Alpha adrenergic receptors mediate angiotensin-induced prostaglandin production in the rabbit isolated vas deferens

The effect of alpha adrenergic receptor antagonists on concentration-dependent response to angiotensins II and III was examined in the electrically stimulated isolated rabbit vas deferens. The force generated by a nonadrenergic neural mechanism was reduced by both peptides whereas the force generated by adrenergic neural mechanisms was enhanced. Angiotensin III-induced inhibition of the nonadrenergic contraction was significantly greater than that of angiotensin II for all groups. Yohimbine (1 X 10(-4) M), an alpha-2 receptor antagonist, attenuated the depression of the nonadrenergic contraction produced by angiotensins II and III. Yohimbine (1 X 10(-5) and 1 X 10(-4) M) also significantly reduced angiotensin II-induced prostaglandin E (PGE) synthesis. Yohimbine only significantly altered the angiotensin III-induced PGE synthesis at an antagonist concentration of 1 X 10(-4) M. Rauwolscine (1 X 10(-8) and 1 X 10(-7) M) attenuated angiotensin II-induced PGE production and at a higher concentration (1 X 10(-6) M) reduced angiotensin III-induced PGE production. The alpha-1 antagonist, prazosin (1 X 10(-6) M), did not alter nonadrenergic contractile or PGE responses to either angiotensin. The alpha-2 agonist, clonidine, both inhibited the nonadrenergic neural contraction and enhanced PGE synthesis. We interpret these data to indicate that angiotensins II and III may act via separate mechanisms to induce PGE synthesis in the vas deferens, with angiotensin II effects being more dependent on norepinephrine release from adrenergic nerves.     

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.     

Denervation-induced changes in electrophysiologic parameters of the smooth muscle of the guinea-pig and rat was deferens

In order to further elucidate the mechanisms by which postganglionic denervation causes changes in the dose-response curves obtained in smooth muscle, microelectrodes have been used to investigate cellular changes in the denervated guinea-pig and rat vas deferens. In the guinea-pig vas deferens, chronic denervation produced a partial depolarization (mean change of 8.5 mV) without any change in threshold for the action potential. In the rat vas deferens there was no change in resting potential but the threshold membrane potential because more negative (6.5 mV). Thus, in both species, but apparently by different mechanisms, the resting and threshold membrane potentials are brought closer together by denervation. Such an effect would clearly contribute to the well documented increase in sensitivity to depolarizing agonists which is produced by chronic denervation. In both species, denervation increased the space constant of the smooth muscle, an indication of increased electrical coupling among the cells. This observation is consistent with morphologic evidence of improved coupling induced by denervation and presented previously from this laboratory. The improved coupling appears to be associated with the increased maximum response of the denervated vasa deferentia of both species. These results are discussed in references to known similarities and differences in electrophysiologic characteristics between normal guinea-pig and rat vasa deferentia.     

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.     

High efficiency coupling of alpha-1 adrenergic receptors to inositol phospholipid metabolism revealed by denervation of rat vas deferens

The effect of surgical denervation on alpha-1 adrenergic receptor-stimulated inositol phosphate (IP) formation was examined in rat vas deferens. Rings of tissue from acutely reserpinized animals were incubated with [3H]inositol in the presence of lithium to block IP degradation and desmethylimipramine to block neuronal uptake of norepinephrine. Eighteen days after denervation the potency of norepinephrine in stimulating [3H]IP accumulation was increased 10-fold. The potency of epinephrine was increased only 3.5-fold, and the potency of phenylephrine was not altered significantly. The potency of norepinephrine in control tissues incubated with 0.1 microM desmethylimipramine was unaffected by addition of cocaine to further block neuronal uptake; however, addition of pyrogallol and pargyline to block metabolic degradation increased the potency of norepinephrine in these tissues by 6-fold. Two days after denervation there was a similar 5-fold increase in the potency of norepinephrine. In denervated tissues, the potency of norepinephrine in stimulating [3H]IP accumulation was decreased about 40-fold after receptor inactivation with 1 microM phenoxybenzamine. These results suggest that there is a substantial alpha-1 adrenergic receptor reserve for stimulating [3H]IP accumulation in rat vas deferens which is normally obscured by rapid inactivation of norepinephrine. The increase in the potency of norepinephrine after denervation appears to be due to removal of these inactivation mechanisms.     

