Effect of glucocorticoid treatment on skin capillary blood flow and viability in cutaneous and myocutaneous flaps in the pig

The effect of methylprednisolone treatment on skin-flap viability and capillary blood flow was studied in a series of four experiments. Intramuscular methylprednisolone injections (30 mg/kg per day), given in single or divided doses preoperatively or postoperatively, had no effect in augmenting skin viability in arterialized cutaneous, myocutaneous, or random skin flaps compared with the control. Capillary blood flow was studied in arterial buttock flaps and latissimus dorsi myocutaneous flaps raised on animals treated preoperatively with methylprednisolone or saline (control), and no significant difference in capillary blood flow was noted between the treatment and control flaps. It was concluded that methylprednisolone has no significant therapeutic effect either in increasing flap viability or in increasing capillary blood flow in skin flaps in pigs.     

Pharmacologic action of isoxsuprine in cutaneous and myocutaneous flaps

The therapeutic effects of isoxsuprine on skin capillary blood flow and viability were studied in arterial buttock flaps, latissimus dorsi myocutaneous flaps, and random skin flaps in pigs. It was observed that parenteral isoxsuprine increased capillary blood flow to the skin of arterial buttock flaps and the skin and muscle of latissimus dorsi myocutaneous flaps in a dose-response manner, with a maximum vascular effect observed at 1.0 mg/kg. However, this maximum effective dose of isoxsuprine did not have any significant effect on skin viability in the cutaneous and myocutaneous flaps compared with the control. Examination of the distribution of capillary blood flow within the flaps at varying distances from the pedicle revealed that isoxsuprine did not increase capillary blood flow or perfusion distance in the distal portion of the skin of arterial buttock flaps, latissimus dorsi myocutaneous flaps, and random skin flaps. The increased capillary blood flow as a result of isoxsuprine treatment was limited only to the arterial portion of the arterial buttock flaps and latissimus dorsi flaps. Therefore, it is concluded that isoxsuprine alone is not effective in augmentation of skin viability in cutaneous and myocutaneous flaps. The pharmacologic action of isoxsuprine on the vasculature in the skin and muscle of flaps was also discussed.     

Hemodynamics and vascular sensitivity to circulating norepinephrine in normal skin and delayed and acute random skin flaps in the pig

Cutaneous circulation in 4 X 10 cm skin samples and delayed and acute random skin flaps constructed on the flanks of castrated Yorkshire pigs (13.3 +/- 0.7 kg; n = 12) were studied during intravenous infusion (0.5 ml per minute) of 5% dextrose solution (vehicle) and 5% dextrose containing norepinephrine (1 microgram/kg per minute). Total and capillary blood flow and A-V shunt flow were measured by the radioactive microsphere technique 6 hours after the raising of 4 X 10 cm single-pedicle acute and delayed random skin flaps using the technique and calculations published previously. Fluorescein dye test was also performed to assess vascular perfusion. It was observed that the capillary blood flow in the single-pedicle delayed skin flaps was similar to that in the normal skin, and the maintenance of this normal skin blood flow was not due to the closing of A-V shunt flow in the delayed skin flaps. Similarly, the significant (p less than 0.01) decrease in capillary blood flow and distal perfusion in the acute skin flaps compared with the delayed skin flaps was not due to the opening of A-V shunts in the acute skin flaps. There was no evidence to indicate that A-V shunt flow per se was the primary factor for the regulation of capillary blood flow in the acute and delayed skin flaps in the pig. Our data seemed to indicate that tissue ischemia in the distal portion of acute skin flaps was likely the result of vasoconstriction of the small random arteries which supplied blood to arterioles and A-V shunts, and locally released neurohumoral substances may play an important role in the pathogenesis of vascular resistance and ischemia in the acute skin flaps.     

