Sidney George Shaw, DPhil (1948-2017)

On March 4, 2017 at the age of 68, Sidney George Shaw (Sid) unexpectedly died from complications following surgery, only four years after retiring from the University of Bern. Trained in biochemistry at Oxford University, Sid had quickly moved into molecular pharmacology and became a key investigator in the field of enzyme biochemistry, vasoactive peptide research, and receptor signaling. Sid spent half his life in Switzerland, after moving to the University of Bern in 1984. This article, written by his friends and colleagues who knew him and worked with him during different stages of his career, summarizes his life, his passions, and his achievements in biomedical research. It also includes personal memories relating to a dear friend and outstanding scientist whose intellectual curiosity, humility, and honesty will remain an example to us all.

Role of PVAT in coronary atherosclerosis and vein graft patency: friend or foe?

Perivascular adipose tissue (PVAT) releases numerous factors and adipokines with paracrine effects on both vascular structure and function. These effects are variable as they depend on regional differences in PVAT among blood vessels and vary with changes in adiposity. There is considerable evidence demonstrating an association between coronary PVAT and the development and progression of coronary artery disease, which is associated with inflammation, oxidative stress, angiogenesis, vascular remodelling and blood clotting. However, PVAT also has a protective role in vascular grafts, especially the no-touch saphenous vein, in patients undergoing coronary artery bypass. This beneficial influence of PVAT involves factors such as adipocyte-derived relaxing factor, nitric oxide (NO), leptin, adiponectin, prostanoids, hydrogen sulphide and neurotransmitters, as well as mechanical protection. This article aims to highlight and compare the dual role of PVAT in the development and progression of coronary atherosclerosis, as well as in increased graft patency. Different deleterious and protective mechanisms of PVAT are also discussed and the inside-outside signalling paradigm of atherosclerosis development re-evaluated. The bidirectional communication between the arterial and venous wall and their surrounding PVAT, where signals originating from the vascular wall or lumen can affect PVAT phenotype, has been shown to be very complex. Moreover, signals from PVAT also influence the structure and function of the vascular wall in a paracrine manner.

LINKED ARTICLES

This article is part of a themed section on Molecular Mechanisms Regulating Perivascular Adipose Tissue - Potential Pharmacological Targets? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.20/issuetoc.

Dual effects of α2 -adrenoceptors in modulating myogenic tone in sheep isolated internal anal sphincter

BACKGROUND

The role of α-adrenoceptors in promoting continence through modulation of sphincter tone has focused primarily on the effects of α1 -adrenoceptors. We have used three clinically available agents, which are selective for α2 -adrenoceptors, to investigate their role in contractile and neurogenic responses on the internal anal sphincter (IAS).

METHODS

IAS strips, which had spontaneously generated tone, were used to investigate the contractile effect of lofexidine, brimonidine, and dexmedetomidine on muscle tone in the presence or absence of subtype selective antagonists. The effect of brimonidine on the magnitude and time course of neurogenic responses generated by electrical field stimulation (EFS) was also examined. The affinity of test compounds at α1 - and α2 -adrenoceptors was established by competition binding with [3H]-prazosin and [3H]-RX821002.

KEY RESULTS

All agonists caused concentration-dependent contraction of the IAS and lofexidine demonstrated an enantiomeric difference in potency with a 10-fold difference between the (-) and (+) isomers. Responses to lofexidine and dexmedetomidine were inhibited in the presence of the α1 -adrenoceptor selective antagonist prazosin, but not in the presence of RX811059 (α2 -adrenoceptor selective antagonist); brimonidine responses were inhibited by RX811059 and, to a lesser extent, by prazosin. Brimonidine affected both magnitude and duration of neurogenic responses, which was reversed in the presence of RX811059.

CONCLUSIONS & INFERENCES

We conclude that α2 -adrenoceptors can mediate contraction of IAS, although this effect is most evident with efficacious imidazoline agonists rather than the most selective ligand. In addition, this receptor subtype can directly inhibit noradrenergic contractile responses to EFS and, indirectly, enhance nitrergic relaxatory responses.

Investigation of the distribution and function of alpha-adrenoceptors in the sheep isolated internal anal sphincter

BACKGROUND AND PURPOSE

We have investigated the distribution of alpha-adrenoceptors in sheep internal anal sphincter (IAS), as a model for the human tissue, and evaluated various imidazoline derivatives for potential treatment of faecal incontinence.

EXPERIMENTAL APPROACH

Saturation and competition binding with (3)H-prazosin and (3)H-RX821002 were used to confirm the presence and density of alpha-adrenoceptors in sheep IAS, and the affinity of imidazoline compounds at these receptors. A combination of in vitro receptor autoradiography and immunohistochemistry was used to investigate the regional distribution of binding sites. Contractile activity of imidazoline-based compounds on sheep IAS was assessed by isometric tension recording.

KEY RESULTS

Saturation binding confirmed the presence of both alpha(1)- and alpha(2)-adrenoceptors, and subsequent characterization with sub-type-selective agents, identified them as alpha(1A)- and alpha(2D)-adrenoceptor sub-types. Autoradiographic studies with (3)H-prazosin showed a positive association of alpha(1)-adrenoceptors with immunohistochemically identified smooth muscle fibres. Anti-alpha(1)-adrenoceptor immunohistochemistry revealed similar distributions of the receptor in sheep and human IAS. The imidazoline compounds caused concentration-dependent contractions of the anal sphincter, but the maximum responses were less than those elicited by l-erythro-methoxamine, a standard non-imidazoline alpha(1)-adrenoceptor agonist. Prazosin (selective alpha(1)-adrenoceptor antagonist) significantly reduced the magnitude of contraction to l-erythro-methoxamine at the highest concentration used. Both prazosin and RX811059 (a selective alpha(2)-adrenoceptor antagonist) reduced the potency (pEC(50)) of clonidine.

CONCLUSIONS AND IMPLICATIONS

This study shows that both alpha(1)- and alpha(2)-adrenoceptors are expressed in the sheep IAS, and contribute (perhaps synergistically) to contractions elicited by various imidazoline derivatives. These agents may prove useful in the treatment of faecal incontinence.

Endothelin-1 and vein graft occlusion in patients undergoing bypass surgery

The saphenous vein is the most commonly used graft for revascularization procedures in patients with coronary artery disease and critical limb ischaemia. However, the patency rate of this vessel is poor, with a high proportion of patients requiring further surgery. Early graft occlusion is caused by vasoconstriction or thrombus formation, with later stages of graft failure being due to neointimal formation or atherosclerosis. Apart from its potent constrictor action, endothelin-1 is also a potent proliferative and proinflammatory peptide that is implicated in a number of vascular diseases. The surgical trauma caused during preparation of the saphenous vein as a bypass graft stimulates the release of a number of factors affecting vascular reactivity and structure, including endothelin-1. Endothelin-1 not only constricts animal and human isolated saphenous vein segments but also causes vascular smooth muscle proliferation and neointimal thickening in vitro, actions that are mediated via endothelin (A and B) receptors. Experimentally, the effects of subtype-selective and dual receptor antagonists have been shown to inhibit endothelin-1-mediated constriction and cell proliferation of the saphenous vein. In this review, data supporting a role of endothelin-1 in vein graft occlusion are presented, and the therapeutic potential of endothelin receptor antagonists in improving graft performance is discussed.

Nitric oxide synthase in critically ischaemic muscle and alterations in isoform expression during revascularization surgery

BACKGROUND

Dysfunction of the nitric oxide pathway is implicated in peripheral arterial disease. Nitric oxide synthase (NOS) isoforms and NOS activity were studied in muscle from patients with critical leg ischaemia (CLI). Alterations in NOS during revascularization surgery were also assessed.

METHODS

Muscle biopsies were taken from patients with CLI undergoing amputation and also from patients undergoing femorodistal bypass at the start of surgery, after arterial clamping and following reperfusion. The presence of NOS within muscle sections was confirmed using reduced nicotinamide adenine dinucleotide phosphate diaphorase histochemistry. NOS isoform distribution was studied by immunohistochemistry. NOS mRNA and protein levels were measured using real-time reverse transcriptase-polymerase chain reaction and western blotting. NOS activity was assessed with the citrulline assay.

RESULTS

All three NOS isoforms were found in muscle, associated with muscle fibres and microvessels. NOS I and III protein expression was increased in CLI (P = 0.041). During revascularization, further ischaemia and reperfusion led to a rise in NOS III protein levels (P = 0.008). NOS activity was unchanged.

CONCLUSION

Alterations in NOS I and III occurred in muscle from patients with CLI and further changes occurred during bypass surgery.

Endothelin and erectile dysfunction: a target for pharmacological intervention?

