The effects of morphine on the release of noradrenaline from the mouse vas deferens.

Electrical field stimulation of the mouse vas deferens (TO and C57/BL strains) caused the release of noradrenaline into the bathing medium. 2 Phenoxybenzamine (30 muM) or phentolamine (36 muM) plus cocaine (13 muM) caused a considerable increase in the noradrenaline output. 3 In the vasa deferentia from TO mice the output per pulse of noradrenaline was constant at frequencies of stimulation from 0.5 to 15 Hz whereas in the vasa deferentia from C57/BL mice the output per pulse of noradrenaline increased two-fold from 1.5 to 15 Hz. 4 Morphine (2 muM) inhibited the contractions of the vasa deferentia from TO mice. This effect was greater at low (0.1-1 Hz) than at high (10 Hz) frequencies of stimulation. Morphine (2 muM) did not inhibit the response of the tissue to exogenous noradrenaline. 5 Morphine (1 muM) reduced the noradrenaline output from the vasa deferentia of TO mice stimulated at 1.5 Hz but did not reduce the noradrenaline output at 15 Hz. At 1.5 Hz the reduction of noradrenaline output was reversed by naloxone (0.05 muM). 6 Morphine (5 muM) did not inhibit the uptake of [3H]-noradrenaline into the vasa deferentia from TO mice. 7 Only in high concentrations (ID50 30.88 muM) did morphine inhibit the contractions of the vasa deferentia from C57/BL mice. 8 Normorphine (100 muM) did not reduce the noradrenaline output from vasa deferentia of C57/BL mice.     

A comparison of the effects of oxodipine and nifedipine on rat vas deferens

The effects of oxodipine, a new dihydropyridine, were studied and compared with those of nifedipine in the complete vasa deferentia and in the prostatic and epididymal halves of the rat vas deferens. Oxodipine and nifedipine, 10(-9) -10(-6)M, produced a dose-dependent inhibition of the contractile responses induced by single pulse stimulation, noradrenaline (3 x 10(-5)M) and high-K (50 mM). The inhibitory effects of oxodipine were significantly reduced in high Ca media. From these experiments it is concluded that oxodipine, like nifedipine, produced a similar and potent inhibitory effect of the contractile responses induced in the rat vas deferens.     

Deamination of hordenine by monoamine oxidase and its action on vasa deferentia of the rat

The selectivity of the naturally occurring amine, N,N-dimethyltyramine (hordenine) for monoamine oxidase (MAO) and its action upon isolated vasa deferentia of the rat was investigated. Hordenine was deaminated by rat liver MAO with a Michaelis constant of 479 microM and maximum velocity of 128 nmol (mg protein)-1 h-1 compared with 144 microM and 482 nmol (mg protein)-1 h-1 for tyramine. Studies, with selective irreversible inhibitors of MAO, showed that hordenine was a highly selective substrate for MAO-B of liver and that it was not deaminated by the MAO-A of intestinal epithelium. In contrast to tyramine, hordenine did not produce contractions of isolated vasa deferentia. However, 25 microM hordenine potentiated contractile responses of vasa, from control animals, to submaximal doses of noradrenaline and inhibited responses to tyramine. It did not alter responses, to noradrenaline, of vasa denervated by chronic pretreatment of rats with guanethidine. Therefore, it appears that hordenine acted as an inhibitor of noradrenaline uptake, in isolated vasa deferentia. These results indicate that dietary-hordenine is unlikely to be deaminated by intestinal MAO as this is predominantly MAO-A. Consequently, it is likely to be absorbed and could affect the sympathetic nervous system, by virtue of its action as an inhibitor of noradrenaline uptake.     

