The Influence of Simultaneous Administration of Clonidine and Atropine on Intraocular Pressure under the Condition of General Anesthesia in the Rat

Clonidine, an α2-adrenocepter agonist, has often been used for sedation and analgesia prior to surgery. Unfortunately, clonidine usually induces some side effects during surgery, such as low blood pressure and bradycardia. Atropine, a muscarinic receptor antagonist, is used for improving some side effects induced by clonidine action during surgery. It is known in the field of ophthalmology that atropine, as well as clonidine, affects intraocular pressure (TOP). However, effects of simultaneous administration of atropine and clonidine on TOP still remain unclear although these drugs have been used during surgery under general anesthesia. The present study examined the influence of clonidine and atropine on IOP under the condition of anesthesia in the rat. Male Wistar rats (250-300 g, n=38) were used. Under urethane anesthesia (1.4 g/kg, i.p.), a catheter was inserted into the jugular vein for administrating drugs and into the femoral artery for measuring the mean arterial blood pressure (MBP). For measuring the IOP, an injection needle (27-gauge) was penetrated into the anterior chamber of the eyeball. The heart rate (HR) was recorded from an electrocardiogram. Statistical analysis was carried out using analysis of variance (ANOVA). A difference was accepted as significant when p < 0.05. Administration of clonidine hydrochloride (5 μg/kg, n=15) significantly decreased the IOP to 81% of the control (100%, before drugs). The MBP and the HR were also significantly reduced 60% and 15% of the control, respectively. Atropine sulphate (60 μg/kg, n=4) significantly increased the HR to 30% of the control, while significant changes in the IOP and the MBP were not observed. Simultaneous administration of clonidine and atropine (n = 7) produced significant decreases of both the IOP and the MBP, whereas no significant change in the HR was observed. The present study suggests that atropine does not alter IOP under normal conditions and improves bradycardia produced by clonidine without changes in the MBP and the IOP.