Selective blockade by nifedipine of ‘purinergic’ rather than adrenergic nerve‐mediated vasopressor responses in the pithed rat

Abstract

1 Nifedipine can attenuate pressor responses to sympathetic nerve stimulation both in the presence and in the absence of a-adrenoceptor blocking agents.2 In the presence of a,fi-methylene ATP, nifedipine produces only a small attenuation of the vasopressor response.3 Nifedipine attenuates the vasopressor response produced by intravenous bolus administration of x,-methylene ATP. 4 The results suggest that the purinergic component of the vasopressor response to stimulation of the sympathetic outflow in the rat is subject to blockade by nifedipine, whereas the a-adrenoceptormediated response to co-transmitter noradrenaline is relatively resistant.

Alpha‐adrenoceptors: A critical review

“…In the rat isolated vas deferens the effect of ATP is associated with an excitatory junctional potential and the contractile actions are susceptible to nifedipine (470). This appears to be supported by other observations in the rabbit isolated saphenous artery (616) and pithed rat (263), which suggest that the effect of ATP will be more widespread over the vascular smooth muscle (electrically coupled and dependent upon voltage-operated channels) than NA which appears to employ pharmacomechanical coupling. Another example of the differential influence of vasoactive factors on contractile response is endothelium-derived vasoactive factors (EDRF).…”

Purinergic Signaling and Blood Vessels in Health and Disease

“…A contribution of ATP to sympathetic vasopressor responses of the pithed rat has also been demonstrated (Grant et al, 1985;Bulloch and McGrath, 1988a;Schlicker et al, 1989). As with the purinergic neurogenic response in isolated mesenteric arteries from rat and dog (Omote et al, 1989;Rummery et al, 2007), the purinergic component of the vasopressor response to stimulation of the sympathetic outflow of the rat can be blocked by nifedipine, indicating an involvement of L-type calcium channels, whereas the a-adrenoceptor-mediated responses to the cotransmitter NA are relatively resistant to nifedipine (Bulloch and McGrath, 1988b). In urethane-anesthetized rats, purinergic cotransmission was shown to play a major role in the pressor sinocarotid reflex (Tarasova and Rodionov, 1992).…”

Characterization of prejunctional 5‐HT receptors mediating inhibition of sympathetic vasopressor responses in the pithed rat

“…Nevertheless, the failure of methiothepin and metergoline to block the inhibition to 5-HT deserves further comment, particularly in terms of their selectivity and considering that the rat sympathetic vasopressor responses involve, to an important extent, activation of vascular al-adrenoceptors (Flavahan et al, 1985;Bulloch & McGrath, 1988).…”