Oxymetazoline inhibits osmotic water permeability (P_f) in the rat cortical collecting duct (CCD) and inner medullary collecting duct (IMCD)

The objective of this study was to determine if the alpha-2 (α₂) adrenoceptor agonist oxymetazoline would inhibit Pf in collecting duct nephron segments. The isolated perfused tubule technique was used to determine Pf by measuring net fluid flux in the presence of a lumen-to-bath osmotic gradient and by calculating P_f via standard equations. One set of studies was conducted using CCDs isolated from Sprague-Dawley rat kidneys and another set was conducted in terminal IMCDs isolated from Wistar rat kidneys. Experimental agents were added to the bathing solution, and all experiments were conducted at 37°C. Arginine vasopresein (AVP) at 220pM was used to increase P_f. Oxymetazoline and the α₂ antagonist atipamezole were used at 1 μM. The sequence of periods and the results (P_f, μm/sec, mean±se) are shown below. Control AVP AVP+Oxy AVP+Oxy+Ati CCDs (n=7) -16±35 748±92* 295±113† 580±93® IMCPs (n=5) 3±1 140±6* 32±3* 76±3* *, † and ® - significantly different from the previous period (p<.001), (p<.005), and (p<.05), respectively. Oxy - oxymetazoline, Ati - atipamezole. We conclude that oxymetazoline, a partial α_2A adrenoceptor agonist, inhibits AVP-stimulated P_f in the rat CCD and IMCD.