Structural and functional alterations caused at the extraneuronal level by sympathetic denervation of blood vessels

Plasticity in adult and ageing sympathetic neurons

The nature of neural plasticity and the factors that influence it vary throughout life. Adult neurons undergo extensive and continual adaptation in response to demands that are quite different from those of early development. We review the main influences on the survival, growth and neurotransmitter expression in adult and ageing sympathetic neurons, comparing these influences to those at work in early development. This "developmental" approach is proposed because, despite the contrasting needs of different phases of development, each phase has a profound influence on the mechanisms of plasticity available to its successors. Interactions between neurons and their targets, whether effector cells or other neurons, are vital to all of these aspects of neural plasticity. Sympathetic neurons require access to target-derived diffusible neurotrophic factors such as NGF, NT3 and GDNF, as well as to bound elements of the extracellular matrix such as laminin. These factors probably influence plasticity throughout life. In adult life, and even in old age, sympathetic neurons are relatively resistant to cell death. However, they continue to require target-derived diffusible and bound factors for their maintenance, growth and neurotransmitter expression. Failure to maintain appropriate neuronal function in old age, for example in the breakdown of homeostasis, may result partly from a disturbance of the dynamic, trophic relationship between neurons and their targets. However, there is no clear evidence that this is due to a failure of targets to synthesize neurotrophic factors. On the neural side of the equation, altered responsiveness of sympathetic neurons to neurotrophic factors suggests that expression of the trk and p75 neurotrophin receptors contributes to neuronal survival, maintenance and growth in adulthood and old age. Altered receptor expression may therefore underlie the selective vulnerability of some sympathetic neurons in old age. The role of neural connectivity and activity in the regulation of synthesis of target-derived factors, as well as in neurotransmitter dynamics, is reviewed.

Denervation-induced supersensitivity to forskolin and pinacidil is not related to changes in the adenylate cyclase transduction pathway in the rabbit femoral artery

1. The present study investigates whether chemical sympathectomy compromises the relaxation of the rabbit femoral artery precontracted with serotonin. The vasodilating agents promoted cyclic adenosine monophosphate (cAMP) accumulation or opening of the potassium channels. The effect of denervation on the adenylyl cyclase transduction pathway was also studied. 2. 6-Hydroxydopamine treatment did not impair the relaxation to adenosine, 8-bromoadenosine-cAMP (a membrane-permeable analog of cAMP) and 3-isobutyl-1-methylxanthine (a cAMP phosphodiesterase inhibitor). Moreover, denervation enhanced the relaxation to forskolin (a direct Gs-type protein activator) and pinacidil (a potassium channel opener). 3. Denervation modified neither adenosine diphosphate ribosylation of Gs- and Gi-proteins nor adenylyl cyclase activity.

Development and maturation of noradrenaline-containing nerves of the rat uterine artery. Effects of acute and chronic oestrogen treatment

The development and maturation of noradrenaline-containing nerves of the rat uterine artery was investigated, histochemically and biochemically, at seven different postnatal age-stages and following acute and chronic treatment with oestradiol. Morphological changes in the vessel were quantitatively evaluated on Toluidine Blue-stained semithin sections and low magnification electronmicrographs. In summary, the uterine artery is innervated at birth; the adult pattern of innervation is established at two weeks of age; the innervation density increases progressively between the infantile and prepubertal periods, accompanying proliferation and growth of smooth muscle cells in the tunica media; changes in the innervation are followed by an increase in the tissue concentration of noradrenaline and neither the endocrine changes characterizing puberty nor acute or chronic treatment with oestradiol have an effect on the pattern of development of the uterine artery and associated noradrenaline-containing nerves. Results are interpreted considering the differential susceptibility of urinogenital organs to sex hormones.

Reversion of phenotype of endothelial cells in brain tissue around glioblastomas

With the aim of studying the putative involvement of peritumoral microvessels in the formation of brain edema, small pieces of peritumoral brain tissue were removed from six patients with glioblastoma multiforme submitted to surgery. All patients had cerebral edema, as shown by preoperative C.T. and N.M.R. Control specimens were obtained from four patients undergoing ventriculo-peritoneal shunt. The tissue fragments were fixed in glutaraldehyde-osmium and embedded in Epon. In semi-thin sections observed under light microscopy peritumoral endothelial cells exhibited voluminous cytoplasm and nucleus. Under the electron microscope, capillary cells from glioblastoma patients differed from controls mainly by showing nuclei rich in euchromatin, cytoplasm rich in pinocytotic vesicles and with occasional fenestrations. All these morphological characteristics are compatible with a process of reversion of phenotype of capillaries around glioblastomas to that of periphery as well as an increase in permeability. Both events may be due to diffusion of a tumoral vascular permeability/endothelial growth factor. This peripheral vessel phenotype of peritumoral microvessels supports their participation in the formation of brain edema and may provide a new clue for therapeutic intervention: for example it fits quite well to the known increase in permeability by leukotrienes and decrease in permeability by corticosteroids in tumoral edema.

