The role of alpha- and beta-adrenoceptors in the response to noradrenaline of lymphatic vessels isolated from the bovine mesentery.

The role of postsynaptic adrenoceptors in the spontaneous activity of isolated bovine mesenteric lymphatic vessels was characterized. Low concentrations of noradrenaline (less than 10(-6) M) increased the amplitude and the frequency of the spontaneous contractions whereas high concentrations (less than 10(-6) M) depressed the activity. beta-Adrenoceptor blockade with propranolol enhanced the stimulation by noradrenaline and suppressed the inhibition. alpha 1-Blockade by prazosin or alpha 2-blockade by idazoxan antagonized the stimulation by noradrenaline and potentiated the inhibition. Activation of alpha 1-adrenoceptors by methoxamine, or of alpha 2-adrenoceptors by clonidine, stimulated lymphatic activity. The increases in the amplitude and frequency of the spontaneous contractions produced by each agonist were competitively antagonized by prazosin and idazoxan, respectively. Our results confirm the presence of postjunctional beta-, alpha 1-and alpha 2-adrenoceptors in lymphatic vessels and show that each of these receptors plays an important role in the adrenergic regulation of the spontaneous activity, with beta-adrenoceptors mediating inhibition, and alpha 1- and alpha 2-adrenoceptors mediating stimulation.