Sodium-dependence of the saturability of carrier-mediated noradrenaline efflux from noradrenergic neurones in the rat vas deferens

The carrier-mediated transport of 3H-noradrenaline out of noradrenergic neurones was studied in vasa deferentia obtained from rats after pretreatment with reserpine and pargyline (to inhibit vesicular storage and monoamine oxidase, respectively). The tissue was first preincubated with various concentrations of 3H-noradrenaline (0.3--100 mumol/1; 30 min) and then washed out for 110 min with amine-free medium. During the last 10 min of washout, carrier-mediated neuronal efflux of 3H-noradrenaline was elicited by exposure to either Na+-free medium or 100 mumol/l veratridine; it was measured at 1-min intervals. While the peak rates of carrier-mediated 3H-noradrenaline efflux elicited by Na+-free medium were linearly related to the 3H-noradrenaline content of the tissue (which cannot be raised beyond a certain maximal value, since uptake is saturable), those evoked in response to veratridine approached saturation as the 3H-noradrenaline level in the tissue was raised. Hence, saturation of 3H-noradrenaline outward transport was demonstrated at high (exposure to veratridine), but not at low (exposure to Na+-free medium) intraneuronal Na+ concentrations. The results indicate that the Km for the mediated outward transport of noradrenaline across the plasma membrane of noradrenergic neurones is inversely related to the internal Na+ concentration, just as the Km for the mediated inward transport of noradrenaline (i.e., the neuronal noradrenaline uptake) is inversely related to the external Na+ concentration.

Denervation-induced supersensitivity to calcium of chemically skinned smooth muscle of the guinea-pig vas deferens

Chronic denervation of the smooth muscle of the guinea-pig vas deferens results in postjunctional supersensitivity. A partial membrane depolarization contributes to the enhanced sensitivity. However, there is evidence that supersensitivity results in part from cellular alterations other than membrane potential changes. In the present study we investigated the possibility that changes in the sensitivity of the contractile proteins may contribute to the phenomenon. The approach was to evaluate the concentration-response relationship for calcium of "skinned" preparations of guinea-pig vas deferens. The tissues were chemically skinned with either triton X-100 or saponin. Concentration-response curves for calcium were constructed 1 week after postganglionic denervation of one of a pair of vasa deferentia. The curve for denervated tissues was shifted significantly to the left of control (1.5-fold at the level of the EC50). In addition to supersensitivity, denervated skinned preparations exhibited a faster rate of contraction. The phenothiazine compounds trifluperazine, fluphenazine and chlorpromazine relaxed skinned muscles which were contracted with calcium. The relaxation was concentration-dependent, and was less pronounced in denervated vasa deferentia than in controls. These results suggest that increased sensitivity of the contractile proteins may contribute to denervation-induced supersensitivity of smooth muscle, and further that this may be related to a change in the activity or amount of calmodulin.

External Ca-independent release of norepinephrine by sympathomimetics and its role in negative feedback modulation

The release of [3H]norepinephrine from isolated mouse vas deferens has been measured. 1-Phenylephrine and 1-norepinephrine significantly enhanced the spontaneous release of radioactivity. As shown by a combination of HPLC and scintillation spectrometry, the release of total radioactivity in response to 1-phenylephrine or 1-norepinephrine consisted mainly of [3H]norepinephrine. Evidence has been obtained that the release of endogenous norepinephrine by exogenous norepinephrine and 1-phenylephrine is independent of the external Ca2+ concentration. The released endogenous norepinephrine in turn inhibits the release of norepinephrine in response to electrical field stimulation. In the presence of yohimbine, the enhancement of spontaneous release due to 1-phenylephrine (or to 1-norepinephrine) was not affected, whereas there was a significant superimposed release of [3H]norepinephrine in response to field stimulation, indicating that the inhibition of stimulation-induced norepinephrine release is an alpha 2-adrenoceptor-mediated process. An important consequence of these findings is to question previous interpretations that the effects of administration of 1-norepinephrine or 1-phenylephrine are due exclusively to their direct effects on the effector cells. The Ca-independent release of endogenous norepinephrine might partly initiate their pharmacological responses. It is concluded that this Ca-independent release is of functional importance, since norepinephrine may accumulate in a concentration sufficient to modulate the release of norepinephrine from varicosities in response to electrical stimulation.