Regional heterogeneity of arterial structural changes

Arterial structural changes in experimental models of hypertension and restenosis differ between vessel types and within vessels. Inspired by the diversity of short-term functional responses to vasoactive agents, hypotheses are presented with respect to the heterogeneity of structural alterations. Considered are the multifactorial nature of smooth muscle cell growth control and the possibility that vascular smooth muscle is not homogeneous but composed of different smooth muscle cell populations. These hypotheses may help explain the origin of both intervascular and intravascular heterogeneity of vascular structural responses.

Effect of sympathetic denervation on the relaxing responses of rabbit arterial smooth muscle

1. The present study reports on the influence of chemical denervation by 6-hydroxydopamine (6-OHDA) on the relaxing responses to carbachol, sodium nitroprusside, zaprinast, adenosine, forskolin and 3-isobutyl-1-methylxanthine (IBMX) of ring preparations of rabbit renal and femoral arteries. 2. Carbachol was found to induce a complete abolition of the tone induced by 5-hydroxytryptamine (0.1-1.0 microM), both in the renal and the femoral arteries. The profile of the carbachol-induced relaxation in both the renal and femoral arteries obtained from 6-OHDA-treated rabbits was similar to that observed in control animals; relaxing responses obtained with some of the concentrations of carbachol were, however, found to be greater (P < 0.01) in denervated arteries. Sodium nitroprusside was also found to be an effective relaxant agent in both renal and femoral arteries, though more potent in the former but was unaffected by denervation. Zaprinast relaxed both renal and femoral artery ring preparations, and again, no significant difference was observed between control and denervated animals. 3. The cyclic AMP-mediated relaxing responses to adenosine, forskolin and IBMX were found to be similar in renal and femoral arteries of control arteries, producing almost complete abolition of pre-existing tone. The adenosine- and IBMX-induced relaxing responses in renal and femoral arteries were found to be similar in control and denervated animals. However, the concentration-response curve to forskolin was shifted to the left by 2.5 and 1.5 log units in preparations of renal and femoral arteries of denervated rabbits, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of sympathetic neurotransmission by melatonin

Melatonin is of considerable interest for its regulatory influence on a variety of physiological processes including biological rhythms and neuroendocrine functions. We showed that melatonin potentiates sympathetic neurotransmission in the prostatic portion of the rat vas deferens, by increasing contractions in response to noradrenaline and ATP released by acetylcholine stimulation of presynaptic nicotinic receptors. Melatonin in vitro (100 pg/ml; for 4 h) increased the maximal acetylcholine-induced contraction only when the hypogastric ganglion was present, and this effect was blocked by cycloheximide (100 micrograms/ml). Melatonin also modulated the sympathetic trophic influence on smooth muscle, since it reduced [35S]methionine incorporation into the vas deferens in the hypogastric ganglion-vas deferens preparation. Thus, it is suggested that the regulation of protein synthesis might be one of the mechanisms whereby melatonin modulates endogenous rhythms and synchronizes them to the environmental light cycle.

Neurotoxicity and induction of fibroblast proliferation by acetaldehyde in the rabbit liver

1. Acetaldehyde may, directly or through the formation of condensation products with biogenic amines, be involved in the pathogeny of alcoholic disease. 2. Rabbits were treated acutely (200 mg kg-1, i.p., 1 h before sacrifice) or subacutely (200 mg kg-1 per day, during 5 days; sacrificed 2 days after end of treatment) with acetaldehyde. Another group was administered 6-OHDA (2 x 50 mg kg-1 on day 0 and on day 1, killed on day 5). 3. Acetaldehyde induced a depletion of hepatic noradrenaline. Both in the acute experiments and 2 days after the subacute treatment with acetaldehyde the levels of hepatic noradrenaline were 25% of control. These effects were similar to, but less intense than those induced by 6-OHDA. 4. Both subacute acetaldehyde and 6-OHDA led to a significant increase in the density of fibroblasts in the portal tract spaces of the rabbit liver. 5. The neurotoxic effects of acetaldehyde and the subsequent increase in liver fibroblast density may play a role in the pathogenesis of alcoholic disease.

