The response of isolated preparations of bovine mammary artery was investigated, with the aim of characterising further the adrenergic receptor subtypes present. Noradrenaline (NA) and the α1 agonist phenylephrine gave sigmoidal dose–response curves with pec50 values of 5.97±0.07 (N=34) and 6.21±0.32 (N=8), respectively. Stimulation of α2 receptors with UK 14,304 produced a weak response with pec50 of 6.78±0.38 (N=7), and maximal contraction of 17.8±9.9% relative to NA. A61603, an α1A agonist, gave a curve parallel to NA, but shifted to the left (pec50 of 6.98±0.19 (N=5)); this drug had an increased potency of 10-fold relative to NA, and 4-fold relative to phenylephrine. Schild analysis of curves obtained with the α1 antagonist prazosin gave a pA2 of 8.70±0.47 (N=6–9), whereas the α2 antagonist yohimbine resulted in a pA2 of 7.65±0.16 (N=4). The α1A receptor antagonists WB4101 and 5-methylurapidil gave pA2 values of 9.39±0.69 (N=4) and 7.72±0.02 (N=2–3), respectively. The irreversible α1B inhibitor CEC reduced the pec50 from 5.39±0.12 to 4.31±0.18 (N=7) only at the highest dose used, and high doses of the α1D antagonist BMY 7378 produced a shift to the right at giving a pA2 of 7.37±0.08 (N=3). These results suggest major involvement of the α1B adrenergic receptor subtype in contraction of the bovine mammary artery, which is similar to the human internal mammary artery.
- mammary artery