OCCURRENCE OF EXCITATORY DOPAMINOCEPTORS IN THE RAT AND GUINEA-PIG VAS DEFERENS

1. Noradrenaline and dopamine produce contractions of isolated preparations of vasa deferentia from the rat or the guinea-pig. 2. Dopamine was three to five times as potent as noradrenaline on the rat vas deferens, but was considerably less potent than noradrenaline on the guinea-pig vas deferens. 3. Phentolamine antagonized responses to noradrenaline and dopamine of vasa deferentia of both species. On the rat vas deferens the pA₂ values against noradrenaline and dopamine were 7.6 and 7.4, respectively. 4. Rmozide, a dopamine antagonist, antagonized responses to dopamine on vasa deferentia of both species, but was not significantly active in antagonizing responses to noradrenaline. On the rat vas deferens, the pA₂ value against dopamine was 7.9. 5. The β-adrenoceptor blocking agents, propranolol and oxprenolol slightly enhanced dopamine-induced contractions on vasa deferentia of both species. 6. It is suggested that dopamine might act on both α-adrenoceptors and dopaminoceptors in the vas deferens, and that the component due to activation of dopaminoceptors is greater in the rat than the guinea-pig.     

NORADRENERGIC REINNERVATION OF THE RAT VAS DEFERENS AFTER VASOVASOSTOMY FOLLOWING VASECTOMY

1. Anastomosis (vasovasostomy) of epididymal and prostatic halves of vasa deferentia was carried out in rats in which unilateral or bilateral medial transection (vasectomy) had been performed 4 weeks previously. 2. Noradrenaline levels in epididymal halves of vasa deferentia, 8 weeks after anastomosis with prostatic halves, were approximately 40% of those in epididymal halves of contralateral, unoperated vasa deferentia. Catecholamine fluorescence was partially restored after anastomosis. 3. Responses of epididymal halves of transected vasa deferentia to electrical field stimulation (1 ms, 60 V, 10 pulses at 0.01-50 Hz) were partially restored 8 and 15 weeks after anastomosis. 4. Noradrenaline was equipotent in causing contraction of epididymal halves of unoperated and anastomosed vasa deferentia at 8 and 15 weeks after vasovasostomy. The ability of nisoxetine (0.1 mumol/l) to potentiate the effects of noradrenaline was partially restored by vas deferens repair. 5. Noradrenaline levels and neurotransmission in prostatic halves of vasa deferentia were relatively unaffected by vasectomy and subsequent vasovasostomy. 6. Fertility was restored 4-8 weeks after bilateral anastomosis performed in a group of eight rats 4 weeks after bilateral vasectomy. 7. These observations show that in the rat the noradrenergic denervation of the epididymal segment of the vas deferens after medial transection is partially reversible by anastomosis 4 weeks later, and that full noradrenergic reinnervation of the organ is not essential for the return of fertility after vasectomy and vasovasostomy in this species.     

SYMPATHETIC DENERVATION OF THE RAT VAS DEFERENS FOLLOWING UNILATERAL VASECTOMY

This paper describes an investigation of the time course of changes in noradrenaline levels in epididymal and prostatic segments of rat vasa deferentia, for up to 91 days following unilateral vasectomy by medial transection, together with an investigation of the responses of isolated preparations of these segments to field stimulation of sympathetic terminals. No atrophy of testes or seminal vesicles, or of the prostatic and epididymal segments of operated vasa deferentia, was evident at 2, 4, 7, 28 and 91 days after unilateral vasectomy. Spectrophotofluorometric assay revealed that noradrenaline levels in epididymal segments of operated vasa deferentia declined rapidly (within 2 days) after unilateral vasectomy and remained below 10% of those in unoperated epididymal segments at days 4, 7, 28 and 91 post-vasectomy. Noradrenaline levels in prostatic segments of operated vasa deferentia were unaffected by vasectomy. Histochemical studies revealed that catecholamine fluorescence in epididymal segments of operated vasa deferentia declined in parallel with the decline in tissue noradrenaline levels; no comparable changes occurred in prostatic segments. Field stimulation (10 pulses, 60 V, 1 ms, applied at 0.1-50 Hz) evoked frequency-dependent contractions of unoperated epididymal segments and of operated and unoperated prostatic segments at 2, 4, 7, 28 and 91 days post-vasectomy. At day 2 and 4 responses of prostatic segments of operated tissues, to frequencies below 5 Hz, exceeded those of corresponding unoperated segments, however, by day 91, there was a small but significant decline in responses.(ABSTRACT TRUNCATED AT 250 WORDS)     

On the mechanism of pancuronium-induced supersensitivity to noradrenaline in rat smooth muscle.

