Effect of cooling on alpha-1 and alpha-2 adrenergic responses in XXXX saphenous and femoral veins.

@entity3160 @entity308 @entity235 @entity3158 @entity3157 @entity2647 @entity3612 @entity1063
Experiments were designed to determine the effects of cooling on alpha-1 and alpha-2 adrenergic responses in isolated @entity235 veins. Rings of saphenous and femoral veins were suspended for isometric tension recording in modified Krebs-Ringer @entity3157 solution, gassed with 95% @entity3612 and 5% @entity3158 . Cooling (from 37-24 degrees C) augmented contractions to @entity1063 in saphenous but caused @entity308 in femoral veins. Cooling (to 24 degrees C) had no effect on alpha-1 adrenergic responses evoked by @entity2647 in saphenous veins but caused @entity308 in femoral veins. Alpha-2 adrenergic responses produced by UK 14,304 were augmented by cooling in the saphenous but were virtually abolished by cooling in femoral veins. Cooling decreased the dissociation constant (i.e., increased affinity) of @entity3160 for alpha-1 adrenoceptors in saphenous and femoral veins (approximately 3-fold), and the dissociation constant of @entity3160 for alpha-2 adrenoceptors in saphenous veins (approximately 7.5-fold). The influence of cooling on alpha adrenoceptor responsiveness was analyzed using computer-generated receptor-models. The results suggest that the differential sensitivity of cutaneous and deep blood vessels to cooling results from differences in efficiency of alpha-1 and alpha-2 adrenoceptor response coupling. In the saphenous vein, there is a large alpha-1 adrenoceptor reserve which buffers the alpha-1 adrenergic response from the inhibitory influence of cooling. This coupled with a cooling-induced increase in alpha-2 adrenoceptor affinity ensures that cooling augments the response to @entity1063 . In the femoral vein, there is no alpha-1 adrenoceptor reserve and cooling therefore depresses alpha-1 adrenergic responses.(ABSTRACT TRUNCATED AT 250 WORDS)
