Evaluation of the permanent sympathectomy produced by the administration of guanethidine to adult rats.

The administration of guanethidine to adult rats has been shown by morphological criteria to destroy sympathetic neurons. The objective of this study was to evaluate by biochemical and functional criteria the degree and permanence of this sympathectomy. Young adult male rats (260-300 g) were injected with saline (controls) or with guanethidine for 5 weeks. The status of the sympathetic nervous system in the animals was evaluated 1, 3 and 6 to 7 months after cessation of treatment. Seven months after cessation of treatment; the activity of tyrosine hydroxylase in the superior cervical ganglia of treated animals was greatly reduced, as were the norepinephrine levels in peripheral tissues. The concentration of epinephrine and the activity of tyrosine hydroxylase in adrenals were not different from controls at any of the times studied. Norepinephrine concentrations in several areas of the central nervous system were unchanged. Increases in blood pressure in response to stimulation of the sympathetic vasomotor outflow in the pithed rat preparation were markedly and permanently reduced in guanethidine-treated animals. Isolated intestinal nerve-muscle preparations from guanethidine-treated animals usually contracted in response to nerve stimulation, rather than relaxing as in controls. The response to stimulation of the hypogastric nerve in vas deferens preparations was reduced 1 month after cessation of treatment. The responses of the vas deferens from guanethidine-treated and control animals were the same 7 months after treatment despite a 93% reduction in norepinephrine concentration. The data demonstrate that the administration of guanethidine to adult rats produces a marked and permanent destruction of the peripheral sympathetic nervous system.     

Biochemical and functional evaluation of the sympathectomy produced by the administration of guanethidine to newborn rats.

The administration of guanethidine to newborn rats has been shown by morphological criteria to destroy sympathetic neurons. Newborn rats were injected with guanethidine (50-100 mg/kg/day for 20 days). Upon maturation (at 10 weeks old), the degree of destruction of the sympathetic nervous system (sympathectomy) was assessed. Marked decreases (80-98%) in the norepinephrine concentration in several tissues (heart, spleen, intestine, mesentery, kidney, uterus, vas deferens) were observed in the guanethidine-treated rats when compared to saline-treated controls. No changes were observed in the epinephrine concentration in the adrenals or in the norepinephrine levels in whole brain. Analysis of brain areas showed no change in the norepinephrine levels in brain stem and cerebrum and a small (18%) decrease in the cerebellum. Stimulation of the sympathetic vasomotor outflow in the pithed rat preparation produced almost no response in guanethidine-treated animals. Periarterial nerve stimulation of the isolated perfused kidney preparation also produced essentially no response in guanethidine-treated animals. Isolated intestinal preparations from guanethidine-treated animals responded to nerve stimulation with contractions rather than relaxation as seen in preparations from control animals. Isolated vas deferens preparations responded normally to nerve stimulation despite a 95% decrease in tissue norepinephrine concentration. These data indicate that administration of guanethidine to newborn rats produces a more complete peripheral sympathectomy, especially of the vasculature, than immunosympathectomy or neonatal administration of 6-hydroxydopamine and does so with no significant effect on central noradrenergic neurons.     

The effects of perhexiline on the sympathetic nervous system.

The effects of perhexiline on sympathetic nervous system function were studied in vitro and in vivo. Perhexiline decreased the field stimulation-induced contractile response of the isolated vas deferens and significantly decreased the quantity of norepinephrine released during stimulation of this preparation. In vivo studies in dogs showed that perhexiline reduced the heart rate response to cardiac accelerator nerve stimulation, an effect not associated with an increase in cholinergic tone or beta adrenergic blockade. Measurements of norepinephrine released from the heart during cardiac nerve stimulation showed that perhexiline (3 mg/kg) decreased norepinephrine release by approximately 35%. These results suggest that a presynatpic effect of perhexiline, which results in a decrease in norepinephrine release, contributes significantly to the attenuated heart rate response which occurs after administration of this drug. A decrease in transmitter release during sympathetic stimulation could play an important role in the mechanism for the protective effects of perhexiline in myocardial ischemic damage.     

Denervation-like supersensitivity in the rat vas deferens induced by local application of colchicine to the hypogastric plexus.

