The effect of AVP‐V1 receptor stimulation on local GFR in the rat kidney

Aim: Arginine vasopressin (AVP) might influence urinary concentration ability by altering the intrarenal distribution of glomerular filtration rate (GFR). Methods: To study this possibility we have measured the intracortical distribution of GFR following acute AVP‐V₁ receptor stimulation in anaesthetized female Sprague–Dawley (SPD) rats during euvolemia and water diuresis by the aprotinin method, allowing two consecutive measurements of zonal GFR in the same kidney. Results: Acute i.v. bolus injection of 50 ng V₁ receptor agonist ([Phe², Ile³, Orn⁸]‐vasopressin) followed by a continuous infusion of 5 ng min^?1 in euvolemic rats reduced GFR by 25% in outer cortex (OC), 20% in middle cortex (MC) and 19% in inner cortex (IC) relative to vehicle infusion (all P < 0.05). In water diuretic rats V₁ receptor agonist reduced GFR by 22% in OC, 10% in MC and 11% in IC relative to vehicle infusion (P < 0.05). GFR decreased slightly more in OC than in MC and IC in both euvolemic and water diuretic rats (P < 0.05) indicating a distribution of GFR towards MC and IC. Acute infusion of the selective non‐peptide V₁ receptor antagonist OPC‐21268 in euvolemic rats reduced GFR by 14% in OC, 13% in MC and 11% in IC relative to vehicle infusion (P < 0.05), with no significant difference between the layers. Conclusions: The change in distribution of GFR not only between OC and IC, but also between OC and MC suggests that the afferent/efferent arterioles and not the medullary vasa recta is the main site of resistance change. We conclude that acute i.v. infusion of V₁ receptor agonist in high doses reduces GFR more in superficial than in deep cortex in both euvolemic and water diuretic rats and that this may be of some importance for water conservation, adding to the V₂‐ receptor effect on water permeability of the collecting ducts.     

Tubular absorption of filtered cystatin-C in the rat kidney

As shown in previous studies, the two basic proteins aprotinin (Ap, 6.5 kDa) and cystatin (Cy, 13.3 kDa) can be used to estimate whole kidney glomerular filtration rate by measuring the renal cortical uptake relative to plasma concentration after i.v. injection. Local uptake of Ap can also be used to estimate local filtration rate, and the present experiments were undertaken to examine whether Cy would give a similar uptake pattern. Ap and Cy were labelled with 131I and 125I, respectively, and injected as an i.v. bolus. Frequent blood samples provided information on the filtered load. Five to 20 min after injection the kidney was clamped, frozen, and five tissue samples of 5-10 mg each were cut out from outer (OC), middle (MC) and inner cortex (IC) to be weighed and assessed for radioactivity. Five minute clearance ratios, Cy:Ap, were 1.36 +/- 0.04, 1.27 +/- 0.03 and 1.19 +/- 0.04 in OC, MC and IC, respectively. The higher Cy clearance was expected from a higher glomerular filtrate:plasma ratio of the less basic Cy (Donnan distribution). However, this does not explain the increase of Cy:Ap clearances going from IC to the OC. A surplus of extracellular uptake of Cy in superficial layers was excluded, leading to the following interpretation. In all cortical layers the proximal convoluted tubule, i.e. the protein uptake segment, is located more superficially than its parent glomerulus. A longer uptake segment for Cy than for Ap will therefore lead to a relative greater transfer of filtered Cy from IC to MC, and from MC to OC. Anatomical studies on single nephrons presented in another article lend strong support to this interpretation.     

Metastasis-associated protein S100A4 induces a network of inflammatory cytokines that activate stromal cells to acquire pro-tumorigenic properties

Tumor cells have the ability to exploit stromal cells to facilitate metastasis. By using malignant melanoma as a model, we show that the stroma adjacent to metastatic lesions is enriched in the known metastasis-promoting protein S100A4. S100A4 stimulates cancer cells to secrete paracrine factors, such as inflammatory cytokines IL8, CCL2 and SAA, which activate stromal cells (endothelial cells and monocytes) so that they acquire tumor-supportive properties. Our data establishes S100A4 as an inducer of a cytokine network enabling tumor cells to engage angiogenic and inflammatory stromal cells, which might contribute to pro-metastatic activity of S100A4.     

Isolation of lymph shows dysregulation of STAT3 and CREB pathways in the spleen and liver during leukemia development in a rat model

Background and aims

Acute myeloid leukemia (AML) is a heterogeneous malignant condition characterized by massive infiltration of poorly differentiated white blood cells in the blood stream, bone marrow, and extramedullary sites. During leukemic development, hepatosplenomegaly is expected to occur because large blood volumes are continuously filtered through these organs. We asked whether infiltration of leukemic blasts initiated a response that could be detected in the interstitial fluid phase of the spleen and liver.

Material and Methods

We used a rat model known to mimic human AML in growth characteristics and behavior. By cannulating efferent lymphatic vessels from the spleen and liver, we were able to monitor the response of the microenvironment during AML development.

Results and Discussion

Flow cytometric analysis of lymphocytes showed increased STAT3 and CREB signaling in spleen and depressed signaling in liver, and proteins related to these pathways were identified with a different profile in lymph and plasma in AML compared with control. Additionally, several proteins were differently regulated in the microenvironment of spleen and liver in AML when compared with control.

