Regional variations in the distribution of noradrenaline along the rat vas deferens

Pharmacological study of several effects of hydralazine in the bisected rat vas deferens

We have studied several effects of hydralazine in the bisected rat vas deferens. Hydralazine produced a shift to the left of the concentration-response curve for noradrenaline, with potentiation of the maximal response in both portions of the vas deferens. In contrast it caused a shift to the right of the concentration-response curve for noradrenaline in preparations pretreated with cocaine (inhibitor of catecholamine neuronal uptake), and of the curve for methoxamine and for CaCl2 (in depolarizing medium with K+ 55 mM), in all cases with depression of the maximal response. Hydralazine enhanced the contractions induced by noradrenaline in Ca(2+)-free medium, except in the presence of cocaine. It had no effect on [3H]noradrenaline neuronal uptake into noradrenergic neurons of the vas deferens, nor did it affect basal or K(+)-induced 45Ca2+ uptake. These results suggest that hydralazine potentiates the contractions elicited by noradrenaline by a mechanism other than blockade of the neuronal uptake of this catecholamine. Our results also suggest that the inhibition by hydralazine of the contractions elicited by Ca2+ (in Ca(2+)-free depolarizing high-K+ 55 mM solution) and by methoxamine is not due to an action on voltage-dependent Ca2+ channels, but may reflect an intracellular site of action.

Modulation of alpha 1-adrenoceptors and functional consequences in the bisected rat vas deferens following chronic inhibition of neuronal noradrenaline uptake

1. The adaptational changes induced after chronic inhibition of neuronal noradrenaline uptake on both functional responsiveness of alpha 1-adrenoceptor activation and [3H]-prazosin binding were investigated in prostatic and epididymal portions of the rat vas deferens. 2. Contractile concentration-response curves to phenylephrine and saturation isotherms of [3H]-prazosin binding to homogenates of each of the portions of the bisected rat vas deferens were determined 48 h after the last injection of desipramine, nomifensine or nisoxetine (10 mg kg-1; i.p. for 14 days). 3. Treatment with both nomifensine and nisoxetine decreased the potency (pD2) of phenylephrine by about 10 and 8 fold respectively in the epididymal portion. However, administration of desipramine only reduced the potency of the alpha 1-adrenoceptor agonist by about 1.8 fold. None of the treatments modified the maximal effect (Emax) elicited by phenylephrine in this portion of the vas deferens. In the prostatic portion only the treatment with nomifensine (1.4 fold) and nisoxetine (1.8 fold) decreased the potency of phenylephrine; the maximal contraction elicited by the agonist after the treatments was also reduced. 4. Chronic treatment with either nomifensine or nisoxetine did not change the KD for [3H]-prazosin binding in either epididymal or prostatic membranes. However, these two treatments resulted in a significant decrease in the [3H]-prazosin Bmax in membranes in both portions of rat vas deferens. The reduction in density of alpha 1-adrenoceptors was higher in the epididymal than the prostatic half. Desipramine reduced the Bmax only in the epididymal portion. 5. These results indicate that differential regulation of ax-adrenoceptors in either portion of the rat vas deferens could result from a greater degree of activation of these receptors in the epididymal half after chronic inhibition of neuronal noradrenaline uptake. The different functional consequences of the loss of alpha l-adrenoceptors in each portion seems to be explained on the basis of a different relationship between the occupancy of the receptor and the response elicited.

Effects of several calcium channels modulators on the [3H]noradrenaline release and 45Ca influx in the rat vas deferens

1. The effects of nifedipine (1 microM), CdCl2 (0.1 mM) and the Bay K 8644 enantiomers (1 microM) on [3H]noradrenaline release and 45Ca uptake in epididymal and prostatic rat vas deferens were investigated. 2. Nifedipine, CdCl2 and Bay K 8644 optical isomers did not affect the basal tritium release. However, the [3H]noradrenaline release evoked by high potassium (50 mM) from both portions of rat vas deferens was markedly inhibited by CdCl2, scarcely affected by nifedipine and not modified by Bay K 8644 enantiomers. 3. (-)-Bay K 8644 increased the basal and potassium (50 mM) induced 45Ca uptake whereas (+)-Bay K 8644, nifedipine and CdCl2 did not alter the basal 45Ca uptake. However, they strongly inhibited the uptake induced by potassium in both portions of rat vas deferens. 4. These results suggest that the calcium channels (mainly L type) are involved on the contractions in rat vas deferens epididymal and prostatic halves; these channels differ from those present in sympathetic nerve terminals (likely of N Type) which modulates the NA release. 5. This study also shows that Bay K 8644 optical isomers possess opposite effects on the L channels of bisected rat vas deferens smooth muscle.

