ALPHA-ADRENOCEPTOR AND BETA-ADRENOCEPTOR AGONIST ACTIVITY IN THE VENOM OF THE AUSTRALIAN HUNTSMAN SPIDERS, DELENA-CANCERIDES AND ISOPEDA-MONTANA

1. Crude venom gland extracts (VGE) were prepared from female Delena c ancerides and Isopeda montana spiders. The VGE were tested in isolated rat atrial, caudal artery and pithed rat preparations for pharmacolog ical activity. 2. In rat isolated atrial preparations, D. cancerides a nd I. montana VGE, each in a concentration of 2 glands/mL, produced in creases in atrial rate which were abolished by propranolol (1 mumol/L) but not by ketanserin (0.1 mumol/L) or reserpine pretreatment (2.5 mg /kg s. c. 24 h prior to experimentation) indicating a direct action on atrial beta-adrenoceptors 3. In rat caudal artery preparations each V GE produced an increase in perfusion pressure, which was taken as an i ndex of vasoconstriction. Pressor responses to D. cancerides VGE (1 gl and/mL) were abolished in the presence of prazosin (1 mol/L) but not b y reserpine pretreatment, indicating an action of the VGE on vascular alpha1-adrenoceptors. Neither prazosin nor reserpine pretreatment had any effect on pressor responses of rat caudal artery preparations to I . montana VGE. Ketanserin (6 nmol/L) produced a small reduction in the degree of vasoconstriction produced by the VGE. This demonstrates a l ack of alpha1-adrenoceptor agonist activity of the VGE. 4. Both VGE pr oduced dose-dependent increases in mean arterial pressure and heart ra te in pithed rat preparations. The use of relatively selective recepto r antagonists indicated that the increases in mean arterial pressure ( MAP) produced by both VGE were mediated by an action on alpha2-adrenoc eptors.