Enhanced presynaptic facilitation of vascular adrenergic neurotransmission in spontaneously hypertensive rats

1. The interaction between the vascular renin-angiotensin system and presynaptic beta-adrenoreceptors was examined in male and female normotensive and spontaneously hypertensive rats, using the in vitro perfused mesentery preparation. 2. Enhancement of the pressor response to periarterial nerve stimulation by isoprenaline was shown to be significantly greater in preparations from male and female spontaneously hypertensive rats compared to corresponding preparations from normotensive Wistar rats. 3. In preparations from normotensive and hypertensive animals, the potentiating effect of isoprenaline was prevented by pretreatment with propranolol or ICI 118 551, but not atenolol, implicating a beta 2-adrenoreceptor. 4. Angiotensin II enhanced the responses to peripheral nerve stimulation in preparation from normotensive and hypertensive animals. Enhancement was significantly greater in preparations from hypertensive animals. 5. The potentiation caused by isoprenaline was blocked by the angiotensin II receptor antagonist [Sar1-Ile8] angiotensin II, and by captopril. The potentiation following angiotensin II was unaffected by ICI 118 551. 6. These results suggest that stimulation of presynaptic beta 2-adrenoreceptors activates a localized angiotensin II system. No significant differences in this facilitatory system were observed between male and female animals, but the potentiation caused by activation of this system was considerably greater in the spontaneously hypertensive rats.