Y₁- and α₁-receptor control of basal hindlimb vascular tone

The role of endogenous Y(1)-receptor activation on skeletal muscle vasculature under baseline conditions is currently debated and no in vivo studies have been performed to address this issue. Therefore, this study was designed to address the effect of Y(1)-receptor and/or alpha(1)-adrenoceptor antagonism on basal hindlimb vascular conductance in male Sprague-Dawley rats in vivo. Left hindlimb vascular conductance, carotid artery mean arterial pressure, and heart rate were measured during low volume infusion of N(2)-(diphenylacetyl)-N-[(4-hydroxyphenyl)methyl]-d-arginine amide (BIBP3226; 100 microg/kg), prazosin (20 microg/kg), and combined blockade to the left hindlimb. Vascular conductance increased 1.5 +/- 0.5 microl.min(-1).mmHg(-1) with BIBP3226 infusion, 1.7 +/- 0.5 microl.min(-1).mmHg(-1) with prazosin infusion, and 4.8 +/- 1.0 microl.min(-1).mmHg(-1) with combined blockade (P < 0.05). Interestingly, systolic vascular conductance increased in all three conditions, but diastolic vascular conductance only increased in the two conditions where BIBP3226 was present. These data indicate that Y(1)-receptor activation plays an important role in the regulation of vascular conductance in the resting rat hindlimb. Furthermore, this effect was of the same magnitude as the alpha(1)-adrenoceptor contribution. The differential flow profiles following alpha(1) blockade with and without Y(1)-receptor blockade supports local differences in receptor distribution.