Organ culture of young rat vas deferens as an in vitro model for the study of denervation supersensitivity

To investigate whether organ culture is a suitable in vitro model for studying the mechanisms of denervation-induced supersensitivity, we cultured 1-week-old rat vas deferens for 3 days with a basic applied tension of 20 mg. Cultured muscles showed supersensitivity to norepinephrine and methacholine with concomitant elevation of the maximal response. To compare these changes with those caused by denervation, young rats were chemically denervated by injecting 6-hydroxydopamine, and consequent sensitivity changes were investigated. Denervated muscles showed non-specific supersensitivity to norepinephrine and methacholine but the maximal response did not increase. When these denervated muscles were organ-cultured, they showed no or only a slight increase in sensitivity to norepinephrine and methacholine, but the maximal response increased greatly. These observations led to the suggestion that the increase in sensitivity may be mediated through the same mechanisms as those for denervation supersensitivity. The elevation of the maximal response was suggested to be produced by the improvement of cell-to-cell conduction as well as some other unknown factor(s) probably specific to organ culture. Thus, it was concluded that organ-cultured 1-week-old rat vas deferens is a useful model to study the mechanisms of denervation supersensitivity.

Potentiation by cholinoceptor agonists of contractions to field stimulation of rat vas deferens

Cholinoceptor agonists (arecoline congruent to carbachol greater than acetylcholine greater than pilocarpine) potentiated contractions to field stimulation of rat vas deferens via the activation of an atropine-sensitive muscarinic receptor. The potentiating effect of carbachol was dependent on the level of calcium in the medium, being more potent at higher calcium concentrations. The potentiating effect of carbachol was more pronounced in the epididymal than in the prostatic segment but was not attenuated by prazosin, an alpha 1-adrenoceptor antagonist. Carbachol did not significantly modify the direct contractile effects of noradrenaline nor alter the field-stimulation-evoked release of noradrenaline from the epididymal vas deferens. It is concluded that the potentiating effect of cholinoceptor agonists on the contractions to field stimulation in the rat vas deferens was not a result of an enhancement of adrenergic neurotransmission.

Influence of temperature on stimulus-secretion coupling in the sympathetic nerves and on neuromuscular transmission, in guinea-pig vas deferens

In guinea-pig isolated vas deferens moderate cooling (within the range 16-41 degrees C) improved, while further cooling depressed, sympathetic neuromuscular transmission. Moderate cooling: (a) enhanced the contractile responses both to electrical nerve stimulation and (although less strongly) to exogenous noradrenaline or to the adenosine 5'-triphosphate (ATP) analogue, alpha, beta-methylene ATP; (b) enhanced the overflow of [3H]noradrenaline evoked by electrical nerve stimulation at 1-8 Hz, but not that caused by direct depolarization of varicosities with 80 mM potassium; (c) reduced the depressing effect of exogenous noradrenaline, as well as the enhancing effect of the alpha-adrenoceptor blocking agent phentolamine, on the secretory responses to electrical nerve stimulation; (d) while not altering the maximal secretion of tracer noradrenaline at infinitely high frequency or external calcium, lowered the frequency or calcium concentration required for half-maximal secretion, both in the absence and in the presence of phentolamine.

IN CONCLUSION

moderate cooling improves sympathetic neuromuscular transmission in guinea-pig vas deferens, both prejunctionally, by enhancing transmitter secretion, and post-junctionally, by increasing the responsiveness of the smooth muscle to transmitter.

Interaction of xylamine with peripheral sympathetic neurons

Xylamine (XYL) administered to intact rats caused a 70-80% reduction in norepinephrine (NE) uptake by the vas deferens but had little or no effect on NE content in that tissue. The vas deferens accumulates 3H-XYL in vitro by a desmethylimipramine (DMI)-sensitive mechanism. Vasa deferentia from 6-hydroxydopamine (6OHDA) pretreated animals exhibited a 80% reduction in both NE content and XYL uptake activity. These results indicate that XYL is taken up by sympathetic nerve terminals and can reduce NE uptake activity without depleting terminals of neurotransmitter.

