Asymmetry of the contractile response of the rabbit ear artery to exogenous amines

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Abstract
Segments of rabbit ear artery were prepared with the adventitial surface outward or with the vessel everted to expose the intima. The amine sensitivity of each preparation was tested by cumulatively adding norepinephrine (NE) or 5-hydroxytryptamine (5HT) allowing the contraction to come to a final steady level of tension between each dose. The segments with the intima exposed showed greater sensitivity (lower ED50) to NE and 5HT than the adventitia exposed segments. This difference for NE was abolished by blockade of neuronal and extraneuronal uptake mechanisms. Before and after uptake blockade the intimal stimuli produced larger responses during the initial rapid phase of contraction than the identical adventitial stimuli. High K+ contractions were not significantly different with the 2 directions of application. The removal of extracellular Ca from the bathing medium abolished the contraction to K+. Both initial and final responses to 5HT were reduced by the Ca2+-free medium. The NE response was reduced only in its final amplitude, with the initial contraction unchanged. The ear artery displays asymmetric responses to amines, with the intima being more sensitive and producing a larger 1st-phase contraction.