In an attempt to induce denervation-like supersensitivity in the smooth muscle of the vas deferens without depriving the tissue of its innervation, a small amount of colchicine was locally applied to the hypogastric plexus of the rat. Colchicine produced supersensitivity and a partial depletion of the tissue norepinephrine. These effects were dose-dependent. The supersensitivity produced by colchicine was qualitatively and quantitatively similar to that induced by denervation. Following application of 20 micrograms of colchicine, the supersensitivity was fully developed by the 4th day. The supersensitivity began to decline by the 6th day but was measurable even after 16 days. Functional neuromuscular transmission was maintained even on the 4th day after colchicine application, although it was significantly less than the control. The time course of the development of supersensitivity was dependent on the length of the adrenergic nerve between the colchicine-applied site and the effector cells. The results indicate that supersensitivity is independent of an irreversible degeneration of the adrenergic nerves. The possible mechanisms of action of colchicine are discussed in relation to the known effects of colchicine on axoplasmic transport.     

Selective inhibitory effects of calcium channel antagonists on the two components of the neurogenic response of guinea pig vas deferens.

The effects of L-type calcium channel antagonists and omega-conotoxin on the contractile responses of guinea pig vas deferens were examined in vitro. Electrical stimulation of the postganglionic hypogastric nerve induced biphasic contraction consisting of rapid phasic and delayed tonic components. L-type calcium channel antagonists, such as diltiazem, verapamil and nicardipine, mainly inhibited the delayed tonic component, whereas omega-conotoxin mainly inhibited the rapid phasic component. Stimulations in the presence of prazosin and alpha, beta-methylene ATP induced rapid transient and delayed contraction, respectively, which were inhibited by omega-conotoxin and L-type calcium channel antagonists, respectively. Short-term stimulation with five pulses induced a small fast phasic contraction. This contraction, which could be desensitized by alpha, beta-methylene ATP, was inhibited by omega-conotoxin, but not by L-type calcium channel antagonists. At the concentrations used in the present study, none of the calcium channel antagonists inhibited the contractions induced by exogenously added ATP or norepinephrine. These findings suggest that L-type calcium channel antagonists and omega-conotoxin inhibit the neurotransmissions mediated by norepinephrine and ATP, respectively, from the postganglionic nerve to the vas deferens of the guinea pig. Inhibition of the voltage-dependent calcium channel is discussed in relation to the mechanism of cotransmission in this preparation.     

Adrenergic nerves mediate angiotensin-induced prostaglandin release in the rabbit vas deferens

The effect of sympathectomy and norepinephrine depletion on prostaglandin (PG) synthesis in response to angiotensins II and III was examined in isolated vasa deferentia of the rabbit. Either 6-hydroxydopamine or surgical denervation significantly depressed norepinephrine concentrations in the vas deferens relative to contralateral controls, thus confirming an effective sympathectomy. Guanethidine also resulted in a significant reduction in norepinephrine concentrations in the vas deferens. Base-line PGE production by the vasa deferentia was not altered by guanethidine but was attenuated by 6-hydroxydopamine and increased by surgical denervation. All the treatments reduced angiotensin-induced PGE synthesis. The effect of denervation on PGE synthesis was greater than that of norepinephrine depletion. We interpret these results to indicate that angiotensins stimulate PGE production by adrenergic nerves in the vas deferens and that released norepinephrine mediates a part of the PGE production in response to the angiotensins. The 6-hydroxydopamine experiments are consistent with the adrenergic nerves being the predominant source of PGE in this preparation.     

Inhibitory presynaptic effect of noradrenaline on the hypogastric ganglion of the guinea pig

The effect of noradrenaline on the hypogastric ganglion of the guinea pig was studied to establish the role of catecholamine-containing sites in the sympathetic ganglia with the hypogastric nerve-vas deferens preparation. In these experiments the ganglion was separated pharmacologically from the muscle by a partition. An application of noradrenaline, adrenaline and isoproterenol each to the ganglion inhibited a twitch response of the vas deferens to preganglionic nerve stimulation at low frequencies. The drug effect decreased with increasing frequencies of stimulation. The inhibitory action of these drugs was antagonized by phentolamine, but not by propranolol. Clonidine also reduced the response to the nerve stimulation in a similar manner as did catecholamines, and the inhibitory action was antagonized by phentolamine. In contrast, phenylephrine had no significant action. The inhibitory effect of noradrenaline and clonidine was antagonized by the alpha-2 antagonist yohimbine, but not by such alpha-1 antagonists as prazosin and E-643. Noradrenaline did not affect the ganglion-stimulating action of acetylcholine. These results suggest that the inhibitory action of noradrenaline may be mediated by alpha-2 adrenoceptors on presynaptic cholinergic nerve endings of the guinea-pig hypogastric ganglion. These data are discussed in relation to the presence of noradrenaline-containing sites in this ganglion.     

