Calcium channel blockade in rats with cyclosporine-induced vasoconstriction

Calcium channel blockade has been found to attenuate nephrotoxicity of cyclosporine. However, it is not known whether intrarenal vasoconstriction caused by cyclosporine is totally mediated by vascular smooth muscle calcium influx. To study the protective effects of two calcium blockers on cyclosporine-induced intrarenal vasoconstriction and renal microvascular blood flow, hydronephrotic rat kidneys were suspended in an environmentally controlled tissue bath. Renal microvessel diameters and microvascular blood flow were determined by in vivo videomicroscopy and Doppler velocimetry. Calcium channel blockade was achieved by adding verapamil hydrochloride (5.6 x 10(-5) M) or diltiazem hydrochloride (2.8 x 10(-5) M) to the tissue bath, which respectively resulted in a 15 +/- 2% and 16 +/- 3% interlobular arteriolar dilation, a 13 +/- 3% and 12 +/- 2% afferent arteriolar dilation, and a 60 +/- 8% and 46 +/- 14% increase in interlobular blood flow. When cyclosporine (1.7 x 10(-3) M) was added to the tissue bath, there was a constriction of the interlobular arterioles to 4 +/- 3% below baseline in rats receiving verapamil and 9 +/- 3% below baseline in rats receiving diltiazem. Microvascular blood flow was reduced by the addition of cyclosporine to 3 +/- 4% above original baseline values in the verapamil group and 22 +/- 6% below baseline in the diltiazem group. Afferent arterioles were similarly constricted by cyclosporine. The results indicate that calcium blockade causes preglomerular vasodilation and protects the microvascular blood flow induced by cyclosporine. Since verapamil or diltiazem did not prevent arteriolar constriction as observed when cyclosporine was added, it was concluded that the mechanism of acute cyclosporine-induced vasoconstriction is not solely mediated by vascular smooth muscle calcium influx through potential dependent channels.

Acute cyclosporine-induced renal vasoconstriction is mediated by endothelin-1

BACKGROUND

Cyclosporine causes intrarenal vasoconstriction, which may account for its nephrotoxic side effects. Plasma levels of the vasoconstrictor peptide endothelin-1 are increased after cyclosporine administration, and endothelin-1 has been shown to cause renal vasoconstriction. In this study we used in vivo microscopy to investigate the role of endothelin-1 in cyclosporine-induced vasoconstriction.

METHODS

Hydronephrotic kidneys in decerebrate rats were suspended in an environmentally controlled tissue bath with neurovascular supply intact. Interlobular, afferent, and efferent arteriolar diameters and flow were measured by videomicroscopy and Doppler velocimetry. Cyclosporine was added to the tissue bath, and measurements were repeated for 60 minutes. In study groups endogenous endothelin-1 was blocked by infusion of either specific endothelin antiserum or an endothelin-1 receptor antagonist.

RESULTS

Cyclosporine caused constriction of the interlobular artery by 20% +/- 2% and a corresponding decrease in blood flow by 66% +/- 4%. The afferent and efferent arterioles constricted to a similar degree. This vasoconstriction was entirely prevented by infusion of either the endothelin antiserum or the receptor antagonist. The antagonist reagents alone had no effect on hemodynamic parameters or renal microvessel diameters.

CONCLUSIONS

The acute renal vasoconstriction induced by cyclosporine is mediated by endothelin-1. Endogenous endothelin-1 has little role in maintaining basal vascular tone.

Endothelins mediate intestinal hypoperfusion during bacteremia

We have previously reported that Escherichia coli bacteremia induces hypoperfusion and vasoconstriction of the rat small intestinal microcirculation. However, the mechanisms which mediate these responses are not clearly defined. Because serum levels of endothelins, a family of potent vasoconstrictor peptides, are increased during bacteremia, we postulated that endothelins contribute to intestinal hypoperfusion during infection. Using intravital microscopy, we characterized the effects of topically applied recombinant endothelin-1 on small intestinal arteriolar diameters and blood flow. Dose-dependent vasoconstriction of both large (A1) and small (A3) arterioles and hypoperfusion were observed. To assess whether endothelins contribute to alterations of the intestinal microcirculation during bacteremia, antiserum was used to inhibit endothelins during E. coli bacteremia. Endothelin inhibition resulted in restoration of blood flow and attenuation of vasoconstriction. Our results suggest that endothelins contribute to intestinal hypoperfusion and arteriolar vasoconstriction during bacteremia.

