Electrical stimulation-induced α1- and α2-adrenoceptors-mediated contractions of isolated canine lymph nodes

The contractile effects of α-adrenoceptor agonists and field electrical stimulation were investigated pharmacologically in canine isolated tracheobronchial lymph nodes. Addition of noradrenaline (NA), phenylephrine (Phe) and UK14,304 caused dose-related contractions of the isolated lymph nodes. Pretreatment with prazosin (3×10−9, 3×10−8 and 3×10−7 M) shifted the concentration–response curve for phenylephrine to the right, whereas yohimbine (3×10−7 M) did not affect the contractile responses to phenylephrine. On the other hand, the concentration–response curve for UK14,304 shifted to the right by treatment with yohimbine (3×10−9, 3×10−8 and 3×10−7 M) but not by prazosin (3×10−7 M). Field electrical stimulation (25 V, 0.7 ms, 16 Hz) produced contractile responses of the lymph nodes. The electrical stimulation-induced contractions were completely reduced by pretreatment with tetrodotoxin (TTX) (3×10−7 M) or bretylium (10−6 M). Furthermore, phentolamine (10−8, 10−7 and 10−6 M), prazosin (3×10−9 and 3×10−8 M) and yohimbine (3×10−8 and 3×10−7 M) significantly reduced the electrical stimulation-induced contractions in the preparations. The present findings suggest that there are both α1- and α2-adrenoceptors located on the smooth muscle cells in canine tracheobronchial lymph nodes, and that the adrenoceptors-mediated excitatory mechanisms of adrenergic innervation exist in the lymph nodes.