Adenosine receptor antagonism attenuates angiotensin II effects on adrenergic neurotransmission in the rabbit isolated vas deferens

Angiotensin II augments adrenergic neurotransmission in the rabbit isolated vas deferens and suppresses purinergic neurotransmission. This study tests the hypothesis that angiotensin II augments adrenergic neurotransmission by depressing the neuronal release of ATP, resulting in suppressed formation of the inhibitory neuromodulator, adenosine or a related purine. Exogenous ATP added to the vasa deferentia increased adenosine formation and depressed adrenergic neurotransmission thus providing indirect support for the hypothesis. The adenosine receptor antagonist, 8-(sulfophenyl)theophylline (10 and 100 microM) depressed responses to exogenous adenosine and ATP but did not alter contractile responses to nerve stimulation or exogenously administered norepinephrine thus indicating that endogenous adenosine had no basal influence upon neurotransmission. However, the 8-(sulfophenyl)theophylline reduced angiotensin II effects on both adrenergic neurogenic contractions and evoked norepinephrine release. Additionally, the augmentation of adrenergic neurogenic contractions by angiotensin II was enhanced in the presence of ATP. These results are consistent with an ATP involvement in angiotensin effects on adrenergic neurotransmission and contrary to the initial hypothesis, suggest that purines enhance adrenergic neurotransmission in the presence of angiotensin II.     

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.     

The effects of photoperiod on the responses of the hamster vas deferens to nerve stimulation

Hamster vas deferens responds to nerve stimulation with a biphasic contraction which is completely blocked by guanethidine and tetrodotoxin. The second component of the contraction is inhibited by phentolamine, whereas the initial component is slightly potentiated by phentolamine. When hamsters are subjected to short photoperiods or castration, the vas deferens becomes supersensitive to nerve stimulation and shows spontaneous mechanical activity. The supersensitivity is not due to increased postsynaptic adrenergic supersensitivity, decreased neuronal uptake of catecholamine, decreased presynaptic feedback by prostaglandin or adrenergic agonist. The supersensitivity is still demonstrable in the presence of 4-aminopyridine, suggesting that the release of transmitter is also not different in animals kept in short photoperiods. The activity of the Na+/K+ pump is increased in vasa deferentia from hamsters kept in short photoperiods and the postsynaptic response to the ATP receptor agonist, diadenosine pentaphosphate, is also enhanced. It is suggested that the supersensitivity induced in the hamster vas deferens by short photoperiod is caused by testosterone withdrawal and is due to increased responsiveness to ATP, which could be acting as a cotransmitter in this tissue.     

Targeted deletion of ectonucleoside triphosphate diphosphohydrolase 1/CD39 leads to desensitization of pre- and postsynaptic purinergic P2 receptors

We previously reported that ATP coreleased with norepinephrine from cardiac sympathetic nerves activates presynaptic P2X purinoceptors (P2XR), thereby enhancing norepinephrine exocytosis. Blockade of ectonucleoside triphosphate diphosphohydrolase 1 (E-NTPDase1/CD39) potentiates norepinephrine exocytosis, whereas recombinant soluble CD39 (solCD39) in-hibits it. This suggested that CD39 gene (Entpd1) deletion would enhance purinergic and adrenergic signaling by preserving ATP and its norepinephrine-releasing activity. However, we found that the neurogenic contractile response of vasa deferentia from Entpd1-null (CD39(-/-)) mice was attenuated and accompanied by reduced activity of pre- and postsynaptic P2XR, whereas contractile responses to K(+) or norepinephrine remained intact. In addition, the magnitude of ATP and norepinephrine exocytosis from cardiac synaptosomes was decreased in CD39(-/-) mice. Inhibition of E-NTPDase1/CD39, or solCD39 administration, did not affect the attenuated contractile response of vasa deferentia from CD39(-/-) mice. Notably, Entpd1 deletion and pharmacological P2XR desensitization in control mice similarly attenuated vasa deferentia responses. Thus, excessive and prolonged ATP exposure resulting from CD39 deletion desensitizes pre- and postjunctional P2XR at the sympathetic neuromuscular junction. This diminishes purinergic activity directly and adrenergic activity indirectly. It remains to be determined whether this desensitization results from receptor internalization, changes in receptor conformation or phosphorylation. Shutdown of ATP signaling in CD39(-/-) mice may represent a defense mechanism for the prevention of purinergic overstimulation. Our findings emphasize the cardioprotective role of neuronal CD39: by reducing presynaptic facilitatory effects of neurotransmitter ATP, CD39 attenuates norepinephrine release and its dysfunctional consequences. Moreover, by virtue of its antithrombotic action CD39 can potentially prevent the transition from myocardial ischemia to infarction.     

