Type V Collagen is Persistently Altered After Inguinal Hernia Repair.

BACKGROUND AND AIMS: Hernia formation is associated with alterations of collagen metabolism. Collagen synthesis and degradation cause a systemic release of products, which are measurable in serum. Recently, we reported changes in type V and IV collagen metabolisms in patients with inguinal and incisional hernia. The aim of this study was to determine if the altered collagen metabolism was persistent after hernia repair. MATERIAL AND METHODS: Patients who had undergone repairs for inguinal hernia (n = 11) or for incisional hernia (n = 17) were included in this study. Patients who had undergone elective cholecystectomy served as controls (n = 10). Whole venous blood was collected 35-55 months after operation. Biomarkers for type V collagen synthesis (Pro-C5) and degradation (C5M) and those for type IV collagen synthesis (P4NP) and degradation (C4M2) were measured by a solid-phase competitive assay. RESULTS: The turnover of type V collagen (Pro-C5/C5M) was slightly higher postoperatively when compared to preoperatively in the inguinal hernia group (P = 0.034). In addition, the results revealed a postoperatively lower type V collagen turnover level in the inguinal hernia group compared to controls (P = 0.012). In the incisional hernia group, the type V collagen turnover was higher after hernia repair (P = 0.004) and the postoperative turnover level was not different from the control group (P = 0.973). CONCLUSION: Patients with an inguinal hernia demonstrated a systemic and persistent type V collagen turnover alteration. This imbalance of the collagen metabolism may be involved in the development of inguinal hernias.

Suction blister lesions and epithelialization monitored by optical coherence tomography.

BACKGROUND/PURPOSE: Our objective was to assess epithelialization of suction blister lesions by optical coherence tomography (OCT) and benchmark it to histology using epidermal thickness (ET) as the primary outcome. METHODS: Thirty-two healthy volunteers were recruited to Study 1 and 2. One 10-mm suction blister was raised on each buttock, and the blister roof was excised. Lesions were covered with moisture-retaining dressing. In Study 1, the lesions were OCT-scanned on day 0 (D0), D2 and D4 and excised for histological examination. In Study 2, the progress of epithelialization and skin barrier function were monitored to D14. RESULTS: ET increased from D0 to D2 by 46 µm (P<.001) and from D2 to D4 by 19 µm (P=.004). Compared with histology, OCT overestimated the presence of the epithelium (P<.0001) and ET on D4. Reliable measurements were obtained when the ET of the lesions reached the ET of the normal epidermis from D5-D7 and onwards. The ET development was reflected in decreased transepidermal water loss. CONCLUSION: We found that the OCT technique was poorly discriminative with respect to the neoepithelium and the moist lesion surface material in the early postinjury period. In the later stages, OCT seemed valuable for estimating the advancement of epithelialization.

Growth factor and proteinase profile of Vivostat® platelet-rich fibrin linked to tissue repair.

BACKGROUND AND OBJECTIVES: Autologous platelet-rich fibrin (PRF(®)) is prepared by the automatic Vivostat(®) system. Conflicting results with Vivostat PRF in acute wound healing prompted us to examine its cellular and biomolecular composition. Specifically, platelets, selected growth factors and matrix metalloproteinase (MMP)-9 were quantified using novel analytical methods. MATERIALS AND METHODS: Ten healthy non-thrombocytopenic volunteers donated blood for generation of intermediate fibrin-I and final PRF. Anticoagulated whole blood and serum procured in parallel served as baseline controls. Leucocyte, erythrocyte and platelet counts in whole blood and fibrin-I were determined by automated haematology analyser. Platelet concentration in PRF was quantified manually by stereologic analysis of Giemsa-stained tissue sections, and the total content of five growth factors and MMP-9 by enzyme-linked immunosorbent assays. RESULTS: The number of leucocytes and erythrocytes was reduced (P < 0·001), whereas platelets increased (P < 0·001) in fibrin-I versus whole blood. PRF contained 982 ± 206 × 10(9) platelets/l representing 3·9-fold (P < 0·001) enrichment relative to whole blood. Growth factor abundance in Vivostat PRF and serum was in descending order: transforming growth factor-ß1 [5·1-fold higher in PRF than serum, P < 0·001] > platelet-derived growth factor (PDGF)-AB [2·5-fold, P < 0·01] > PDGF-BB [1·6-fold, P < 0·05] > vascular endothelial growth factor > basic fibroblast growth factor [75-fold, P < 0·001]. MMP-9 was reduced 139-fold (P < 0·001) compared with serum, reflecting leucocyte depletion in PRF. CONCLUSION: The gained knowledge on platelet enrichment and biomolecular constituents may guide clinicians in their optimal use of Vivostat PRF for tissue regenerative applications.