Systemic hemodynamic and microvascular responses in spontaneously hypertensive rats during Escherichia coli bacteremia

Renovascular hypertension profoundly alters skeletal muscle arteriolar responses to sepsis, yet systemic hemodynamics to sepsis are not affected by hypertension. In this study, we hypothesized that microvascular responses of skeletal muscle and systemic hemodynamics are changed during high- and low-cardiac-output Escherichia coli bacteremia in normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). During high-cardiac-output bacteremia, blood pressure and heart rate increased in WKY, but blood pressure decreased in SHR. During low-cardiac-output bacteremia, blood pressure initially decreased in WKY, while in SHR, pressure dropped significantly and remained severely depressed. Heart rate increased by 50% in SHR, but only by 10-15% in WKY during low-cardiac-output bacteremia. Large A1 and A2 arterioles constricted in both WKY and SHR during both phases of bacteremia. Small A3 and A4 arterioles dilated in WKY during bacteremia, but this small arteriole dilation was blunted in SHR. However, nitroprusside, an endothelium-derived relaxing factor (EDRF)-independently acting vasodilator, caused maximal dilation of these small arterioles of SHR. We conclude that there are profound changes and differences in systemic hemodynamics during bacteremia between the normotensive and the genetically hypertensive groups, whereas despite a possibly decreased endothelium-dependent vasodilator responsiveness in small arterioles of SHR during bacteremia, overall blood flow changes in skeletal muscle were similar among the two groups.

Factors affecting renal microvascular blood flow in rat hyperdynamic bacteremia

To determine whether angiotensin II and alpha-adrenergic activity contribute to the mechanism of impaired renal microvascular blood flow during hyperdynamic live Escherichia coli (E. coli) bacteremia, we used in vivo video microscopy in the chronic unilateral hydronephrotic kidney of decerebrate male Sprague-Dawley rats. Intravenous infusion of E. coli caused arteriolar constriction to 83 +/- 4% of baseline (BL) in cortical radial arteries (CRA), 82 +/- 3% of BL in afferent (AFF) arterioles, and decreased flow to 54 +/- 9% of BL. Subsequent local inhibition of renal prostaglandin synthesis with mefenamate increased preglomerular arteriolar constriction to 55 +/- 6% of BL in CRA and 51 +/- 6% of BL in AFF arterioles and decreased renal microvascular blood flow to 26 +/- 8% of BL values in E. coli animals but had no effect on control animals. Subsequent local renal angiotensin II receptor blockade with saralasin acetate increased renal microvascular blood flow in E. coli animals to 64 +/- 9% of BL by dilating CRA to 78 +/- 5% of BL and AFF arterioles to 89 +/- 5% of BL. Phentolamine caused further dilation of CRA to 104 +/- 7% BL and AFF arterioles to 116 +/- 109% and increased flow to 99 +/- 8% of BL. Acetylcholine increased diameters further to 110 +/- 3% of BL in CRA and 136 +/- 12% of BL in AFF arterioles. These data indicate that in our chronic hydronephrotic kidney model during E. coli bacteremia, renal microvascular tone is due to increased angiotensin II and alpha-adrenergic activity and some other, as yet, undefined factor.

Microvascular vasoconstriction and mucosal hypoperfusion of the rat small intestine during bacteremia

Our previous studies have demonstrated that bacteremia induces vasoconstriction and hypoperfusion of the small intestinal microcirculation. The present study used time-transit doppler flowmetry, intravital microscopy, and laser doppler fluximetry to measure superior mesenteric artery (SMA) blood flow, intestinal microvascular blood flow, and mucosal perfusion. The aim of this study was to determine the relative importance of the intestinal macro- and microcirculations in the development of mucosal hypoperfusion. Animals were infused with 5 x 10(8) colony-forming units of Escherichia coli/100 g body weight or saline as control. Bacteremia induced a normotensive, normodynamic state. SMA blood flow was unaffected by bacteremia, but arteriolar vasoconstriction (approximately -30%) and microvascular hypoperfusion (approximately -70%) occurred. Mucosal perfusion decreased by 40% from baseline, and was temporally correlated with microvascular hypoperfusion. From these data, we conclude that the microcirculation has a central role in the development of mucosal hypoperfusion during bacteremia.