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.     

Pharmacological differentiation of angiotensin effects in the rabbit isolated vas deferens with dithiothreitol and pertussis toxin

Angiotensin II inhibits nonadrenergic (purinergic) neurotransmission in the vas deferens and potentiates adrenergic neurotransmission and prostaglandin (PG)E synthesis. Other angiotensin responses are sensitive to either dithiothreitol or pertussis toxin. The present study tested the hypothesis that dithiothreitol or pertussis toxin selectively depress angiotensin responses in the vas deferens. The dithiothreitol (10 mM) eliminated the potentiation of both adrenergic neurotransmission and PGE synthesis but did not alter the depression of purinergic neurotransmission. In contrast, pertussis toxin (100 ng/ml for 3 hr) eliminated the depression of purinergic neurotransmission but had no effect on adrenergic neurotransmission or PGE synthetic responses to angiotensin II. The results are consistent with the existence of at least two transduction pathways for angiotensin II, one enhancing adrenergic neurotransmission and PGE synthesis and the other depressing purinergic neurotransmission. The results indicate that the vas deferens is a useful preparation in defining selective actions of angiotensin receptor agonists or antagonists.     

Norepinephrine and potassium induced calcium translocation in rat vas deferens

To understand calcium regulation in smooth muscle, we studied both potassium- and norepinephrine-mediated alterations in the movement of calcium in the smooth muscle of rat vas deferens. We employed 45Ca to measure agonist-mediated calcium influx and efflux, as well as tissue calcium content. In addition we labeled tissues with [3H]myoinositol to measure the effect of norepinephrine on inositol phosphate generation. Stimulation of the vas deferens with 50 mM potassium caused a rapid influx of 45Ca (6-fold). Norepinephrine stimulation, even at a concentration maximal for contraction of the tissue (1 mM), did not result in any alteration in 45Ca influx by itself but inhibited potassium-stimulated 45Ca influx (IC50 = 3 microM). This alpha receptor-mediated effect of norepinephrine was not diminished by either pretreatment with reserpine or adrenergic denervation. Studies of the efflux of 45Ca from vas deferens revealed that efflux was not affected by potassium but was significantly stimulated by norepinephrine. Alpha receptor stimulation of vas deferens smooth muscle caused a marked elevation in the appearance of inositol phosphates, particularly inositol trisphosphate, that was not dependent on extracellular calcium. We conclude that norepinephrine does not stimulate calcium influx in vas deferens smooth muscle but leads to the release of calcium from intracellular stores via formation of inositol trisphosphate and that the resulting increase in intracellular calcium may lead to inactivation of the potential-dependent calcium channel.     