Effect of postoperative diclofenac on anastomotic healing, skin wounds and subcutaneous collagen accumulation: a randomized, blinded, placebo-controlled, experimental study.

BACKGROUND: Retrospective studies have drawn attention to possible detrimental effects of non-steroidal anti-inflammatory drugs (NSAIDs) on the anastomotic leakage rate after colorectal resection. In this study, we examined the effects of the NSAID diclofenac on the breaking strength of an experimental colonic anastomosis and a skin incision as well as subcutaneous collagen accumulation. METHODS: This was a randomized, blinded, placebo-controlled experimental study in 60 male Wistar rats treated with diclofenac 4 mg/kg/day or placebo. In each rat, a colonic anastomosis was performed and an expanded polytetrafluoroethylene (ePTFE) tube was placed subcutaneously. Incisional and anastomotic wound breaking strength and hydroxyproline content in the ePTFE tubes were measured 7 days after the operation. RESULTS: We found no significant differences in any of the breaking strength measurements, but showed a median 38% reduction in hydroxyproline deposition as a result of diclofenac treatment (p = 0.03). In the placebo group, subcutaneous collagen deposition tended to correlate positively with skin incisional but negatively with anastomotic bio-mechanical strength. CONCLUSION: Postoperative diclofenac treatment significantly inhibited collagen deposition in subcutaneous granulation tissue. Anastomotic strength and skin wound strength were not significantly affected. The ePTFE model is suitable for assessing the effect of various drugs on collagen formation and thus on wound healing.

Collagen levels are normalized after decompression of experimentally obstructed colon.

AIM: Our aim was to define the dynamics in collagen concentrations in the large bowel wall following decompression of experimental obstruction. METHOD: Colonic obstruction was created in 28 male rats by the placement of a silicone ring around the distal colon. The ring was removed after 4 days to mimic endoscopical decompression by stent deployment. Colon circumference and collagen concentration were measured proximal to the obstructed segment immediately and at 3 and 10 days after decompression. The corresponding colonic sites of 23 sham-operated and eight nonoperated control animals were subjected to identical analyses. RESULTS: Four days of obstruction resulted in a more than twofold increase in colonic circumference (20 vs 8 mm), with a concomitant 43% reduction (P = 0.001) in collagen concentration in the bowel wall proximal to the obstruction compared with sham animals. Three days after decompression, collagen concentrations remained reduced (P < 0.05), while there was no significant difference after 10 days with either sham-operated or nonoperated controls. Colonic circumference of the obstructed colon remained slightly distended (11 mm) on day 10 and tended to correlate (r(S) = 0.51, P = 0.053) with total matrix metalloproteinase activity. CONCLUSION: The marked reduction in collagen concentration in an experimentally obstructed colon is normalized 10 days after decompression. These findings may have clinical implications for the timing of surgical resection.

S100A8/A9 deficiency in nonhealing venous leg ulcers uncovered by multiplexed antibody microarray profiling.