Beta2-adrenoceptor-mediated prejunctional facilitation and postjunctional inhibition of sympathetic neuroeffector transmission in the guinea pig vas deferens.

This study examines the role of prejunctional and postjunctional beta-adrenoceptors in the modulation of sympathetic cotransmission in the guinea pig vas deferens. The prejunctional involvement of beta-adrenoceptors was evaluated by testing the effects of several agonists and antagonists on the nerve stimulation-evoked overflow of ATP and norepinephrine (NE) from the "in vitro" vas deferens. The nonsubtype-selective beta-adrenoceptor agonist isoproterenol and the beta2-subtype-selective agonist clenbuterol increased, to a similar degree, the overflow of ATP and NE, while the beta1-subtype-selective agonist xamoterol and the beta3-subtype-selective agonist BRL 37 344 had no effect. Pretreatment with ICI 118, 551, a beta2-subtype-selective antagonist, abolished the facilitation of cotransmitter release by isoproterenol and clenbuterol, while the beta1-subtype-selective antagonist atenolol had no effect. Activation of beta-adrenoceptors by either isoproterenol or clenbuterol, but not by xamoterol and BRL 37 344, reduced the amplitude of contractions evoked by exogenously applied ATP. Pretreatment with propranolol or ICI 118, 551, but not atenolol, prevented these inhibitory effects. Isoproterenol in lower concentrations produced dose-dependent reduction of the purinergic but not the adrenergic phase of nerve stimulation-induced contraction of the guinea pig vas deferens. When applied in concentrations greater than 1 microM, isoproterenol, but not clenbuterol, actually produced a concentration-dependent facilitation of contractions evoked by both nerve stimulation and exogenously applied ATP. Antagonists of alpha-adrenoceptors blocked these facilitatory effects. Together, these results demonstrate that beta2-adrenoceptors can influence sympathetic neuroeffector transmission both prejunctionally, where they facilitate equally well the release of sympathetic cotransmitters and postjunctionally, where they inhibit smooth muscle contractions evoked by ATP.     

Diurnal variation of the rat vas deferens contraction induced by stimulation of presynaptic nicotinic receptors and pineal function.

A rhythmic variation of maximal contraction induced by acetylcholine in the prostatic portion of rat vas deferens was tested. This contraction is due to the release of norepinephrine and ATP from sympathetic nerve terminals. Male Wistar rats (4 months old) were housed on a light/dark cycle (12 hr/12 hr, lights on at 6:00 A.M.). The diurnal variation of acetylcholine-induced contraction was determined on animals sacrificed every 3 hr during the day. The maximal contractile response shows a circadian (24:00 hr) and an ultradian (12:20 hr) rhythm. Otherwise, the sensitivity to acetylcholine (pD2 values) and the maximal contraction or pD2 values to norepinephrine, ATP and K+ did not change throughout the day. The blocking effect of hexamethonium on the contraction induced by field stimulation was higher at 9:00 P.M. than at 3:00 P.M., indicating a diurnal variation of the effect of endogenous released acetylcholine. When melatonin released by the pineal gland is suppressed by constant illumination or superior cervical ganglionectomy, the circadian rhythm was abolished and the period of the ultradian rhythm changed to 6:30 hr. The acetylcholine-induced contraction of vasa deferentia from animals sacrificed at 3:00 P.M. and incubated "in vitro" with melatonin (100 pg/ml) increased reaching nocturnal values. In conclusion, it seems that a functional pineal gland, most probably through the synthesis and release of melatonin, is necessary for expression (circadian) and modulation (ultradian) of the rhythmicity in the maximal acetylcholine-induced contraction in the prostatic portion of the rat vas deferens.     

