Distribution of α‐adrenergic receptors in the arteriolar network of the rat gastrocnemius (1170.13)

Results of previous studies examining adrenergic receptor subtype distribution have varied. The purpose of this study was to determine the distribution of adrenergic receptor subtypes throughout the arterial tree of the rat gastrocnemius muscle. Feed arteries (FA) and first (1A), second (2A), and third (3A) order arterioles from the gastrocnemius muscle of male Sprague‐Dawley rats were isolated and cannulated for videomicroscopic study. Cumulative dose‐response curves (10 ‐9 to 10 ‐4 M) were performed using the non‐selective agonist norepinephrine (NE), α 1 ‐agonist phenylephrine (PE), and α 2 ‐agonist UK14304 (UK) to determine constrictor responses. All branch orders constricted similarly to NE and PE (% constriction in FA: NE = 75.4% ± 5.4, PE =70.1% ± 6.6; 1A: NE = 91.1% ± 2.1, PE= 83.7% ± 2.8; 2A: NE= 92.4% ± 2.4, PE= 88.8% ± 2.3; 3A: NE = 81.3% ± 8.7, PE= 79.3% ± 5.0). No branch order constricted significantly to UK or to the β‐agonist isoproterenol. Constrictor responses to NE and PE were abolished by the α 1 ‐antagonist prazosin (10 ‐7 M) in all branch orders. Neither the α 2 ‐antagonist rauwolscine (10 ‐6 M) nor the β‐antagonist propranolol (10 ‐6 M) reduced constriction in any branch order. These results indicate that constrictor responses to NE are mediated almost entirely by α 1 ‐adrenergic receptors in all examined branch orders of the rat gastrocnemius with little to no contribution from α 2 ‐adrenergic receptors.