BACKGROUND: Knowledge on the underlying mechanisms for nonhealing chronic wounds is fragmentary. OBJECTIVES: To increase our understanding of the pathogenesis, the relationship between healing ability and a large panel of proteins was studied using a specially designed wound-healing antibody-based microarray. METHODS: Wound fluid from nondiabetic patients with nonhealing venous leg ulcers was compared with that from patients with healing open granulating acute wounds. The high-throughput method enabled simultaneous measurement of the relative levels of 48 different proteins representing major categories of wound-healing modulators. RESULTS: Unexpectedly, several of the examined proteins, including various proinflammatory cytokines, proteinases and antiproteinases, were not significantly (P>0·001) changed in chronic wound fluid. For example, levels of matrix metalloproteinase-9 and one of its substrates type IV collagen were similar in the two groups. The wound fluid samples displayed similar degrees of fragmentation of fibronectin by Western blot analysis and the total fibronectin levels were doubled (P<0·001) in chronic compared with acute wounds. The increased fibronectin originated from α-smooth muscle actin-positive myofibroblasts and not from the circulation. S100A8/A9 was the sole protein that was reduced (P<0·001) in wound fluid from venous ulcers [median 226 µg mL(-1) (interquartile range 213-278)] compared with healing wounds [455 µg mL(-1) (382-504)], probably reflecting a difference in inflammatory cell composition. CONCLUSION: The molecular anomalies in chronic wounds are more subtle than the current paradigm and neither excessive proteinase activity nor deficiencies of examined extracellular matrix proteins, growth factors or angiogenic/angiostatic factors appear to contribute significantly to the nonhealing state of venous leg ulcers.

Effects of amelogenins on angiogenesis-associated processes of endothelial cells.

OBJECTIVE: To study the effects of an amelogenin mixture on integrin-dependent adhesion, DNA synthesis and apoptosis of cultured human dermal microvascular endothelial cells and angiogenesis in an organotypic assay. METHOD: Immobilised antibodies against specific integrins (alpha-1, alpha-2, alpha-3, alpha-4, alpha-5, alpha-v, ß1, ß2, ß3, ß4, ß6, alpha-vß3, alpha-vß5 and alpha-5ß1) were used to capture treated human dermal microvascular endothelial cells, which were detected colourimetrically. DNA synthesis of the cells was monitored by 5-bromo-2'- deoxyuridine incorporation and apoptosis by a TdT-mediated dUTP nick-end labelling technique. Tubule formation from aortic arches of 13-d-old chick embryos were followed over 48h. RESULTS: The amelogenin mixture increased microvessel outgrowth by 76% (p < 0.01, n=12) from the aortic explants. Also, amelogenins increased the adhesion (p < 0.01, n = 5) by multiple angiogenesis associated integrin subunits and alpha-vß3, alpha-vß5 and alpha-5ß1 heterodimers on human dermal microvascular endothelial cells at a non-mitogenic concentration (100 µg/ml). Conversely, amelogenins at 1,000 µg/ml decreased microvessel formation possibly due to attenuation of corresponding integrins despite increasing (p < 0.001, n = 8) DNA synthesis. No significant apoptosis was detected in human dermal microvascular endothelial cells cultured on Matrigel with and without amelogenins. CONCLUSION: Increased surface expression of integrins on endothelial cells may contribute to the proangiogenic property of amelogenins.

Effect of diclofenac on cyclooxygenase-2 levels and early breaking strength of experimental colonic anastomoses and skin incisions.