Correlation between the release of the sympathetic neurotransmitter ATP and soluble nucleotidases from the guinea pig vas deferens

Recently, we have shown that by releasing specific nucleotidases the sympathetic nerves of the guinea pig vas deferens may regulate the metabolism of extracellular adenine nucleotides and consequently, the inactivation of neurotransmitter ATP. Based on the evidence for tetrodotoxin sensitivity and calcium dependence of the nerve stimulation-evoked overflow of enzyme activity, we have suggested that soluble nucleotidases may be stored in synaptic vesicles within the sympathetic nerves and released upon arrival of nerve action potentials by a mechanism similar to that for release of neurotransmitters. To further test this hypothesis we studied the time course of nerve stimulation-evoked overflow of ATP, norepinephrine (NE), releasable ATPase (r-ATPase) activity, and releasable AMPase (r-AMPase) activity under control conditions and in the presence of drugs known to selectively modulate sympathetic neurotransmission. The results show that the time course of overflow of r-ATPase and r-AMPase activities resembles the transient pattern of overflow of ATP but not the tonic pattern of overflow of NE. Vasa deferentia dissected from animals treated with reserpine release ATP, r-ATPase, and r-AMPase, whereas the overflow of NE is completely abolished. Guanethidine, on the other hand, inhibits equally well the overflow of the two neurotransmitters and the releasable nucleotidase activities. Agonists of the alpha(2)-adrenergic receptors abolish the overflow of ATP, r- ATPase, and r-AMPase but not the overflow of NE. This evidence supports the idea that the sympathetic nerves of the guinea pig vas deferens store and release ATP together with specific nucleotidases responsible for the inactivation of this neurotransmitter.     

Potent excitatory effect of scaritoxin on the guinea-pig vas deferens, taenia caeci and ileum

Scaritoxin (STX), a potent toxic substance isolated from poisonous fish induced a dose-dependent contraction of the isolated guinea-pig vas deferens at concentrations of 10(-8) to 10(-6) g/ml. This contraction was abolished or inhibited by tetrodotoxin, low Na+ medium, phentolamine or reserpine, but not by atropine, chlorpheniramine or methysergide. STX shifted to the left the dose-contractile response curve for norepinephrine, KCI or acetylcholine in the vas deferens. STX caused a release of norepinephrine from the vas deferens, in a dose-dependent manner, which was blocked by tetrodotoxin, Mg++ or Ca++-free medium. In the guinea-pig taenia caeci or ileum, STX elicited a dose-dependent contraction. The contractions of both tissues were blocked completely by tetrodotoxin and were inhibited markedly by atropine but not by mecamylamine or chlorpheniramine. These results suggest that the STX-induced contraction is the result of an indirect action mediated through the norepinephrine release from adrenergic nerve terminals of the vas deferens and acetylcholine release from cholinergic nerve endings of the taenia caeci or the ileum. It is also suggested that STX causes an increase in Na+ permeability of the cell membrane of these tissues, which may play an important role in the release of chemical transmitters induced by STX.     

Inhibitory effect of calcitonin gene-related peptide on excitation and contraction of smooth muscles of the rat vas deferens

Calcitonin gene-related peptide (CGRP) inhibits the twitch response of the rat vas deferens induced by nerve stimulation. Inasmuch as CGRP-like immunoreactive nerves were demonstrated to be present in the rat vas deferens, the effect of CGRP on the contractile activity of the tissue was pharmacologically and electrophysiologically analyzed in vitro. The twitch response of the vas deferens induced by transmural nerve stimulation was inhibited by rat CGRP, porcine CGRP and human CGRP (hCGRP). Both ED50 values and the extent of the maximum inhibition of the twitch response were the same for these CGRP groups. hCGRP (10(-8) to 10(-7) M) hyperpolarized the resting membrane potential of smooth muscle cells but did not affect the amplitude of excitatory junction potentials induced by nerve stimulation. Neither the frequency of occurrence nor the amplitude of spontaneous junction potentials were affected by hCGRP. The threshold potentials for the generation of action potentials were less negative in the presence of hCGRP. hCGRP reduced slightly the contraction of the tissue induced by norepinephrine and by adenosine 5'-triphosphate. hCGRP reduced markedly the contractions induced by direct electrical stimulation of both denervated and normal tissues in the presence of tetrodotoxin. These results indicate that CGRP does not affect the release of a sympathetic neurotransmitter. CGRP appears to attenuate the contraction of the rat vas deferens through suppression of both the excitability and excitation-contraction coupling of the smooth muscle.     

