Role of sympathetic cholinergic pathway in the neurogenous control of tissue-type plasminogen activator release into the blood

The changes in conductivity of skeletal muscle vessels of the hind leg and tissue-type plasminogen activator (t-PA) activity in outflowing blood after electrostimulation (5 V, 0.5 ms, 20 Hz, 30 s) at the L4-L5 level of the peripheral end of the transected isolated sympathetic chain were studied in experiments on anaesthetized cats. Stimulation of the sympathetic chain induced vasoconstriction and release of t-PA from the vascular wall into the blood. Pretreatment with the beta-adrenoblocker propranolol neither changed the character of vascular reactions nor blocked t-PA secretion. Efferent stimulation of the sympathetic chain against a background of alpha-adrenoceptor blockade by dihydroergotoxin increased blood flow and was accompanied by a rise in t-PA activity. The M-cholinergic blocker atropine suppressed both vascular relaxation and release of t-PA into the blood. Vasodilatation accompanied by t-PA secretion could be induced by intraarterial infusion of acetylcholine and blocked by atropine. The existence of a neurogenic mechanism controlling t-PA release from the vascular wall involving a sympathetic cholinergic pathway and connected with excitation of vascular M-cholinoceptors by acetylcholine is suggested.