BACKGROUND: Recently, there has been a focus on the effect of the nonsteroidal anti-inflammatory drugs on the anastomotic leakage rate after colorectal surgery. METHODS: An experimental, randomized, placebo-controlled prospective study on 32 male Wistar rats was carried out. We examined the effect of diclofenac 4 mg/kg/day on the cyclooxygenase-2 (COX-2) enzyme in the anastomotic tissue and on the breaking strength of anastomotic and incisional wounds. The operation was performed with colonic resection and hand-sewn anastomosis. After 3 days, the rats were sacrificed and the breaking strength and the COX-2 content of the anastomosis were measured. RESULTS: There was a significantly reduced level of COX-2 in the rats treated with diclofenac (p = 0.001); no significant differences in any of the breaking strength measurements and no significant correlation between COX-2 levels and breaking strength of the anastomotic or incisional wounds could be found (p = 0.073 and p = 0.727). CONCLUSION: This study for the first time showed that a diclofenac dose of 4 mg/kg/24 h was sufficient to reduce the level of COX-2 enzymes in the anastomotic tissue in rats. This inhibition of the inflammatory response did not lead to reduced breaking strength of either anastomotic or incisional wounds. Whether there is a detrimental effect of COX inhibition on colorectal anastomoses in the clinical setting remains controversial.

Connective tissue alteration in abdominal wall hernia.

BACKGROUND: The aetiology and pathogenesis of abdominal wall hernia formation is complex. Optimal treatment of hernias depends on a full understanding of the pathophysiological mechanisms involved in their formation. The aim of this study was to review the literature on specific collagen alterations in abdominal wall hernia formation. METHODS: A computer-assisted search of the medical databases PubMed and Embase was performed, together with a cross-reference search of eligible papers. RESULTS: Fifty-two papers were included. Collagen alteration depended on the type of hernia; there were more pronounced changes in patients with a direct inguinal hernia than in those with an indirect inguinal hernia, recurrent inguinal hernia or incisional hernia. A consistent finding was a significant increase in immature type III collagen relative to the stronger type I collagen in patients with a hernia. This resulted in thinner collagen fibres with a correspondingly diminished biomechanical strength. It has been suggested that these alterations are due to variation in the synthesis, maturation or degradation of collagen by matrix metalloproteinases, in combination or alone. CONCLUSION: Hernia formation and recurrence is associated with altered collagen metabolism manifested by a decreased type I:III collagen ratio.

Evaluation of a near-senescent human dermal fibroblast cell line and effect of amelogenin.

BACKGROUND: Fibroblast senescence may delay healing of chronic wounds. OBJECTIVES: To characterize a chronic human dermal fibroblast cell line (CRL-7815) with near-senescent properties, cell proliferation and production of wound-healing modulating cytokines, and biosynthesis and remodelling of collagen were compared with normal human dermal fibroblasts. Also, the response of CRL-7815 fibroblasts to the extracellular matrix protein amelogenin that is beneficial in the treatment of stalled chronic wounds was studied. METHODS: Fibroblast proliferation was monitored by time-resolved growth curves and factors secreted into the culture medium containing 10% fetal bovine serum were measured by enzyme-linked immunosorbent assays. Fibroblast-mediated reorganization was examined in three-dimensional type I collagen matrices. RESULTS: Cell proliferation over 9 days was significantly (P < 0.01) slower for CRL-7815 than for normal fibroblasts. Amelogenin at 1 mg mL(-1) increased (P < 0.01) CRL-7815 proliferation to the level of the normal fibroblasts. The neutrophil chemoattractant interleukin (IL)-8 was low while the constitutive production of monocyte chemoattractant protein (MCP)-1 was highly elevated in medium from cultured CRL-7815 fibroblasts. Amelogenin augmented IL-8 but attenuated MCP-1 secretion in CRL-7815 fibroblasts. The elevated vascular endothelial growth factor production in CRL-7815 fibroblasts was further increased with amelogenin while increased type I collagen synthesis by CRL-7815 was reduced with 0.1 mg mL(-1) amelogenin. The dramatically impaired collagen matrix remodelling with CRL-7815 fibroblasts (P < 0.001) was slightly improved with amelogenin (P = 0.0011). CONCLUSIONS: The near-senescent cell line CRL-7815 shares functional anomalies with fibroblasts isolated from nonhealing chronic cutaneous wounds. Amelogenin has the capacity to switch chronic fibroblasts into an acute-like phenotype.