Age-related changes in neuronal uptake of noradrenaline

Age-related changes in the neuronal uptake of noradrenaline were studied in the vas deferens of 4-, 12- and 20-months old rats by determining the potentiating effect of cocaine on concentration-effect curves to noradrenaline and by evaluating the kinetic parameters (Vmax and apparent Km) of neuronal 3H-noradrenaline uptake. Since the neurotransmitters released by nerve terminals and the density of noradrenergic innervation are different in the epididymal and prostatic portion of the vas, the experiments were carried out in these two portions of the organ. In the epididymal portion, the ratio between EC50 for noradrenaline in the presence and in the absence of cocaine was reduced in tissues of middle-aged (12-months) and old (20-months) animals when compared with young (4-months) animals. The pD2 values for noradrenaline in the absence of cocaine and the kinetic parameters for neuronal 3H-noradrenaline uptake were not modified by ageing. Thus, in the epididymal portion there was no age-related change in neuronal uptake. The age-related decrease in the cocaine-induced supersensitivity to noradrenaline was due to an age-related decrease in the pD2 value for noradrenaline observed in the presence of cocaine, suggesting postsynaptic changes. In the prostatic portion, the ratio between EC50 for noradrenaline in the presence and in the absence of cocaine was also reduced in tissues of old animals (20-months) when compared with middle-aged and young animals. The pD2 value for noradrenaline in the absence of cocaine obtained in the prostatic portion of 20-months old rats was higher than that in the younger groups (4- and 12-months).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic innervation of the ductus deferens in young and aging rats: a morpho-functional investigation

The pattern of adrenergic innervation and the responsiveness to alpha-agonists of the epididymal and prostatic portions of the ductus deferens from young and aging rats were examined. The histochemical pictures showed that the distribution of the adrenergic fibres varies between the 2 ends of the ductus deferens, with a greater density in the prostatic portion. Tissues from rats aged 20 months showed the same difference in the adrenergic pattern between the 2 portions. Generally, the fluorescent bundles from the tissues of senescent animals seemed to be more numerous and compact. The functional data appear to be in contrast with the morphological observations, because the epididymal tract of young rats showed the highest responsiveness to alpha-agonists. An inverse correlation between the number of adrenergic fibres and receptor responsiveness is hypothesized.

Regional distribution of dopamine, 5-hydroxytryptamine, and noradrenaline in the rat vas deferens

The concentrations of dopamine (DA), 5-hydroxytryptamine (5-HT) and noradrenaline (NA) in the rat vas deferens divided in eight or four sections were determined by high performance liquid chromatography with electrochemical detection. Dopamine and NA had the same regional distribution; their concentrations were maximal near the prostatic end and decreased towards the epididymis. The concentration of 5-HT also decreased from the prostatic to the epididymal end, but 5-HT did not follow the same regional distribution as DA and NA. Reserpine (0.02 or 0.2 mg/kg, i.p., 24 hr) and 6-hydroxydopamine (2 x 80 mg/kg, i.v., 6 days) decreased the contents of DA and NA; the concentrations of both amines were modified to a similar extent. Reserpine also diminished the content of 5-HT. Pargyline (200 mg/kg, i.p., 2 hr) increased the concentration of 5-HT while p-chlorophenylalanine (300 mg/kg, oral, 3 days) decreased the contents of the amine in some sections of the vas deferens. This study suggests that DA and NA co-exist in the same sympathetic neurons. Some of the 5-HT could be stored in mast cells as previously proposed, but the finding that tissue content of 5-HT changes after inhibiting the deamination or synthesis of the amine suggests that other source(s) of 5-HT distinct from mast cells exist in the rat vas deferens.