Reserpine-induced potentiation of the inhibitory action of neuropeptide Y on the rat vas deferens neurotransmission

The inhibitory action of neuropeptide Y (NPY) on the muscular activity of the prostatic end of the rat vas deferens elicited by transmural electrical stimulation was examined in control and in reserpinized rats. Pretreatment with 1 mg/kg reserpine for 48 h induced a 6-fold increase in NPY potency. Likewise, the potency of clonidine to inhibit the electrically induced muscular activity or noradrenaline to contract the ductus musculature was also potentiated. It is hypothesized that reserpine via a denervation super-sensitivity-like process increases the density of the NPY receptors. The functional significance of NPY in the motor activity of the vas deferens is discussed.

Effect of calcitonin gene-related peptide on the neuroeffector mechanism of sympathetic nerve terminals in rat vas deferens

In order to evaluate the mode of action of calcitonin gene-related peptide (CGRP) on the neuroeffector mechanism of peripheral sympathetic nerve fibers, the effects of CGRP were tested on the electrical stimulated and the non-stimulated preparations of the isolated rat vas deferens. The contractile responses, which were mediated predominantly by activation of postganglionic noradrenergic nerve fibers, were dose-dependently inhibited by CGRP in concentrations ranging from 0.1 to 10 nM. The inhibitory response produced by CGRP in high concentrations (greater than 2 nM) usually returned to the control level at 20-30 min and were rarely tachyphylactic. The inhibitory action of CGRP was not modified by pretreatment with 10(-7) M propranolol or 10(-7) M atropine. Contractions produced by exogenous norepinephrine (NE) and 5-hydroxytryptamine (5-HT) in unstimulated preparations were not affected by pretreatment with CGRP in a low concentration (less than 2 nM). On the other hand, the contractions were slightly reduced 1 min after pretreatment with CGRP in high concentrations (greater than 5 nM), which recovered in 15 min after constant flow washout. High concentrations of CGRP also caused a concentration-dependent relaxation on the precontracted preparations produced by high potassium (60 mM K+) solution. These results suggest that CGRP in high concentrations (greater than 5 nM) may have a non-specific inhibitory action on the postsynaptic plasma membrane of the smooth muscle cell and a postulated CGRP receptor exists presynaptically in the rat vas deferens and that CGRP may inhibit the release of NE during adrenergic nerve stimulation.

Effect of the dihydropyridine Bay K 8644 on the release of [3H]-noradrenaline from the rat isolated vas deferens

The effects of Bay K 8644 on the release of [3H]-noradrenaline evoked by potassium, electrical stimulation or tyramine from the rat isolated vas deferens labelled with [3H]-noradrenaline were investigated. Bay K 8644 (1 microM) by itself did not affect the spontaneous release of tritium from the rat isolated vas deferens. However, it increased the calcium-dependent release of tritium elicited by both high potassium (59 mM) and electrical field stimulation. The exposure of rat vas deferens to phentolamine (10 microM) increased the release of tritium induced by potassium (59 mM) and electrical field stimulation. Bay K 8644 (1 microM) failed to increase further the release of tritium elicited by both stimuli in preparations previously treated with phentolamine (10 microM). The calcium-independent release of [3H]-noradrenaline evoked by tyramine (10 microM) was not affected by Bay K 8644 (1 microM). The results of our study support the view that alpha2-adrenoceptors modulate noradrenaline release by restricting calcium influx into sympathetic nerve terminals through voltage-dependent channels.

alpha-Bungarotoxin and P15 toxin binding site in mammalian sympathetic ganglia

alpha-Bungarotoxin (alpha-Bgtx) demonstrates a specific and saturable binding to rat superior cervical ganglion, yet it does not block ganglionic response mediated by nicotinic receptors in the guinea pig vas deferens-hypogastric nerve preparation. P15 toxin, a probe for ganglionic nicotinic receptor, prevents the binding of alpha-Bgtx to rat ganglia, and alpha-Bgtx prevents the ganglioplegic action of hexamethonium. Hexamethonium does not block the binding of alpha-Bgtx and P15 to rat ganglia. It is concluded that alpha-Bgtx and P15 bind to ganglionic nicotinic receptor at a common site which is different from that of cholinergic agonists and antagonists.