A study of the neuronal and non-neuronal stores of dopamine in rat and rabbit kidney

The present study has examined the effects of 6-hydroxydopamine (6-OHDA) alone and in combination with pargyline, desipramine and GBR 12909 and denervation as induced by occlusion of the renal artery (RAO) on the endogenous dopamine (DA) and noradrenaline (NA) contents in rat and rabbit renal tissues; the effects of chemical denervation on catecholamine levels in the left ventricle were also studied. In rat and rabbit renal medulla and rat renal cortex, 6-OHDA and pargyline plus 6-OHDA selectively reduced NA (85-92% reduction) without a parallel decrease in DA tissue content (19-27% reduction). This 6-OHDA- and pargyline plus 6-OHDA-insensitive DA pool was found to be resistant to denervation as induced by RAO. The NA-depleting effect of 6-OHDA in these renal areas was found to be prevented by the previous administration of desipramine, but not with that of GBR 12909. In the rabbit renal cortex, 6-OHDA selectively reduced NA (90% reduction) without a parallel depletion of DA (20% reduction); previous treatment with pargyline abolished this selectivity. Again, only desipramine, but not GBR 12909, was found to prevent the NA and DA depleting effect of 6-OHDA in the rabbit renal cortex. Denervation induced by RAO was also found to produce a parallel depletion of DA and NA tissue levels in this renal area. In the left ventricle, 6-OHDA alone or in combination with pargyline produced a parallel depletion of DA and NA tissue levels (79-88% reduction) in both species. These results provide evidence against the presence of independent dopaminergic neurones in rat and rabbit kidney and suggest that in rat and rabbit renal medulla and rat renal cortex most of DA is stored in a non-neuronal compartment; in rabbit renal cortex some of the DA appears to be located in noradrenergic neurones, in a store different from that which contains NA.

Resting and maximal forearm skin blood flows are reduced in hypertension

To find whether the vasodilator capacity of nonacral skin is reduced in hypertension, we measured forearm blood flow by venous occlusion plethysmography in 10 seated normotensive (mean +/- SD mean arterial pressure, 94 +/- 5 mm Hg) and 10 hypertensive (112 +/- 9 mm Hg) men at rest for 39 minutes while the forearm was heated with water at 42 degrees C, a maneuver known to selectively and maximally vasodilate skin. Blood pressure, measured every 5 minutes, did not change with heating. We found that in the normotensive group resting forearm blood flow was higher (3.64 +/- 1.12 versus 2.48 +/- 0.58 ml/100 ml tissue per minute, p less than 0.001; normotensive group versus hypertensive group) and resting forearm vascular resistance lower (30.17 +/- 10.99 versus 48.88 +/- 17.37 mm Hg.min.100 ml tissue per minute, p less than 0.05; normotensive group versus hypertensive group), and maximal forearm blood flow with local heating was higher (29.32 +/- 11.99 versus 18.19 +/- 4.50 ml/100 tissue per minute, p less than 0.018; normotensive group versus hypertensive group and vascular resistance lower (4.07 +/- 1.04 versus 6.54 +/- 1.17 mm Hg.min.100 ml tissue per minute, p less than 0.005; normotensive group versus hypertensive group). To find whether this degree and duration of local warming maximally vasodilated the skin in hypertensive subjects (as it does in normotensive subjects), we measured forearm skin blood flow before and during local heating plus 10 minutes of ischemia using a laser Doppler flowmeter.(ABSTRACT TRUNCATED AT 250 WORDS)

The inhibition of glutamine synthetase in rat corpus striatum in vitro by methionine sulfoximine increases the neurotoxic effects of kainate and N-methyl-D-aspartate

Coronal slices of rat brain were incubated in Krebs bicarbonate medium containing kainate (300 microM), or N-methyl-D-aspartate (500 microM). Degeneration of striatal neurons by both these toxins was apparent after 40 min incubation, and was accompanied by a 33% (kainate) and 21% (N-methyl-D-aspartate) reduction in striatal glutamine synthetase activity. Pre-incubation of the slices with 500 microM L-methionine sulfoximine, an inhibitor of glutamine synthetase, for 20 min prior to the exposure to either kainate or N-methyl-D-aspartate, again showed extensive degeneration of striatal neurons, and a supra-additive reduction in glutamine synthetase activity in the tissue. The activity of the neuronal marker enzyme, neuron-specific enolase, was also reduced by pre-incubation of the slices with L-methionine sulfoximine before the addition of kainate or N-methyl-D-aspartate, but to a much lesser extent than glutamine synthetase. The results are discussed in terms of a possible mechanism of interaction between either kainate or N-methyl-D-aspartate, and glial cell metabolism.