Activation and desensitization of presynaptic alpha 2-adrenoceptors after inhibition of neuronal uptake by antidepressant drugs in the rat vas deferens

The isolated field-stimulated vas deferens of the rat (0.1 Hz, 3 ms, 30-40 V) was used to study the relationship between the in vivo inhibition of neuronal uptake of noradrenaline (NA) by cyclic antidepressant drugs and the subsequent activation/desensitization of presynaptic alpha 2-adrenoceptors. Receptor activation was indirectly measured by quantifying the ability of each drug to inhibit basal twitch responses after their acute administration. Receptor desensitization was also indirectly measured by quantifying the ability of the drugs to reduce the inhibitory effects of selective alpha 2-adrenoceptor agonists on the electrically-induced twitch responses after their long-term administration. The acute in vivo administration of desipramine and other antidepressants (0.5-10 mg kg-1; i.p.; 2 h) resulted in dose-dependent inhibitions of the basal twitch responses which were rapidly reversed to control values by idazoxan (10-5 M). In vitro, desipramine and other antidepressants also inhibited in a concentration-dependent manner (10(-9)-10(-5) M) the twitch responses. In rats pretreated 12 h earlier with reserpine (1 mg kg-1; i.p.) or oxypertine (4 mg kg-1; i.p.), desipramine (10 mg kg-1; 2 h) did not induce inhibition of the basal twitch responses or it induced a smaller effect, respectively. For the various antidepressants the degree of inhibition of the basal twitch responses (desipramine greater than protriptyline greater than nortriptyline greater than maprotiline = imipramine greater than amitriptyline greater than viloxazine greater than iprindole much greater than zimelidine) was highly correlated (r = 0.914) with the potency for blockade of [3H]-NA uptake into rat brain synaptosomes. Clonidine and xylazine inhibited in a concentration-dependent manner (10(-9)-10(-6) M) the twitch responses. The long-term (7-14 days) administration of antidepressants or cocaine (10 mg kg-1, i.p.) resulted in significant decreases in sensitivity to clonidine or xylazine. Short-term (3 days) treatment with desipramine did not reduce the sensitivity to clonidine. The results indicate that the acute in vivo inhibition of NA neuronal uptake by antidepressants leads to the activation (through endogenous NA) of presynaptic inhibitory alpha 2-adrenoceptors which results in inhibition of the twitch responses. In contrast, prolonged in vivo inhibition of NA reuptake is followed by a slow desensitization process of the same receptors which results in a reduction of sensitivity to clonidine.

Pre- and postsynaptic bradykinin responses in the rat vas deferens: asymmetric distribution of the postsynaptic effect

The application of bradykinin to isolated segments of the epididymal or prostatic portion of the rat vas deferens increased the basal muscular tension mainly of the epididymal portion of the organ. Upon low frequency transmural electrical stimulation, the epididymal and the prostatic end of the organ both reacted to the application of bradykinin with an increase of twitch height. The increase in muscular tension observed in the epididymal portion of the ductus was resistant to tetrodotoxin but obliterated by 1 microM verapamil or nifedipine. The augmentation of the magnitude of the electrically driven muscle twitches was blocked by tetrodotoxin but not affected by 1 microM verapamil or nifedipine. Preincubation of the segments of the ductus with 10 microM indomethacin significantly reduced the increase in basal muscular tension caused by low concentrations of bradykinin but did not affect the electrically driven muscle twitches. Results suggest the existence of bradykinin receptors in the nerve endings of the adrenergic terminals of the organ and in the smooth muscle membrane. Whereas the neurogenic response found in both segments of the organ was of equal magnitude, the musculotropic response was predominantly found in the epididymal half of the organ.

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.