Acute local subcutaneous VEGF165 injection for augmentation of skin flap viability: efficacy and mechanism

Distal skin ischemic necrosis is a common complication in skin flap surgery. The pathogenesis of skin flap ischemic necrosis is unclear, and there is no clinical treatment available. Here, we used the 4 x 10 cm rat dorsal skin flap model to test our hypothesis that subcutaneous injection of vascular endothelial growth factor 165 (VEGF165) in skin flaps at the time of surgery is effective in augmentation of skin flap viability, which is associated with an increase in nitric oxide (NO) production, and the mechanism involves 1) an increase in skin flap blood flow in the early stage after surgery and 2) enhanced angiogenesis subsequently to sustain increased skin flap blood flow and viability. We observed that subcutaneous injection of VEGF165 in skin flaps at the time of surgery increased skin flap viability in a dose-dependent manner. Subcutaneous injection of VEGF165 at the dose of 2 microg/flap increased skin flap viability by 28% (P < 0.05; n = 8). Over 80% of this effect was blocked by intramuscular injection of the NO synthase (NOS) inhibitor Nomega-nitro-L-arginine (13 mg/kg) 45 min before surgery (P < 0.05; n = 8). The VEGF165 treatment also increased skin flap blood flow (2.68 +/- 0.63 ml x min(-1) x 100 g(-1)) compared with the control (1.26 +/- 0.10 ml x min(-1) x 100 g(-1); P < 0.05, n = 6) assessed 6 h postoperatively. There was no change in skin flap capillary density at this time point. VEGF165-induced increase in capillary density (32.2 +/- 1.1 capillaries/mm2; P < 0.05, n = 7) compared with control (24.6 +/- 1.4 capillaries/mm2) was seen 7 days postoperatively. There was also evidence to indicate that VEGF165-induced NO production in skin flaps was stimulated by activation of NOS activity followed by upregulation of NOS protein expression. These observations support our hypothesis and for the first time provide an important insight into the mechanism of acute local VEGF165 protein therapy in mitigation of skin flap ischemic necrosis.     

Clinical use of amrinone (a selective phosphodiesterase III inhibitor) in reconstructive surgery.

Amrinone is a selective phosphodiesterase III inhibitor that increases cyclic adenosine monophosphate by preventing its breakdown. It is effective in the treatment of congestive heart failure because of its ability to increase myocardial contractility and vascular smooth muscle relaxation. This study was designed to clarify the potential efficacy of amrinone in plastic surgery by clinically assessing its ability to enhance flap blood flow after reconstructive surgery and relieve intraoperative vasospasm. Its effects were compared with those of prostaglandin E1 and lidocaine, which are widely approved agents for improving the hemodynamics of flaps. In the first clinical study, the effects on flap blood flow after flap transfers were investigated. Twenty-six patients underwent reconstructive surgery with vascularized free or pedicled flaps. Blood flow was measured before and 60 minutes after intravenous infusion of lactated Ringer solution (control), amrinone (10 microg/kg/min), or prostaglandin E1 (10 ng/kg/min) using a laser Doppler flowmeter. In the second study, the effects on relief of vasospasm during operation were evaluated. The blood flow of 28 island flaps was measured by laser Doppler flowmetry immediately after flap elevation and 10 minutes after topical application of saline (control), amrinone (5 mg/ml), or lidocaine (10%) to the pedicle in an attempt to resolve the vasospasm. In both clinical studies, the effects of amrinone were statistically no less than those of prostaglandin E1 and lidocaine. The results show that amrinone positively influences the microcirculatory blood flow of transferred flaps and relieves intraoperative vasospasm in clinical cases. The present study suggests that amrinone could be useful for postoperative and intraoperative care in reconstructive surgery.     

Effect of capsulectomy on the hemodynamics and viability of random-pattern skin flaps raised on expanded skin in the pig