Conclusion

Interstitial fluid, and its surrogate efferent lymph, can be used to provide unique information about responses in AML-infiltered organs and substances released to the general circulation during leukemia development.     

Brainstem lesion with coma for five years following manipulation of the cervical spine

Summary A woman, aged 38, lost consciousness immediately after manipulation of the cervical spine and remained in coma for nearly 5 years in a combined decorticate and decerebrate state. Cerebral angiography revealed impaired circulation in the vertebrobasilar system. The EEG initially showed generalized cerebral dysrhythmia but tended, over the years, to become more normal with desynchronized fast activity of low voltage. Neuropathological examination postmortem revealed a large cystic lesion in the pressure equalization area of the carotid and basilar circulation in the upper pons, mesencephalon, posterior hypothalamus and basal thalamus.No definite stenosis or occlusion was seen in the cerebral vessels on angiography or at the postmortem examination. The mechanism of the lesion is considered to have been temporary interference with the blood flow in the vertebrobasilar system during manipulation of the cervical spine sufficient to cause ischemia and subsequent infarction of the brainstem.The pathogenesis of vascular lesions of the brainstem following manipulation of the cervical spine is discussed briefly.

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Zusammenfassung Bericht über einen tödlichen Fall von Hirnstammläsion im Anschluß an Manipulationen der Halswirbelsäule bei einer 38jährigen Frau. Die Patientin verlor unmittelbar nach der Manipulation das Bewußtsein und blieb in einem Koma, welches sowohl Charakteristika der Dekortikation wie der Dezerebration aufwies während annähernd 5 Jahren. Angiographisch konnten Hinweise für eine gestörte Zirkulation im vertebrobasilären Gebiete gewonnen werden. Das EEG zeigte eine generalisierte Dysrhythmie, aber wurde im Laufe der Jahre normaler mit desynchronisiert rascher Aktivität von niedriger Spannung. Bei der Autopsie zeigte sich neuropathologisch eine große Zyste, welche im Endstromgebiet an der Kontaktstelle von Carotis und Basilariszirkulation in der cranialen Pons, im Mesencephalon, im hinteren Hypothalamus und im basalen Thalamus lag.Es wurden keine eindeutigen Stenosen oder Verschlüsse in den cerebralen Gefäßen bei der Arteriographie und bei der Autopsie nachgewiesen. Es wird angenommen, daß die Läsion durch eine vorübergehende Beeinträchtigung des Blutflusses im vertebrobasilären System während der Manipulation der Halswirbelsäule entstand, wobei dies genügte, um eine Ischämie mit anschließendem Hirnstamminfarkt zu verursachen.Es wird kurz auf die Pathogenese bei vaskulären Hirnstammläsionen nach Manipulation der Halswirbelsäule eingegangen.

     

Interstitial exclusion of albumin in rabbit lung during development of pulmonary oedema

The modifications of the macromolecular sieving properties of the pulmonary extracellular tissue matrix were studied in adult anaesthetized rabbits ( n = 10) exposed to increased tissue hydration. Exclusion of albumin from the perivascular pulmonary interstitial space was determined by using the continuous infusion method coupled with direct sampling of interstitial fluid performed through the wick technique. The rabbits underwent an intravenous infusion of saline amounting to 10 ( n = 5) or 20 % ( n = 5) body weight. Extracellular albumin distribution volume was derived from the steady state tissue concentration of radioactive rabbit serum albumin (¹²⁵I-RSA). Pulmonary extracellular and intravascular fluid volumes ( V _x and V _v, respectively) were measured as distribution volumes of ⁵¹Cr-EDTA and ¹³¹I-RSA, respectively, and interstitial fluid tracer concentrations were determined in interstitial fluid collected through implanted wicks. At the highest degree of hydration, interstitial fluid volume ( V _i= V _x− V _v) and extravascular albumin distribution volume ( V _a,w) significantly increased by 38.5 and 240.2 %, respectively, compared to control. Albumin-excluded volume ( V _e,a= V _i− V _a,w) was 398.9 ± 17 μl (g dry tissue weight)⁻¹; the albumin-excluded volume fraction ( F _e,a= V _e,a/ V _i) was 0.23 ± 0.01, 33.2 % of the control value. Data indicate that, at variance with what is observed in tissues like skin and muscle, pulmonary F _e,a is highly sensitive to tissue fluid content.     

The role of the extracellular matrix in tissue distribution of macromolecules in normal and pathological tissues: potential therapeutic consequences

The interstitial space is a dynamic microenvironment that consists of interstitial fluid and structural molecules of the extracellular matrix, such as glycosaminoglycans (hyaluronan and proteoglycans) and collagen. Macromolecules can distribute in the interstitium only in those spaces unoccupied by structural components, a phenomenon called interstitial exclusion. The exclusion phenomenon has direct consequences for plasma volume regulation. Early studies have assigned a major role to collagen as an excluding agent that accounts for the sterical (geometrical) exclusion. More recently, it has been shown that the contribution of negatively charged glycosaminoglycans might also be significant, resulting in an additional electrostatical exclusion effect. This charge effect may be of importance for drug uptake and suggests that either the glycosaminoglycans or the net charge of macromolecular substances to be delivered may be targeted to increase the available volume and uptake of macromolecular therapeutic agents in tumor tissue. Here, we provide an overview of the structural components of the interstitium and discuss the importance the sterical and electrostatical components have on the dynamics of transcapillary fluid exchange.