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)

One the importance of agonist concentration-gradients within isolated tissues. Increased maximal responses of rat vasa deferentia to (--)-noradrenaline after blockade of neuronal uptake

It is assumed often that blockade of agonist uptake processes in isolated tissues results only in shifts to the left of the concentration-response curves to the agonist with no concomitant increase in the maximal response. This may not be true in tissues where diffusion is not fast enough to permit penetration of the agonist to a sufficient number of muscle cells for production of tissue maximal response. Under these circumstances an agonist-concentration gradient is created within the tissue which, when altered, could lead to an increase in the maximal response to the agonist. The increased maximal responses of rat visa deferentia to (--)-noradrenaline after blockade of neuronal uptake by either cocaine or desmethylimipramine have been analysed in terms of a concentration-gradient hypothesis. The data are compared with a theoretical calculation based on a model of restricted diffusion of enzyme-substrates into structured tissues. Both the experimental data and theoretical calculations suggest that an altered concentration-gradient of (--)-noradrenaline within the muscle layers of rat vasa deferentia is responsible for the increased maximal response. The effects of such gradients are discussed in terms of quantitation of drug-receptor phenomena and as a caveat to ascribing increases in maximal responses to post-synaptic effects of uptake inhibitors.

Relationship between the uptake of 3H-(+/-)metaraminol and the density of adrenergic innervation in isolated rat tissues

1. The uptake of 3H-(+/-)metaraminol (MA) by tissue slices or pieces was studied in vitro in several peripheral rat organs of varying density of sympathetic innervation (the tissue level of endogenous noradrenaline ranging from 1.7-99.1 nmoles/g). In each individual tissue preparation amine uptake was corrected for entry into the 14C-D-sorbitol space. 2. When the tissues were incubated with 1.4 muM MA, the rate of total amine uptake (i.e., neuronal plus extraneuronal uptake of MA) remained virtually constant for up to 7 min. Therefore, rates of uptake were determined after 2 min of incubation with substrate concentrations ranging from 0.25-12.2 muM. In all tissues the total uptake of MA was saturable. 3. Under the condition of inhibition of neuronal uptake by the presence of 100 muM cocaine, the uptake of MA (considered as extraneuronal amine uptake) was no longer saturable. When tissues were exposed to 1.4 muM MA, the relative contribution by extraneuronal (measured in the presence of cocaine) to total amine uptake (measured in the absence of cocaine) was inversely correlated with the log endogenous noradrenaline content. 4. After correction of the rates of total MA uptake for the cocaine-resistant distribution of the amine, a saturable component of uptake was obtained for each tissue. This uptake was considered to be neuronal; it was subjected to kinetic analysis. 5. Apparent Km values for the neuronal uptake of MA were very similar in all tissues and did not show any dependence on the tissue level of endogenous noradrenaline (average Km = 1.2 muM). 6. V max values for the neuronal uptake of MA were linearly correlated with the endogenous noradrenaline content of the tissues (r = 0.976; P less than 0.001), the V max for the vas deferens being excluded. When related to the content of endogenous noradrenaline, the V max obtained in the vas deferens was lower than that for all other tissues. 7. The results presented here strongly suggest that the membrane site involved in neuronal amine uptake (operationally characterized by the Km of MA) is likely to be identical in all rat tissues and that the number of uptake sites available per nerve terminal does not vary greatly between tissues.

Junction potentials in response to ortho- and anti-dromic stimulation of hypogastric nerve in mouse vas deferens

The interaction of the junction potentials in response to ortho- and antidromic hypogastric nerve stimulation in mouse vas deferens was studied, using an extracellular recording method. Ortho-dromic repetitive hypogastric nerve stimulation (10 Hz, 5 min) simultaneously depressed the amplitude of the junction potentials in response to both ortho- and anti-dromic hypogastric nerve stimulation (post-te-tanic depression). No time-lag in recovery from the post-tetanic depression was observed between the junction potentials recorded from two separate electrodes, indicating that the proximodistal axonal flow of available transmitter was not involved in the recovery process. Double shocks, with intervals from 10 msec to 1 sec, were applied to the hypogastric nerve. The junction potentials in response to ortho- and ortho-dromic or anti- and anti-dromic double shock were markedly facilitated. On the contrary, the junction potentials in response to ortho- and anti-dromic double shocks were not facilited. The findings indicate that facilitation of the junction potentials is produced by the impulses propagated in the same direction along the terminal axon and also that the origin of the facilitation may be at a pre-junctional site.