Although erectile dysfunction (ED) is not life threatening, this common problem can significantly affect the quality of life and psychological and social well-being. The Massachusetts male ageing study (1,290 men aged 40 - 70 years) showed that 52% of men reported some degree of ED (17.1% mild, 25.2% moderate, 9.6% total). In the UK, an estimated 17 - 19% of men are thought to suffer from ED. This problem is more common with advancing age and since this proportion of the population is increasing, the prevalence of ED is expected to rise. Endothelin-1 (ET-1) belongs to a family of potent vasoconstrictor peptides consisting of 21 amino acids. We review the evidence showing that ET-1 plays a role via (ET(A) and ET(B) receptors) in the regulation of cavernosal smooth muscle tone. We also consider the various risk factors that are involved in the pathogenesis of ED and how these relate to the action of ET-1. In particular, the role of diabetes, hypertension, smoking and dyslipidaemia are discussed. The pharmaceutical industry has declared an interest in the development of ET antagonists for use in the treatment of various diseases including ED. We briefly comment on experimental ET-1 antagonists that may be of therapeutic benefit in ED.

Human saphenous vein and coronary bypass surgery: ultrastructural aspects of conventional and "no-touch" vein graft preparations

Coronary artery bypass graft surgery (CABG) is routinely used to restore blood flow to diseased cardiac muscle due to coronary artery disease. The patency of conventional grafts decreases with time, which is due to thrombosis and formation of neointima. A primary cause of graft failure is the mechanical damage inflicted to the graft during harvesting, including removal of surrounding tissue accompanied by high pressure saline distension to overcome vasospasm (both causing considerable mechanical trauma). The aim of this study was to compare the ultrastructural features of human saphenous vein (SV) grafts harvested conventionally and grafts prepared using an atraumatic 'no-touch' harvesting technique introduced by Souza (1996). The results of this study showed a better preservation of the lumenal endothelium and medial vascular smooth muscle (SM) in 'no-touch' versus conventional grafts. A 'fast' (within 30 min) response of SM cells to conventional harvesting was noted where features of both SM cell division and apoptosis were observed. It is concluded that the 'preserved' nature of the 'no-touch' aortocoronary SV grafts renders them less susceptible to thrombotic and atherosclerotic factors than grafts harvested conventionally. These features are suggested to contribute to the improved early patency rate described using the no-touch technique of SV harvesting.

Altered endothelin-1 levels in acute lower limb ischemia and reperfusion

Tourniquet-induced ischemia is often used in orthopedic and reconstructive procedures. This is associated with muscle damage and dysfunction, which limits tourniquet application time. Endothelin-1 (ET-1) is a potent vasoconstrictor, which has been implicated in ischemic conditions and ischemia-reperfusion injury. This study aimed to investigate the role of ET-1 in human skeletal muscle subjected to tourniquet-induced acute ischemia and reperfusion. Thirteen patients undergoing total knee replacement were studied. Plasma and muscle ET-1 concentrations were measured at the start of surgery, after an hour of acute ischemia, and 15 minutes following reperfusion. ET-1 receptor binding was also studied by use of autoradiography, and ET-1 mRNA expression investigated by use of real-time polymerase chain reaction (RT-PCR). Tissue ET-1 increased following the period of acute ischemia and persisted during reperfusion. ET-1 was associated with microvessels and macrophages in the muscle. No changes in circulating ET-1 levels, ET-1 mRNA expression, or ET-1 receptor binding were found. It is concluded that the ET-1 pathway is involved in acute ischemia and reperfusion and it may contribute to the muscle injury that occurs during surgical procedures.

Down-regulation of nitric oxide synthase in the diabetic rabbit kidney: potential relevance to the early pathogenesis of diabetic nephropathy

OBJECTIVES

Nephropathy is a well-recognised complication of diabetes mellitus (DM). The aim of this study was to investigate the effect of DM on the density and distribution of nitric oxide (NO) synthase (NOS) in the rabbit kidney. Quantification of the NOS radioligand on slide-mounted sections was compared with the nitroblue tetrazolium reaction, where the intensity of the reaction varies with the nicotinamide adenine dinucleotide diaphorase (NADPH-d) activity of NOS.

MATERIALS AND METHODS

DM was induced with alloxan in six New Zealand White (NZW) rabbits. Plasma creatinine, urea and electrolytes were monitored at monthly intervals. The kidneys were removed following 6 months of DM. Transverse serial sections were cut and low-resolution autoradiography was performed using a radioligand for NOS ([(3)H]-NOARG). Histochemical localisation of NADPH-d activity was also performed. Densitometric analysis was performed on the autoradiographs and the results compared with those obtained from six age-matched control rabbits.

RESULTS

There was a significant (p < 0.01) rise in plasma creatinine levels in the diabetic rabbits, although the mean values remained within the reference range. There was a significant (p < 0.0001) down-regulation of NOS binding sites in both the cortex and medulla of the DM kidney when compared with the controls. A similar decrease in NADPH-d activity was seen in the diabetic renal cortex and medulla. In addition, NADPH-d activity also appeared to be reduced in the diabetic glomeruli when compared with controls.

CONCLUSIONS

NOS binding sites and NADPH-d activity are significantly decreased in the DM renal cortex and medulla. These changes are associated with a mild deterioration in renal function and may be an early event that could subsequently play a role in the progression of DM nephropathy. Manipulating the NO pathway during the early stages of DM nephropathy may be beneficial.

Evidence for the involvement of endothelin-1 but not urotensin-II in chronic lower limb ischaemia in man

BACKGROUND

endogenous vasoconstrictor peptides may play a role in the pathophysiology of critical limb ischaemia (CLI). This study investigated endothelin-1 (ET-1) and urotensin-II (U-II) mRNA expression, peptide distribution and ET receptor subtype binding in chronically ischaemic muscle.

METHODS

open muscle biopsies were taken from patients undergoing amputations for CLI and from patients undergoing coronary artery bypass surgery (controls). ET-1 and U-II mRNA expression in muscle biopsies was studied using real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR). ET-1 and U-II immunohistochemistry was performed on muscle sections and ET receptor binding studied using in vitro autoradiography.

RESULTS

ET-1 mRNA expression was significantly increased in CLI compared to controls (p<0.05) whilst no significant change in U-II expression occurred. ET-1 immunoreactivity was also increased in CLI with no difference in U-II immunostaining observed. ET(B) receptor binding was significantly increased in CLI (median 4, range 1-8 vs 2, range 1-3, dpm x 10(3)/mm(2), p=0.01, Mann-Whitney test) whilst ET(A) receptor binding was not significantly raised. Binding was associated with microvessels and macrophages.

CONCLUSIONS

in CLI, the ET-1 pathway is upregulated but U-II is unaffected. ET-1 may vasoconstrict microvessels and mediate inflammation in chronically ischaemic muscle. ET-1 binding to ET(B) receptors in particular may play an important role in the pathophysiology of CLI underscoring the therapeutic potential of ET(B) receptor antagonists in the management of CLI.

Endothelin-1 and Nitric Oxide in the Pathogenesis of Urinary Tract Disorders Secondary to Bladder Outlet Obstruction

Bladder outlet obstruction (BOO) is a common disorder that is associated with urinary tract symptoms. Nitric oxide (NO), synthesized by NO synthase (NOS) is a potent vasodilator that is present throughout the urinary tract and the corpus cavernosum. Endothelin-1 (ET-1) conversely is a potent vasoconstrictor peptide that is similarly distributed throughout the urinary tract. ET-1 and NO as well as possessing opposing actions regulate each other's synthesis. The disruption of the balance between ET-1 and NO is associated with various vascular pathologies. However, their potential roles in the pathogenesis of urinary tract disorders, secondary to BOO, is not well established. New Zealand White rabbits with BOO are considered to be a suitable model of the human condition. Hence, using this model, we systematically investigated the potential roles of ET-1 and NO in the pathogenesis of the various urological disorders associated with BOO. In this review we discuss the results of our studies, which support the concept that an imbalance between ET-1 and NO may be associated with the pathogenesis of urinary tract disorders secondary to BOO. We also discuss the potential clinical implications of this association. This review is based on the Bard Silver Medal Lecture given (by MAK) at the 2002 British Association of Urological Surgeons (BAUS) annual meeting.