Arterial wall and smooth muscle cell development in young Wistar rats and the effects of surgical denervation

Development of the muscular saphenous artery and the effect of surgical denervation on normal development was investigated in young rats at 3 and 6 weeks of age. During this interval, the weight and blood pressures (systolic, diastolic, and mean) of the animals increased significantly. The tunica media of the artery and the lumen increased significantly with age, but the proportion of smooth muscle cell to paracellular matrix did not alter. Computer-assisted three-dimensional reconstructions were used to investigate the smooth muscle cells. They increased significantly in length, volume, and angle of orientation within the vessel wall with age but maintained an approximate surface area-to-volume ratio. The cells in any one vessel tended to be oriented in either a clockwise or counterclockwise direction. The size of the nucleus also increased significantly in length and volume with age, but an approximate surface area-to-volume ratio and a constant nucleocytoplasmic ratio were maintained. The nuclei tended to be eccentrically located, with less than half of all nuclei wholly within the middle third of the cell. Surgical denervation at 10 days of age resulted in abnormalities of growth in vessel dimensions, thinner tunica media at 3 weeks (denervated 11 days previously), and smaller lumen at 6 weeks (denervated 32 days previously). Elevated amounts of paracellular matrix occurred in both age groups, but denervation did not alter smooth muscle cell size. In the 3-week-old animals, denervation resulted in smooth muscle cells with hypertrophied nuclei. This may account for the increase in growth of the tunica media between 3 and 6 weeks of age in the denervated artery.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term administration of 1,3-dipropyl-8-sulfophenylxanthine causes arterial hypertension

Adenosine has been shown recently to be the main factor responsible for the trophic effects of sympathetic innervation. As sympathetic denervation causes hypertrophic and hyperplastic changes reminiscent of those occurring in blood vessels of spontaneously hypertensive rats, we decided to study the effect of a continuous blockade of adenosine receptors on both blood vessel structure and blood pressure. A continuous infusion of 1,3-dipropyl-8-sulfophenylxanthine (DPSPX; 30 micrograms/kg per h for 7 days) to Wistar rats caused hyperplastic changes in peritoneal fibroblasts and mesenteric arterioles, hypertrophic changes in the smooth muscle of the tail artery and significant increase in the size of left ventricle myocardial cell nuclei. Both diastolic and systolic blood pressure increased significantly above control values. The results confirmed the trophic effects of adenosine and showed that chronic blockade of adenosine receptors causes arterial hypertension.

Mediation by adenosine of the trophic effects exerted by the sympathetic innervation of blood vessels

Chemical or surgical sympathetic denervation of blood vessels causes marked changes of the effector cells. Since postganglionic sympathetic cotransmission by noradrenaline and adenosine 5'-triphosphate is well established, the role of these transmitters as putative trophic factors was investigated. Whereas noradrenaline was ineffective in preventing morphological changes due to denervation, both adenosine and N-ethylcarboxamido-adenosine totally prevented them. In conscious rats, the adenosine receptor antagonist dipropylsulphophenylxantine (DPSPX) caused alterations of the blood vessel wall similar to those described for denervation. These results strongly suggest that adenosine is the trophic factor of sympathetic innervation.

Smooth muscle growth in the mature rat: role of sympathetic innervation

The role of sympathetic innervation in maintaining smooth muscle structure and function was investigated in the mature rat. Superior tarsal muscle volume, smooth muscle cell nuclear size and packing density, and alpha-adrenoceptor-mediated contractions were assessed in Sprague-Dawley rats at 3 months of age, and in rats at 6 months of age in which one muscle had intact sympathetic innervation and the contralateral mate was sympathectomized at 3 months. Body weight was stable between 3 and 6 months. In contrast, both maximum contraction and muscle volume increased by more than 50% in the innervated organ, while chronic sympathectomy prevented these increases. Both nuclear packing density and nuclear size increased with age. The greater packing density was abolished by sympathectomy, but nuclear enlargement was not. Adrenoceptor supersensitivity was not observed, although the agonist dose producing 50% maximum contraction varied as a function of contractile capacity. It is concluded that superior tarsal smooth muscle growth continues independently of changes in body weight in the mature rat. Structural and functional deficits observed following chronic sympathetic denervation of this muscle are attributable to prevention of growth rather than regressions in size and contractile capacity.

