Abstract
1. Noradrenaline release and radioligand binding studies were carried out in the cat hypogastric nerve ligated in vito 2 cm distal to the inferior mesenteric ganglion for different time periods, and in different effector organs.2. Large quantities of noradrenaline and dopamine beta-hydroxylase (DBH) accumulated in the segments of nerve immediately proximal (P(1)) and distal (D(1)) to the ligation, with rates of about 100 and 25 mm/24 hr for the orthograde and retrograde transport, respectively.3. Nicotine evoked the release of noradrenaline from P(1) and atrial slices; the secretory response to nicotine was completely antagonized by mecamylamine. [(3)H]alpha-bungarotoxin biding to membranes from P(1) allowed the estimation of a K(D) of 2.97 nm and a B(max) of 1639 f-mole/mg protein.4. Acetylcholine inhibited the release of endogenous noradrenaline evoked by high K(+) stimulation in atrial slices, but not in P(1) segments. Similarly, carbachol decreased [(3)H]noradrenaline release induced by electrical stimulation (twenty-six shocks, 2 Hz, 5 msec) in the atrium but not in P(1).5. [(3)H]Quinuclydinilbenzylate ([(3)H]QNB) specifically binds to membranes from P(1) and vas deferens, following a saturation curve. In the case of P(1) segments taken 48 hr after ligation a K(D) of 0.35 nm and a B(max) of 129 f-mole/mg protein were found.6. The fact that the B(max) in P(1) and D(1) increased with the time of ligation suggests that orthograde and retrograde axonal transports of muscarinic binding sites exist in this nerve, with approximate rates of transport of 15 and 8 mm/24 hr, respectively.7. As far as adrenoceptors are concerned, we observed that yohimbine or phentholamine did not modify transmitter release from P(1), evoked by high K(+) or electrical stimulation. However, yohimbine enhanced the release of [(3)H]noradrenaline induced by electrical stimulation from splenic slices of the same animals.8. [(3)H]Clonidine, [(3)H]dihydroergocryptine or [(3)H]dihydroalprenolol ([(3)H]DHA) did not specifically bind to membranes from P(1), in spite of the fact that they showed typical saturation curves for specific binding in cortex and atrial membranes from the same cats.9. In conclusion, these data (a) further show that the ligated hypogastric nerve is a good model of noradrenergic nerve terminal free of effector cell; (b) provide direct evidence for the neural location of nicotinic receptors whose activation trigger noradrenaline release from noradrenergic neurones; (c) demonstrate the neural location and axonal transport of muscarinic receptor sites, but leave certain doubts about its functional role in this noradrenergic neurone; and (d) do not support the hypothesis that alpha and beta-adrenoceptors which modulate noradrenaline release from peripheral noradrenergic nerve terminals are neurally (or prejunctionally) located.