Escherichia coli bacteremia exacerbates cyclosporine-induced renal vasoconstriction

The clinical observation that cyclosporine (CSA) nephrotoxicity is particularly severe in patients during and following bacterial infections has recently been made. Transplant recipients develop a marked deterioration of graft function following Escherichia coli bacteremia secondary to urinary tract infection. CSA causes intrarenal vasoconstriction which may account for its nephrotoxicity. We therefore undertook a study using the split hydronephrotic kidney model to investigate the direct in vivo effects of CSA and E. coli bacteremia on the renal microcirculation. Hydronephrotic kidneys in Sprague-Dawley rats were suspended in an environmentally controlled tissue bath. Interlobular arterial (ILA) and afferent (AFF) and efferent (EFF) arteriolar diameters were measured by in vivo videomicroscopy and red cell velocity by Doppler velocimetry. Topical administration of CSA to the kidney in the tissue bath caused a 23 +/- 1% constriction of the ILA and a 67 +/- 5% reduction in blood flow. AFF and EFF arterioles were also constricted by 21 +/- 3 and 16 +/- 2%, respectively. The intravenous infusion of live E. coli was also followed by decreases in ILA diameters and flow (38 +/- 4 and 68 +/- 4%) and AFF diameters (22 +/- 5%) while EFF diameters were unchanged. The infusion of E. coli following addition of CSA to the tissue bath resulted in a dramatically increased constriction of ILA (49 +/- 4%) and AFF (31 +/- 2%) vessels and almost abolished ILA flow (90 +/- 2%). We conclude that in this model, E. coli bacteremia exacerbates CSA-induced preglomerular vasoconstriction and suggests a scientific basis for the severe renal dysfunction noted in transplant recipients during bacterial infection.

In vivo effects of endothelin on the renal microcirculation

Endothelin-1 (ET) is a recently discovered vasoconstrictor peptide which is released by renal vascular endothelial cells in response to a number of pathologic insults including ischemia, endotoxemia, bacteremia, and cyclosporine nephrotoxicity. Because microvascular vasoconstriction is an integral component of the acute renal dysfunction associated with these conditions, this study was undertaken to determine the in vivo effects of ET on the renal microcirculation. We used the split hydronephrotic kidney model in decerebrate Sprague-Dawley rats to study vessel diameter and red cell velocity responses to ET using intravital videomicroscopy and doppler velocimetry. Topical administration of increasing concentrations of ET caused a dose-dependent constriction of interlobular arteries which reached a maximum of 27 +/- 5% at an ET concentration of 10(-8) M. A corresponding decrease of 64 +/- 8% in interlobular arterial blood flow was observed. Afferent and efferent arteriole diameters were reduced by 39 +/- 2% and 27 +/- 5%, respectively. These vascular effects were completely prevented by the systemic preinfusion of anti-endothelin antiserum. Infusion of antiserum alone had no effect on systemic hemodynamics or renal microvascular variables, suggesting that ET has little or no role in maintaining basal vascular tone in the kidney. We conclude that ET is a potent in vivo constrictor of the renal microcirculation and may be involved in mediating pathologic vasoconstriction.