The effect of diltiazem on noradrenaline release

The effects of diltiazem in rat tail arteries and guinea-pig vasa deferentia have been investigated. Superfusion of the rat tail artery with diltiazem (10(-6) - 10(-4) M) resulted in a dose-related increase in 3H-overflow (P less than 0.001) both in Wistar Kyoto (WKY) and in spontaneously hypertensive (SHR) rats. Release of 3H by transmural stimulation (1 Hz, 2 ms, 10 V) was also much greater in vessels perfused with diltiazem; this effect was dose-dependent. Diltiazem did not significantly alter the proportion of noradrenaline and its metabolites in 3H-overflow, as analysed by column chromatography. In the vasa deferentia of guinea-pigs, diltiazem (10(-9) - 10(-5) M) increased spontaneous 3H-release. The results indicate that diltiazem acts on sympathetic nerves and causes the release of noradrenaline.

Relative pre- and postjunctional roles of noradrenaline and adenosine 5'-triphosphate as neurotransmitters of the sympathetic nerves of guinea-pig and mouse vas deferens

Experiments were designed to examine the relative roles of noradrenaline and adenosine 5'-triphosphate (ATP) as mediators of the contractile responses of the guinea-pig and the mouse vas deferens to electrical nerve stimulation. To study possible prejunctional actions of the agents used, in some experiments their effects on the secretion of [3H]noradrenaline were determined. The contractile responses were recorded with force displacement transducers. Pharmacological techniques were employed to examine the pre- and/or postjunctional effects mediated by noradrenaline and ATP, respectively. Noradrenaline-mediated components were "removed" by depleting the neuronal stores of noradrenaline (by pretreatment with reserpine), or by addition of adrenoceptor-blocking agents. ATP-mediated components were "removed" by desensitizing ATP receptors (with the stable analogue alpha, beta-methylene ATP). The results permit three major conclusions: (1) In both species noradrenaline and ATP "auto-inhibit" mechanisms responsible for transmitter secretion; the prejunctional effects of ATP are less marked in the mouse vas deferens, and in both species much weaker than those mediated by noradrenaline, acting via alpha 2-adrenoceptors. (2) In these species, both noradrenaline and ATP participate in the generation of both phases of the contractile responses to nerve stimulation. The relative roles of each vary with the frequency and train length of stimulation, and also with the species. The main transmitter of "phase I" contractions in guinea-pig vas deferens is ATP, and in the mouse vas deferens, noradrenaline. "Phase II" contractions are triggered mainly by noradrenaline, in both species. Sympathetic neuroeffector transmission in these tissues can be accounted for almost entirely in terms of dynamic interplay between pre- and postjunctional actions of noradrenaline and ATP. (3) The results are compatible with the hypothesis that ATP is a co-transmitter with noradrenaline in these sympathetic nerves.

Evidence for differential localization of noradrenaline and neuropeptide Y in neuronal storage vesicles isolated from rat vas deferens

Using the technique of homogenization and subsequent density gradient centrifugation combined with ultrastructural analysis, the subcellular localization of noradrenaline and neuropeptide Y (NPY) was studied in vas deferens of castrated male rats. Noradrenaline showed two peaks in the gradient: one major peak at low density and another at high density. Only one NPY peak was seen, which coincided with the high density peak of noradrenaline. Electron microscopic analysis revealed high proportions of small and large vesicles in the light and heavy fractions, respectively. The present results indicate a differential subcellular localization of noradrenaline and NPY in the noradrenergic nerve endings of vas deferens. Thus, small vesicles seem to contain only noradrenaline, whereas the large vesicles may contain both noradrenaline and NPY.

Functional evaluation of new experimental model of microsurgical tubulovasostomy in rat

The function of a new experimental microsurgical model of tubulovasostomy is evaluated. The model is represented by an end-to-end tubulodeferential anastomosis after removal of the proximal (juxtaepididymal) half of the vas deferens and segmental unfolding of the distal part of the epididymal tubule. Both anastomosed segments are evaluated for responsiveness to norepinephrine and field stimulation. The results are discussed in terms of accurate selection of segments to be anastomosed on the basis of their morphofunctional correlates; in fact, it seems worth replacing the segments removed only with others endowed with equivalent properties.