Blockade of the Superior Hypogastric Plexus Block for Visceral Pelvic Pain

Abstract: Visceral pelvic pain is a common problem with variable etiology. The sympathetic nervous system plays an important role in the transmission of visceral pain independent of its etiology. Five major pathways by which pelvic pain is transmitted can be identified. One of them, the superior hypogastric plexus, an extension of the preaortic plexus, is easily assessable to blockade by local anesthetics and neurolytic agents. Several techniques have been described. Long-lasting pain relief with this procedure has been achieved in patients with pelvic cancer pain. However, there is a discrepancy between diagnostic and therapeutic blockade in patients with nonmalignant pain. Because a diagnostic blockade can give significant pain relief in a large variety of patients, it is worthwhile to investigate new methods that provide lasting neural blockade of the superior hypogastric plexus and long-lasting relief of this devastating condition.     

CH-38083, a selective, potent antagonist of alpha-2 adrenoceptors

The selectivity and specificity of CH-38083 [7,8-(methylenedioxi)-14-alpha-hydroxyalloberbane HCl], a berbane derivative for alpha adrenoceptors has been studied and compared with yohimbine and idazoxan in peripheral tissues and in the central nervous system. In isolated tissue experiments CH-38083 was a competitive antagonist at presynaptic alpha-2 adrenoceptors on the axon terminals of the rat vas deferens (pA2 against xylazine = 8.17 +/- 0.06) and of the longitudinal muscle strip of guinea pig ileum (pA2 against xylazine = 8.07 +/- 0.20). As far as its postsynaptic alpha-2 adrenoceptor antagonistic activity is concerned its affinity in rat vas deferens (pA2 = 4.95 +/- 0.11) against l-phenylephrine and in rabbit pulmonary artery (pA2 = 5.38 +/- 0.33 against l-norepinephrine) was markedly less than that displayed for presynaptic sites. From pA2 values obtained in rat vas deferens the calculated alpha-1/alpha-2 adrenoceptor selectivity ratios for yohimbine, idazoxan and CH-38083 were 4.7, 117.5 and 1659, respectively. CH-38083 failed to show any affinity for histamine and muscarinic receptors and it even potentiated the effect of serotonin on atropinized longitudinal muscle strip of guinea pig ileum. It enhanced the release of [3H]norepinephrine from electrically stimulated mouse vas deferens loaded previously with labeled [3H]norepinephrine. In binding studies carried out in rat brain membrane preparations using [3H]prazosin and [3H]idazoxan, the selectivity ratios (Ki alpha-1/Ki alpha-2) proved to be 32.5, 289.5 and 1368 for yohimbine, idazoxan and CH-38083, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Geographutoxin II, a novel peptide inhibitor of Na channels of skeletal muscles and autonomic nerves

Geographutoxin II (GTX II, 3 X 10(-9) to 10(-7) M) from a cone shell Conus geographus inhibited twitch responses of the isolated mouse diaphragm to direct stimulation in a dose-dependent manner. The contraction of the diaphragm induced by grayanotoxin I or veratridine was abolished by GTX II (3 X 10(-7) M), whereas the contractile response to KCI or caffeine was not affected. GTX II induced similar effects on isolated bullfrog sartorius muscles, but required higher concentrations (6 X 10(-7) to 3 X 10(-6) M). GTX II (greater than 10(-6) M) inhibited or abolished the action potential evoked in sartorius muscles markedly. In the isolated guinea pig vas deferens and ileum, GTX II caused a dose-dependent inhibition of the twitch responses to indirect nerve stimulation at concentrations of 3 X 10(-8) to 10(-6) M and 10(-7) to 10(-6) M, respectively. But the toxin had no effect on the dose contractile-response curves for norepinephrine, carbamylcholine or KCI in the vas deferens and for carbamylcholine or histamine in the ileum. GTX II (5 X 10(-8) to 10(-6) M) decreased norepinephrine release induced by veratridine from the vas deferens in a dose-dependent manner. These results suggest that GTX II blocks the voltage-sensitive Na channels in the cell membrane of skeletal muscles and autonomic nerves and these may play an important role in the mechanism of inhibitory effects of GTX II on contractile responses of these tissues to electrical stimulation.     