Detection of glucagon receptor mRNA in the rat proximal tubule: potential role for glucagon in the control of renal glucose transport

Glucagon is known to affect glomerular filtration rate and renal tubular solute and fluid transport, although it is only thought to act directly on the thick ascending limb (TAL) and collecting duct (CD). Indeed, previous studies have detected glucagon-sensitive adenylate cyclase exclusively in these nephron segments, suggesting the presence of glucagon receptors. In the present study, we have demonstrated for the first time that glucagon receptor mRNA is expressed in the rat proximal tubule, as well as in the TAL and CD. By autoradiography, we have also shown that specific binding of glucagon occurs in both the renal cortex and medulla. In addition, using proximal tubule brush-border membrane (BBM) vesicles for studies of glucose transport, we have established that glucagon stimulates glucose uptake via a facilitative GLUT-mediated transport process (by 58%; P < 0.005), whereas cAMP stimulates only the sodium glucose-linked transporter ('SGLT')-mediated glucose uptake (by 53%; P < 0.05). Taken together, these findings suggest that glucagon could have a role in controlling proximal tubular transport function, including glucose reabsorption, but unlike in the TAL and CD, the proximal tubule glucagon receptor might not be coupled primarily to adenylate cyclase.

Enhanced relaxation of diabetic rabbit cavernosal smooth muscle in response to nitric oxide: potential relevance to erectile dysfunction

New Zealand white rabbit cavernosal smooth muscle strips (n=6) were mounted in organ baths. Relaxations to nitric oxide (10(-7)-10(-4) mol/l) were measured and the same procedure was repeated on strips from rabbits 6 months after alloxan-induced diabetes (n=6). Transverse cavernosal sections were obtained from the same penises. Low and high resolution autoradiographs were prepared using [(3)H]-L-N(G)-nitroarginine (an index of nitric oxide binding sites) and analysed densitometrically. Histochemical analysis was performed on adjacent sections using NADPH diaphorase (an index of nitric oxide synthase activity). Nitric oxide relaxed control rabbit cavernosal smooth muscle strips in a concentration-dependent manner. Diabetic rabbit cavernosal smooth muscle strips were significantly (P<0.03) more sensitive to nitric oxide (mean IC(50)=3.9 x 10(-6) mol/l). Nitric oxide synthase binding sites were localised to the cavernosal endothelium and smooth muscle. Nitric oxide synthase activity was increased in 6 month diabetic cavernosal smooth muscle. These findings suggest impairments in the L-arginine-nitric oxide pathway may play a role in the pathophysiology of diabetic erectile dysfunction.

Does external stenting reduce porcine vein-graft occlusion via an action on vascular nerves?

BACKGROUND

Neural reorganization occurs in porcine vein grafts and placement of an external stent reduces graft occlusion.

AIM OF THE STUDY

To determine the effect of external stenting on the innervation of porcine vein grafts.

METHODS

Saphenous vein into carotid artery grafting (with and without external stents) was performed in 16 pigs. After one and six months, grafts were removed, nerves were counted, and neointima was assessed.

RESULTS

In vein graft compared to ungrafted vein, there was a significant (p < 0.05) decrease in medial perivascular nerves, but a dramatic increase in paravascular nerves in the adventitia (p < 0.05). In stented vein grafts there was also a reduction of perivascular nerves and the paravascular nerve proliferation observed in vein grafts at one month was inhibited (p < 0.05). Neointima formation and the appearance of large paravascular nerve bundles in the adventitia of vein grafts were abolished by external stenting.

CONCLUSIONS

Neural reorganization plays a role in vein-graft failure, possibly through the local release of mitogens; the prevention of this reorganization contributes to the inhibitory effect of the external stent on neointima formation.

Potential role of endothelin 1 in ischaemia-induced angiogenesis in critical leg ischaemia

BACKGROUND

Ischaemia-induced angiogenesis occurs in critical leg ischaemia (CLI) and endothelin (ET) 1 may be involved in this process. The aim of this study was to quantify microvessels and study ET receptor expression and distribution in critically ischaemic leg muscle.

METHODS

Leg muscle biopsies were taken from 12 patients with CLI and 12 patients with no leg ischaemia. Microvessels were identified immunohistochemically on muscle sections, and the number of immunopositive cells was quantified. ETA and ETB receptor messenger RNA (mRNA) expression was studied using real-time quantitative reverse transcriptase-polymerase chain reaction, and receptor binding was localized and assessed by in vitro autoradiography.

RESULTS

The number of microvessels in CLI muscle biopsies was 2.6 times higher than that in controls (P < 0.01). ETB receptor mRNA expression and binding were significantly increased in CLI tissue (P < 0.05), while ETA receptor levels were not significantly raised. High-resolution autoradiography showed that ET receptor binding was associated with microvessels.

CONCLUSION

Angiogenesis occurs in CLI and raised ETB receptors within the muscle were associated with microvessels, suggesting that ET-1 may mediate angiogenesis via these receptors in critically ischaemic muscle.

Recent strategies to reduce vein graft occlusion: a need to limit the effect of vascular damage

Despite early identification and aggressive modification of atherosclerotic risk factors, many patients still require surgical revascularisation for established atherosclerotic vascular disease. However, bypass surgery is hampered by a high incidence of vein graft failure. New strategies are being introduced to improve these results, with early data suggesting that improved patency rates are possible. These vary from the use of adjuvant pharmacological agents and local gene transfer strategies to the modification of vein harvesting techniques in order to reduce vascular damage to all layers of the graft. Advances in vascular biology have resulted in new insights into the role of the endothelium and adventitia in vein graft remodelling. Although recent pharmacological adjuvant therapy and molecular techniques have been described that may be used to reduce the incidence of vein graft occlusion a more desirable approach for improved graft patency rates may be achieved simply by using atraumatic surgical techniques aimed at minimising vascular damage during vessel harvesting and subsequent anastamoses during bypass surgery.

Endothelin receptors in the aetiology and pathophysiology of varicose veins

INTRODUCTION

varicose veins are tortuous and poorly contractile. Their aetiology remains unclear. Neovascularisation has been suggested as a possible explanation. Endothelins are mitogenic, promoting proliferation and migration of endothelial cells via endothelin-B receptors. We hypothesise that endothelial cells and endothelin receptor density and distribution may play a role in the development of varicosis.

METHODS

saphenous vein segments from nine patients with varicose veins were compared to six controls. Slide-mounted sections were incubated in radioactive labelled endothelin-1 and receptor subtype-selective ligands and binding sites assessed using autoradiography. Endothelin-1 and endothelial cells were identified by immunohistochemistry and CD31-positive staining cells counted.

RESULTS

radioactive labelled endothelin-1 and endothelin-B receptor binding was reduced in varicose compared to control veins (p=0.04). Endothelin-A receptor binding was diffuse, with no difference in density in both groups (p=0.58). Endothelin-B receptor binding was diffuse with superimposed clusters. Although the density of medial endothelin-B receptor binding was reduced in the varicose group, more clusters were identified in this group compared to controls (p=0.005). CD-31 staining identified these clusters as endothelial cells.

CONCLUSION

the reduced endothelin-1 binding and endothelin-B receptor density may be partially responsible for the reduced vasocontractility in varicose veins. We speculate that the increase in endothelin-B receptor binding CD31-positive endothelial cells in varicose veins may potentially stimulate mitogenesis and migration, leading to new vessel formation.

Preserved endothelial integrity and nitric oxide synthase in saphenous vein grafts harvested by a 'no-touch' technique

BACKGROUND

The saphenous vein is the most commonly used conduit for coronary artery bypass surgery, but 1-year occlusion rates as high as 30 per cent have been reported. In conventional surgery, considerable damage to the vein occurs during harvesting. The aim of this study was to compare endothelial integrity and nitric oxide synthase (NOS) in saphenous veins harvested by a novel 'no-touch' technique and veins harvested conventionally.

METHODS

Immunohistochemistry was used to study endothelial integrity, and a combination of histochemistry and autoradiography was employed to identify NOS in human saphenous veins harvested by conventional and no-touch techniques.

RESULTS

The endothelial lining of conventional grafts was reduced compared with that of no-touch grafts (52 versus 73 per cent; P = 0.04). This was associated with a concomitant reduction of NOS availability; NOS was also present in the adventitial vasa vasorum of no-touch vessels.

CONCLUSION

Some of the sites with potential for nitric oxide release in vivo are removed during conventional saphenous vein harvesting. These sites were preserved after no-touch harvesting, suggesting the potential to improve coronary artery bypass graft patency.