Scope and mechanisms of control of stimulus-secretion coupling in single varicosities of sympathetic nerves

Recent electrophysiological evidence from studies of sympathetic nerves in the guinea-pig vas deferens [1, 2] indicate that the transmitter content of a vesicle is the quantum secreted, that nerve impulses only intermittently evoke transmitter secretion from the average individual varicosity (P about 0.01) (cf. [3]), that transmitter secretion from a varicosity is monoquantal, and that release of both quanta of a ‘pair’ is followed by long secretory silence in that site. The sympathetic transmitter responsible for these effects is apparently not noradrenaline but adenosine 5'-trisphosphate (ATP) [4], presumably secreted as a co-transmitter with noradrenaline [4a, 4b]. If both transmitters are secreted in parallel, then on the evidence quoted above the maximal rate of secretion would be that at which every nerve impulse releases the noradrenaline contents of one vesicle from each varicosity. In the present study of the overflow of [3H]noradrenaline, selected pharmacological agents are used to examine this possibility. The results are interpreted in the light of the above-mentioned electrophysiological evidence, in an attempt to evaluate the scope and mechanisms of α-adrenoceptor-mediated control of stimulus-secretion coupling in the average individual varicosity of the sympathetic nerves of vas deferens.

Evidence for ATP and noradrenaline as cotransmitters in sympathetic nerves

Sympathetically innervated smooth muscles, including those in some arteries, arterioles, cat nictitating membrane and vas deferens, have α1-adrenoceptors which respond to exogenously applied noradrenaline (NA) by producing contractions which can be abolished by α1-adrenoceptor antagonists such as prazosin. Stimulation of the sympathetic nerves innervating these muscles causes release of NA and a contractile response. However, this contraction is (at least partly) resistant to specific α1-adrenoceptor antagonists. This apparent contradiction could be explained by a variety of ad hoc explanations (such as high transmitter concentrations within the nerve-muscle junction, or prejunctional enhancement of transmitter release by the antagonist due to prejunctional α2-adrenoceptor blockade etc.) but recently two hypotheses have been advanced which may have more fundamental implications for sympathetic neurotransmission. First, Hirst and Neild and their colleagues suggested that the electrical and mechanical responses of some smooth muscles were resistant to α-adrenoceptor antagonists because neuronally released NA was acting not only on α-adrenoceptors but also on a new class of adrenoceptors which they designated γ-receptors, located near the nerve-muscle junction. The crucial experiments in support of this hypothesis were originally performed on the arterioles of the guinea-pig submucosa [1], but the idea has been extended to include many other sympathetically innervated smooth muscles [2], including guinea-pig vas deferens, which was also the smooth muscle preparation in which the experimental evidence for an alternative hypothesis was obtained by Fedan et al. [3]. They proposed that the α-blocker-resistant portion of the contractile response to sympathetic nerve stimulation was mediated by ATP, acting as a cotransmitter with NA. Full details of the early development of the concept of cotransmission in sympathetic nerves have been reviewed previously [4, 6, 7].

The experimental evidence relating to the co-transmission hypothesis is outlined below, drawing mainly on results obtained in guinea-pig vas deferens, where most of the more recent experiments have been performed.

Intimacy of the neuroeffector junction and resistance to alpha-adrenoceptor-blockade of the neurogenic contractile response in vasa deferentia from guinea pig and rat

The effect of phentolamine on the neurogenic contractile response in vasa deferentia from rat and guinea pig was studied during Wallerian degeneration. This response was also investigated after partial denervation (surgery or chemical sympathectomy by guanethidine treatment) in vasa deferentia from guinea pig. During Wallerian degeneration the response showed a gradual increase in sensitivity to phentolamine and was abolished in the late stages. The neurogenic contractile response of the partially denervated vas deferens was blocked by low concentrations of phentolamine. It is concluded that decreased intimacy of the neuroeffector junctions leads to increased susceptibility to alpha-adrenoceptor blockade of the contractile response to nerve stimulation. It is further concluded that the motor transmission in the vas deferens is essentially adrenergic. The resistance to alpha-adrenoceptor blockade of the initial phase of the contractile response to nerve stimulation of intact vasa deferentia from guinea pig and rat might well be explained by the "proximity theory" of Dale & Gaddum although participation of supplementary mediators cannot be excluded.

Effect of sympathetic denervation of rat internal genitalia on daily sperm output

Using the technique of vasocystostomy, daily sperm output was determined in rats undergoing surgical removal of the sympathetic nerves to the internal genitalia. Between ten and fourteen days after denervation, the daily sperm output significantly (p less than 0.001) decreased below presurgical rates and those of sham-operated control animals (p less than 0.01). This change occurred without changes in plasma testosterone concentration or testicular histology. These data suggest neural control of sperm transport in the rat.