Evidence against serotonin as a vasoconstrictor neurotransmitter in the rabbit basilar artery

It has been suggested recently that serotonergic nerves distinct from the known adrenergic innervation are present in cerebral blood vessels. We have confirmed that serotonin is present in the wall of rabbit cerebral arteries using a high-performance liquid chromatography technique, with levels in the basilar artery of 0.27 +/- 0.04 microgram/g wet wt. Furthermore, adrenergic denervation in vitro with 6-hydroxydopamine, while substantially reducing norepinephrine content, did not alter serotonin levels in the basilar artery. However, it was not possible to demonstrate specific accumulation of [3H]serotonin into distinct serotonergic nerves. Both the basilar artery and ear artery (which has been shown not to be innervated with serotonergic nerves) accumulated [3H]serotonin when incubated with a low concentration (10(-8) M). However, [3H]serotonin accumulation was reduced markedly in 6-hydroxydopamine-treated vessels as well as in the presence of the norepinephrine uptake blocker, desmethylimipramine. Furthermore, pretreatment with the serotonin uptake blocker, fluoxetine, did not inhibit selectively [3H]serotonin accumulation in the basilar artery. Thus, the majority of [3H]serotonin accumulation can be attributed to adrenergic nerves. The possibility that serotonergic nerves contribute to the neurogenic constrictor response of the rabbit basilar artery was also tested. Adrenergic denervation with 6-hydroxydopamine in vitro abolished the constrictor response to transmural nerve stimulation completely, but levels of endogenous serotonin were not affected. Thus, although the presence of endogenous serotonin in cerebral arteries has been confirmed, this substance does not appear to contribute to the neurogenic vasoconstriction seen in this vessel.     

Electrophysiological analysis of adrenergic neurotransmission and its modulation by chronic denervation in canine saphenous veins

The present experiments were undertaken to investigate the electrophysiological responses of the canine saphenous vein evoked by perivascular nerve stimulation, norepinephrine or selective alpha adrenergic agonists before and after chronic sympathetic denervation. Unilateral sympathectomy was performed from T12 to L9 in adult female dogs. After 3 to 5 weeks, the denervated saphenous veins were removed. Innervated saphenous veins were obtained from unoperated dogs. In innervated but not in denervated veins, electrical stimulation generated excitatory junction potentials and a slow depolarization. The slow depolarization was inhibited by rauwolscine or phentolamine, but not by prazosin, whereas excitatory junction potentials were not inhibited by alpha adrenergic blockers. Exogenously applied norepinephrine caused a depolarization of the membrane that was inhibited by rauwolscine but not by prazosin. The selective alpha-1 adrenergic agonist, phenylephrine, and the selective alpha-2 adrenergic agonist, UK 14,304, caused depolarization. In denervated veins, the threshold concentrations of norepinephrine or UK 14,304 required to depolarize the smooth muscle cell membrane were reduced. Responses to phenylephrine were not affected by denervation. These results indicate that in the canine saphenous vein norepinephrine, whether added exogenously or released from sympathetic nerves, causes predominant depolarization by activating alpha-2 adrenergic receptors. Denervation augments selectively the electrical response to alpha-2 adrenergic stimulation.     

Specific changes in the cholinergic system in guinea-pig vas deferens after denervation

A small rapid phase (1st phase) was distinguished from a concomitant phase (2nd phase) in contraction of guinea-pig vas deferens. The vas deferens 4 days after denervtion exhibited supersensitivity to stimulants. The supersensitivity in the 2nd phase of contraction was nonspecific, but that in the 1st phase was specific to muscarinic cholinergic agonists. The increase in sensitivity resulted in a shift of the dose-response curve to lower concentrations without significant change in the maximal response. Muscarinic cholinergic receptors in the vas deferens, determined by measuring binding of [3H]quinuclidinyl benzilate, changed after denervation. The maximal binding sites increased from 115 to 165 fmol/mg of protein with no significant change in the dissociation constant. The affinity of the receptor for agonist also did not change significantly. Studies on [3H]WB4101 binding indicated no significant change in alpha adrenergic receptors after denervation. Thus, specific supersensitivity of the cholinergic mechanism mediated by muscarinic acetylcholine receptors occurred after denervation of guinea-pig vas deferens. This increased sensitivity is discussed in relation to the amount of receptor.     