Fibroblast matrix gene expression and connective tissue remodeling: role of endothelin-1

This study examines endothelin-induced modulation of extracellular matrix synthesis and remodeling by fibroblasts, and its potential role in the pathogenesis of systemic sclerosis (scleroderma). Endothelin-1 promoted fibroblast synthesis of collagen types I and III, but not fibronectin, by a mechanism dependent upon both ETA and ETB receptors. Conversely, endothelin-1 inhibited both protein expression of matrix metalloproteinase 1 and zymographic activity exclusively via ETA receptors. A dual regulatory role for endothelin-1 in transcriptional regulation was suggested by the ability of endothelin-1 to enhance steady-state levels of collagen mRNA and activate the proalpha2(I) collagen (Col1a2) promoter, but in contrast to reduce matrix metalloproteinase 1 transcript expression and suppress transcription of a human matrix metalloproteinase 1 promoter reporter construct in transient transfection assays. Although endothelin-1 significantly enhanced remodeling of three-dimensional collagen lattices populated by normal fibroblasts, this was not observed for lattices populated by systemic sclerosis fibroblasts. Promotion of matrix remodeling was dependent upon ETA receptor expression and was blocked by specific inhibitors of tyrosine kinases or protein kinase C. Reverse transcriptase polymerase chain reaction, S1 nuclease, and functional cell surface binding studies showed that normal and systemic sclerosis fibroblasts express both ETA and ETB receptors (predominantly ETA), but that ETA receptor mRNA levels and ETA binding sites on fibroblasts cultured from systemic sclerosis skin biopsies are reduced by almost 50%. Endothelin-1 is thus able to induce a fibrogenic phenotype in normal fibroblasts that is similar to that of lesional systemic sclerosis fibroblasts. Moreover, reduced responsiveness to exogenous endothelin-1 in systemic sclerosis suggests that downstream pathways may have already been activated in vivo. These data further implicate dysregulated endothelin-receptor pathways in fibroblasts in the pathogenesis of connective tissue fibrosis.

High early patency of saphenous vein graft for coronary artery bypass harvested with surrounding tissue

BACKGROUND

Surgical trauma to the saphenous vein, used as a conduit for coronary artery bypass grafting, affects their occlusion rate. This study evaluates the early patency of saphenous vein grafts harvested with a pedicle of surrounding tissue that protects the vein from spasm and trauma.

METHODS

Fifty-two patients underwent coronary artery bypass grafting with saphenous veins harvested with surrounding tissue. Forty-five patients, who received a total of 124 vein grafts and 42 left internal mammary arteries, underwent angiographic follow-up at a mean of 18 months (9 to 24 months).

RESULTS

Patency for saphenous vein grafts was 95.4% and for left internal mammary arteries, it was 93.3%. Twenty-nine of 30 (96.7%) vein grafts anastomosed to arteries 2.0 mm or more, 65 of 67 (97%) grafts to 1.5 mm, and 10 of 13 (77%) anastomosed to 1-mm arteries were patent. Nineteen of 22 (86.4%) vein grafts with flow rates 20 mL/min or less, 32 of 34 (94.1%) with flow between 20 and 40 mL/min, and 50 of 51 (98%) with flow more than 40 mL/min were patent. Other registered surgical and clinical factors did not contribute to vessel occlusion.

CONCLUSIONS

Early patency rate of saphenous veins harvested with surrounding tissue is very high, even in saphenous vein grafts demonstrating low blood flow. Preservation of graft endothelium using our harvesting technique may be the explanation of this success.

Altered cavernosal endothelin-B-receptor binding sites in the rabbit model of partial bladder outlet obstruction

Erectile dysfunction (ED) is a common problem that significantly affects the quality of life. Benign prostatic hyperplasia (BPH) is the commonest known benign proliferative disorder. Recently there has been growing evidence to suggest that patients with high BPH symptom scores have an increased incidence of ED. Endothelin-1 (ET-1) is a potent vasoconstrictor peptide that is thought to play an important role as a modulator of erectile physiology and dysfunction. We investigated whether there are any changes in the density and distribution of ET-1 and its receptor subtypes in the corpora cavernosa (CC) of a rabbit model of partial bladder outflow obstruction (BOO). ET-1, endothelin-A- and -B- (ET(A) and ET(B)) receptor binding sites were primarily localized to the smooth muscle cells (SMC) of the CC and the endothelium lining the cavernosal space. ET(B)-receptor binding sites were significantly decreased (p = 0.04) in the 6-week BOO cavernosal tissue. ET-1 may play a role in the pathophysiology of ED associated with BPH. This may be partly a result of enhanced vasoconstrictor actions and SMC proliferation secondary to a reduction in ET(B)-receptors. Further work is needed to evaluate this possibility.

A potential role for endothelin-1 in peripheral vascular disease

The distribution of endothelin-1 (ET-1) and its receptors (ET(A)/ET(B)) has been studied in segments of femoral artery obtained from patients undergoing operation for peripheral vascular disease (PVD) using a combination of immunohistochemistry and autoradiography. Both receptor subtypes were located on the tunica media of vessel segments, with ET(A)-receptors predominating. Densitometric analysis showed that there was no difference in receptor binding to proximal/distal arterial segments from PVD patients. High-resolution autoradiography identified ET(B) binding to vascular nerves and vasa vasorum, mainly in distal portions of femoral arteries. Immunoreactive ET-1 was also identified that was associated with the vasa vasorum.

Neural reorganisation in porcine vein grafts: a potential role for endothelin-1

Vein grafts are associated with adventitial remodelling which may influence innervation of the graft. Since there is also evidence that endothelin-1 (ET-1) plays a role in the adventitial remodelling process, we investigated neural distribution in porcine vein grafts 1 and 6 months after implantation, as well as the localisation of immunoreactive ET-1 and its receptors in the same tissues. Saphenous vein-carotid artery interposition grafting was performed in Landrace pigs. One and 6 months after surgery, vein grafts and ungrafted saphenous veins were excised; neural tissue and ET-1 were identified by immunocytochemistry and ET receptors were identified using in vitro autoradiography. In ungrafted saphenous veins, abundant perivascular nerves were located in the outer region of the media with only a few paravascular nerves in the adventitia. In vein grafts at 1 month after implantation, there was almost complete depletion of perivascular nerves in the media. In contrast, in the neoadventitia, there was an emphatic appearance of large paravascular nerve bundles and a marked increase in small paravascular nerves. These changes were more pronounced at 6 months after surgery, although the principal changes had occurred within 1 month. Immunoreactive ET-1 (index of ET-1 content) was associated with paravascular nerve bundles, appearing as a dark, dense ring at the perineurium. Furthermore, within the nerve bundles, positive ET-1 immunoreactivity was associated with positive alpha-actin staining, indicating that ET-1 is associated with (neural) microvessels. Also, dense 125I-labelled BQ3020 (ET(B)-selective) binding to nerve bundles was observed, indicating the presence of ET(B) receptor subtypes. ET(A) receptor subtypes were not detected in neural tissue. These data demonstrate neural reorganisation in vein grafts and indicate that ET-1 content and binding may play a role in this process. The functional consequences of these changes on neointima formation, a major cause of vein graft failure, remain to be determined.

Doxazosin modifies serotonin-mediated rabbit urinary bladder contraction. Potential clinical relevance

5-Hydroxytryptamine (5-HT) induces rabbit detrusor contractions via 5-HT3 receptors. Similarly, 5-HT4 receptors are known to be present in the human bladder. Doxazosin, a non-selective alpha1 antagonist, is used for the symptomatic relief of bladder outflow obstruction. Previous work has shown that doxazosin inhibits 5-HT2-mediated platelet shape change. Hence, the aim of this study was to assess, using organ baths and autoradiography, whether doxazosin has any 5-HT-inhibiting activity in the rabbit detrusor. Detrusor strips from adult New Zealand White rabbits were placed in organ baths; phenoxybenzamine (10(-5) M) was added to block alpha-receptors. After KCl responses were assessed, the tissues were exposed to 10(-3) M 5-HT. Subsequently, the strips were incubated with doxazosin or ondansetron (10(-5) M; 5-HT3 antagonist) followed by a further exposure to 5-HT. In some experiments, after the initial 5-HT-induced contractions, the tissues were washed and then re-exposed to 5-HT. These latter experiments acted as controls. Low-resolution autoradiography was performed on detrusor sections to assess the effect of doxazosin on 5-HT binding. These sections were analyzed densitometrically. Doxazosin and ondansetron produced a significant reduction in 5-HT-mediated contractions. Inhibition by doxazosin was in a concentration-dependent manner. Autoradiography demonstrated a significant reduction in [3H]-5-HT binding by doxazosin. Doxazosin significantly inhibits 5-HT-mediated contractions in the rabbit detrusor. This effect appears to be mainly mediated via 5-HT3 receptor inhibition. Autoradiographic evidence suggests that doxazosin reduces 5-HT binding in the rabbit detrusor. The beneficial effects of doxazosin in bladder outflow obstruction may be due, at least in part, to 5-HT antagonism.