Amphetamine-clonidine interaction on neurotransmission in the vas deferens of the rat

The interaction between amphetamine and clonidine on neurotransmission in the rat vas deferens was studied. In the whole vas deferens, clonidine 0.037 mumol/l displaced to the right the frequency-response curve evoked by either hypogastric or field stimulation. The frequency of stimulation that produced 50% of the maximal response (EF 50) was: control 4.0 Hz, clonidine 18.3 Hz (P less than 0.001 n = 4), for hypogastric nerve stimulation; and 2.1 Hz in controls and 17.1 Hz in clonidine-treated preparations, for field stimulation (P less than 0.001 n = 5). Preincubation with 5.4 mumol/l amphetamine antagonized the effect of clonidine (EF 50 amphetamine alone 6.2 Hz, amphetamine + clonidine 7.3 Hz; P greater than 0.5). After 12 min of incubation with clonidine 0.037 mumol/l the responses to 6.4 Hz (3 s, 0.5 ms) were decreased by 77 +/- 2.2%. Both yohimbine and amphetamine, in a concentration-dependent manner, attenuated the inhibition. Washout of clonidine produced a slow recovery of the responses. Inhibition of the motor response to nerve stimulation (6.4 Hz, 3 s) by 30 mumol/l 2',3'-cAMP was increased by 10 mumol/l dipyridamole and impaired by 100 mumol/l theophylline. Amphetamine, in a concentration that markedly reduced clonidine inhibition of neurotransmission failed to antagonize 2',3'-cAMP. In the bisected vas deferens clonidine inhibited the peak motor response to short trains of field stimuli in the prostatic portion ("non-adrenergic") and the sustained response in the epididymal portion ("adrenergic"). Yohimbine potentiated both types of responses and fully prevented the effect of clonidine. In the prostatic portion amphetamine slightly inhibited the peak motor response and attenuated the inhibitory effect of clonidine in both portions of the vas.(ABSTRACT TRUNCATED AT 250 WORDS)

Saturation of monoamine oxidase by intraneuronal noradrenaline accumulation

After pretreatment of the rats with reserpine and pargyline (to inhibit vesicular uptake and MAO), after an additional in vitro treatment with pargyline, and in the presence of U-0521 (to inhibit COMT), the adrenergic nerve endings of vasa deferentia were loaded with 3H-(-)-noradrenaline by exposure to various concentrations of this amine. Subsequently, tissues were washed out with amine-free solution, and the neuronal efflux of tritium was analysed. During 180 min of wash-out the apparent rate constant for the efflux of tritium decreased with increasing tritium content of the tissue. Prolongation of the wash-out period to 305 min revealed that efflux curves for tritium from heavily loaded tissues became steeper after the 180th min of wash-out. This phenomenon is indicative of saturation (followed by desaturation) of a process that limits the efflux of tritium from heavily loaded tissues. Analysis of the radioactivity of the efflux revealed a characteristic efflux curve for DOPEG: the formation of DOPEG appears to be saturated when the 3H-(-)-noradrenaline content of the tissue is high, in order to become desaturated during prolonged wash-out. These results cannot distinguish between MAO and alcohol dehydrogenase as the saturable enzyme. The formation of the mainly deaminated metabolites (during 60 min of wash-out) was determined in lightly and in heavily loaded tissues. The ratio "formation of metabolites/3H-(-)-noradrenaline content" was lower in heavily than in lightly loaded tissues; the relative decline in DOPEG formation was not accompanied by a compensatory increase in the formation of DOMA.(ABSTRACT TRUNCATED AT 250 WORDS)

The frequency of perineurial ductules in vasitis nodosa

In a retrospective histologic study, 154 vasovasostomy specimens (77 patients) yielded 50 examples of vasitis nodosa. These cases were examined for nerve invasion by proliferating ductules; benign neural invasion was present in four instances, and four additional cases were found on step sectioning the vasovasostomy specimens, totaling eight cases (16%) of the 50 studied. Usually only one or two nerves were invaded. The number of glands within individual nerves varied from one to eight. The findings are discussed in the context of benign glandular invasion of nerves in other locations.