1. Pancuronium bromide (5 x 10(-5) M) caused supersensitivity to noradrenaline in the rat isolated vas deferens and hepatic portal vein. This supersensitivity was manifest as a parallel leftward shift of the dose-response curve for noradrenaline with no alteration of the maximum response to the agonist. 2. Pancuronium did not potentiate the response of the vas and portal vein to St 91, an alpha-adrenoceptor agonist which is not a substrate for Uptake1. 3. Pancuronium did not potentiate the response of the vas to CaCl2. 4. In vasa deferentia made supersensitive to noradrenaline by treatment with cocaine (1 x 10(-5) M) pancuronium induced no further potentiation of the response to noradrenaline. However, the supersensitivity to noradrenaline induced by pancuronium alone was augmented by the addition of cocaine. 5. Histofluorescence studies showed that pancuronium inhibited neuronal uptake of alpha-methyl noradrenaline in various noradrenergically-innervated tissues from reserpine-treated rats. 6. This study, with support from the literature, suggests that pancuronium induces noradrenaline supersensitivity by blockade of Uptake1.     

Effects of amiloride on contractions and the release of tritium from rat vas deferens preloaded with [3H]-noradrenaline.

1 The effect of amiloride was studied on contractions and tritium release from rat vas deferens preloaded with [3H]-noradrenaline. 2 Amiloride had no effect on the resting tension and maximal contractile force of the vas deferens and did not alter the ED50 of noradrenaline. 3 Amiloride (10(-4)-10(-3)M) decreased the response of vas deferens to electrical stimulation dose-dependently without inhibiting the response to KCI (60mM). 4 The effect of amiloride was not prevented by preincubation of the tissue with phentolamine, propranolol, atropine or indomethacin. 5 Amiloride did not alter the spontaneous outflow of radioactivity from [3H]-noradrenaline labelled vasa deferentia. 6 Amiloride decreased the release of tritium induced by electrical stimulation or nicotine but did not inhibit the release of radioactivity induced by KCI or tyramine. 7 It is concluded that amiloride may inhibit the contractions of rat vas deferens by inhibiting the release of noradrenaline.     

Characterization of the receptor subtype involved in alpha-adrenoceptor-mediated modulation of serotonin release from rat brain cortex slices

Rat brain cortex slices preincubated with 3H-5-hydroxytryptamine and superfused with physiological salt solution were stimulated electrically at a frequency of 3 Hz. 1. The electrically evoked 3H-overflow was decreased by clonidine, noradrenaline and B-HT 920 in a concentration-dependent manner (negative logarithms of the IC30 values: 6.66, 6.55 and 4.40, respectively) 2. Phenylephrine 10-5 M (which increased basal 3H-efflux) and methoxamine 10-4 M decreased the impulse-evoked 3H-overflow by less than 25% whereas lower concentrations were ineffective. 3. Yohimbine produced a shift to the right of the concentration-response curves of noradrenaline (apparent pA2: 6.93) and clonidine (apparent pA2: 7.06) for their inhibitory effects on evoked 3H-overflow. Rauwolscine also shifted the concentration-response curve of noradrenaline to the right (apparent pA2: 7.29), whereas prazosin (10-6 and 3.2 x 10-6 M) was ineffective in this respect. These results suggest that the alpha-adrenoceptors on the serotoninergic nerve fibres belong to the alpha2-subtype.     

Evidence for autoinhibition of stimulation-induced noradrenaline release from vasa deferentia of the guinea-pig and rat.