Sympathetic denervation causes atrial natriuretic peptide-storing granules to appear in the ventricular myocardium of the rat

Sympathetic denervation of the rat heart was produced by 6-hydroxydopamine. In denervated ventricles abundant "atrial" granules were observed whereas in controls no such granules were seen. Denervated ventricles and atria showed a very high content of atrial natriuretic peptide-like immunoreactivity (greater than 10 times higher than in control animals). We suggest that the sympathetic nervous system exerts a repressive effect upon synthesis of atrial natriuretic peptide-like material and upon the formation of atrial natriuretic peptide-storing granules in the ventricular myocardium.

Effects of sympathetic denervation on liver fibroblasts: prevention by adenosine

1. The effect of chemical denervation with 6-hydroxydopamine (6-OHDA) upon portal tract fibroblasts of dogs and rabbits was studied. 2. Denervation led to a significant increase in the density of portal tract fibroblasts both in the dog and in the rabbit. 3. Mast cells, present in the dog but not in the rabbit liver, were also significantly increased by denervation. 4. Noradrenaline depletion induced by reserpine did not increase the density of fibroblasts in the liver portal spaces of the dog. Mast cell density, however, was actually decreased when compared with control. 5. Continuous i.v. infusions of adenosine (10 micrograms kg-1h-1) to dogs totally prevented the effects of 6-OHDA-induced denervation upon fibroblast and mast cell densities in the portal space connective tissue. 6. It is concluded that the sympathetic nervous system is exerting a repressive effect on liver fibroblasts, as was found to occur in various other mammalian tissues. Mast cells, which are known to be activated in various pathological processes of fibrosis, appear to share with fibroblasts a modulating effect from the sympathetic nervous system. 7. The results strongly support the hypothesis of adenosine being the sympathetic trophic factor involved in the control of fibroblasts in the connective tissue of dog liver. A similar role for adenosine had previously been found in the dog saphenous vein.

Purine agonists prevent trophic changes caused by sympathetic denervation

Surgical denervation of the lateral saphenous vein of the dog causes marked extraneuronal changes, both of a morphological and functional type. In an attempt to investigate the factor(s) responsible for the trophic effects exerted by the sympathetic innervation on the dog saphenous vein we studied the effects of noradrenaline, adenosine, inosine and N-ethylcarboxamidoadenosine (NECA) on vascular tissue after sympathetic denervation. The saphenous vein was denervated using either surgical or chemical (6-hydroxydopamine, 6-OHDA) methods. Noradrenaline (0.1 microgram/kg per h), adenosine (10 micrograms/kg per h), inosine (10 micrograms/kg per h) or NECA (0.1 microgram/kg per h) were delivered continuously for 5 days through Alzet minipumps connected to the vein. 6-OHDA-induced denervation resulted in morphological changes similar to those described for surgical denervation. Smooth muscle cells and fibroblasts showed ultrastructural signs of increased synthetic activity and their size was significantly increased. In confirmation of earlier studies, constant i.v. infusions of noradrenaline did not prevent the morphological changes induced by denervation. Adenosine prevented the morphological changes induced by chemical or surgical denervation. Similarly to adenosine, infused NECA prevented the structural consequences of denervation. In contrast, inosine did not prevent the changes caused by surgical denervation. The results are compatible with an involvement of purines in the trophic effects of sympathetic innervation. Moreover, the effects of adenosine do not appear to be mediated by inosine.

