Persistent vascular congestion in male spontaneously hypertensive rats contributes to delayed recovery of renal function following ischemia-reperfusion compared to females

Transmission of high arterial pressure into renal microvessels during venous-clamping augments ischaemia/reperfusion-induced acute kidney injury in anaesthetized rats

AIM

In two recent studies, we observed that a 30-min renal vein clamping caused formation of interstitial haemorrhagic congestion in ischaemic and ischaemic/reperfused kidney along with the development of severer acute kidney injury (AKI) than renal artery or pedicle clamping. It was suggested that the transmission of high arterial pressure into renal microvessels during vein occlusion probably causes the occurrence of interstitial haemorrhagic congestion that augments AKI. The present investigation aimed to evaluate this suggestion by reducing renal perfusion pressure (RPP) during renal venous occlusion.

METHODS

Anaesthetized male Sprague-Dawley rats were divided into three groups (n = 8), which underwent a 2-h reperfusion period following 30-min bilateral renal venous clamping along with reduced RPP (VIR-rRPP group) or without reduced RPP (VIR group) and an equivalent period after sham-operation (Sham group).

RESULTS

The VIR-rRPP group compared with VIR group had lower levels of kidney malondialdehyde and tissue damages as epithelial injuries of proximal tubule and thick ascending limb, vascular congestion, intratubular cast and oedema, along with the less reductions in renal blood flow, creatinine clearance, Na+ -reabsorption, K+ and urea excretion, urine osmolality and free-water reabsorption. Importantly, the formation of intensive interstitial haemorrhagic congestion in the VIR group was not observed in the VIR-rRPP group.

CONCLUSION

These results indicate that the transmission of high arterial pressure into renal microvessels during venous occlusion leads to rupturing of their walls and the formation of interstitial haemorrhagic congestion, which has an augmenting impact on ischaemia/reperfusion-induced renal structural damages and haemodynamic, excretory and urine-concentrating dysfunctions.

Pathophysiology of Red Blood Cell Trapping in Ischemic Acute Kidney Injury

Red blood cell (RBC) trapping describes the accumulation of RBCs in the microvasculature of the kidney outer medulla that occurs following ischemic acute kidney injury (AKI). Despite its prominence in human kidneys following AKI, as well as evidence from experimental models demonstrating that the severity of RBC trapping is directly correlated with renal recovery, to date, RBC trapping has not been a primary focus in understanding the pathogenesis of ischemic kidney injury. New evidence from rodent models suggests that RBC trapping is responsible for much of the tubular injury occurring in the initial hours after kidney reperfusion from ischemia. This early injury appears to result from RBC cytotoxicity and closely reflects the injury profile observed in human kidneys, including sloughing of the medullary tubules and the formation of heme casts in the distal tubules. In this review, we discuss what is currently known about RBC trapping. We conclude that RBC trapping is likely avoidable. The primary causes of RBC trapping are thought to include rheologic alterations, blood coagulation, tubular cell swelling, and increased vascular permeability; however, new data indicate that a mismatch in blood flow between the cortex and medulla where medullary perfusion is maintained during cortical ischemia is also likely critical. The mechanism(s) by which RBC trapping contributes to renal functional decline require more investigation. We propose a renewed focus on the mechanisms mediating RBC trapping, and RBC trapping-associated injury is likely to provide important knowledge for improving AKI outcomes. © 2024 American Physiological Society. Compr Physiol 14:5325-5343, 2024.

Sustained activation of 12/15 lipoxygenase (12/15 LOX) contributes to impaired renal recovery post ischemic injury in male SHR compared to females

BACKGROUND

Acute kidney injury (AKI) due to ischemia-reperfusion (IR) is a serious and frequent complication in clinical settings, and mortality rates remain high. There are well established sex differences in renal IR, with males exhibiting greater injury following an ischemic insult compared to females. We recently reported that males have impaired renal recovery from ischemic injury vs. females. However, the mechanisms mediating sex differences in renal recovery from IR injury remain poorly understood. Elevated 12/15 lipoxygenase (LOX) activity has been reported to contribute to the progression of numerous kidney diseases. The goal of the current study was to test the hypothesis that enhanced activation of 12/15 LOX contributes to impaired recovery post-IR in males vs. females.

METHODS

13-week-old male and female spontaneously hypertensive rats (SHR) were randomized to sham or 30-minute warm bilateral IR surgery. Additional male and female SHR were randomized to treatment with vehicle or the specific 12/15 LOX inhibitor ML355 1 h prior to sham/IR surgery, and every other day following up to 7-days post-IR. Blood was collected from all rats 1-and 7-days post-IR. Kidneys were harvested 7-days post-IR and processed for biochemical, histological, and Western blot analysis. 12/15 LOX metabolites 12 and 15 HETE were measured in kidney samples by liquid chromatography-mass spectrometry (LC/MS).

