FUNCTIONAL-CHARACTERIZATION OF POSTJUNCTIONAL ADRENERGIC-RECEPTOR SUBTYPES IN BOVINE INTRAMAMMARY ARTERIES

We examined the functional role of adrenergic receptor subtypes (ARs) in bovine intra-mammary arteries (IMAs), 1.5-2.5 mm internal diameter, Norepinephrine (NE) and phenylephrine (PE) produced concentration-dep endent increases in tone in segments maintained at a previously determ ined optimal basal tension in vitro, The sensitivity of the tissue to NE and PE, based on -log molar ED50s was 6.87 +/- 0.17 and 7.05 +/- 0. 35, respectively, in addition a Schild analysis yielded antagonist aff inities for the receptor mediating contractile responses to NE (pA2 va lue) of 10.46 +/- 0.85 for prazosin and 6.29 +/- 0.18 for yohimbine. T hese data indicate a dominance of functional alpha 1 (alpha(1)) over a lpha 2 (alpha(2))-ARs in this tissue, Based on the inhibitory effects of chloroethylclonidine (CEC) on PE responses and the further reductio n in sensitivity when nifedipine was added to the CEC, also in the pre sence of PE, we conclude that there is more than one alpha(1)-AR subty pe, with a predominant role for alpha(IB)-ARs in phenylephrine respons es, Stimulation of beta (beta)-ARs, resulted in relatively small reduc tions in tone (the highest magnitude of response was 25.94 +/- 6.46% o f the papaverine maximum at 3 x 10(-6) M isoproterenol): in addition, propranolol did not significantly alter tissue sensitivity to NE. Addi tional characterization of functional autonomic receptor populations i n this circulatory bed will form a basis for future studies on circula tory dynamics in the mammary gland.