renin-angiotensin system | Definition & Facts | jingle-bells.info
Relationships between renin, aldosterone, and hour ambulatory blood pressure in obese adolescents. Renin-angiotensin system (RAS) activation and abnormalities of ambulatory blood pressure Research Support, Non-U.S. Gov't. The renin–angiotensin system (RAS) or the renin–angiotensin–aldosterone system (RAAS) is a .. Interaction. Help · About Wikipedia · Community portal · Recent changes · Contact page. Relationships in Normal Renin Essential Plasma aldosterone (PA) and plasma renin activity (PRA) levels were determined with the subjects .. In support of.
Five consecutive BP readings were obtained using an appropriately sized cuff, 30—60s apart. The average of the five readings was taken as the BP. The frequency of identical consecutive recordings was 0. Standard laboratory blood tests were performed. Urinary electrolyte excretion rates. Timed urine samples were obtained over a h period after discarding urine obtained immediately before the start of the collection period. The quality of urine sample collection was determined as previously described.
Blood samples were obtained in the supine position after 10min of rest in the morning between The assay is sensitive with intra-assay coefficients of variation ranging from 1.
Low renin hypertension
The assay is sensitive with intra-assay coefficients of variation ranging from 2. There is metabolic alkalosis due to increased urinary hydrogen excretion mediated by hypokalemia and by the direct stimulatory effect of aldosterone on distal acidification. Inhibition of sodium transport in the ascending limb of the loop of Henle during aldosterone escape is associated with a decline in magnesium reabsorption and hypomagnesemia.
Aldosterone may raise the glomerular filtration rate GFR and renal perfusion pressure independent of systemic hypertension. Most antihypertensive medications can be continued and posture stimulation is not required. However, mineralocorticoid receptor antagonist spironolactone and eplerenone should not be initiated until the evaluation is completed. In patients already receiving spironolactone, therapy should be discontinued for at least six weeks.
Other potassium-sparing diuretics, such as amiloride and triamterene, usually do not interfere with testing. Thus, in a patient treated with one of these drugs, a detectable PRA level does not exclude the diagnosis of PA. Plasma aldosterone PAC is increased. PRA varies from 0. Thus an increased PAC is essential for diagnosis. Other studies have suggested that a ratio 50 or higher rather than 30, or measurement of the ratio 60 to 90 minutes after a single dose of 25 to 50 mg of captopril or 50 mg of losartan may increase sensitivity.
In all other situations aldosterone suppression testing is performed. The Endocrine Society Guidelines suggest fludrocortisone suppression or captopril challenge tests as two additional alternative confirmatory tests in addition to saline loading. Oral sodium loading is done after hypertension and hypokalemia are controlled hypokalemia suppresses aldosterone secretionand stopping spironolactone and eplerenone for 6 weeks.
Patients can be given oral sodium chloride tablets e. On the third day of the high sodium diet, serum electrolytes are measured and a hour urine specimen is collected for measurement of aldosterone, sodium and creatinine. The hour urine sodium excretion should exceed meq to document adequate sodium loading.
Sodium loading increases kaliuresis and hypokalemia hence serum potassium should be measured daily and replacement with potassium chloride should be prescribed. Saline infusion test can be performed instead of oral test by the intravenous administration of two liters of isotonic saline over four hours from 8 AM to noon while the patient is recumbent.
A hour urine collection for potassium is required in those cases of hypertension and hypokalemia where PRA is not suppressed, PAC is not elevated, or there is a suspicion of vomiting or laxative abuse.
A low rate of potassium excretion suggests either extra renal losses vomiting, diarrhea or diuretic treatment with the urine being collected after the diuretic effect has worn off. A high-sodium diet can also be given as a provocative test in patients with an initial serum potassium concentration in the normal or low-normal range.
Sodium-induced hypokalemia is strongly suggestive of no suppressible hyperaldosteronism. Classification Once the diagnosis of primary aldosteronism has been established, a unilateral aldosterone-producing adenoma APA must be distinguished from bilateral hyperplasia idiopathic hyperaldosteronism, IHA.
Adenomas account for approximately 35 percent of cases and should be considered for surgical removal. Bilateral adrenal hyperplasia, which accounts for approximately 60 percent of cases, is a milder disease with less hyper secretion of aldosterone and less hypokalemia. Adrenal CT Endocrine Society Guidelines state that adrenal CT should be the initial study to determine subtype adenoma versus hyperplasia and exclude adrenal carcinoma.
CT has superior spatial resolution when compared to MRI for adrenal imaging.
- Renin–angiotensin system
- Low renin hypertension
- There was a problem providing the content you requested
An abnormality in both glands suggests adrenal hyperplasia. Adrenal vein sampling Measurement of aldosterone in samples of adrenal venous blood, obtained by an experienced radiologist, is the standard test to distinguish between unilateral adenoma and bilateral hyperplasia. Unilateral disease is associated with a marked usually fourfold greater than contra lateral adrenal increase in PAC on the side of the tumor, whereas there is little difference between the two sides in patients with bilateral hyperplasia The Endocrine Society recommends AVS to confirm unilateral disease in all patients with primary aldosteronism who are candidates for surgical management unilateral adrenalectomy.
Angiotensin II stimulates the hypertrophy of renal tubule cells, leading to further sodium reabsorption. In the adrenal cortexangiotensin II acts to cause the release of aldosterone. Aldosterone acts on the tubules e. This increases blood volume and, therefore, increases blood pressure. In exchange for the reabsorbing of sodium to blood, potassium is secreted into the tubules, becomes part of urine and is excreted. Angiotensin II causes the release of anti-diuretic hormone ADH also called vasopressin — ADH is made in the hypothalamus and released from the posterior pituitary gland.
As its name suggests, it also exhibits vaso-constrictive properties, but its main course of action is to stimulate reabsorption of water in the kidneys. ADH also acts on the central nervous system to increase an individual's appetite for salt, and to stimulate the sensation of thirst.
These effects directly act together to increase blood pressure and are opposed by atrial natriuretic peptide ANP. Local renin—angiotensin systems[ edit ] Locally expressed renin—angiotensin systems have been found in a number of tissues, including the kidneysadrenal glandsthe heartvasculature and nervous systemand have a variety of functions, including local cardiovascular regulation, in association or independently of the systemic renin—angiotensin system, as well as non-cardiovascular functions.
Medications aimed at the systemic system may affect the expression of those local systems, beneficially or adversely. Renin levels are high in the fetus, while angiotensin II levels are significantly lower; this is due to the limited pulmonary blood flow, preventing ACE found predominantly in the pulmonary circulation from having its maximum effect.
Clinical significance[ edit ] Flowchart showing the clinical effects of RAAS activity and the sites of action of ACE inhibitors and angiotensin receptor blockers. ACE inhibitors —inhibitors of angiotensin-converting enzyme are often used to reduce the formation of the more potent angiotensin II.