Studies were conducted on 15 adult male Sprague-Dawley rats (Charles River Laboratories, Wilmington, MA) aged 60 days and weighing 180 to 200 g. Rats were anesthetized by intraperitoneal injection of a mixture of ketamine hydrochloride (27.5 mg/kg; Sano Winthrop, New York, NY) and xylazine hydrochloride (Rompun, 2.5 mg/kg; Miles, Shawnee Mission, KS). Osmotic mini-pumps (Alzet, model no. 2ML4; Alza Corporation, Palo Alto, CA) were implanted subcutaneously in a dorsal interscapular configuration. These pumps deliver solution at a rate of 2.5 μL/h and provide constant infusion for at least 28 days. Pumps were loaded with saline vehicle alone (
n = 5) or saline containing the α-adrenoceptor antagonist phentolamine (Sigma, St. Louis, MO;
n = 5) or the β-adrenoceptor antagonist propranolol (Sigma, St. Louis, MO;
n = 5). Both drugs were delivered at dosages of 1 mg/d.
Table 1 provides the systolic and diastolic blood pressures at kill. Blood pressure was measured under anesthesia using a tail cuff (Kent Scientific, Torrington, CT). Although systolic blood pressure was not significantly reduced, this was likely because of the short duration of the treatment and the low doses used. We have previously shown that these drugs administered at these doses are effective for maintaining adrenoceptor blockade.
26–28 At 21 days after pump implantation, rats were killed, and their eyes were removed for analyses. All animal procedures adhered to the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research and were approved by the Institutional Animal Care and Use Committee of the University of Tennessee Health Science Center and conformed to National Institutes of Health guidelines.