Localization and action of adenosine A2a receptors in regions of the brainstem important in cardiovascular control

In vitro autoradiography and central microinjections of a P1 adenosine A2a receptor antagonist have been employed to investigate a possible role for centrally located adenosine A2a receptors in modulation of the baroreceptor reflex. In vitro autoradiography using [125I]4-(2-[7-amino-2-[2-furyl][3,2,4]triazolol[2,3-a][1,3,5]tr iazin-5-yl-amino]ethyl)phenol ([125I]ZM241385), the high-affinity adenosine A2a receptor antagonist, revealed a heterogeneous distribution of adenosine A2a binding sites within the lower brainstem of the rat. Image analysis showed high levels of binding in rostral regions of both the nucleus tractus solitarius and the ventrolateral medulla. Intermediate levels of binding were observed in the commissural nucleus tractus solitarius and the dorsal vagal motor nucleus, with low levels of binding in caudal regions of the nucleus tractus solitarius and the ventrolateral medulla, and the hypoglossal nucleus. Unilateral microinjections of unlabelled ZM241385 into the nucleus tractus solitarius had no effect on baseline levels of arterial pressure, heart rate and phrenic nerve activity recorded in anaesthetized, artificially ventilated rats. However, microinjections of ZM241385 reduced the bradycardia evoked by stimulation of the ipsilateral aortic nerve. In contrast, ZM241385 had no effect on the depressor response or the reduction in phrenic nerve activity evoked by aortic nerve stimulation. Our results indicate that adenosine A2a binding sites are located in a number of brainstem regions involved in autonomic function, consistent with the idea that adenosine acts as a neuromodulator of a variety of cardiorespiratory reflexes. Specifically, the data support the hypothesis that adenosine A2a receptors located within the nucleus tractus solitarius are activated during baroreceptor stimulation and have an important modulatory role in the pattern of cardiovascular changes associated with this reflex.

Structural and cellular adaptation of duodenal iron uptake in rats maintained on an iron-deficient diet

Iron deficiency induced in rats maintained on a commercial diet with a low iron content has been used to investigate adaptive mechanisms that enhance duodenal iron uptake. These adaptive changes have been divided into those that result from changes in villus surface area (structural adaptation) and those that reflect changes in the way individual enterocytes express iron transport function (cellular adaptation). Cellular adaptation was assessed by carrying out microdensitometry of autoradiographs prepared from duodenal tissue previously incubated for 5 min in 200 micromol/l 59Fe2+-ascorbate. Structural adaptation was studied by performing image analysis of microdissected and sectioned villi. Cellular adaptation involved increased iron uptake by enterocytes present in the lower villus. Thus iron deficiency resulted in a threefold enhanced expression of uptake in the lower 100 microm villus (3.9+/-2.4 versus 12.6+/-1.5 arbitrary units, P<0.001). Maximal uptake was reached in the upper region of both control and iron-deficient villi, but iron deficiency had no effect on cellular uptake at this part of the villus. Structural adaptation involved the lengthening (+16%, P<0.05) and broadening (+14%) of villi in the duodenum of iron-deficient rats. The resultant expansion in villus area caused a further increase in uptake that was mostly expressed in the upper villus. Maximal uptake corrected for structure occurred in the middle third of villi from control and iron-deficient rats. Cellular plus structural adaptation produced a twofold increase in iron uptake. More than half of this effect was caused by changes in villus structure. [3H]Thymidine labelling experiments revealed a slightly earlier expression of enterocyte iron uptake in iron deficiency.

Potential role of endothelin and nitric oxide in physiology and pathophysiology of the lower urinary tract

Endothelium-derived vasoactive mediators (endothelin-1 with its vasoconstrictive and mitogenic properties and nitric oxide with its vasodilatory and antiproliferative properties) play an important role in the regulation of vascular smooth muscle tone and cellular proliferation. Several recent studies have now demonstrated the presence of these vasoactive agents in the urinary tract where they are thought to play a prominent role in urinary tract physiology and disease. This article reviews the synthesis, localisation and actions of endothelin and nitric oxide in the lower urinary tract and examines the possible role of these mediators in disease.

Up-regulation of endothelin (ET(A) and ET(B)) receptors and down-regulation of nitric oxide synthase in the detrusor of a rabbit model of partial bladder outlet obstruction

Bladder outlet obstruction (BOO) is associated with altered bladder structure and function. Endothelin-1 (ET-1) has mitogenic and potent contractile properties. There are two ET receptors: ET(A) and ET(B). Nitric oxide synthase (NOS) is the enzyme responsible for the synthesis of nitric oxide (NO) which is involved in smooth muscle relaxation. We investigated whether there are any changes in the density of ET-receptors and NOS in the detrusor and bladder neck in a rabbit model of BOO. Partial BOO was induced in adult male New Zealand White rabbits. Sham operated age-matched rabbits acted as controls. After six weeks the urinary bladders were excised and detrusor and bladder neck sections incubated with radioligands for ET-1, ET(A) and ET(B) receptors and with [3H]-1-NOARG (a ligand for NOS). NADPH histochemistry was also performed. BOO bladder weights were significantly increased (P = 0.002). ET-1 binding and ETA receptor binding sites were significantly increased in the BOO detrusor smooth muscle (P = 0.04, P = 0.03 respectively) and urothelium (P = 0.002, P = 0.02 respectively). ET(B) receptor binding sites were also significantly increased in the BOO detrusor smooth muscle (P = 0.04). However, there was no change in the BOO bladder neck. NOS was significantly decreased in the detrusor smooth muscle (P = 0.003) and urothelium (P = 0.0002). In the bladder neck NOS was also significantly reduced in the urothelium (P = 0.003). NADPH staining was decreased in the detrusor and bladder neck. The up-regulation of ET receptors along with the down-regulation of NOS in the detrusor may contribute to the symptoms associated with BOO. Since ET-1 has a mitogenic role, especially via its ETA receptors, the increase in ETA receptors may also be involved in detrusor hyperplasia and hypertrophy in BOO. ET antagonists may therefore have a role in the treatment of patients with BOO.

Time-dependent up-regulation of endothelin-A receptors and down-regulation of endothelin-B receptors and nitric oxide synthase binding sites in the renal medulla of a rabbit model of partial bladder outlet obstruction: potential clinical relevance

OBJECTIVE

To assess the density of endothelin (ET) receptors (ET-1 is a potent vasoconstrictor peptide acting on two known receptors, ETA and ETB ) and nitric oxide synthase (NOS) binding sites in the kidney of a rabbit model of bladder outlet obstruction (BOO).

MATERIALS AND METHODS

Partial BOO was created in adult New Zealand White rabbits; after 1, 3, 4 and 6 weeks of BOO, kidney sections were incubated with radioligands for ET-1, ETA, ETB receptors and with [3H]-NOARG (a ligand for NOS). Autoradiographs were generated and analysed densitometrically. Sections were also assessed by NADPH histochemistry. Plasma creatinine, urea and electrolyte levels were regularly monitored. The control and 6-week BOO kidneys were also evaluated ultrastructurally by electron microscopy.

RESULTS

There was no significant change in plasma creatinine, urea and electrolyte levels. ETA and ETB receptor density was significantly greater in the medulla than in the cortex (P<0.001) in all animals. There was an up-regulation of ETA receptors (P=0.03) and down-regulation of ETB receptors (P=0.03) and NOS binding sites (P<0.001), as well as decreased NADPH staining in the medulla of 6-week partial BOO kidneys. Electron microscopy detected glomerular disruption of the obstructed kidneys.

CONCLUSION

The time-dependent changes in ETA and ETB receptors, NOS binding sites and NADPH staining in the renal medulla, as well as ultrastructural changes, occur despite normal renal function. These changes appear to be an early event and may play a role in the development of renal failure. Hence, the use of ETA receptor antagonists at this early stage may prevent the development of renal failure/impairment in BOO.

Upregulation of endothelin A receptor sites in the rabbit diabetic kidney: potential relevance to the early pathogenesis of diabetic nephropathy

BACKGROUND/AIM

Nephropathy is an important complication of diabetes mellitus (DM). The plasma endothelin 1 (ET-1) levels are increased in DM, and ET-1 may cause deleterious effects on renal function. We, therefore, investigated whether changes in ET receptors occur in the DM rabbit kidney.

METHODS

Nine adult New Zealand White rabbits were injected with alloxan, of which 6 became diabetic; the other 3 acted as alloxan-treated controls. Six age-matched healthy rabbits served as controls. At 6 months, following cervical dislocation, the kidneys were removed, and sections (cortex and medulla) were incubated with ET(A) and ET(B) radioligands to produce low- and high-resolution autoradiographs. Immunohistochemical localization of ET-1 immunoreactivity was also performed.