Sympathetic denervation caused by long-term noradrenaline infusions; prevention by desipramine and superoxide dismutase

1. The effects of continuous intravenous infusion of noradrenaline (0.01 and 0.1 microgram kg-1 h-1) were studied in both the infused lateral saphenous vein and the contralateral saphenous vein of normal dogs. Noradrenaline, saline, noradrenaline + desipramine or noradrenaline + superoxide dismutase were infused using Alzet osmotic minipumps. 2. After a 5 day infusion period, the noradrenaline content in plasma and in both saphenous veins was determined, and the venous tissues submitted to light microscope morphometry and ultrastructural study and used for the determination of their O-methylation capacity (with [3H]-isoprenaline as a substrate). 3. Noradrenaline caused dose-dependent damage to the sympathetic nerve endings of the lateral saphenous veins. Concomitant changes in extraneuronal structure and function were observed (hypertrophy of smooth muscle cells, nuclear dysmorphy, thickening of the vessel wall, impairment in O-methylation capacity). 4. Desipramine and superoxide dismutase prevented or reduced the effects of noradrenaline on both the morphological and the biochemical parameters; the protection afforded by superoxide dismutase was more marked than that by desipramine. 5. It is concluded that moderately high doses of noradrenaline exert a 6-hydroxydopamine-like effect and that this chemical sympathectomy is partially or totally prevented by desipramine or superoxide dismutase. The data suggest that a substance derived from noradrenaline, in the formation of which free oxygen radicals are involved and which is subject to neuronal uptake, is the chemical entity responsible for the neurotoxic effect observed.

Spontaneous and ouabain-induced efflux of catecholamines and dihydroxyphenylglycol in two canine blood vessels

The spontaneous efflux of endogenous noradrenaline, dopamine, dihydroxyphenylglycol (DOPEG) from adrenergic nerve endings of 2 canine blood vessels (the mesenteric artery and the saphenous vein) were studied during 8 successive incubation periods of 15 min each. Extraneuronal uptake and O-methylation were minimized by the presence of adequate concentrations of tropolone and hydrocortisone. Both vessels had an efflux characterized by a decline in the 3 catechols, which was most marked for noradrenaline; the mesenteric artery lost larger amounts than the saphenous vein. Ouabain caused a large increase in the efflux of noradrenaline and dopamine and a reduction of DOPEG efflux. Cocaine had only a modest effect, more evident in the case of the mesenteric artery, increasing noradrenaline and reducing DOPEG effluxes. The combination of ouabain and cocaine had no additive effects, and the effects of ouabain were even reduced (on some parameters) by cocaine. Accordingly, the noradrenaline:DOPEG ratio was markedly increased by ouabain, but not by cocaine; cocaine significantly reduced the effects of ouabain. The ratio dopamine:noradrenaline was decreased by cocaine and by ouabain. Comparison of tissue content and efflux allowed us to conclude that apparently no significant de novo synthesis of noradrenaline occurred during the incubation period. We conclude that a fast and early component of spontaneous efflux is due to loss from the neurons and that its greater magnitude in the mesenteric artery may be due to differences in neuronal [Na+] and/or to differences in neuronal membrane adenosine triphosphatase activity. The results also suggest that neuronal reuptake plays only a minor role in the handling of spontaneously released noradrenaline.

Endothelium-dependent responses in autogenous femoral veins grafted into the arterial circulation of the dog

Endothelium-dependent responses differ in arteries and veins of the dog. Experiments were performed to determine whether chronic grafting of veins into the arterial circulation would alter the endothelium-dependent responses of the veins. Segments of femoral veins were grafted to the femoral artery of the dog. 6 wk after surgery the venous grafts were removed from the dog, cut into rings, and suspended in organ chambers for isometric tension recording. In some rings the endothelial cells were removed. Acetylcholine and alpha 2-adrenergic agonists did not cause endothelium-dependent relaxations in venous grafts. The calcium ionophore (A23187) initiated such relaxations which were not mediated by prostanoids. Endothelium-dependent relaxations were also observed in venous grafts to ADP, thrombin, and arachidonic acid. In segments of graft where myo-intimal hyperplasia was prominent, relaxations to ADP, thrombin, and A23187 were blunted and in some segments contractions were observed. These results demonstrate the ability of the endothelium of venous grafts to initiate changes in tone of the smooth muscle.

