Subendothelial beta 2-adrenoceptors in the rat vena cava: facilitation of noradrenaline release via local stimulation of angiotensin II synthesis

Preparations of the cranial segment of the rat inferior vena cava preincubated with 3H-noradrenaline were superfused in the presence of desipramine and corticosterone. Tritium overflow was stimulated electrically (2 Hz). The experiments were carried out in spirally cut strips with or without intima or in segments ligated at both ends and superfused either on the adventitial side ("conventionally") or "inside out". In spirally cut strips electrically evoked 3H overflow was increased by isoprenaline and procaterol, but much less so by prenalterol. Adrenaline 1 nmol/l increased overflow, but at high concentrations it reduced it, just as noradrenaline did at all concentrations. The concentration-response curve for isoprenaline was shifted to the right by propranolol (apparent pA2:8.29) and even more so by ICI 118-551, whereas atenolol was less potent (apparent pA2:6.42). Rauwolscine which, given alone, increased the evoked 3H overflow antagonized the inhibitory effect of noradrenaline (apparent pA2:7.58). These findings indicate that beta 2- and alpha 2-adrenoceptors mediating facilitation and inhibition of noradrenaline release, respectively, are present in the vena cava. The response to isoprenaline (at all concentrations) was co...Continue Reading