Effect of nerve stimulation and angiotensin on the accumulation of 3H-norepinephrine and the endogenous norepinephrine level in guinea pig vas deferens

Abstract

The effect of angiotensin on the endogenous norepinephrine (NE) content and on the accumulation of 3H-NE was studied in the isolated guinea pig vas deferens stimulated at both the pre- and postganglionic level (hypogastric nerve and transmural stimulation). It was found that angiotensin blocked 3H-NE accumulation (uptake and retention and produced a depletion of endogenous NE in the unstimulated vas deferens. Continuous pre- and postganglionic stimulation at low-frequency (6/sec) did not produce any significant changes in the endogenous NE level, while high-frequency (50/sec) stimulation reduced it by 30–40 per cent. The accumulation of 3H-NE was impaired by continuous pre- and postganglionic stimulation and was dependent on the frequency of stimulation. With a high-frequency (50/sec), the accumulation was only 5–6 per cent of the control, suggesting that depolarization of the neuronal membrane, produced by nerve stimulation, blocks the re-uptake of NE and favors its release. It appears, therefore, that these two phenomena are sequential for a certain area of the neuronal membrane. Angiotensin abolished the inhibiting effect of nerve stimulation on 3H-NE uptake and retention. It is concluded that the effect of angiotensin on the endogenous NE level and on the accumulation of 3H-NE depends on the degree of impulse activity in the sympathetic nerve and the concentration of angiotensin used. The duality (or plurality) of the action of angiotensin in the stimulated and unstimulated guinea pig vas deferens suggests a possible modulating role of angiotensin in adrenergic neurotransmission.