Effects of denervation induced by 6-hydroxydopamine on cell nucleus activity of arterial and cardiac cells of the dog

1 Denervation was induced in dogs by 6-hydroxydopamine (6-OHDA) treatment. The effects of this on cell nucleus activity of smooth muscle cells and fibroblasts of the mesenteric artery (main trunk and jejunal branches) and of myocardial cells, fibroblasts and endothelial capillary cells of the heart were studied. 2 Changes in the nucleii or cell size measured with light microscopy morphometric techniques and frequency of nucleoli in myocardial cells were chosen as indices of cell nucleus activity state. 3 Noradrenaline depletion 5 days after initiation of 6-OHDA administration was much more marked in the heart (with a content of 10% of control values) than in the arterial vessels (with a content of 50% of control values). 4 Denervation by 6-OHDA led to an increase in the synthetic activity state of the cell nucleus in all cell types and tissues. 5 Plasma noradrenaline and adrenaline levels were strikingly increased by 6-OHDA treatment. 6 The results strongly support the hypothesis of a nuclear modulating effect of the sympathetic innervation upon the effector cells. The incapacity of high noradrenaline plasma levels to prevent the consequences of sympathetic denervation on the effector cells appears to indicate that in the sympathetic innervation there is a 'trophic factor' which is not identical with noradrenaline.

Cocaine-sensitive O-methylation of noradrenaline in dental pulp of the rabbit: comparison with the rabbit ear artery

Incisor pulp from the rabbit metabolises exogenous noradrenaline in concentrations between 0.12 and 1.2 mumol/l mainly to NMN. Effects of chronic sympathetic denervation indicated that in incisor pulp the NMN is extraneuronal in origin, and that DOPEG and DOMA formation, as well as a major part of the noradrenaline which accumulates in the tissue, are associated with the sympathetic nerves. NMN formation was unaffected by hydrocortisone 210 mumol/l, but was strongly inhibited by cocaine 30 mumol/l. These effects contrasted with those in the rabbit ear artery, where NMN formation was increased by cocaine 30 mumol/l and decreased by hydrocortisone 210 mumol/l. In COMT-inhibited denervated pulp, cocaine inhibited the accumulation of noradrenaline. Monoamine fluorescence histochemistry of pulp exposed to noradrenaline 50 mumol/l indicated that cocaine-sensitive uptake occurred in fibroblasts. It is concluded that O-methylation of noradrenaline in dental pulp involves prior uptake of the amine by a process resembling uptake1 but which is distinguished from uptake1 by its extraneuronal location.

Trophic interactions between rat nerves and blood vessels in denervated peripheral arteries and in anterior eye chamber transplants

This investigation was undertaken to examine trophic interrelationships between nerves and arteries in male Wistar rats. Two approaches were used. (1) Surgical denervation of two peripheral muscular arteries in the thigh (the superficial epigastric and saphenous) was carried out on young animals (5-20 days old). (2) Arteries from young adults, either with a high density of innervation in situ (the tail artery), or virtually uninnervated (the femoral artery), were transplanted into intact or sympathectomized anterior eye chambers of adult rat hosts. In the denervation experiments, the maximum length of time before reinnervation occurred was 15 days postoperatively. The only evidence of morphological change in the vessel wall was in the external elastic lamina that became irregular and laminated. Reinnervation followed the typical developmental sequence, and was accelerated in the younger animals and by a double lesion. Translocating the proximal part of the nerve carrying the vasomotor innervation indicated that sprouting was directional toward the muscular arteries, bypassing an artery with very sparse innervation. The transplant experiments into the anterior eye chamber showed that only an artery densely innervated in situ (the tail artery) could induce reinnervation by iridean nerve sprouting. The tail artery, in the chamber lacking adrenergic innervation of the iris, became reinnervated by terminals with small agranular vesicles. These vesicles were part of Schwann cell complexes, at a similar relative density, occupying the same position in the vessel wall, as the ingrowing nerves in the fully innervated iris. The latter also had a proportion of terminals with the small clear vesicles. A small population of large granular vesicles could also be found in both types of terminals. Therefore, tissue normally having only sympathetic innervation cannot be assumed to be completely noninnervated when transplanted into a sympathectomized anterior eye chamber. The denervation and transplant experiments described here demonstrated the presence of trophic interactions between nerves and arteries, but also revealed a heterogeneity of response between vessels with very high and extremely low levels of innervation in situ.

A study of the relationship between dopamine and noradrenaline content and transmural pressure in the mesenteric arteries of the dog

Transmural pressure was measured in the main trunk and in a proximal branch of the mesenteric artery from normotensive dogs. Dopamine and noradrenaline content were determined in both mesenteric arterial segments. For each vessel transmural pressure values and dopamine and noradrenaline content were plotted for calculation of linearity of regression. A positive correlation was found between transmural pressure values and catecholamine content in both segments of the mesenteric artery; i.e. in the main trunk and in the proximal branch. These findings suggest a reciprocal regulation between structure/function of these blood vessels and their sympathetic innervation.