ABLATION OF THE MYENTERIC PLEXUS IMPAIRS ALPHA-ADRENERGIC BUT NOT BETA-ADRENERGIC RECEPTOR-MEDIATED MECHANICAL RESPONSES OF RAT JEJUNAL LONGITUDINAL MUSCLE

  • 1 October 1986
    • journal article
    • research article
    • Vol. 239  (1) , 9-14
Abstract
The mechanical responses produced by alpha and beta adrenergic receptor agonists were evaluated in control and myenteric neuron-ablated rat jejunal longitudinal muscle. The myenteric plexus of the jejunum was destroyed by serosal application of benzalkonium chloride (BAC). The beta adrenergic receptor agonists isoproterenol and sulfonterol produced a concentration-dependent relaxation of both control and BAC-treated jejunum. Dose-response curves obtained in control and BAC-treated jejunum were nearly superimposable regardless of the beta agonist used. Isoproterenol-induced relaxation was antagonized by the beta receptor antagonists propranolol and practolol but not by butoxamine. The alpha-1 selective agonists phenylephrine and methoxamine were more potent and efficacious in producing relaxation of control than BAC-treated jejunum. The relaxant responses of methoxamine and phenylephrine in control jejunum were blocked by prazosin but not by yohimbine. The supposed alpha-2 selective agonist clonidine also produced a concentration-dependent, prazosin-sensitive, yohimbine-resistant relaxation which was markedly greater in control than BAC-treated jejunum, consistent with alpha-1 receptor stimulation. Clonidine tested in the presence of prazosin and the alpha-2 selective receptor agonists UK-14,304, M-7 and B-HT 920 all produced a concentration-dependent contraction of control but not BAC-treated jejunum. The contractile response produced by UK-14,304 was antagonized by yohimbine but not by atropine. Our results suggest that in rat jejunal longitudinal muscle: 1) beta adrenergic receptors mediate relaxation and are located on the smooth muscle; 2) alpha-1 adrenergic receptors mediate relaxation and are located on both the smooth muscle and myenteric plexus; and 3) alpha-2 adrenergic receptors mediate contraction and are located on the myenteric plexus.