Abstract P283: CCL5 Acts As A Vasoconstrictor On Penetrating Arterioles In The Cerebral Circulation By Enhancing 20-HETE Activity

20-HETE is synthesized from arachidonic acid by cytochrome P450 (CYP) enzymes 4A and 4F. Inactivating mutations in the CYP enzymes that produce 20-HETE are associated with hypertension and stroke in man. We previously revealed that inactivating variants of CYP4A/F enzymes are associated with dementia in the Atherosclerosis Risk in Communities Neurocognitive Study (ARIC-NS) population. 20-HETE is involved with sodium regulation in the kidney and is a powerful vasoconstrictor. It was recently discovered that CCL5 and 20-HETE share the same receptor, GPR75. We previously found that 20-HETE constricts and augments the myogenic response (MR) of the middle cerebral artery (MCA) and renal afferent arteriole. However, whether CCL5 has any effect on penetrating arterioles (PAs) and interacts with 20-HETE is unknown. We found that GPR75 is expressed in PAs and pericytes in the brain. CYP4A is also expressed in pericytes and is inversely proportional to levels of GPR75 in the brain. In the present study, we found that 20-HETE contributes to the basal myogenic tone of PAs in SD rats. Administration of HET0016, a 20-HETE synthesis inhibitor, dilated the PA by 34 ± 3% (n = 6) under 10 mmHg perfusion pressure. Administration of WIT003, a 20-HETE agonist, constricted the vessel by 23 ± 4% (n = 6) under the same perfusion pressure. We found that CCL5 also reduced PA diameter by 20 ± 4% (n = 7) in SD rats under 10 mmHg perfusion pressure. Moreover, we compared the response to CCL5 in SS rats that are 20-HETE deficient and SS.CYP4A1 transgenic rats in which 20-HETE production is restored. PAs isolated from SS rats treated with 0.1 nM CCL5 constricted by 9 ± 5% (n = 6) while those treated with 10 nM constricted by 12 ± 3% (n = 6). CCL5 had a greater response in PAs from the SS.CYP4A1 strain, and the diameter of the PAs constricted by 14 ± 2% (n = 5) and 24 ± 5% (n = 5) in response to 0.1 and 10 nM CCL5, respectively. These results demonstrate that CCL5 has a direct effect on PAs similar to 20-HETE that acts via the GPR75 receptor. However, further study is needed to determine how CCL5 and 20-HETE interact to promote vasoconstriction. These studies would help further understand the involvement of 20-HETE in disease and potentially identify novel drug targets.

Clinical characteristics and outcomes in elderly patients undergoing transsphenoidal surgery for nonfunctioning pituitary adenoma

OBJECTIVELife expectancy has increased over the past century, causing a shift in the demographic distribution toward older age groups. Elderly patients comprise up to 14% of all patients with pituitary tumors, with most lesions being nonfunctioning pituitary adenomas (NFPAs). Here, the authors evaluated demographics, outcomes, and postoperative complications between nonelderly adult and elderly NFPA patients.METHODSA retrospective review of 908 patients undergoing transsphenoidal surgery (TSS) for NFPA at a single institution from 2007 to 2019 was conducted. Clinical and surgical outcomes and postoperative complications were compared between nonelderly adult (age ≥ 18 and ≤ 65 years) and elderly patients (age > 65 years).RESULTSThere were 614 and 294 patients in the nonelderly and elderly groups, respectively. Both groups were similar in sex (57.3% vs 60.5% males; p = 0.4), tumor size (2.56 vs 2.46 cm; p = 0.2), and cavernous sinus invasion (35.8% vs 33.7%; p = 0.6). Regarding postoperative outcomes, length of stay (1 vs 2 days; p = 0.5), extent of resection (59.8% vs 64.8% gross-total resection; p = 0.2), CSF leak requiring surgical revision (4.3% vs 1.4%; p = 0.06), 30-day readmission (8.1% vs 7.3%; p = 0.7), infection (3.1% vs 2.0%; p = 0.5), and new hypopituitarism (13.9% vs 12.0%; p = 0.3) were similar between both groups. Elderly patients were less likely to receive adjuvant radiation (8.7% vs 16.3%; p = 0.009), undergo future reoperation (3.8% vs 9.5%; p = 0.003), and experience postoperative diabetes insipidus (DI) (3.7% vs 9.4%; p = 0.002), and more likely to have postoperative hyponatremia (26.7% vs 16.4%; p < 0.001) and new cranial nerve deficit (1.9% vs 0.0%; p = 0.01). Subanalysis of elderly patients showed that patients with higher Charlson Comorbidity Index scores had comparable outcomes other than higher DI rates (8.1% vs 0.0%; p = 0.006). Elderly patients’ postoperative sodium peaked and troughed on postoperative day 3 (POD3) (mean 138.7 mEq/L) and POD9 (mean 130.8 mEq/L), respectively, compared with nonelderly patients (peak POD2: mean 139.9 mEq/L; trough POD8: mean 131.3 mEq/L).CONCLUSIONSThe authors’ analysis revealed that TSS for NFPA in elderly patients is safe with low complication rates. In this cohort, more elderly patients experienced postoperative hyponatremia, while more nonelderly patients experienced postoperative DI. These findings, combined with the observation of higher DI in patients with more comorbidities and elderly patients experiencing later peaks and troughs in serum sodium, suggest age-related differences in sodium regulation after NFPA resection. The authors hope that their results will help guide discussions with elderly patients regarding risks and outcomes of TSS.