RESULTS

There was greater ET(A) and ET(B) receptor binding in the control (ET(A) p = 0.0003; ET(B) p < 0.0001) and DM (ET(A) p = 0.001; ET(B) p < 0.0001) rabbits in the medulla as compared with the cortex. DM kidneys showed a significant increase in ET(A), but not ET(B), binding in the cortex (p < 0.0001) and in the medulla (p < 0.0001). High-resolution autoradiographs revealed striking [(125)I]-ET-1 receptor binding predominantly to the glomeruli. Immunohistochemistry revealed dense ET-1 immunoreactivity associated with the renal tubules, but the glomeruli exhibited no staining. Alloxan-treated controls had similar results to age-matched controls.

CONCLUSION

There are regional differences in both ET(A) and ET(B) binding in control and DM kidneys. ET(A) receptor binding sites are increased in the DM kidney (cortex and medulla). ET-1 may act in a paracrine fashion on the glomeruli. These changes may contribute to the pathogenesis of diabetic nephropathy.

Down-regulation of endothelin-B receptor sites in cavernosal tissue of a rabbit model of partial bladder outlet obstruction: potential clinical relevance

Erectile dysfunction (ED) is a common problem that significantly affects quality of life and psychological well-being. Benign prostatic hyperplasia (BPH) is the commonest known benign proliferative disorder. Recently there has been growing evidence to suggest that patients with high BPH symptom scores have an increased incidence of ED. Endothelin-1 (ET-1) is a potent vasoconstrictor peptide that is thought to play an important role as a modulator of erectile physiology and dysfunction. We investigated whether there were any changes in the penile histology and in the density and distribution of ET-1 and its receptor subtypes in the corpora cavernosa of a rabbit model of partial bladder outflow obstruction (BOO). BOO was induced in 12 adult New Zealand White rabbits; 12 sham-operated rabbits acted as controls. Penises were excised after 3 and 6 weeks (n=6 each for control and BOO). Low- and high-resolution autoradiography was performed using radioligands for ET-1, ET(A) and ET(B) receptors and the results were analysed densitometrically. Ultrastructural evaluation of the corpus cavernosum (CC) was also performed. ET-1, ET(A) and ET(B) receptor-binding sites were primarily localised to the smooth-muscle cells (SMC) of the CC and to the endothelium lining the cavernosal space. ET(B) receptor-binding sites were significantly decreased (P=0.04) in the 6-week BOO cavernosal tissue. These receptor changes were accompanied by ultrastructural changes in the CC. ET-1 may play a role in the pathophysiology of ED associated with BPH. This may partly be due to enhanced vasoconstrictor actions and SMC proliferation secondary to a reduction in ET(B) receptors. Further work is needed to evaluate this possibility.

Time-dependent up-regulation of neuronal 5-hydroxytryptamine binding sites in the detrusor of a rabbit model of partial bladder outlet obstruction

Serotonin (5-hydroxytryptamine; 5-HT), a vasoactive bioamine with potent contractile activity, is thought to act indirectly in the urinary bladder by the stimulation of its presynaptic receptors. This results in the release of acetylcholine (ACh), which then acts on muscarinic receptors to produce bladder contractility. Bladder outlet obstruction (BOO) can lead to detrusor instability associated with denervation supersensitivity to ACh. Using a rabbit model of partial BOO, we investigated whether there were any associated changes in the neuronal 5-HT binding sites. Partial BOO was induced in adult male New Zealand White rabbits. Sham-operated age-matched rabbits acted as controls. After 1, 3 and 6 weeks the urinary bladders were excised. Detrusor sections were incubated with [(3)H]-5-HT. Autoradiographs were generated and analysed densitometrically. The presence of nerves was detected using immunohistochemistry with NF200. Autoradiography demonstrated a time-dependent, significant (P < 0.0001) up-regulation of [(3)H]-5-HT binding sites in the detrusor smooth muscle after the induction of BOO. Immunohistochemistry confirmed that the [(3)H]-5-HT binding sites were neuronal. In the rabbit model of partial BOO there was a significant time-dependent up-regulation of neuronal [(3)H]-5-HT binding sites in the detrusor. This change may influence 5-HT-mediated ACh release, resulting in increased bladder contractility. This, in turn, may play a role in detrusor instability associated with denervation post-junctional supersensitivity. These results provide a possible rationale for further investigation into the use of 5-HT antagonists in the treatment of detrusor instability associated with BOO.

Up-regulation of endothelin-B (ETB) receptors and ETB receptor-mediated rabbit detrusor contraction in partial bladder outlet obstruction

OBJECTIVE

To investigate, in a rabbit model of bladder outlet obstruction (BOO), whether ETB receptors initiate any contractile activity, and to assess the density of these receptors.

MATERIALS AND METHODS

Partial BOO was produced in male New Zealand White rabbits, with age-matched sham-operated rabbits acting as controls. One and 3 weeks later, the detrusor and bladder neck strips were incubated in organ baths with either BQ788 (an ETB antagonist), BQ123 (an ETA antagonist) or vehicle. Concentration-response curves were constructed using IRL-1620 (a selective ETB agonist). Low-resolution autoradiography was performed on serial detrusor and bladder neck sections from control and partial BOO (3-week) rabbits using radioligands for ETA and ETB.

RESULTS

In strips from controls and after 1 week of partial BOO, IRL-1620 induced no contractions, but after 3 weeks of BOO, IRL-1620 induced significant concentration-dependent detrusor contractions (producing 12%, 25% and 70% of the KCl response at 10-8, 10-7 and 10-6 mol/L, respectively). The ETA antagonist had no effect on IRL-1620-mediated contractions. In contrast, the ETB antagonist completely abolished these contractions. Autoradiography showed the presence of ETA and ETB receptors in the detrusor and bladder neck of normal and obstructed animals, and a significant up-regulation of ETA and ETB receptors only in the obstructed detrusor smooth muscle.

CONCLUSIONS

In BOO, ETB receptors initiate detrusor contractile activity. This is a time-dependent process that may depend on the up-regulation of ETB receptors in the detrusor. Therefore, ETB receptors may play a role in the pathophysiology of partial BOO.

Nitric oxide and penile erection: is erectile dysfunction another manifestation of vascular disease?

There is convincing evidence that the prevalence of erectile dysfunction is increased among men with ischaemic heart disease. This association may be attributed to the fact that both erectile dysfunction and ischaemic heart disease share similar risk factors (e.g. hypertension, dyslipidaemia, diabetes and smoking). Nitric oxide (NO) activity is adversely affected, in penile and vascular tissue, by these risk factors. It is therefore not surprising that a defect in NO activity is thought to play a role in the pathogenesis of both erectile dysfunction and ischaemic heart disease. We consider this evidence and propose that defective NO activity provides a unifying explanation for the association between these two conditions. Further research in this area may improve our understanding of the pathogenesis of cardiovascular diseases as a whole.

Altered endothelin-1 binding following balloon angioplasty of pig coronary arteries: effect of the ETA receptor antagonist, LU 135252

OBJECTIVE

Since raised levels of endothelin-1 (ET-1) have been detected in the human coronary sinus following percutaneous transluminal angioplasty (PTCA) we investigated the role of ET-1 in the etiology of vascular restenosis.

METHODS

Balloon angioplasty of coronary arteries was performed in pigs and the animals were treated with placebo or the endothelin (ETA) receptor antagonist LU 135252 (30 mg/kg/day). After 4 weeks vascular stenosis and the distribution of endothelin and its receptors was evaluated.

RESULTS

The pronounced neointima formation in the control group (neointima:media ratio = 0.87 +/- 0.36) was significantly reduced by LU 135252 (0.43 +/- 0.30, P < 0.001). Angioplasty caused a significant increase in medial ETA (approximately 275%, P < 0.026) and ETB (approximately 250%, P < 0.001) binding to injured, compared with non-injured segments, an effect that was also reduced by LU 135252 (ETA = 11.5% increase; ETB = 14% increase). The neointima of control animals exhibited ET-1 like immunoreactivity as well as ETA and ETB binding sites.

CONCLUSION

These data indicate that endothelin is locally-released from endothelial and vascular smooth muscle cells following angioplasty which binds to ETA and ETB receptor sites in the neointima and media. Since administration of the ETA antagonist LU 135252 markedly reduces neointima formation and medial ET binding, we conclude that vascular smooth muscle cell proliferation and subsequent neointima formation is mediated predominantly via ETA receptors. These data underscore the therapeutic potential of ETA antagonists in reducing the degree of restenosis following vascular injury.

Alterations in the nitric oxide synthase binding sites and non-adrenergic, non-cholinergic mediated smooth muscle relaxation in the diabetic rabbit bladder outlet: possible relevance to the pathogenesis of diabetic cystopathy

PURPOSE

To investigate the effect of diabetes mellitus (DM) on the density and distribution of nitric oxide synthase (NOS) and the smooth muscle responses to non-adrenergic, non-cholinergic (NANC) nerve stimulation and exogenous nitric oxide (NO) in the rabbit lower urinary tract.