Skin flaps constructed on expanded skin usually include the underlying capsular tissue. It has been hypothesized that capsulectomy may jeopardize the viability of the expanded skin flap. The experiments reported herein were designed to test this hypothesis. Specifically, we studied the hemodynamics and viability of random-pattern skin flaps (8 X 20 cm) raised on delayed bipedicle flaps (group A) and on expanded skin pockets with capsulectomy at the time of flap elevation (group B) or with intact underlying capsular tissue (group C). Each group was randomly assigned to each flank in 16 pigs. Skin pockets were expanded by inflation of subcutaneous silicone tissue expanders with sterile saline (299 +/- 7 ml; X +/- SEM) over a period of 3 weeks. At the end of this period, the bipedicle flaps were constructed. Eight days later, random-pattern skin flaps were raised on bipedicle flaps and skin pockets. The length and area of skin flap viability, judged by the fluorescein dye test performed 1 day postoperatively, were not significantly different (p greater than 0.05) among groups A, B, and C (n = 31 to 32). There also were no significant differences (p greater than 0.05) in total skin capillary blood flow measured 1 day postoperatively (A = 2.6 +/- 0.4, B = 2.4 +/- 0.4, and C = 2.7 +/- 0.6 ml/min per flap; n = 15 to 16) and in skin viability assessed 7 days postoperatively (A = 74 +/- 2, B = 75 +/- 2, and C = 76 +/- 2 percent; n = 16) among delayed skin flaps and skin flaps raised on expanded skin pockets with or without capsulectomy. The results of this flap viability study were confirmed in 5 minipigs in a separate experiment. We conclude that capsulectomy did not have a detrimental effect on the hemodynamics and viability of random-pattern skin flaps raised on expanded skin. Furthermore, we hypothesize that skin flaps raised on expanded skin are similar to delayed skin flaps in that the skin blood flow is optimally augmented; therefore, the capsular tissue does not add significant blood supply to the overlying skin.     

The effects of continuous infusions of prostacyclin-Na (epoprostenol-sodium) on platelet counts, ADP-induced aggregation, and cyclic AMP levels in normal volunteers

Six male volunteers received either 0 (buffer), 2.5 or 5.0 ng/kg/min PGI2 X Na for 72 hrs. Various platelet parameters were monitored for an additional 72 hrs. Each morning, for seven consecutive days, and +1 and +6 hrs after the termination of the infusion, blood was drawn and platelet rich plasma (PRP) was prepared. The PRP was immediately exposed to 100 ng/ml PGI2 X Na, and the subsequent increase in platelet cyclic AMP was measured by radioimmunoassay. Aggregation in response to 2 or 4 microM ADP was measured simultaneously. Three volunteers returned for a second 72 hr infusion of 5.0 ng/kg/min PGI2 X Na. After 72 hrs, the infusion rate was gradually "tapered off" over a 12 hr period at which time the infusion was terminated. The sensitivity of the PRP to ADP-induced aggregation was recorded before, during, and after the "tapering off" regimen. Platelet counts were not altered by any of the infusions. The responsiveness of the platelet adenylate cyclase to exogenous PGI2 X Na was inversely related to the concentration of PGI2 X Na infused. Desensitization occurred and was more severe after 72 hrs of infusion than after either 24 or 48 hrs. For example, after 72 hrs at 5.0 ng/kg, platelets lost approximately 50% of their responsiveness to PGI2. ADP-induced aggregation was not significantly inhibited ex vivo by the infusion of 2.5 ng/kg/min PGI2. During the infusion of 5.0 ng/kg/min PGI2, ADP-induced aggregation was inhibited at 24 and 48 hrs, but by 72 hrs, the platelets began to respond to ADP more like control cells even though the PGI2 X Na infusion was continuing. When the infusion was abruptly terminated a hyperaggregable response (rebound) to exogenous ADP was observed. In subjects where the 5.0 ng/kg/min infusion was gradually "tapered off" over a 12 hr period, there was no evidence of platelet hyperaggregability at the time points studied.     

Prostaglandins in enhanced pressor response in renal prehypertensive rabbits

The role of prostaglandins (PGs) in the pressor response to norepinephrine (NE) was examined in one-kidney, one clip rabbits with renal artery stenosis for 3-day's duration (3-day clipped rabbits) and in sham operated rabbits with one-kidney without renal artery stenosis. An exaggerated pressor response to NE, 800 ng/kg/min, was observed in the 3-day clipped rabbits, and it was abolished by angiotensin II antagonist, [Sar1, Ile8] angiotensin II (AIIA). Treatment with indomethacin, 10 mg/kg, induced hyperresponsiveness to NE in the sham operated rabbits and also produced a further increase in the response in the 3-day clipped rabbits: the enhanced responses with similar levels were not attenuated by AIIA in both groups. A subdepressor dose of PGE2, 800 ng/kg/min, abolished the hyperresponsiveness in the 3-day clipped rabbits, while subdepressor or depressor dose of PGI2, 10 or 20 ng/kg/min did not, but the concurrent infusion of AIIA with PGI2 attenuated it. These results indicate that PGs, in particular PGE2 might be involved in the enhanced pressor response to NE in the 3-day clipped rabbits in addition to the altered renin-angiotensin system.     

