Table 1.

Demonstration of effective receptor blockade

		Alpha-1, ml/min		Alpha-2, ml/min		P2x, ml/min		NPY, ml/min
Group	Intensity	Pre	Post	Pre	Post	Pre	Post	Pre	Post
Young	Rest	46 ± 8	14 ± 5	52 ± 21	32 ± 6	41 ± 13	24 ± 6	24 ± 7	3 ± 1
	2.5 miles/h	138 ± 17	18 ± 8	97 ± 13	25 ± 6	84 ± 22	12 ± 7	95 ± 14	6 ± 2
	4 miles/h 2.5% grade	145 ± 22	21 ± 5	113 ± 16	24 ± 6	110 ± 11	21 ± 6	95 ± 17	3 ± 1
Old	Rest	39 ± 9	9 ± 3	56 ± 15	22 ± 3	32 ± 11	13 ± 2	20 ± 5	4 ± 2
	2.5 miles/h	124 ± 8	22 ± 3	101 ± 14	33 ± 6	72 ± 16	16 ± 5	74 ± 24	9 ± 2
	4 miles/h 2.5% grade	124 ± 16	17 ± 4	125 ± 29	24 ± 5	83 ± 19	37 ± 5	83 ± 22	6 ± 1

Values are expressed as means ± SE. All post values are significantly different from prevalues P < 0.01. The following selective agonists and doses were utilized for each receptor type: Alpha-1 receptors: phenylephrine (0.1 μg·ml⁻¹·min⁻¹); Alpha-2 receptors: Clonidine (1 μg·ml⁻¹·min⁻¹); P_2x: α,β-methylene ATP; (1 μg·ml⁻¹·min⁻¹); NPY: [Leu³¹, Pro³⁴] NPY (1 μg·ml⁻¹·min⁻¹). The change in experimental limb blood flow in response to intra-arterial infusion of selective receptor agonist before (pre) and after (post) administration of the corresponding receptor antagonist.