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Jeffrey Kiel, Alma Maldonado; Ocular hypertensive effect of pilocarpine in the anesthetized rat. Invest. Ophthalmol. Vis. Sci. 2013;54(15):2005.
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A previous study by Pang et al. (Exp Eye Res 80: 207-214, 2005) reported that pilocarpine tended to increase IOP in conscious rats one hour after dosing but the effect was not significant. The present study sought to determine if continuous IOP measurement before and after application would detect a more robust and rapid response.
In rats (n=14) anesthetized with ketamine plus xylazine, we measured femoral mean arterial pressure (MAP) and IOP by direct cannulation, carotid blood flow (BFcar) by transit time ultrasound and heart rate (HR) by a digital cardiotachometer. The protocol entailed 10 min of baseline followed by 20 min of measurement after topical application of pilocarpine (1%). The data (mean +/- standard error) were analyzed by paired t-test.
The systemic parameters were unchanged (p>0.05 for MAP, BFcar and HR) before and after pilocarpine (MAP: 96 +/- 4 Vs 92 +/- 4 mmHg; BFcar: 4.2 +/- 0.3 Vs 4.0 +/- 0.3 ml/min; HR: 268 +/- 9 Vs 268 +/- 9 bpm). IOP increased significantly from 12.6 +/- 0.7 to 14.8 +/- 1.0 mmHg (p<0.01). The IOP response began within minutes after application and began to decline slowly after 30-45 min.
In contrast to its hypotensive effect in humans and primates, pilocarpine causes a rapid, transient increase in IOP in anesthetized rats. The rapidity of the IOP response suggests an episcleral venous pressure mediated mechanism that warrants further investigation.
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