Effect of parenteral zinc sulfate on colon anastomosis repair in the rat.

BACKGROUND AND AIMS: To prevent colonic anastomotic dehiscence, pharmaceutical interventions should inhibit degradation of existing submucosal collagen fibers and accelerate the synthesis of new collagen molecules. Zinc has multiple functions in collagen metabolism and was recently found beneficial in colonic anastomosis repair. We have investigated the effect of daily intraperitoneal zinc (2 mg/kg) injections on the development of the biomechanical integrity of left colon anastomoses. MATERIALS AND METHODS: Sixty Sprague-Dawley male rats (median 245 g) were allocated to treatment with zinc sulfate in saline (n = 30) or with saline alone (n = 30) starting 1 h before the anastomoses were made. Serum zinc levels and anastomotic breaking strength were determined on postoperative days 3 (n = 30) and 7 (n = 30). The initial breaking strength or suture-binding capacity was determined in additional ten non-treated animals (277 g). RESULTS: The breaking strength of the anastomoses decreased in the two groups combined (n = 30) by 50% (p < 0.001) on day 3 but was regained by postoperative day 7 compared with the initial anastomotic biomechanical strength. Serum zinc levels also increased from day 3 to day 7 in both intervention groups and correlated significantly with breaking strength (r = 0.57, p < 0.001). Although the median serum zinc level was 14% higher (p < 0.01) on day 7 in zinc-treated than in saline-treated animals, the breaking strength did not differ significantly between zinc-treated and saline-treated rats on either day 3 (p = 0.95) or day 7 (p = 0.70). CONCLUSION: In contrast to previous report in rabbits, we failed to demonstrate the beneficial effects of parenteral zinc supplementation on colon anastomosis repair in a rat model.

Biophysical effects of repetitive removal of adhesive dressings on peri-ulcer skin.

OBJECTIVE: To study the effect of repeated removal of four different adhesive dressings on peri-ulcer skin using quantitative non-invasive techniques. METHOD: Forty-five patients with open (n = 29) or healed (n = 16) venous leg ulcers were included. Peri-ulcer skin was treated for 14 days with patches of two different hydrocolloid-based adhesive dressings, one polyurethane adhesive and one soft silicone adhesive dressing. Normal skin of the patients' ventral forearm was also treated identically. Adhesive patches of the dressings were replaced every second day. The skin barrier function was assessed by measuring transepidermal water loss and stratum corneum hydration by measuring electrical conductance. RESULTS: Thirty-nine patients completed the study. The hydrocolloid adhesives increased transepidermal water loss and conductance while the polyurethane and soft silicone adhesives did not influence these parameters significantly compared with adjacent non-treated peri-ulcer skin. For normal forearm skin, similar relative effects among the four adhesives were found. CONCLUSION: Repetitive treatment with hydrocolloid-based adhesive dressings induced major functional alterations of the stratum corneum. In contrast, a polyurethane adhesive and a soft silicone adhesive dressing did not alter transepidermal water loss or conductance of peri-ulcer skin.

Epithelial regeneration from bioengineered skin explants in culture.