Both phenoxybenzamine and idazoxan increased the efflux of radioactivity elicited by a train of stimulation (4 pulses at 5 Hz) in vasa deferentia preincubated with [3H]-noradrenaline. Phenoxybenzamine increased the release of radioactivity from vasa stimulated with a single pulse, whereas idazoxan did not. The contractile response in both guinea-pig and rat vasa was biphasic: phenoxybenzamine enhanced the initial twitch component and reduced the second component in guinea-pig vasa stimulated with a single pulse or a train of pulses. Idazoxan enhanced both phases of the response of guinea-pig vasa stimulated with a train of pulses but did not affect the response to stimulation with a single pulse. The effect of phenoxybenzamine in increasing the efflux of radioactivity produced by a single pulse of stimulation was abolished by cocaine, indicating that the increase in efflux was due to blockade of noradrenaline uptake. Contractile responses of guinea-pig vasa stimulated with a single pulse in the presence of cocaine were unaltered by phenoxybenzamine, whereas with a train of stimulation the twitch component was enhanced and the second phase was reduced. The effects of phenoxybenzamine or idazoxan on the efflux of radioactivity from rat vasa portions were qualitatively the same as were observed in whole vasa. The contractile response of the prostatic portion consisted of a rapid twitch with a single pulse of stimulation, but was biphasic with a train of stimulation; the response of the epididymal portion was biphasic with either a single pulse or a train of pulses. These results suggest that there is no inhibitory feedback modulation of noradrenaline release with a single pulse of stimulation in guinea-pig and rat vasa deferentia whereas, with a train of stimulation, there is autoinhibition of noradrenaline release.     

Abolition of neurally evoked motor responses of the vas deferens by 6-hydroxydopamine

Contractions of isolated guinea-pig or rat vasa deferentia evoked by stimulation through ring electrodes were abolished after incubation with 6-hydroxydopamine?HBr. After this treatment it was no longer possible to demonstrate the presence of fluorescent nerves by the Falk-Hillarp technique and most preparations became supersensitive to noradrenaline. It is concluded that the motor innervation of rat and guinea-pig vasa deferentia is noradrenergic.     

Formation of dopamine and noradrenaline in rat vas deferens: comparison with guinea-pig vas deferens.

1 The formation of [14C]-3,4-dihydroxyphenylalanine (DOPA) from [14C]-tyrosine, in the presence of the amino acid decarboxylase inhibitor, brocresine (3-hydroxy-4-bromobenzyloxyamine dihydrogen phosphate), was greatly enhanced in rat vasa deferentia depolarized by a KCl-enriched Krebs-Henseleit solution (52 mM KCl) compared with tissues maintained in unmodified Krebs-Henseleit solution. 2 When the conversion of tyrosine was allowed to proceed as far as catecholamine (brocresine absent) no significant difference was observed between the accumulation of [14C]-catecholamines (CA) in depolarized rat vasa deferentia and the accumulation in control (non-depolarized) tissues. 3 Endogenous CA levels in the depolarized rat vasa deferentia fell to 67% of the controls after a 1 h incubation period and to 53% at the end of 2 hours. 4 Chromatographic separation on Amberlite CG-120 columns of the newly synthesized CA and catechol metabolites from the rat vas deferens revealed that a very high proportion was present as dopamine. The percentage distribution after 1 h incubation in control Krebs-Henseleit was: noradrenaline (NA): 30.6 +/- 5.2; dopamine 56.9 +/- 5.9; acid metabolites: 12.8 +/- 1.1; and in KCl-rich Krebs-Henseleit, NA: 32; dopamine: 44.7 and acid metabolites 23.3. In contrast to the newly synthesized (14C-labelled) CA, endogenous dopamine comprises only 10% of the endogenous CA stores in rat vas deferens. 5 The distribution of newly synthesized NA and dopamine in rat vas deferens is strikingly different from that of guinea-pig vas deferens where more than 80% of newly formed amine is present as NA. In the latter tissue depolarization with K+ causes a striking increase in CA biosynthesis.     