Pathogenesis of ischemic necrosis in random-pattern skin flaps induced by long-term low-dose nicotine treatment in the rat

The objectives of the present experiments were to study the effects of long-term low-dose nicotine treatment on skin hemodynamics, viability, and microvascular morphology in 4 x 10 cm dorsally based acute random-pattern skin flaps in the rat. In addition, the reversibility of the nicotine-induced detrimental effects on skin-flap viability following cessation of nicotine treatment also was investigated. Low-dose nicotine (0.6 mg/kg) administered twice daily and subcutaneously for 24 weeks significantly (p less than 0.05) decreased skin-flap capillary blood flow, distal perfusion, and length and area of skin viability compared with the saline-treated control (n = 15). However, these same parameters in rats (n = 15) whose nicotine treatment had been withheld for 2 weeks prior to skin-flap surgery were not significantly different from the control, thus indicating that the detrimental effects of this long-term, low-dose nicotine treatment were reversible. The mean plasma level of nicotine in the nicotine-treated rats was 8.1 +/- 0.4 micrograms/dl and was within the range of plasma nicotine levels reported for human heavy cigarette smokers. Light and electron microscopic studies did not show evidence of histologic damage to the cutaneous microvasculature in acute random-pattern skin flaps and samples of normal (nonoperated) skin in nicotine-treated rats. It is concluded that long-term plasma levels of nicotine similar to those of heavy cigarette smokers are detrimental to the capillary blood flow and viability of random-pattern skin flaps in the rat. These deleterious effects can be avoided if skin flaps are raised 2 weeks after cessation of nicotine treatment. This low-dose nicotine treatment does not cause histologic damage to the microvasculature. Other pathogenic mechanisms of nicotine-induced skin flap ischemia are discussed.     

Effect of a "minimal natriuretic and diuretic" dose of prostaglandin E1 (PGE1) on the intratubular and peritubular pressures in anaesthetized rats

A "minimal natriuretic and diuretic" dose (3.4--4.2 ng/min/kg) of prostaglandin E1 (PGE1) as previously estimated was infused into the aorta in anaesthetized rats. During the PGE1 infusion parameters for renal haemodynamics, Na+ and water excretion, intra- and peritubular pressures were studied ("electronic servo nulling device"). During the solvent period parameters for the infused left kidney did not differ from those on the control side. Diuresis and Na+ excretion were increased significantly due to PGE1 infusion in both series of investigations. Cortical blood flow (radio isotope labelled microsphere technique) and glomerular filtration (inulin clearance) did not change significantly. Oncotic pressure in the afferent arteriole was not affected by PGE1, whereas it was reduced significantly in the efferent arteriole (control, 22.9 +/- 1.7; PGE1, 19.2 +/- 0.9 mmHg). Transit times to the early and late distal tubules were not affected by PGE1. There were no changes in the hydrostatic pressure in the proximal tubule and efferent arteriole, whereas the peritubular capillary hydrostatic pressure was significantly increased (control, 9.6 +/- 0.3; PGE1, 11.2 +/- 0.2 mmHg). The present results indicate that PGE1 is capable of enhancing Na+ and water excretion without affecting RBF and GFR, and peritubular physical factors might play an auxiliary role in this effect.     

Prevention of blockage of partially obstructed coronary arteries with prostacyclin correlates with inhibition of platelet aggregation.