MATERIALS AND METHODS

Transverse sections of detrusor, bladder neck and urethra, from control and six months alloxan-induced DM New Zealand White rabbits were incubated with a radioligand for NOS ([3H]-L-N(G)-nitroarginine). Densitometric analysis was performed on the autoradiographs. NADPH diaphorase histochemistry was also used as a marker for NOS activity. Responses to NANC nerve stimulation (5 to 20 Hz) and to NO (10(-6) to 3x10(-4) M.) on smooth muscle strips from detrusor, bladder neck and urethra were measured in organ baths.

RESULTS

NOS binding sites were significantly (p<0.03) more dense in the bladder neck than in the detrusor in both DM and control groups. In DM bladder neck, NOS binding sites were significantly (p<0.04) increased compared with the controls. NADPH diaphorase activity appeared markedly increased in the detrusor, bladder neck and urethra of DM animals compared with controls. The mean IC50 for exogenous NO in control versus DM were not statistically different in the bladder neck (1.03x10(-4) M versus 9.8x10(-5) M) and urethra (8.1x10(-5) M versus 8.8x10(-5) M), but the relaxations to 5x10(-6) M of NO were significantly impaired (p<0.04) in the DM urethral smooth muscle. NANC nerve-mediated relaxations were significantly impaired (p<0.001) in the DM urethral smooth muscle.

CONCLUSIONS

Alterations of both the NOS binding sites and functional responses to NANC nerve stimulation suggest that NO may have a pathophysiological role in the urinary bladder dysfunction associated with DM.

Increased expression of endothelin B receptors in the diabetic rabbit urinary bladder: functional relevance

OBJECTIVES

To determine the effect of diabetes mellitus on the density and distribution of endothelin A (ETA ) and endothelin B (ETB ) receptor subtypes in the rabbit urinary bladder, and to assess the in vitro functional properties of endothelin-1 (ET-1) receptors in bladder smooth muscle strips from diabetic and healthy rabbits.

MATERIALS AND METHODS

Diabetes mellitus was induced in six male New Zealand White rabbits with alloxan and their urinary bladders excised 6 months after the induction of diabetes. On serial detrusor and bladder neck sections, low- and high-resolution autoradiography was performed using radioligands for ET-1, ETA and ETB receptors; these sections were then analysed densitometrically. The results were compared with those from six age-matched healthy control rabbits. Functional responses were investigated using isometric tension studies.

RESULTS

ETA and ETB receptor binding sites were localized to both the urothelium and smooth muscle of the detrusor and bladder neck. There were significantly more ETB receptor binding sites in the diabetic detrusor and bladder neck sections than in controls. ET-1 smooth muscle contractile responses were ETA receptor-mediated. The smooth muscle contractile responses to ET-1 were unaltered in the detrusor, but significantly impaired in the bladder neck of diabetic animals compared with controls.

CONCLUSION

Alteration in the expression of ETB receptors and in vitro contractile smooth muscle responses to ET-1 in the diabetic rabbit urinary bladder neck may play a role in the pathophysiology of diabetic cystopathy.

Nitric oxide, prostacyclin and cyclic nucleotide formation in externally stented porcine vein grafts

Non-restrictive, porous, external stents inhibit neointima formation in porcine vein grafts. Since the mechanisms underlying these effects are unknown we investigated the impact of this external stent on factors known to inhibit vascular smooth muscle cell proliferation: prostacyclin (PGI2), nitric oxide (NO), cAMP and cGMP formation in different regions of stented and unstented porcine vein grafts. Paired stented and unstented saphenous vein-carotid artery interposition grafting was carried out in Landrace pigs. One month after surgery, the vessels were excised and the formation of PGI2, cAMP and cGMP determined using radioimmunoassay and nitric oxide synthase (NOS) distribution studied using autoradiography and histochemistry. There were no significant differences between PGI2, cAMP and cGMP (nitroprusside-stimulated) formation in the medial/intimal regions of grafts of stented vein graft and ungrafted saphenous vein whereas all were significantly reduced in unstented vein graft. A23187-stimulated cGMP formation (mediated by NO release) and NOS content was significantly greater in the medial/intimal region of stented and unstented vein graft compared to ungrafted saphenous vein, indicating induction of endothelial NOS (eNOS) in both types of graft. This normalisation of the PGI2-cAMP axis and guanylyl cyclase activity in the medial/intimal region may contribute to the beneficial impact of the external stent on vein graft thickening. The increase in eNOS in both stented and unstented vein grafts mitigates against this isoform as playing a role in mediating the inhibitory effect of the stent on neointima formation. In the adventitia of both stented and unstented grafts there was an increase in PGI2, cAMP and cGMP formation compared to ungrafted saphenous vein, the production being greater in the stented compared to the unstented graft. In the adventitia of stented veini grafts, NOS, detected with NAPDH diaphorase staining, was associated with microvessels as well as with inflammatory cells. Taken together, these data are suggestive of a role for PGI2 and NO in promoting microangiogenesis in the adventitia of stented vein grafts which may in turn minimize graft hypoxia, an established contributory factor to neointima formation.

Regional variations in endothelin-1 and its receptor subtypes in human coronary vasculature: pathophysiological implications in coronary disease

Endothelin-1 is a potent vasoconstrictor peptide and mitogen for vascular smooth muscle cells. Increased plasma or tissue levels of endothelin-1 have been described after myocardial infarction and in atherosclerosis, suggesting that this peptide may play a pathophysiological role in various coronary syndromes. Here, we have studied regional variations in ET-1 and its receptors in control and atherosclerotic human coronary vasculature using standard immunohistochemistry and in vitro autoradiography. ET-1 immunoreactivity was associated with luminal endothelial cells and smooth muscle cells at regions of atherosclerosis. ET(A) receptors were present on smooth muscle cells of coronary arteries and on cardiac myocytes. Medial ET(B) receptor binding at the proximal region of coronary arteries was weak, but increased significantly towards distal regions of this vessel (p<0.005 in control and p<0.0005 in ischaemic heart disease). Microvascular endothelial cells in the adventitia of coronary arteries, myocardial microvessels and the endocardial endothelium expressed the ET(B) receptor exclusively. The receptor variations revealed in this study provide supporting evidence that ET-1 is associated with (1) vascular smooth muscle and endothelial cell proliferation, including areas of intimal hyperplasia and regions of neovascularization (2) increased ET-1-induced reactivity of distal portions of the human coronary artery, (3) ET-1-mediated constriction of myocardial microvessels. These results provide new insights into different potential roles for this peptide in healthy and diseased human coronary vasculature.

Postnatal development of multiple opioid receptors in the spinal cord and development of spinal morphine analgesia

The postnatal ontogeny of mu, delta and kappa opioid receptor binding sites in the spinal cord of rat pups at various postnatal days was determined using in vitro autoradiographical methods. The functional effect of spinal morphine was also assessed using in vivo electrophysiological methods in rats at P14, P21 and adults (P56). Both mu and kappa opioid receptor binding-sites are present from P0 and spread relatively diffusely throughout the spinal cord. Overall binding peaks at P7 and subsequently decreases to adult levels with the mu opioid receptor binding sites regressing to become denser in the superficial dorsal horn. delta Opioid receptor binding was first seen at P7, and no distinction between superficial and deeper laminae was seen. In the adult, the relative proportions of the opiate receptors in the superficial dorsal horn are 63%, 22% and 15%, for mu, delta and kappa receptor binding sites, respectively. C-fibre evoked dorsal horn neuronal responses recorded from anaesthetized rat pups were highly sensitive to spinal morphine at P21, (EC50 0.005 microgram), compared to the adult (EC50 0.9 microgram). However, the EC50 (0.2 microgram) at P14 was greater than at P21 despite the fact that mu receptor binding was greater at P14. Opioid receptor binding is developmentally regulated and undergoes substantial postnatal reorganization. However, the number of mu receptor binding sites appears not to be the only determinant of functional sensitivity to spinal morphine. Other factors, such as coupling of the receptors are likely to be important.

Endothelin-1 and endothelin receptors in porcine saphenous vein-carotid artery grafts

The regional distribution of endothelin-1 (ET-1) and its receptor subtypes (ETA and ETB) in porcine saphenous vein into carotid artery interposition grafts was studied 1 month after surgery and compared to ungrafted saphenous vein and carotid artery. ET-1 immunoreactivity was identified by immunohistochemistry and ET receptor subtypes were studied using in vitro autoradiography. In vein grafts, there was a higher density of ETA compared to ETB receptor binding in both the tunica media and the neointima. ETA binding to the tunica media of ungrafted saphenous vein was greater than that in the carotid artery or vein grafts, but greater in the vein graft compared to the carotid artery. Immunoreactive ET-1 was located in endothelial cells and throughout the neointima of the vein graft. Dense ETA and ETB binding was also associated with adventitial microvessels in the graft, and ETB binding was also identified to neutrophils, which accumulated at the subendothelium and within the adventitia. ETA receptors may play a role in vein graft thickening at the medial and neointimal vascular smooth-muscle cell level, whereas ETB receptors may play a role in microangiogenesis. The high levels of ETA receptors in the tunica media of ungrafted saphenous vein, relative to the carotid artery and vein graft, may also render this conduit susceptible to neointimal formation. These data indicate that studies of the effect of ET receptor antagonists on the pathobiology of vein graft disease are warranted.