Supersensitivity to noradrenaline in vas deferens from morphine-dependent mice is confirmed

Vasa deferentia isolated from morphine-treated mice were subsensitive (tolerant) to the inhibitory effect of morphine on field stimulation-induced contractions (4.1 fold at the IC50 level) and exhibited supersensitivity to exogenously added noradrenaline. The magnitude of the supersensitivity to noradrenaline was not affected by the absence (2.6 fold) or presence (2.9 fold) of morphine in the bathing medium thus ruling out, as previously suggested, that the absence of morphine in the bathing solution could induce an 'in vitro morphine withdrawal'. Addition of naloxone to such vasa deferentia increased the maximum response to noradrenaline without a significant change of the sensitivity to the neurotransmitter. It is concluded that isolated morphine-tolerant vasa deferentia exhibit supersensitivity to exogenously added noradrenaline. Naloxone added in vitro to such vasa deferentia enhanced the maximum response to noradrenaline.     

Effect of omega-conotoxin GVIA on noradrenaline release from postganglionic sympathetic neurones in rabbit aorta

The aim of the present work was to examine the effect of the selective N-type calcium blocking agent omega-conotoxin GVIA on stimulation-evoked release of noradrenaline from sympathetic nerves in rabbit isolated aorta with regard to stimulation frequency, extracellular Ca2+ concentration, and transmitter uptake. Rings of rabbit isolated aorta were preloaded with (-)-3H-noradrenaline and the fractional 3H-overflow evoked by electrical-field stimulation was determined by liquid scintillation spectrometry. Omega-conotoxin GVIA (3 x 10(-10)-3 x 10(-8) M) did not alter the spontaneous 3H-outflow. Omega-conotoxin GVIA (3 x 10(-10)-3 x 10(-8) M) caused a slowly developing reduction of stimulation-evoked 3H-overflow at 1 and 30 Hz. The Emax for the omega-conotoxin-induced inhibition was less (70%) at 30 Hz than that (96%) seen at 1 Hz. Short-term incubation with omega-conotoxin GVIA caused a subsequent steady-state inhibition. The inhibitory action of omega-conotoxin GVIA (3 x 10(-10)-3 x 10(-9) M) was inversely related to the extracellular Ca2+ concentration (6.5 x 10(-4)-2.7 x 10(-3) M). Cocaine (3 x 10(-5) M) plus corticosterone (4 x 10(-5) M), neuronal and extraneuronal uptake inhibitors, respectively, did not alter the inhibitory effect of omega-conotoxin GVIA (3 x 10(-9) M) on 3H-overflow evoked by stimulation at a frequency of either 1 or 30 Hz. It is concluded that omega-conotoxin GVIA acts on prejunctional N-type calcium channels to inhibit stimulation-evoked noradrenaline release from sympathetic neurone terminals in rabbit aorta. At a high frequency, another subtype calcium channel may possibly be involved. The action of omega-conotoxin GVIA is independent of neuronal and extraneuronal uptake mechanisms for noradrenaline, but dependent on the amount of Ca2+ to be transported across the neurilemma from the extracellular space into the neurone.     

The effects of chronic morphine administration to mice on the contractile activity in vitro of the vas deferens without and with morphine

Chronic treatment of mice with morphine enhances maximal responses to noradrenaline in isolated vasa deferentia. Addition of morphine to the bath further increases the responses to noradrenaline (facilitatory effect). Vasa deferentia from reserpine-pretreated mice showed increased responses to noradrenaline, but upon addition of morphine to the bath no further facilitatory response to noradrenaline. The facilitatory response was not inhibited by naloxone and it was not elicited by narcotic analgesics other than morphine. High calcium in the medium (3.8 mM) suppressed the enhanced maximal responses to noradrenaline of vasa deferentia from mice chronically treated with morphine and also suppressed the facilitatory response to noradrenaline. Low calcium in the medium (1.43 mM) had the opposite effects. Reserpine-induced changes of noradrenaline responses were not affected by alteration of the calcium concentration in the medium. In the K-depolarized vas deferens, a reduction of the depressant effect of morphine on the calcium-induced contractions was observed after chronic administration of morphine.     