Coronary arteries (circumflex or left anterior descending) of anesthetized dogs were partially obstructed to approximately 5% of the normal lumen size by fitting a plastic cylinder around the vessel. Under these conditions, blood flow in the artery was not maintained but, instead, gradually declined over a few minutes until the vessel was completely blocked. Shaking the plastic obstructor restored blood flow temporarily, however, flow gradually declined again to zero. Sometimes flow was spontaneously restored by immediate increases that occurred at irregular intervals while, on other occasions, blood flow had to be restored by shaking the obstructor every time the rate declined to near zero. Intravenous infusion of prostacyclin (PGI2) at 15 to 150 ng/kg/min reversed and prevented the blockage of the coronary arteries. The efficacy of PGI2 in preventing blockage correlated with inhibition of ADP-induced platelet aggregation in platelet rich plasma prepared from blood samples withdrawn from the dogs during PGI2 infusion. Other coronary vasodilators, nitroglycerin and PGE2, that have no antiaggregatory effects, failed to prevent blockage whereas PGE1 and indomethacin, which do block aggregation, also prevented blockage of the vessels. PGI2 or its precursor, PGH2, dripped topically on the obstructed site prevented the blockage of the artery. This local effect of IGI2 could be obtained with amounts too small to cause systemic inhibition of platelet aggregation. The results show that PGI2 prevents blockage of partially obstructed coronary arteries and this effect correlates with inhibition of platelet aggregation. Furthermore, the data suggest that locally produced PGI2 may have a local antiaggregatory effect without inhibiting platelet aggregation in the general circulation.     

The effects of prostacyclin on glycemia and insulin release in man

Prostacyclin /PGI2/ administered intra-arterially or intravenously to patients with peripheral vascular disease exerted a hyperglycemic effect. In normoglycemic patients receiving PGI2 at a dose of 5 ng/kg/min these effects were barely detectable, but they became unmasked by a rapid glucose injection. In diabetic patients the same PGI1 dose led to distinct elevation in blood glucose. Prostacyclin at a dose of 10 ng/kg/min raised blood glucose levels both at rest and after stimulation with glucose, and opposed effectively hypoglycemic action of tolbutamide in non-diabetic patients. PGI2 repressed glucose-induced insulin release in some normoglycemic patients but in others it either increased it or did not affect it. While hyperglycemic effects are reversible when PGI2 infusion is stopped, and do not interfere with the usual therapeutic administration of prostacyclin for a few days they, nevertheless, might constitute a risk in a patient with poorly controlled diabetes.     

Augmentation of transmidline skin perfusion and viability in transverse rectus abdominis myocutaneous (TRAM) flaps in the pig.

The aim of this experiment was to design a clinically relevant TRAM flap in the pig and to use this flap model to study the effectiveness of preoperative ligation of the dominant vascular pedicle in augmentation of muscle and skin capillary blood flow and skin viability in the TRAM flap. This TRAM flap model was based on the deep inferior epigastric vascular pedicle, with the center of the transverse skin paddle attached to the underlying rectus abdominis muscle at the superior end of the muscle and extending bilaterally from its attached muscle. The transverse skin paddle (8 x 30 cm) included a contralateral and ipsilateral random portion of skin. This flap model was based on the deep inferior epigastric rather than the superior epigastric vascular pedicle because the deep inferior epigastric vascular pedicle is the smaller of the two in the pig and augmentation of its blood supply by ligation of the dominant superior epigastric vascular pedicle resembles more closely the clinical situation. It was observed that ligation of the dominant superior epigastric vascular pedicle 14 days prior to raising the TRAM flap significantly (p less than 0.05; n = 5) increased the total muscle and skin capillary blood flow and skin viability in the transverse skin paddle compared with the sham-operated control (n = 5).(ABSTRACT TRUNCATED AT 250 WORDS)     

Peripheral neovascularization of muscle and musculocutaneous flaps in the pig.

Late loss of free muscle flaps following surgical or accidental trauma to the dominant vascular pedicle has been reported. In this study, time-dependent ligation of the dominant vascular pedicle was undertaken in denervated latissimus dorsi musculocutaneous or muscle-only island flaps in the pig. Muscle flaps were covered with a skin graft, and silicon rubber sheets were inserted between the flaps and their bases to simulate a poorly vascularized bed. Hemodynamic and viability studies were then performed using intravenous fluorescein (skin viability), tetrazolium blue (muscle viability), and radiolabeled 15-micron microspheres (capillary blood flow). Blood flow did not change in acutely raised musculocutaneous flaps (n = 10) but was significantly elevated in acutely raised muscle-only flaps (n = 10), suggesting that the skin paddle may steal blood flow from the underlying muscle in musculocutaneous flaps. Peripheral neovascularization at 1 day to 8 weeks was assessed (n = 30). Viability increased during the first week of revascularization and was not different in musculocutaneous and muscle-only flaps. Revascularization of muscle-only flaps was enhanced compared with musculocutaneous flaps in the 2- to 8-week period.     

