentobarbital. Clonidine (1 to 100 mug per kilogram, intraveno...

Under controlled conditions, infant rats emit ultrasonic vocalizations during extreme cold exposure and after administration of the alpha(2) adrenoceptor agonist, clonidine. Previous investigations have determined that, in response to clonidine, ultrasound production increases through the 2nd-week postpartum and decreases thereafter. Given that sympathetic neural dominance exhibits a similar de...

Objectives. The aim of this study was to assess the effects of clonidine on intraoperative analgesia, sedation, intraocular and blood pressure, arrhythmia, and ischemia. Methods. Forty patients undergoing cataract surgery were allocated into two groups. They were monitored with Holter machine, the pupil was dilated, and 30 minutes later, 20 patients received clonidine (4 µg/kg), while the other...