Age-related differences in intestinal microvascular responses to low-flow states in adult and suckling rats

We used in vivo videomicroscopic techniques to compare the intestinal microvascular responses of 8- to 12-wk-old adult rats with those observed in 8- to 12-day-old suckling rats. Changes in intestinal microarteriolar diameters and blood flow were measured during hemorrhage (5 and 10 ml/kg), hypoxia (10% O2 breathing environment), and hypothermia (surface cooling to 34 degrees C and 31 degrees C). Intestinal blood flow (as measured by optical Doppler velocimetry) was decreased by a similar amount in both adult and suckling rats during all three periods of stress. Large arteriolar diameter changes were also similar in adult and suckling rats. In contrast, there were substantial differences in the responses of the small premucosal arterioles. These premucosal arterioles selectively dilated in adult rats, suggesting a redistribution of blood flow toward the mucosa during each of the three periods of stress. These same microvessels failed to dilate in the suckling rats during each of the three periods of stress, suggesting that the intestinal microvasculature in the immature rat lacks vasodilator mechanisms that are active in the adult rat. We propose that altered microvascular control could make the developing intestine prone to mucosal damage during periods of decreased perfusion.

In vivo assessment by videomicroscopy of acute renal microvascular responses to cyclosporin

Nephrotoxicity limits the use of cyclosporin A for immunosuppression after organ transplantation and may be caused by glomerular hypoperfusion. Indirect studies have shown that cyclosporin A increases renal vascular resistance and reduces total renal blood flow. This study used direct in vivo videomicroscopy to define the effects of the drug on the renal microcirculation of the rat. An intravenous infusion of cyclosporin A (20 mg per kg body-weight) caused a 13 per cent acute constriction of the proximal interlobular artery and an associated 29 per cent reduction in preglomerular interlobular arterial blood flow. There was a simultaneous increase in mean arterial blood pressure of 34 per cent caused by cyclosporin A and a 23 per cent increase in systemic vascular resistance. Cyclosporin acutely reduces renal microvascular blood flow by vasoconstriction and affects the central circulation, suggesting that a generalized peripheral vasoconstriction is induced.

Pentoxifylline preserves small-intestine microvascular blood flow during bacteremia

BACKGROUND

Intestinal mucosal ischemia with subsequent mucosal dysfunction has been implicated in the pathogenesis of ongoing sepsis and multiple systems organ failure. We have previously reported vasoconstriction and hypoperfusion in the intestinal microcirculation during sepsis. Efforts to improve microcirculatory blood flow during sepsis may lead to more effective treatment or prevention of multiple systems organ failure. Pentoxifylline improves survival and visceral organ perfusion in experimental sepsis and hemorrhage. The purpose of this study was to determine whether pentoxifylline would improve microvascular blood flow in the small intestine during bacteremia.

METHODS

In vivo videomicroscopy was used to quantitate alterations of the small-intestine microcirculation during Escherichia coli bacteremia in rats pretreated with either intravenous pentoxifylline or saline solution. Systemic hemodynamic and microvascular variables were measured every 15 minutes for 2 hours.

RESULTS

Tachycardia and increased cardiac output developed in bacteremic rats while they remained normotensive. Intestinal vasoconstriction and hypoperfusion occurred in bacteremic rats treated with saline solution. Microvessel diameters and blood flow remained within 5% to 10% of baseline in bacteremic rats pretreated with pentoxifylline. Pentoxifylline in nonbacteremic rats resulted in intestinal vasodilation and increased blood flow.

CONCLUSIONS

Pentoxifylline prevented small-intestine vasoconstriction and preserved microvascular blood flow during hyperdynamic sepsis. Pentoxifylline in nonbacteremic rats increased microvascular blood flow.

Altered endothelial mechanisms blunt skeletal muscle microcirculatory responses to live E. coli sepsis in 1K1C hypertension

While renovascular (1K1C) hypertension significantly attenuates small arteriole dilation to sepsis in skeletal muscle of rats, maximal dilation of these small arterioles is not altered in response to an endothelium-independent vasodilator (nitroprusside). This suggests that 1K1C hypertension modifies a receptor-level mechanism to reduce small arteriole vasodilation during sepsis. To test this hypothesis, we used hydroquinone (HQ) to block an endothelium-derived relaxing factor (EDRF) in skeletal muscle arterioles of sodium pentobarbital (45 mg/kg BW)-anesthetized 1K1C-renovascular hypertensive male Sprague-Dawley rats which were then made septic. We found that responses of large and small arterioles to sepsis were blunted in hypertensive rats and that these responses were unchanged during the presence of HQ. This suggests 1) that blockade of some vasodilator mechanisms does not unmask an enhanced vasoconstrictor influence during sepsis in 1K1C hypertension and 2) that EDRF mechanisms are blunted by 1K1C hypertension. To further test this second idea, we examined the responses of small arterioles to acetylcholine (ACH) in normotensive and renovascular (1K1C) hypertensive rats before and after EDRF blockade. Skeletal muscle small arterioles were essentially not reactive to ACH in the hypertensives and HQ did not change this response. However, some vasodilation in hypertensives occurred under very high ACH concentrations even during the presence of HQ. These data suggest that sepsis-induced small arteriole dilation in skeletal muscle is blunted because endothelium-mediated responses are impaired in renovascular hypertension. Nevertheless, EDRF-independent mechanisms appear to be left intact during this form of hypertension.