Intravenous prostacyclin (PGI2) infusion to 108 patients with ischaemic peripheral vascular disease: phase II-open study.

We recently reported the results of a double-blind trial of PGI2 in 108 patients with ischaemic peripheral vascular disease Stage II according to Fontaine. They were randomly allocated to receive an intravenous infusion of either PGI2 (6 ng/kg/min over 8 hours daily for 5 consecutive days) or placebo and classified as treatment responders or non-responders on the basis of changes in absolute and relative walking times. Patients treated with placebo and those who did not improve in this double blind trial entered an open trial in which they all received infusion of PGI2 (6 ng/kg/min over 8 hours daily for 5 consecutive days). The results of this open trial are reported here. Patients who had been allocated to PGI2 in the blind trial had significantly (p less than 0.01) longer walking times as compared to placebo-treated patients prior to receiving the second (PGI2) infusion. PGI2-infusion caused significant (p less than 0.01) prolongation of walking times in both groups up to the 2nd follow-up month. One month after infusion 52% (23 patients) of the initially placebo-treated patients and 31% (14 patients) of the initially PGI2-treated patients were scored as positive treatment responders (p less than 0.01).     

The effect of PGI2 on canine renal function and hemodynamics.

The effect of prostaglandin I2 (prostacyclin) on renal and intrarenal hemodynamics and function was studied in mongrel dogs to elucidate the role of this novel prostaglandin in renal physiology. Starting at a dose of 10(-8) g/kg/min, PGI2 decreased renal vascular resistance and redistributed the blood flow away from the outer cortex (zone 1) and towards the juxtamedullary cortex (zone 4). At 3 X 10(-8) g/kg/min, the renal vascular resistance decreased even further, but at this dose the mean arterial blood pressure also declined 13% indicating recirculation of this prostaglandin. PGI2 infusion at a vasodilatory dose resulted in natriuresis and kaliuresis. With a decline in filtration fraction, these changes were most likely secondary to the hemodynamic effects of this prostaglandin. Unlike PGE2, PGI2 had no direct effect on free water clearance indicating lack of activity at the collecting duct. PGI2 may be the important renal prostaglandin involved in modulating renal vascular resistance and intrarenal hemodynamics as well as influencing systemic blood pressure.     

Prostacyclin I2 (PGI2) increases left ventricular ejection fraction (LVEF)

In order to evaluate the effect of PGI2 on left ventricular ejection fraction (LVEF) an intravenous infusion in 10 patients (3 males, 7 females; 36 to 63 years) with an impaired LVEF (34.7 +/- 14.8%) was performed. LVEF was determined by means of 99mTc-pertechnetate radionuclide ventriculography. An increase of LVEF to 36.2 +/- 13.5% during administration of PGI2 at a rate of 1 ng/kg/min for 15 min and to 43.8 +/- 15.8% during a rate of 5 ng/kg/min (p less than 0.01) for an additional 15 min was observed. Analyzing the data in more detail in 6 patients, an improvement in LVEF became obvious during the administration of 1 ng/kg/min (108, 109, 116, 118, 121, and 123% of pre-infusion value, respectively). In 5 out of these 6 patients a dose-increment to 5 ng/kg/min further increased LVEF (139, 179, 187, 148, and 128% of pre-infusion value, respectively). In contrast, in the other 4 patients no response of LVEF to PGI2 at a rate of 1 ng/kg/min could be observed. However, in 2 out of these 4 patients LVEF increased during the administration of 5 ng/kg/min (111 and 117% of pre-infusion value). Individual changes in hemodynamic parameters showed no correlation to the improvement seen in LVEF in response to PGI2. It is concluded that PGI2 may exert beneficial effects on LVEF, and might be used in certain clinical conditions, such as before heart transplantation, to achieve a temporary improvement in LVEF.     