BACKGROUND: Artificial skin substitutes are beneficial in the treatment of chronic wounds although their performance relative to authentic human skin is unclear. OBJECTIVES: We compared the rate of outgrowth and morphology of neoepidermis from a bioengineered skin construct (Apligraf) with normal adult human skin explants on de-epidermized human dermal growth substrate with or without intact epidermal basement membrane zone. METHODS: Epithelial outgrowth of air-exposed cultures in serum-supplemented keratinocyte medium was quantified by fluorescence imaging, morphology by light microscopy, biomarkers of keratinocyte activation, proliferation and migration by immunohistochemical analysis, and gelatinases by zymography. RESULTS: Resurfacing from bioengineereed skin explants started earlier than from normal skin but subsequently, from day 3 to day 9, the rate of epidermalization from bioengineered skin was only 40% (206 +/- 23 microm day(-1), mean +/- SEM) of that of authentic skin (521 +/- 17 microm day(-1), P < 0.001). At culture termination at day 11, normal human skin had formed a multilayered and well-structured neoepidermis covering 41.0 +/- 1.2 mm2 of the dermal substrate while bioengineered skin produced a thinner, less organized epithelium covering 20.4 +/- 3.0 mm2. At this later stage, a higher expression of beta-defensin-2, keratin 16, Ki67 and matrix metalloproteinase (MMP)-9 was found in neoepidermis formed from authentic skin than from bioengineered skin. Activated MMP-2 was elevated in bioengineered skin-derived neoepidermis. Minor epithelial outgrowth was noted with either skin type on the dermal substrate devoid of basement membrane zone. CONCLUSIONS: Cultured normal skin explants produced a more uniform and expansive in vivo-like neoepidermis than bioengineered skin explants.

Effect of a matrix metalloproteinase activity and TNF-alpha converting enzyme inhibitor on intra-abdominal adhesions.

BACKGROUND: Formation of intra-abdominal adhesions depends, in part, on the activity of serine proteinases. Matrix metalloproteinases (MMP) are required for epithelialization of skin wounds but their involvement in mesothelialization of peritoneal wounds and in adhesion pathogenesis is not known. Early tumor necrosis factor-alpha (TNF-alpha) levels have been proposed to reflect propensity to adhesion formation. OBJECTIVE: The impact of MMP activity and secreted TNF-alpha on peritoneal adhesion formation and healing was investigated through systemic administration of the synthetic broad-spectrum MMP and TNF-alpha-converting enzyme (TACE) inhibitor GM 6001. METHODS: Female Sprague-Dawley rats of 4-6 weeks of age were injected subcutaneously daily with GM 6001 100 mg/kg (n = 12) or vehicle (n = 10) starting two days before surgery. In each rat, two standardized peritoneal wounds, 20 mm x 5 mm, were made. One peritoneal wound was sutured whereas the contralateral wound healed by secondary intention. Adhesion formation and peritoneal healing, cell proliferation, and hydroxyproline concentrations were evaluated on postoperative day 7. RESULTS: Total serum TNF-alpha levels increased in vehicle-treated rats (p = 0.019) while GM 6001 treatment effectively prevented the rise in the postoperative phase (p < 0.001). No significant differences were observed in the extent of adhesion formation (p = 0.67) between control (65.0%) and GM 6001-treated (61.5%) animals, or peritoneal wound healing or cell proliferation. Hydroxyproline levels increased in the wounds (p = 0.014) but were not different between the two groups (p = 0.14). CONCLUSIONS: Lack of a striking effect of the MMP and TACE antagonist GM 6001 on postoperative adhesions suggests that MMP activity and TNF-alpha might not be major adhesiogenic factors.

The release of zinc ions from and cytocompatibility of two zinc oxide dressings.

OBJECTIVE: These in vitro studies examined the release of zinc ions from and the response of human dermal fibroblasts to two zinc oxide-medicated dressings: one with zinc oxide in an ointment base and one using polyvinylpyrrolidone (PVP), a hydrophilic polymer for the binding of zinc oxide particles. METHOD: Zinc release from the dressings in buffered-saline (pH 7.4) was studied through a high-pore-density membrane (pore size, 0.40 microm) in a two-compartment model at 37 degrees C for three hours. Cytocompatibility of the dressings and 500 micromol/l of zinc ions was assessed using the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay after exposure to monolayers of confluent normal human dermal fibroblasts to the dressing extracts for four hours. RESULTS: The zinc release rate from PVP-bound zinc oxide was more than two-fold higher than from zinc oxide in the ointment. Extract of the zinc oxide ointment, containing 150 micromol/l solubilised zinc, elicited a cytotoxic reaction, while the zinc oxide-PVP extract, containing 410 micromol/l solubilised zinc, and 500 micromol/l zinc chloride were non-cytotoxic to the fibroblasts. CONCLUSION: Zinc release in a simulated wound milieu appears to be inhibited when zinc oxide is incorporated in a lipophilic vehicle. It is hypothesised that the ointment vehicle induced cytotoxicity rather then the solubilised zinc oxide. DECLARATION OF INTEREST: None.