Effects of verapamil on [3H]norepinephrine release

If calcium entry blocking drugs affect norepinephrine release, this may alter their cardiovascular action by modifying the activity of baroreceptor reflexes. We investigated the effect of verapamil on 3H-release in [3H]norepinephrine-incubated rat arteries and guinea pig vas deferens. Superfusion of tail artery with verapamil (10(-6) - 10(-4) M) increased the 3H-overflow induced by transmural stimulation (1 Hz, 2 ms, 10 V) both in Wistar Kyoto and in spontaneously hypertensive rats. The effect was present also in vessels pretreated with cocaine to inhibit neuronal uptake or with yohimbine to block alpha 2-adrenoceptors. The greatest increase in 3H-overflow--around 400% in the various groups--was observed after perfusion with 10(-4) M verapamil. In other experiments, we found that verapamil also enhanced 3H-overflow from vessels not stimulated transmurally; this effect again was dose-related (p less than 0.001). In the vas deferens of the guinea pig, 10(-5) M verapamil increased spontaneous and electrical stimulation-induced 3H-release (p less than 0.001), whereas superfusion of the tissue with 10(-9) and 10(-7) M verapamil was ineffective. The results indicate that verapamil can act on sympathetic nerves to release norepinephrine.     

The binding of 1,3-[3H]-dipropyl-8-cyclopentylxanthine to adenosine A1 receptors in rat smooth muscle preparations.

1. The binding of 1,3-[3H]-dipropyl-8-cyclopentylxanthine ([3H]-DPCPX), an antagonist radioligand selective for adenosine A1 receptors, was studied in rat duodenum, colon muscularis mucosae and longitudinal muscle, urinary bladder and vasa deferentia. 2. [3H]-DPCPX bound with high affinity to a single site in all membrane preparations studied with the exception of the rat urinary bladder in which no specific binding was detected. The affinity (Kd) of the binding site for [3H]-DPCPX was similar in all membrane preparations, the colon longitudinal muscle (1.18 +/- 0.47 nM), colon muscularis mucosae (0.84 +/- 0.15 nM), duodenum (1.59 +/- 0.18 nM) and vasa deferentia (0.93 +/- 0.17 nM). The density of [3H]-DPCPX binding sites was similar in the duodenum (38.8 +/- 4 fmol mg-1 protein), muscularis mucosae (43 +/- 3.5 fmol mg-1 protein) and vasa deferentia (43.3 +/- 12.2 fmol mg-1 protein), but in the longitudinal muscle 6-7 fold more binding sites (295 +/- 70 fmol mg-1 protein) were identified. 3. Inhibition studies using DPCPX (0.1-100 nM), N6-cyclopentyladenosine (CPA) (0.1-100 nM), 5'-N-ethylcarboxamidoadenosine (NECA) (2 nM-10 microM) and (R)-N6-phenylisopropyladenosine (R-PIA) (1 nM-1 microM) to displace the binding of [3H]-DPCPX at a concentration around the Kd value (1 nM), demonstrated an order of potency of displacement in all tissues of DPCPX > or = CPA > R-PIA > NECA. This potency order is characteristic of an A1 receptor, indicating that [3H]-DPCPX binds to adenosine A1 receptors in the rat duodenum, colon and vasa deferentia.(ABSTRACT TRUNCATED AT 250 WORDS)     

The role of diacylglycerol and activation of protein kinase C in alpha 1A-adrenoceptor-mediated contraction to noradrenaline of rat isolated epididymal vas deferens.