Endothelins: effect on matrix biosynthesis and proliferation in normal and scleroderma fibroblasts

We investigated the effect of endothelin-1 (ET-1) in normal and systemic sclerosis (SSc) dermal fibroblasts. Collagen type I, collagen type III, and MMP-1 levels in culture supernatants were measured by competition ELISA and cellular mRNA expression was examined by Northern blotting. Mitogenic responses to ET-1 were assessed by [3H]TdR incorporation. ET receptor mRNA expression was examined by RT-PCR analysis of fibroblast RNA and with surface binding studies using radiolabeled ET receptor ligands and specific receptor antagonists. ET-1 enhanced release of collagen types I and III by control and SSc fibroblast strains, but the effects were significantly greater for control cells (p < 0.05). This effect appeared to involve both ETA and ETB receptor subtypes. SSc fibroblasts demonstrated lower constitutive MMP-1 production than control fibroblasts (p < 0.01), but ET-1 treatment decreased MMP-1 in normal fibroblasts to levels observed in SSc. Mitogenic response (percent control [3H]TdR incorporation) to ET-1 for SSc fibroblasts was 130 +/- 34, significantly less (p < 0.01) than that for normal fibroblasts strains (290 +/- 25). This response appeared to be predominantly mediated via the ETA receptor subtype. Surface binding studies suggested a significantly lower level of ETA binding sites in SSc compared with normal fibroblasts (p < 0.05). These data suggest that ET-1 induces a fibrogenic phenotype in normal dermal fibroblasts that resembles that seen in fibroblasts grown from lesional SSc skin. Moreover, SSc cells appear to be refractory to these effects, and this reduced responsiveness is associated with an altered ratio of ETA:ETB receptor expression, supporting a role for ET-1 in the fibrotic pathology of SSc.

Endothelin-1 regulation of intercellular adhesion molecule-1 expression in normal and sclerodermal fibroblasts

We investigated the potential modulation of cell surface intercellular adhesion molecule-1 (ICAM-1) expression and function by ET-1 in fibroblasts grown from skin biopsies of scleroderma (SSc) patients compared with healthy controls. Surface ICAM-1 expression was quantified by cell-bound ELISA and by FACS analysis. ICAM-1 function was investigated by measuring cell adhesion, and we studied ICAM-1 gene expression using RT-PCR. Fibroblast ET-1 binding sites were measured using 125I-labeled ET-1, and the modulation of ICAM-1 function by ET-1 was determined by measuring the binding of human U937 cells to fibroblasts in the presence of a mixed ETA/B receptor antagonist (bosentan) or a neutralizing anti-ICAM-1 antibody. ICAM-1 expression was significantly higher in SSc fibroblasts compared with normal controls. ET-1 increased ICAM-1 on both normal and SSc fibroblasts to comparable levels. RT-PCR demonstrated that ICAM-1 mRNA was upregulated by ET-1, and results from binding studies showed fibroblasts exposed to ET-1 supported more U937 cells than controls, a process that could be inhibited by bosentan and ICAM-1 neutralizing antibody. Autoradiography showed ET-1 receptors on both normal and SSc fibroblasts. Our findings indicate that SSc fibroblasts express intrinsically elevated levels of surface ICAM-1 and message. ET-1 can induce normal fibroblasts to express some SSc phenotypes and may function as a potent proinflammatory mediator, similar to cytokines, and therefore may also have immunoregulatory functions for immune cells infiltrating and binding to connective tissues.

Distribution of endothelin-1 (ET) receptors (ET(A) and ET(B)) and immunoreactive ET-1 in porcine saphenous vein-carotid artery interposition grafts

Proliferation of vascular smooth muscle cells (VSMC) is a principal event in neointima formation in saphenous vein-coronary artery bypass grafts. Since endothelin-1 (ET-1) promotes VSMC replication and ET-1 receptor antagonists inhibit neointima formation in arterial injury models, it is reasonable to propose that ET-1 may be involved in neointima formation in vein grafts. However, it is not known what alterations of ET-1 and its receptors (if any) occur in vein grafts. The objective of this study, therefore, was to investigate the distribution of ET-1 and ET-1 receptor subtypes (ET(A) and ET(B)) in porcine vein grafts. Unilateral interposition saphenous vein grafting was performed by end to end anastomosis after excision of a segment of carotid artery in Landrace pigs. One month after surgery, vein grafts, ungrafted saphenous veins and carotid arteries were excised, ET-1 immunoreactivity identified by immunocytochemistry and ET(A) and ET(B) receptor subtypes studied using autoradiography. In vein grafts, there was a greater density of ET(A) compared to ET(B) receptors in both the tunica media and neointima. ET(A) binding in the tunica media of ungrafted saphenous vein was greater than that in the carotid artery or vein grafts, but greater in the vein graft compared to the carotid artery. Immunoreactive ET-1 was located in endothelial cells and throughout the neointima of the vein graft. Dense ET-1 binding (to both ET(A) and ET(B) receptors) was also associated with microvessels in the adventitia within the graft. In vein grafts, there was strong ET(B) binding to neutrophils which were present in high numbers at the subendothelium and within the adventitia. It is concluded ET(A) receptors may play a role in vein graft thickening at the medial and neointimal VSMC level, whereas ET(B) receptors may play a role in microangiogenesis. The higher levels of ET(A) receptors in the tunica media of ungrafted saphenous vein relative to the carotid artery and vein graft may also render this conduit susceptible to neointima formation. These data indicate that studies on the effect of ET receptor antagonists on the pathobiology of vein graft disease is warranted.

Effect of angioplasty and grafting on porcine vascular nerves: a potential neurotropic role for endothelin-1

The most commonly performed procedure for treating coronary artery stenosis is percutaneous transluminal coronary angioplasty (PTCA) and, where the vessel lumen is severely narrowed, coronary artery bypass grafting (CABG). In PTCA, regions of atherosclerotic plaques are disrupted, and the vessel lumen increased by inflating a balloon catheter. In CABG an autologous saphenous vein into coronary artery interposition graft is performed in order to bypass occluded regions of epicardial coronary arteries. Both interventions cause varying degrees of vascular damage and the long-term efficacy of these procedures is limited by a high incidence of neointimal formation and subsequent vascular restenosis (Bach et al. 1994; Bryan & Angelini, 1994).

The endothelium-derived constrictor peptide, endothelin-1 (ET-1) (Yanagisawa et al. 1988), also possesses mitogenic activity on vascular smooth muscle cells (Hirata et al. 1989) and has been suggested as playing a role in atherosclerosis (Dashwood et al. 1993; Zeiher et al. 1994) and intimal hyperplasia (Dashwood et al. 1993; Douglas et al. 1994).

Down-regulation of endothelin-B receptor sites in cavernosal tissue of hypercholesterolaemic rabbits

OBJECTIVE

To investigate the density and distribution of endothelin-1 (ET-1) and endothelin receptor subtypes in cavernosal tissue of healthy New Zealand White (NZW) rabbits (controls) and to assess any changes in a genetic model of hypercholesterolaemia (the Watanabe rabbit).

MATERIALS AND METHODS

Penises were excised from six hypercholesterolaemic (HC) rabbits 6 months after birth. Low- and high-resolution autoradiography was performed on cavernosal sections using radioligands for ET-1, endothelin A (ETA) and endothelin B (ETB) receptors, and the autoradiographs analysed densitometrically. The results were compared with those from six age-matched control rabbits. Immunohistochemical localization of ET-1-like immunoreactivity was also performed on adjacent cavernosal sections.

RESULTS

ET-1, ETA and ETB receptor binding sites were primarily localized to the smooth muscle cells of the corpus cavernosum and the endothelium lining the cavernosal spaces. There was a significant decrease in ETB receptor binding sites in cavernosal tissue from HC rabbits when compared to age-matched healthy controls.

CONCLUSIONS

The findings suggest that ET-1 may have a role in the pathophysiology of erectile dysfunction in HC. These effects may partly be due to enhanced vasoconstrictor actions and smooth muscle cell proliferation, consequent on a reduction in endothelial ETB receptors.