Intestinal blood flow is restored with glutamine or glucose suffusion after hemorrhage

Intestinal blood flow has been shown to be impaired after resuscitated hemorrhagic shock. Enteral feeding has been proposed as an adjunct for preserving mucosal integrity and decreasing translocation-related morbidities during stress. The purpose of this study was to determine if an ileal mucosal suffusion with an isotonic glucose or glutamine solution begun after resuscitation would prevent development of this blood flow impairment. The distal ileum of anesthetized Sprague-Dawley rats was prepared for in vivo videomicroscopy. Animals were bled to 50% of baseline blood pressure for 60 min and then resuscitated with their shed blood and an equal volume of lactated Ringer's. After resuscitation was complete, the mucosa was suffused with isotonic glucose, glutamine, or saline (control). Resuscitation restored cardiac output and mean arterial pressure to baseline in all groups; however, first-order arteriolar blood flow remained 50% below baseline in the saline group. Glucose-treated animals demonstrated a 34% increase over baseline in first-order arteriolar blood flow 120 min after resuscitation due to submucosal and previllus arteriolar dilation. This effect became evident 30 min after initiating the suffusion, suggesting an effect mediated via locally generated vasodilators. Glutamine suffusion attenuated the flow impairment by dilation of previllus arterioles but to a lesser degree than that observed in glucose-treated animals. These data demonstrate that mucosal suffusion with an isotonic glucose solution overrides the residual effects of hemorrhagic shock on the intestinal microcirculation and suggest a mechanism for preserving mucosal integrity with the addition of glutamine to standard enteral formulations.

The Association for Academic Surgery: what a concept!

I hope that I have neither bored you nor spoken of things that anyone could question or take as offensive. My simple intent was to relate what I truly believe. The discipline of surgery is indeed a noble profession. The portion of this profession that we identify as academic surgery represents a most prestigious and advantageous vocation. It places us in a position to aid our fellow man in a time of true need and vulnerability, to satisfy our intellectual curiosity, and to be good stewards of our time and talents. But, most of all, it gives us each and every day a sense of purpose, accomplishment, and fulfillment. I believe the Association for Academic Surgery represents a concept that helps each of us attain these goals. It has for me. During this past year, it has been both an honor and an enjoyment to be your President. For that I am most grateful. Thank you.

EDRF as a possible mediator of sepsis-induced arteriolar dilation in skeletal muscle

Vascular endothelial cells influence microvessel diameters in vivo and in vitro and participate in host-defense mechanisms during sepsis. We examined whether small arteriole dilation in skeletal muscle during high cardiac output bacteremia (HOB) and low cardiac output live Escherichia coli sepsis (LOS) is mediated by an endothelium-derived relaxing factor (EDRF). Local chemical blockade of EDRF by hydroquinone (HQ) substantially blunted acetylcholine-induced dilation of small arterioles. HQ also prevented large arteriole (55-135 microns) constriction and small arteriole (6-22 microns) dilation in the cremaster muscle of rats during HOB. In LOS, small arteriole dilation was also prevented by HQ but only during the early period when blood pressure was unchanged from baseline. HQ did not alter large arteriole constriction during LOS. We conclude that small arteriole vasodilation in skeletal muscle is mediated at least in part by EDRF during bacteremia. Because EDRF cannot mediate large arteriole constriction and because HQ blunted large arteriole constriction during HOB, we now suspect that HQ also interferes at least in part with some large arteriole vasoconstrictor mechanism, possibly leukotrienes or an endothelium-derived constricting factor, which mediates large arteriole constriction during HOB. Our data also suggest that large arteriole constriction during LOS is partly mediated by factors that are unaffected by HQ. The endothelium appears to play an important role in the microcirculatory responses of skeletal muscle to live E. coli sepsis through more than one mechanism.