RESULTS

Male SHR exhibited delayed recovery of renal function post-IR vs. male sham and female IR rats. Delayed recovery in males was associated with activation of renal 12/15 LOX, increased renal 12-HETE, enhanced endoplasmic reticulum (ER) stress, lipid peroxidation, renal cell death and inflammation compared to females 7-days post-IR. Treatment of male SHR with ML355 lowered levels of 12-HETE and resulted in reduced renal lipid peroxidation, ER stress, tubular cell death and inflammation 7-days post-IR with enhanced recovery of renal function compared to vehicle-treated IR male rats. ML355 treatment did not alter IR-induced increases in plasma creatinine in females, however, tubular injury and cell death were attenuated in ML355 treated females compared to vehicle-treated rats 7 days post-IR.

CONCLUSION

Our data demonstrate that sustained activation 12/15 LOX contributes to impaired renal recovery post ischemic injury in male and female SHR, although males are more susceptible on this mechanism than females.

Perinatal intermittent hypoxia increases early susceptibility to ANG II-induced hypertension in adult male but not in female Sprague-Dawley rats

Prenatal, perinatal, and adulthood exposure to chronic intermittent hypoxia (IH) increases blood pressure in rodents. Males exposed to chronic IH have higher blood pressure versus females. However, it is unknown if this same-sex difference exists with acute perinatal IH. We tested the hypothesis that acute perinatal IH increases baseline blood pressure and enhances sensitivity to angiotensin II (ANG II)-induced hypertension in male Sprague-Dawley rats. Male and female pups were randomized to control (room air) or IH (10 min of ∼10% O2 for 3 times/day) for the first 8 days of life. IH decreased oxygen saturation, as confirmed via a pulse oximeter. Pups were weaned at postnatal day 21. Blood pressure was measured via telemetry beginning at 14 wk of age and analyzed separately into light and dark phases to assess circadian rhythm. Osmotic minipumps to deliver ANG II were implanted at 15 wk of age. Perinatal IH exposure did not alter baseline blood pressure. One week of ANG II treatment increased blood pressure in light and dark periods in males exposed to IH versus control; there was no effect in females. Blood pressure among the groups was comparable following 2 wk of ANG II infusion. Perinatal IH did not change the circadian rhythm. Following ANG II treatment, indexes of renal injury were measured. Perinatal IH did not alter kidney size, structure, nephron number, or creatinine clearance. These data indicate that acute perinatal IH enhances early ANG II-induced hypertension in males, independent of nephron loss or decreases in body weight or kidney function.NEW & NOTEWORTHY The impact of acute intermittent hypoxia (IH) in early life on blood pressure in adulthood is unknown. This study used a new model exposing female and male rat pups to acute IH in the first 8 days of life, without exposing the dam. Although baseline blood pressure was not altered in adulthood, IH increased susceptibility to angiotensin II hypertension only in males, supporting increased susceptibility of males exposed to IH to a second cardiovascular stressor.

The effect of intraurethral heparin on inflammation and spongiofibrosis in a rat model of experimentally induced urethral trauma

AIM

To determine the effect of heparin administered during the early post urethral trauma period on inflammation and spongiofibrosis in rats.

MATERIALS AND METHODS

The study included 24 male rats that were randomized into 3 groups of 8 each. The urethra was traumatized using a 24-G needle sheath in all rats. Group 1 (control group) received intraurethral saline 0.9% injected b.i.d. for 27 days, group 2 received intraurethral Na-heparin (liquemine-Roche) 1500 IU kg^-1 injected b.i.d. for 27 days, and group 3 received intraurethral Na-heparin 1500 IU kg^-1 injected b.i.d and saline 0.9% s.i.d. for 27 days. On day 28 the rats' penises were degloved and penectomy was performed. Inflammation, spongiofibrosis, and congestion in the urethra were investigated in each group.

RESULTS

A statistically significant difference was found between the three groups (control, heparin, and heparin + saline) in the histopathological status of spongiofibrosis, inflammation, and congestion, respectively (P = 0.0001, P = 0.002, P = 0.0001). Severe spongiofibrosis was observed in six (75%) of the rats in group 1 (control group), whereas severe spongiofibrosis was not observed in group 2 (heparin) or group 3 (heparin + saline).

CONCLUSION

We observed that intraurethral Na-heparin 1500 IU kg^-1 injectioned during the early posturethral trauma period in rats significantly decreased inflammation, spongiofibrosis, and congestion.