Sympathetic denervation does not alter the density or properties of alpha-1 adrenergic receptors in rat vas deferens

Alpha-1 adrenergic receptors in surgically denervated rat vas deferens were studied using radioligand binding assays of [125I] BE 2254 ([125I]BE) and contraction measurements. Scatchard analysis of saturation isotherms of specific [125I]BE binding showed no change in the affinity or density of binding sites 4, 7 or 14 days after denervation of rat vas deferens. The potency of norepinephrine in inhibiting specific [125I]BE binding was also unchanged 7 days after denervation of vas deferens. The potency of phenylephrine in causing contraction in vitro did not change 4, 7 or 14 days after denervation of vas deferens; however, there was a significant increase in the maximum contractile response to phenylephrine at all time points. After partial inactivation of alpha-1 adrenergic receptors in vitro with phenoxybenzamine, there was an equivalent reduction in the number of [125I]BE binding sites in the control and 14-day denervated vas deferens. The equilibrium dissociation constants calculated from contractile measurements for norepinephrine were the same in the control and denervated tissues. However, there was a 2.2-fold increase in contractile sensitivity to norepinephrine 14 days after denervation and a 3.6-fold increase in contractile sensitivity to methacholine 7 days after denervation. These results show that surgical denervation of the rat vas deferens results in an increase in contractile sensitivity to norepinephrine and methacholine and an increase in maximum contraction. However, there is no change in alpha-1 adrenergic receptor density or properties at any time after denervation. Thus, alterations in alpha-1 adrenergic receptors do not contribute to contractile supersensitivity of denervated rat vas deferens.     

Excitatory effect of the most potent marine toxin, maitotoxin, on the guinea-pig vas deferens

The most potent marine toxin, maitotoxin (MTX) (10(-9) to 3 X 10(-8) g/ml) caused a slower contraction of the isolated guinea-pig vas deferens (second component) in a dose-dependent manner after the first rapid phasic contraction (first component). The second component of the MTX-induced contraction was markedly inhibited by phentolamine and reserpine, whereas the first component remained unaffected. Both components were inhibited or abolished by verapamil or a Ca-free medium, but were not affected by atropine, chlorpheniramine or tetrodotoxin. The tissue Ca content of the vas deferens was increased by MTX 10(-9) to 3 X 10(-8) g/ml) in a dose-dependent manner. Furthermore, MTX (10(-9) to 3 X 10(-8) g/ml) caused a dose-dependent release of norepinephrine from the tissue, which was inhibited or abolished by verapamil or a Ca-free medium. In Na+-free medium, MTX still caused a profound increase in the tissue Ca content and a marked release of norepinephrine from the vas deferens. These results suggest that the major part of the first component is the result of a direct action of MTX on smooth muscle membrane, whereas the second component is primarily the result of indirect action mediated through the norepinephrine release from the adrenergic nerve terminals. It is also suggested that both components are possibly due to an increased Ca++ permeability of the voltage sensitive Ca++ channels in smooth muscle and nerve membrane.     

Effect of castration on the smooth muscle cells of the internal sex organs of the rat: influence of the smooth muscle on the sympathetic neurons innervating the vas deferens, seminal vesicle and coagulating gland.