A possible crossed histamine-containing pathway adjacent to the sympathetic system of the rat vas deferens

Studies using nerve degeneration techniques (ganglionectomy, interganglionic section, postganglionic axotomy, uni- or bilateral hypogastric nerve section and right pelvic ganglionectomy) and fluorometric determinations of histamine and norepinephrine have shown the presence of nervous pathways containing histamine adjacent to the sympathetic system of the rat vas deferens. The findings suggest that these pathways cross between the ganglionic clusters located at the angle formed by the seminal vesicle and the vas deferens. They are not structurally related to the central nervous system by way of the hypogastric or pelvic ganglion. The histamine-containing pathways are independent of the noradrenergic pathways as dissociation between norepinephrine depletion and histamine depletion can be shown under nerve degeneration. The time course of nerve degeneration over a long period after sympathectomy shows a biphasic effect on histamine levels of the vas deferens. The early histamine depletion would be indicative of degeneration of histamine-containing pathways, and the delayed histamine increasing phase has been considered as due to accumulation of mast cells in the degenerating nerve sheaths. A possible role for the histamine-containing pathways in the modulation of sympathetic activity is envisaged.     

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.     

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.     

Sensitivity changes in the smooth muscle of the guinea-pig isolated vas deferens after treatment of animals with 6-hydroxydopamine

Postjunctional supersensitivity of the smooth muscle of the guinea-pig vas deferens induced by denervation, decentralization and treatment of animals with reserpine has been attributed, in part, to a partial membrane depolarization (8-10 mV) resulting from reduced electrogenic Na+,K+-pumping activity. This study was undertaken to characterize sensitivity changes which occur after treatment of animals with 6-hydroxydopamine (100 mg/kg + 250 mg/kg i.v., 1 day apart). Seven days after the second injection, concentration-response curves for isometric contractile responses to norepinephrine, methoxamine, acetylcholine and histamine were shifted 40.6-, 1.7-, 3.6- and 2.7-fold, respectively, to the left of control; however, the sensitivity to KCl was not increased, which contrasts with the results after denervation, decentralization and reserpine treatment. Ouabain (10(-5) M) produced 1.8- and 1.3-fold leftward shifts of the KCl concentration-response curves in tissues from control and 6-hydroxydopamine-treated animals, respectively. The pronounced effect of ouabain in tissues from treated animals may be an indication that 6-hydroxydopamine treatment does not result in as much inhibition of electrogenic Na+,K+-pumping, and resultant membrane depolarization, as other methods which induce supersensitivity of the guinea-pig vas deferens.     

The Adrenergic Control of Lower Esophageal Sphincter Function: AN EXPERIMENTAL MODEL OF DENERVATION SUPERSENSITIVITY

To evaluate the adrenergic regulation of lower esophageal sphincter (LES) function, LES pressure, LES relaxation during swallowing, and blood pressure were measured in the anesthetized opossum, Didelphis virginiana, during intravenous administration of alpha and beta adrenergic agonists and antagonists. Studies were done in controls and animals adrenergically denervated with 6-hydroxydopamine. Alpha adrenergic agonists (norepinephrine, phenylephrine) increased LES pressure and blood pressure, whereas a beta adrenergic agonist (isoproterenol) decreased both pressures. Alpha adrenergic antagonism (phentolamine) reduced basal LES pressure by 38.3+/-3.8% (mean +/-SEM) (P < 0.001). Beta adrenergic antagonism (propranolol) had no significant effect on either basal LES pressure or percent of LES relaxation with swallowing. After adrenergic denervation with 6-hydroxydopamine, basal LES pressure was reduced by 22.5+/-5.3% (P < 0.025) but LES relaxation during swallowing was unaltered. In denervated animals, both LES pressure and blood pressure dose response curves showed characteristics of denervation supersensitivity to alpha but not to beta adrenergic agonists. These studies suggest: (a) a significant portion of basal LES pressure is dependent upon alpha adrenergic stimulation; (b) LES relaxation during swallowing is not an adrenergically mediated response; (c) the LES pressure response to alpha adrenergic agonists after 6-hydroxydopamine may serve as a model of denervation supersensitivity in the gastrointestinal tract.