Efficacy and mechanism of adenovirus-mediated VEGF-165 gene therapy for augmentation of skin flap viability

Skin ischemic necrosis due to vasospasm and/or insufficient vascularity is the most common complication in the distal portion of the skin flap in reconstructive surgery. This project was designed to test our hypothesis that preoperative subdermal injection of adenoviral vectors encoding genes for vascular endothelial growth factor-165 (Ad.VEGF-165) or endothelial nitric oxide (NO) synthase (Ad.eNOS) effectively augments skin viability in skin flap surgery and that the mechanism of Ad.VEGF-165 gene therapy involves an increase in synthesis/release of the angiogenic and vasodilator factor NO. PBS (0.5 ml) or PBS containing Ad.VEGF-165, Ad.eNOS, or adenovirus (Ad.Null) was injected subdermally into the distal half of a mapped rat dorsal skin flap (4 x 10 cm) 7 days preoperatively, and skin flap viability was assessed 7 days postoperatively. Local subdermal gene therapy with 2 x 10(7)-2 x 10(10) plaque-forming units of VEGF-165 increased skin flap viability compared with PBS- or Ad.Null-injected control (P < 0.05). Subdermal Ad.VEGF-165 and Ad.eNOS gene therapies were equally effective in increasing skin flap viability at 5 x 10(8) plaque-forming units. Subdermal Ad.VEGF-165 therapy was associated with upregulation of eNOS protein expression, Ca2+ -dependent NOS activity, synthesis/release of NO, and increase in capillary density and blood flow in the distal portion of the skin flap. Injection of the NOS inhibitor Nomega-nitro-L-arginine (15 mg/kg im), but not the cyclooxygenase inhibitor indomethacin (5 mg/kg im), 45 min preoperatively completely abolished the increase in skin flap blood flow and viability induced by Ad.VEGF-165 injected subdermally into the mapped skin flap 7 days preoperatively. We have demonstrated for the first time that 1) Ad.VEGF-165 and Ad.eNOS mapped skin flap injected subdermally into the mapped skin flap 7 days preoperatively are equally effective in augmenting viability in the rat dorsal skin flap compared with control, 2) the mechanism of subdermal Ad.VEGF-165 gene therapy in augmenting skin flap viability involves an increase in NO synthesis/release downstream of upregulation of eNOS protein expression and Ca2+ -dependent NOS activity, and 3) the vasodilating effect of NO may predominantly mediate subdermal Ad.VEGF gene therapy in augmenting skin flap blood flow and viability.     

The effect of nifedipine on skin-flap survival

Nifedipine, a calcium-channel blocker, is a peripheral vasodilator and has been shown to increase blood flow to skin. The hypothesis that nifedipine would thereby improve skin-flap viability was tested by comparing the extent of necrosis of long pedicle flaps in control and nifedipine-treated rats. Thirty male Sprague-Dawley rats were randomized to receive either 2.5 mg/kg nifedipine in chocolate PO t.i.d. or plain chocolate according to protocols. Serum nifedipine levels were determined by gas chromatography. Dorsal cephalad-based random vascular pedicle flaps (2 X 6 cm) were elevated, sutured to their beds, and photographed for computer-aided surface area determinations. The extent of distal flap necrosis was expressed as a percentage of the total flap area, and differences were studied by one-way analysis of variance. The differences between the mean percentages of necrosis at 1 and 2 weeks for the groups were not statistically significant. We conclude that nifedipine has no effect on the extent of necrosis of the random skin flap in the rat.     

Augmentation of blood flow in delayed random skin flaps in the pig: effect of length of delay period and angiogenesis

Skin capillary blood flow and angiogenesis were studied by radioactive microsphere and morphometry technique, respectively, in delayed random skin flaps in the pig. Skin flaps were delayed for 2, 3, 4, 6, or 14 days. Blood flow was measured 6 hours after complete raising of acute and delayed random skin flaps on the opposite flanks of the same pig. It was observed that the capillary blood flow increased significantly (p less than 0.05) within 2 days of delay compared to the acute skin flaps. This capillary blood flow further increased by about 100 percent between days 2 and 3, started to plateau after day 3, and remained unchanged between days 4 and 14 of delay. This increase in capillary blood flow was mainly in the distal portion of the delayed skin flaps. There was no indication of an increase in the density of arteries in all delay periods studied. Our observations did not support the hypotheses that the delay phenomenon involves angiogenesis or long-term adaptation to ischemia, as have been hypothesized previously. The possible mechanism of delay is discussed.