Wet weights of vas deferens, seminal vesicle and coagulating gland were reduced by almost 80 to 90% 10 weeks after castration. Endogenous norepinephrine content and dopamine-beta-hydroxylas activity of these tissues were also reduced to the same degree. One week after castration there was approximately a 50% loss in the weight of all three organs. However, this was accompanied by an equal reduction in norepinephrine content and dopamine-beta-hydroxylase activity only in the vas deferens. Two weeks later the degree of reductions in wet weight, norepinephrine content and dopamine-beta-hydroxylase activity was almost identical for all three organs. Treatment of 40-day castrate rats with testosterone (10 mg/kg s.c.) not only restored the wet weights of the internal sex organs to normal but their norepinephrine content and dopamine-beta-hydroxylase activity as well. Castration of immature rats (10-14 days old) resulted in retardation of growth of the vas deferens and seminal vesicle by 90-95%, and similar reductions in norepinephrin content and dopamine-beta-hydroxylase activity, when compared to the tissues of control littermates on the 90th postoperative day. Histological examination of normal and castrate rats indicated that, along with a reduction in epithelial cells, the smooth muscle cells of the vas deferens, seminal vesicle and coagulating gland was markedly reduce in size as well. Administration of testosterone completely reversed these changes. Furthermore, deoxyribonucleic acid content of the seminal vesicle and coagulating gland was reduced by 50% after castration and then restored to control level after testosterone treatment. Taken together, it seems that atrophy of the internal sex organs following castration is a combined effect of reduction in size and number of smooth muscle cells. Therefore, it is concluded that any alteration in the size of smooth muscle cells or loss of such cells of the internal sex organs indirectly influences their sympathetic nerves in such a manner that norepinephrine concentrations, and thereby the density of innervation, are maintained at normal levels.     

Pre- and postjunctional actions of hydralazine in vascular and nonvascular smooth muscle in vitro

This study investigated the in vitro prejunctional and postjunctional actions of hydralazine in vascular and nonvascular smooth muscle. Low concentrations (micromolar) of hydralazine blocked phenylephrine-induced increases in perfusion pressure in the innervated rat kidney, whereas high concentrations (greater than 10 microM) were required in the perfused, innervated rabbit ear artery. High concentrations of hydralazine were required to block phenylephrine-induced contractions of innervated rat vas deferens and anococcygeus muscle. After in vitro denervation, rabbit ear arteries became sensitive to low concentrations of hydralazine, but this was not observed in the rat vas deferens or anococcygeus muscle. Hydralazine (1-3 microM) was without effect on 3H-release from rat vas deferens, anococcygeus muscle and kidney previously incubated with [3H]norepinephrine. Hydralazine (1 microM) decreased field stimulation-induced 3H-release from [3H]norepinephrine-loaded rabbit ear arteries. The results from the rabbit ear artery confirm that in some vessels the presence of sympathetic nerve terminals can modify the postjunctional actions of low concentrations of hydralazine. However, the other vascular tissue studied (rat renal vascular bed) was sensitive to low concentrations of hydralazine while innervated. In conclusion, the existence of a postjunctional relaxant effect of hydralazine, observed in vitro at concentrations compatible with therapeutic blood levels found in humans, has been confirmed using two different vascular preparations. The relevance of the prejunctional effect of hydralazine remains to be ascertained.     

Atrial natriuretic factor inhibits adrenergic and purinergic neurotransmission in the rabbit isolated vas deferens

This study tests the hypothesis that atrial natriuretic factor (ANF) acts to inhibit neurotransmission in the rabbit vas deferens. The vas deferens is a unique model of autonomic neurotransmission in that it is composed of primarily nonvascular smooth muscle and has both a purinergic or twitch contraction and an adrenergic or phasic contraction associated with its response to electrical stimulation. In this study ANF was found to inhibit both adrenergic and purinergic neurotransmission in the rabbit vas deferens. ANF inhibited both the electrically induced phasic contraction and electrically induced norepinephrine release in a concentration-dependent manner over the ANF concentration range of 10(-10) to 10(-7) M. ANF at a concentration of 10(-7) M had no effect on norepinephrine-induced or ATP-induced contractions. Therefore, the neuromodulatory effect of ANF in the rabbit vas deferens appears to be prejunctional, on the release of the neurotransmitters norepinephrine and ATP from the nerve terminal and not postjunctional on the smooth muscle. Neither the alpha-2 antagonist rauwolscine nor the cyclooxygenase inhibitor indomethacin had any effect on the inhibitory effect of ANF on electrically induced twitch or phasic contractions. Additionally, ANF did not affect vasa deferentia prostaglandin E production. Therefore, the inhibitory neuromodulatory ANF effect is not mediated via alpha-2 adrenergic receptors or prostaglandin E production. The observed inhibitory neuromodulatory effects in this study may be involved in the hypotensive effects of ANF including natriuresis, diuresis and vasodilation.