A new paradigm of sodium regulation in inflammation and hypertension

Dysregulation of sodium (Na+) balance is a major cause of hypertensive cardiovascular disease. The current dogma is that interstitial Na+ readily equilibrates with plasma and that renal excretion and reabsorption is sufficient to regulate extracellular fluid volume and control blood pressure. These ideas have been recently challenged by the discovery that Na+ accumulates in tissues without commensurate volume retention and activates immune cells, leading to hypertension and autoimmune disease. However, objections have been raised to this new paradigm, with some investigators concerned about where and how salt is stored in tissues. Further concerns also include how Na+ is mobilized from tissue stores and how it interacts with various organ systems to cause hypertension and end-organ damage. This review assesses these two paradigms of Na+ regulation in the context of inflammation-mediated hypertension and cardiovascular disease pathogenesis. Also highlighted are future perspectives and important gaps in our understanding of how Na+ is linked to inflammation and hypertension. Understanding mechanisms of salt and body fluid regulation is the sine qua non of research efforts to identify therapeutic targets for hypertension and cardiovascular disease.

Hyponatremia/Hypernatremia

lSodium is the most abundant cation in the extracellular fluid and is important for regulation of plasma water concentrations and cell volume. Sodium cannot readily cross the blood-brain barrier, and changes in plasma sodium levels by altering free water movement can expand or shrink brain cells. Changes in brain cell volume can cause brain cell dysfunction and apoptosis. Correction of both high and low sodium levels must be done gradually, as rapid correction of dysnatremias can also damage brain cells. In this chapter we review the physiology of sodium regulation, and discuss the clinical implications of these disorders as well as present a treatment plan for safe correction.

Abstract P337: Angiotensin 1-7 Mitigates Oxidative Stress, Protects Renal Dopamine D1 Receptor Function and Prevents Development of Hypertension

The role of angiotensin in etiology of cardiovascular diseases especially in hypertension is well established. Renin-angiotensin-aldosterone contributes to the development and maintenance of hypertension directly by increases in vascular tone and renal sodium reabsorption or indirectly by increasing oxidative stress and inflammation. Contrary to this pathological arm, angiotensin (Ang) 1-7 via Mas receptors has been reported to protect the cardiovascular function although the exact mechanism is not yet clear. We have previously shown that oxidative stress leads to renal dopamine D1 receptor (D1R) dysfunction which could disrupt sodium regulation and subsequently lead to hypertension. In here we wanted to test whether chronic administration of Ang 1-7 in mice could mitigate oxidative stress, protect renal D1R function and prevent development of hypertension. Mice (C57BL) were implanted with telemetry probes and concomitantly treated with L-buthionine sulfoximine (BSO, in drinking water) and Ang 1-7 (via jugular vein by osmotic pumps). Control (C, no treatment) and shams (implanted with saline filled pumps) exhibited similar behavioral and physiological parameters. Mice treated with BSO alone exhibited increased oxidative stress and high BP as compared to controls. Ang 1-7 treatment did not affect oxidative stress and BP in control mice but prevented the increase in BP and oxidative milieu in BSO treated mice. Mean arterial pressure (mmHg), C: 78.5 ± 2.3*; BSO: 97.3 ± 3.8; Ang 1-7: 80.1* ± 4.1; BSO+Ang 1-7: 83.2 ± 3.4*, *P <0.05 vs BSO. SKF38393, a D1R agonist, increased urine and sodium excretion in control mice but failed to induce diuresis or natriuresis in BSO-treated mice. Treatment with Ang 1-7 protected D1R function as both natriuresis and diuresis was observed in mice treated with BSO plus Ang 1-7. Chronic Ang 1-7 had no effect on D1R function in the absence of BSO. These data show that oxidative stress leads to hypertension by disrupting renal D1R dependent sodium regulation. Ang 1-7 mitigates oxidative stress, protects renal D1R function and prevents increase in BP. This study provides a new insight on how beneficial arm of Ang system could protect renal D1R-mediated sodium regulation and prevent development of hypertension during oxidative stress.

Cerebral salt wasting syndrome

Traumatic brain injury (TBI) is on the rise, especially in today’s fast-paced world. TBI requires not only neurosurgical expertise but also neurointensivist involvement for a better outcome. Disturbances of sodium balance are common in patients with brain injury, as the central nervous system plays a major role in sodium regulation. Hyponatraemia, defined as serum sodium <135 meq/L is commonly seen and is especially deleterious as it can contribute to cerebral oedema in these patients. Syndrome of inappropriate antidiuretic hormone secretion (SIADH), is the most well-known cause of hyponatraemia in this subset of patients. Cerebral Salt Wasting Syndrome (CSWS), leading to renal sodium loss is an important cause of hyponatraemia in patients with TBI. Although incompletely studied, decreased renal sympathetic responses and cerebral natriuretic factors play a role in the pathogenesis of CSWS. Maintaining a positive sodium balance and adequate hydration can help in the treatment. It is important to differentiate between SIADH and CSWS when trying to ascertain a case for patients with acute brain injury, as the treatment of the two are diametrically opposite.