Superior results with combined kidney-pancreas transplants

From February of 1987 to February of 1991 the authors performed 23 pancreas transplants for Type I diabetes mellitus. Eight of the pancreas transplants were in patients who had a previous kidney transplant, 14 were simultaneous kidney and pancreas transplants, and 1 was in a pre-uremic diabetic. Two patients have been retransplanted after losing first grafts. All pancreata were retrieved from heart-beating cadaver donors. Pancreata were transplanted into the iliac fossa of the recipient using the iliac artery and vein as arterial inflow and venous outflow, respectively. Drainage of the pancreatic ductal system was accomplished by anastomosing either a patch or segment of duodenum surrounding the ampulla of Vater to the urinary bladder. All pancreata functioned initially with no patient requiring insulin 6 hours after surgery. Two grafts were lost early due to thrombosis of the venous drainage of the transplant; 4 grafts were lost to acute rejection; 3 were lost to chronic rejection; and 1 patient died with a functioning pancreas. One-year graft survival for all pancreatic grafts is 62 per cent. One-year patient survival is 96 per cent. One-year pancreatic graft and patient survival for the 14 combined kidney-pancreas transplants is 88 per cent and 100 per cent, respectively. Two kidneys transplanted with pancreata also were lost to acute rejection. Pancreas transplantation has proven to be a viable treatment alternative for selected patients with Type I diabetes mellitus. Long-term results are best when pancreas transplantation is done in combination with renal transplantation.

Kentucky's first liver transplant program

Forty-nine patients have been referred to our institution for evaluation of orthotopic liver transplantation since our program started in 1990. Fourteen patients have been excluded for medical or psychosocial reasons. Eleven were accepted for future transplantations and are reevaluated every 3 months. Eight patients died while waiting for a suitable donor. Sixteen patients have undergone transplantations. One patient underwent transplantation a second time for refractory rejection of the first allograft. Five patients have died after liver transplantation. Eleven recipients are alive and well. Nine of the 11 have returned to normal activity.

There is an answer to the shortage of organ donors

From a retrospective review of 32,562 deaths that occurred in 1988 in the service area of Kentucky Organ Donor Affiliates, an area with a population of 3.4 million, 173 potential solid organ donors were identified for a rate of 50.8 donors per million population base. There were only 38 actual solid organ donors from this potential pool. The physician failed to recognize the potential for donation in 29 instances and in 92, the family refused consent for donation. In the second phase of the study, we analyzed 155 consecutive medically suitable organ donor referrals for one year. A specific focus on the process and timing of the request for donation was made in this review. In 143 of these instances (92 per cent), a clear temporal separation of the explanation of death or the certainty of family acceptance of death before the request for donation yielded a donor success in 53 of 82 instances. In contrast, only 11 of 61 instances resulted in a consent when the discussion of death and donation were combined into one discussion with the family (p less than 0.05). From this study, there seemed to be adequate numbers of organs available to provide for the current pool of recipients within the state of Kentucky. Educational assistance and an ongoing individual patient review of each death improved the donor rate during the time frame of this study. It is essential to allow a temporal separation between the explanation of death and the request for organ donation to maximize actual organ donation.