1. The mechanism of contraction to noradrenaline (pEC50 5.6 +/- 0.1) in the rat epididymal vas deferens (mediated via alpha 1A-adrenoceptors) has been studied in functional experiments. 2. Contractions to noradrenaline at 10(-6) M were potentiated by the diacylglycerol (DAG) kinase inhibitor R 59022 (3 x 10(-7) M) from 49 +/- 4% to 63 +/- 3% maximum response and the time taken from initiation of contraction to the maximum response was reduced from 16 +/- 2 s to 9 +/- 1 s. The same contractions were not significantly potentiated by the DAG lipase inhibitor, U-57,908, 10(-5) M (51 +/- 2% control and 53 +/- 4% in the presence of U-57,908) nor was the time taken from initiation of contraction to the maximum response significantly altered (17 +/- 1 s control and 16 +/- 1 s in the presence of U-57,908). 3. Concentration-dependent contractions to noradrenaline (NA) were reduced by staurosporine (10(-7) M) and the selective protein kinase C inhibitor, calphostin C (10(-6) M) from 68 +/- 2% (NA, 3 x 10(-6) M) to 28 +/- 2% and 20 +/- 2% respectively and from 94 +/- 2% (NA, 3 x 10(-5) M) to 50 +/- 2% and 44 +/- 2% respectively. Contractions to K+ (40 +/- 2% maximum response to NA) were also significantly reduced by staurosporine (10(-7) M) (35 +/- 2%) but not by calphostin C (43 +/- 3%). 4. The phorbol ester, phorbol-12,13-dibutyrate (PDBu), produced a phasic, concentration-dependent contraction (10(-7) M - 10(-4) M) which was 41 +/- 2% of the maximum response to NA at 10(-4) M PDBu. The contraction to PDBu (10(-5) M) was reduced by calphostin C (10(-6) M) from 33 +/- 5% to 4 +/- 1% maximum response to NA. 5. Non-cumulative contractions to NA (10(-8) M - 10(-4) M) were abolished in Ca(2+)-free Krebs solution containing EGTA (1 mM) and were reduced in the presence of nifedipine (10(-6)M) in normal Krebs solution by 91 +/- 2% at 10(-4)M NA. The contraction to PDBu (10(-5)M, 33 +/- 5% maximum response to NA) was also abolished in Ca(2+)-free Krebs solution containing EGTA (1 mM) or by the presence of nifedipine (10(-6)M) in normal Krebs solution. 6. When NA (10(-4)M) was added to vasa deferentia in Ca(2+)-free Krebs solution containing EGTA (1 mM), following its wash out (and with EGTA later removed from the Krebs solution), readdition of Ca2+ (2.5 mM) to the Krebs solution produced no response. Cyclopiazonic acid (10(-5)M), which can deplete Ca2+ from intracellular stores, also produced no contraction. Therefore influx of extracellular Ca2+ is not a consequence of depletion of intracellular Ca2+ stores (capacitative Ca2+ influx). 7. Pre-incubation of tissues for 30 min with either cyclopiazonic acid (10(-5)M) or ryanodine (10(-4)M), which can both deplete intracellular Ca2+ stores, did not reduce the contractions to NA (3 x 10(-6)M). Pre-incubation of vasa deferentia with cyclopiazonic acid (1 or 3 min, when any rise in [Ca2+]i produced by cyclopiazonic acid might still exist) did not potentiate the contraction to PDBu (10(-5)M). Thus mobilization of intracellular Ca2+ may not be required for the activation of protein kinase C involved in these contractions. 8. In conclusion, the contraction of the rat epididymal vas deferens to NA mediated by alpha 1A-adrenoceptors appears to depend upon activation of protein kinase C by diacylglycerol, resulting in the influx of extracellular Ca2+ through voltage-gated Ca2+ channels. There was no evidence for a role of inositol trisphosphate in the contraction to noradrenaline in this tissue.     

A comparison of the sensitivities of innervated and denervated rat vasa deferentia to agonist drugs

1. One vas deferens of a rat was denervated by stripping away the serous coat; the other vas was left intact as a control. One week later the sensitivity in vitro of both vasa deferentia to noradrenaline, adrenaline, dopamine, oxymetazoline or acetylcholine was measured.2. Log concentration response curves for the mean responses of both vasa from a group of four rats for each drug were plotted. Denervated vasa were more sensitive than control vasa to noradrenaline (16-fold), to adrenaline (8-fold), to dopamine (2-fold) and to oxymetazoline (2-fold). Denervated vasa were more sensitive to acetylcholine over the lower half of the concentration range only.3. It is concluded that these results support the theory that at least part of the increased sensitivity of denervated smooth muscle to catecholamines is due to an abolition or reduction of the neuronal uptake process. There is also a small non-specific increase in sensitivity.