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Functional characterization of post‐junctional adrenergic receptor subtypes in bovine intra‐mammary arteries
Author(s) -
Pereira F. J.,
Will J. A.
Publication year - 1997
Publication title -
journal of veterinary pharmacology and therapeutics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.527
H-Index - 60
eISSN - 1365-2885
pISSN - 0140-7783
DOI - 10.1046/j.1365-2885.1997.00082.x
Subject(s) - phenylephrine , prazosin , endocrinology , yohimbine , medicine , propranolol , circulatory system , chemistry , stimulation , receptor , adrenergic , antagonist , biology , blood pressure
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‐dependent increases in tone in segments maintained at a previously determined optimal basal tension in vitro . The sensitivity of the tissue to NE and PE, based on ‐log molar ED 50s was 6.87 ± 0.17 and 7.05 ± 0.35, respectively. In addition a Schild analysis yielded antagonist affinities for the receptor mediating contractile responses to NE (pA2 value) of 10.46 ± 0.85 for prazosin and 6.29 ± 0.18 for yohimbine. These data indicate a dominance of functional alpha 1 (α 1 ) over alpha 2 (α 2 )‐ARs in this tissue. Based on the inhibitory effects of chloroethylclonidine (CEC) on PE responses and the further reduction in sensitivity when nifedipine was added to the CEC, also in the presence of PE, we conclude that there is more than one α 1 ‐AR subtype, with a predominant role for α 1B ‐ARs in phenylephrine responses. Stimulation of beta (β)‐ARs, resulted in relatively small reductions in tone (the highest magnitude of response was 25.94 ± 6.46% of the papaverine maximum at 3×10 −6 M isoproterenol); in addition, propranolol did not significantly alter tissue sensitivity to NE. Additional characterization of functional autonomic receptor populations in this circulatory bed will form a basis for future studies on circulatory dynamics in the mammary gland.