The role of intrarenal prostaglandins and angiotensin II in acute cyclosporine-induced vasoconstriction

Cyclosporine causes intrarenal vasoconstriction, which may account for its nephrotoxic effects. In this study we investigated the role of endogenous prostaglandins and angiotensin II in cyclosporine-induced intrarenal vasoconstriction. Split hydronephrotic kidneys in decerebrate rats (n = 16) were suspended in an environmentally controlled tissue bath. Interlobular, afferent, and efferent arteriolar diameters and red blood cell velocity were measured by in vivo video-microscopy and Doppler velocimetry. After topical application of cyclosporine to the kidney in the tissue bath, a 12% +/- 2% constriction of the interlobular and a 28% +/- 5% reduction in interlobular blood flow occurred. The afferent and efferent arterioles also constricted by 13% +/- 2% and 10% +/- 3%, respectively. Prostaglandin inhibition with mefenemate augmented this vasoconstriction (16% +/- 2% at interlobular and 21% +/- 4% at afferent arterioles) and reduction in interlobular blood flow (38% +/- 8%) below baseline values. Mefenemate alone resulted in a 35% +/- 5% reduction in interlobular blood flow, which was not further augmented by cyclosporine. In contrast, local competitive angiotensin II-receptor inhibition with saralasin maintained blood flow after cyclosporine and prevented intrarenal vasoconstriction by cyclosporine. This suggests that prostaglandins protect against intrarenal vasoconstriction and that acute cyclosporine-induced vasoconstriction is mediated through angiotensin II receptors.

Pentoxifylline restores intestinal microvascular blood flow during resuscitated hemorrhagic shock

We studied the intestinal microvascular blood flow responses to hemorrhage and resuscitation with pentoxifylline by in vivo video microscopy. Male Sprague-Dawley rats were hemorrhaged to 50% of baseline mean arterial pressure for 45 minutes and then blindly randomized to receive pentoxifylline (25 mg/kg bolus + 0.2 mg/kg/minute) or an equivalent volume of saline plus return of shed blood and an additional bled volume of Ringer's lactate solution. Hemorrhage caused intestinal microvascular blood flow to decrease to 10% to 15% of baseline values. In the control group, resuscitation restored cardiac output and mean arterial pressure to baseline values, but intestinal microvascular blood flow remained at 30% of baseline values. In contrast, addition of pentoxifylline to the resuscitation regimen resulted in an immediate hyperemic response with an increase in intestinal microvascular blood flow to significantly greater than baseline values followed by return to baseline. Arteriolar dilation was not responsible for the improvement in flow implicating improved flow dynamics between erythrocytes, granulocytes, and vascular endothelia within the microcirculation. We conclude that addition of pentoxifylline to resuscitation from hemorrhagic shock restores intestinal microvascular blood flow.

The influence of the cyclosporine vehicle, cremophor EL, on renal microvascular blood flow in the rat

Cyclosporine nephrotoxicity may be due to glomerular hypoperfusion. Previous experimental and clinical studies have demonstrated a decrease in renal blood flow and an increase in renal vascular resistance. Cremophor EL, which is the vehicle in which CsA is dissolved, is thought to be a factor involved in intrarenal arteriolar vasoconstriction. To determine the relative contributions of the vehicle and CsA to intrarenal arteriolar vasoconstriction, we used in vivo videomicroscopy and Doppler velocimetry to measure changes in renal microvascular blood flow in the rat. A 5-min intravenous infusion of 20 mg/kg of CsA resulted in a 17% mean reduction (P less than 0.05) in the diameter of preglomerular interlobular arterioles and an associated 60% reduction (P less than 0.05) in microvascular blood flow by 15 min. Cremophor EL/ethanol equivalent caused less vasoconstriction (up to 10%) but resulted in a 42% mean decrease (P less than 0.05) in microvascular blood flow, probably secondary to a 38% mean decrease (P less than 0.05) in cardiac output and 13% decrease in arterial pressure. We conclude that cremophor EL does contribute to in vivo reduction of preglomerular microvascular blood flow in the rat. This may be particularly important when using this intravenous preparation in the study of CsA nephrotoxicity.