Matrix metalloproteinases and colon anastomosis repair: a new indication for pharmacological inhibition?

Excessive matrix metalloproteinase activities have been implicated in the pathogenesis of intestinal anastomotic dehiscence, a serious and potentially life-threatening complication following gastrointestinal surgery. In this review, the properties of matrix metalloproteinases are summarized followed by presentation of clinical therapeutic interventions with synthetic matrix metalloproteinase inhibitors and novel experimental data on colon anastomosis repair that warrant exploration of these drugs in surgical colorectal patients.

Minimal erythema dose after multiple UV exposures depends on pre-exposure skin pigmentation.

BACKGROUND/PURPOSE: Phototherapy consists of multiple ultraviolet (UV) exposures. Most previous studies have focused on erythema following a single UV exposure in fair-skinned persons. Although it is well known that phototherapy lowers the daily UV-threshold dose for erythema in clinical practice, this is insufficiently documented under controlled experimental conditions. The purpose of this study was to quantify the change in the daily threshold for a dose specific erythema grade after 1-4 consecutive daily UV exposures. METHODS: Forty-nine healthy volunteers (skin type II-V) with varying pigmentation quantified by skin reflectance. Two UV sources were used: a narrowband UVB (Philips TL01) and a Solar Simulator (Solar Light Co.). Just perceptible erythema after 24 h was chosen as the minimal erythema dose (+); besides + and ++ were assessed. RESULTS: We found a positive and significant exponential relationship between skin pigmentation and UV dose to elicit a specific erythema grade on the back after 1-4 UV exposures. After repetitive UV exposures the UV dose had to be lowered more in dark-skinned persons compared with fair-skinned persons to elicit a certain erythema grade. This applied to both UV sources and all erythema grades. CONCLUSION: In the dark-skinned persons the daily UV dose after the 4 days UV exposure should be lowered by 40-50% to avoid burns compared with the single UV exposure. For the most fair-skinned persons essentially no reduction in the daily UV dose was needed. Our results indicate that the pre-exposure pigmentation level can guide the UV dosage in phototherapy.

beta-Adrenoceptor agonist sensitizes the dopamine-1 receptor in renal tubular cells.

The renal effects of dopamine are mainly mediated via the dopamine-1 receptor (D1 receptor). This receptor is recruited from intracellular compartments to the plasma membrane by dopamine and atrial natriuretic peptide (ANP), via adenylyl cyclase activation. We have studied whether isoproterenol, a beta-adrenoceptor (beta-AR) agonist that may interact with dopamine in the regulation of rat renal Na+, K+-adenosine triphosphatase (ATPase) activity, can recruit D1 receptors to the plasma membrane. The spatial regulation of D1 receptors was examined using confocal microscopy techniques in LLCPK cells and the functional interaction between dopamine and isoproterenol was examined by studying their effects on Na+, K+-ATPase activity in microdissected single proximal tubular segments from rat. Isoproterenol was found to translocate the D1 receptors from the interior of the cell towards the plasma membrane. The recruitment of dopamine 1 receptors was found to be cyclic adenosine phosphate (cAMP) dependent, while protein kinase C (PKC) activation was not involved. The functional studies on Na+, K+-ATPase activity showed that the effect of isoproterenol was abolished by a D1-like receptor antagonist (SCH 23390), and mediated via protein kinase A (PKA) and PKC dependent pathways. The results provide an explanation for the interaction between G protein-coupled receptors. The effects of isoproterenol on Na+, K+-ATPase activity can be explained by a heterologous recruitment of D1 receptors to the plasma membrane.