Pentoxifylline but not saralasin restores hepatic blood flow after resuscitation from hemorrhagic shock

After determining that hepatic blood flow remains impaired after resuscitation from hemorrhagic shock, we used the angiotensin II receptor antagonist saralasin and pentoxifylline to investigate their respective effects on hepatic blood flow responses after resuscitation from hemorrhagic shock. Rats were bled to 50% of baseline blood pressure for 60 min and resuscitated with shed blood and an equal volume of lactated Ringer's solution. Saralasin [10 micrograms/kg per min (n = 6)], pentoxifylline [25 mg/kg bolus and 12.5 mg/kg per hr (n = 7)], or saline (n = 11) were started with the onset of resuscitation. Total hepatic blood flow measured by ultrasonic transit time flow meter, effective nutrient hepatic blood flow measured by galactose clearance, mean arterial pressure, and cardiac output were recorded at 15-min intervals for 2 hr after resuscitation. Hemorrhage decreased cardiac output 57% below baseline and decreased total hepatic blood flow 64% below baseline. Resuscitation restored cardiac output to baseline levels in all three groups. Despite restoration of cardiac output, total hepatic and effective hepatic blood flow remained significantly below baseline in the saline control and saralasin groups but was restored to baseline levels in the pentoxifylline group. These data indicate that angiotensin II does not contribute significantly to the hepatic blood flow impairment after resuscitation from hemorrhagic shock. Improvement in flow with pentoxifylline implies that hemorrhage and resuscitation impair hepatic microvascular hemorrheology and that addition of pentoxifylline to standard resuscitation corrects the impairment.

Prostaglandins mediate the compensatory responses to hemorrhage in the small intestine of the rat

We examined the effect of fixed-volume hemorrhage (10 ml/kg) on microvascular diameters and blood flow in the small intestine of the rat using in vivo videomicroscopic techniques. We found that hemorrhage in the absence of a potent cyclooxygenase inhibitor results in a transient decrease in intestinal blood flow and a preferential redistribution of intramural blood flow toward the mucosa because of a localized vasodilator response of the premucosal microvessels. In the presence of the selective cyclooxygenase inhibitor, mefenamic acid, the decrease in intestinal blood flow was more substantial and prolonged, and the localized vasodilator response of the premucosal microvasculature was abolished. Our results suggest that vasodilator prostaglandins contribute to the compensatory response of the intestine to hemorrhage and are responsible for the shunting of blood toward the mucosa during hemorrhagic hypotension.

Thigh bleeding time as a valid indicator of hemostatic competency during surgical treatment of patients with advanced renal disease

We compared the usefulness of the modified Ivy bleeding time performed in the forearm (arm bleeding time) with that performed in the thigh (thigh bleeding time) as an indicator of hemostatic competence during surgical treatment in 16 patients with chronic renal failure. In 22 normal adults, the arm bleeding time (mean plus or minus standard deviation, 6.6 +/- 1.4 minutes) was significantly longer than the value in the thigh (mean plus or minus standard deviation, 4.1 +/- 1.3 minutes) (p less than 0.001), and there was no correlation between arm and thigh bleeding time. Preoperatively, the arm bleeding time in patients with renal disease was markedly prolonged (greater than 20 minutes) in 15 patients and slightly prolonged in one patient. There was no abnormal perioperative bleeding in 13 patients whose preoperative thigh bleeding time was seven minutes or less. Prolonged and excessive perioperative bleeding was observed in three patients whose thigh bleeding time was 8.0, 9.5 and 26.5 minutes. These findings suggest that thigh bleeding time is a better indicator of competence of primary hemostasis during the operation than the arm bleeding time in patients with advanced renal failure.

Absorptive hyperemia restores intestinal blood flow during Escherichia coli sepsis in the rat

Enteral nutritional support has been found to result in better maintenance of mucosal integrity during stress than parenterally administered nutritional support. In our experiments, we employed in vivo microvascular techniques to examine the effect of mucosally applied glucose on intestinal microvascular blood flow during hyperdynamic live Escherichia coli bacteremia in the rat. We observed a significant decrease in intestinal microvascular blood flow during bacteremia when the mucosa was suffused with a nonglucose solution. Blood flow was rapidly restored to above-baseline values after glucose was added. The restoration of blood flow resulted from dilation of arterioles at all branch orders and was associated with dilation of premucosal arterioles to above-baseline diameters. Our results show that glucose-induced absorptive hyperemia restores intestinal blood flow during live E coli bacteremia. Restoration of intestinal microvascular blood flow may be a contributing factor to the improved maintenance of mucosal integrity associated with enteral feeding.