1. Aldosterone Biosynthesis

 The site of production of the mineralocorticoid aldosterone is the adrenal zona glomerulosa cell, which employs a variety of signal transduction mechanisms that include receptors for angiotensin II, ACTH, dopa mine, and the atrial natriuretic peptide as well as a K+ modulated voltage-gated Ca2+ channel. The dominant agonist is angiotensin II, but under appropriate physiological circumstances the other agonists are also effective. Within seconds of exposure to angiotensin II, IP3, diacylglycerol (DAG), and intracellular Ca2+ concentrations all increase, followed shortly thereafter by an elevated biosynthesis of aldosterone.

2. Aldosterone Actions

In humans, the principal biologically active mineral ocorticoid is aldosterone; the structure of aldosterone is shown in Figure 1A.

Fig1. Structure and production of aldosterone and a cellular model of the actions of aldosterone on Na+ and K+ transport processes in the mucosal cells of the cortical collecting duct of the kidney nephron. (A) The structure of aldosterone is shown. Chapter 2 of Hormones focuses on steroid chemistry, biosynthesis, and metabolism of all the steroid hormones, including aldosterone. The chemical structure of aldosterone, a mineralocorticoid, is shown. Chapter 2.. (B) Mode of action of aldosterone in a kidney’s cortical collecting duct cell in stimulating the reabsorption of Na+. The steroid hormone aldosterone produces biological responses via stimulation of gene expression related to kidney tubule Na+ reabsorption. The focus is on the role of aldosterone in mucosal cells of the kidney’s cortical collecting duct. The figure illustrates the four steps which are operative in the presence of aldosterone. In step ➀, aldosterone (Aldo) enters the cell (blue oval) and in ➁ localizes in the nucleus where it binds to its specific high affinity aldosterone receptor (AR; magenta color) creating a 1:1 homodimer of the AR-Aldo. The AR-Aldosterone dimer then is translocated to the specific hormone DNA response elements in the promoter region of the specified genes (➂). This stimulates the rate of transcription of selected mRNAs which generate several aldosterone-induced proteins indicated in the green box as “new proteins” (➃). These include the α- and β-subunits of the Lumen Na+ permease pump 4A & 4D (all step labels are inside a circle), which are believed to be the rate-limiting step in Na+ reabsorption. The newly synthesized Na+/K+ ATPase (step 4B) is responsible for (i) pumping Na+ from the cortical collecting duct cell’s cytoplasm on the peritubular side of the cell, into the cell membrane and (ii) release of Na+ into the peritubular extracellular fluid. This increases the removal of Na+ from the interior of the cell (step 4E) on its way to the blood. Increasing the concentration of the citrate lyase (step 4C) results in an increase in the rate of biosynthesis of citric acid which, after traversing the mitochondrial oxidative pathways, gives rise to the production of correspondingly more ATP which is required as a substrate for the Na+/K+ ATPase (step 4E).

The mineralocorticoids mediate their actions on ion balance principally in the kidney, and also to some limited extent in the salivary glands, gut, and sweat glands.

In the kidney, the actions of the aldosterone result in an increased cortical collecting tubule reabsorption of Na+ with a concomitant secretion of K+. Only a fraction of the Na+ filtered by the glomerulus is actually reabsorbed as a consequence of aldosterone’s action. However, this fraction can effect significant consequences on electrolyte balance.

The steroid hormone aldosterone by binding to its nuclear receptor produces biological responses via stimulation of selected gene expression related to kidney tubule Na+ transport. The focus of aldosterone is on the mucosal cells of the kidney’s cortical collecting duct. In the absence of aldosterone, there is only a minimal basal uptake of Na+ from the lumen (extracellular) side of the collecting duct cell by the Na+ permease. Figure 1B illustrates the four steps in the cortical collecting duct cell which are operative in the presence of aldosterone. The presence of aldosterone binding to its nuclear receptor stimulates the gene transcription of several proteins that are essential to supporting the overall entrance of Na+ into the cell via a Na+ permease. Since the extracellular concentration of Na+ is significantly higher (~140 mM) than the intracellular concentration of Na+ (~10mM;), the Na+ in the cortical collecting duct cell’s cytosol must utilize the Na+ /K-ATPase (see Figure 1B) to transfer the Na+ across the peritubular cell membrane, against a concentration gradient, and release it into the extracellular fluid.

اخر الاخبار

اخبار العتبة العباسية المقدسة

قسم الشؤون الفكريّة يُهدي إصداراته العلمية إلى مكتبات محافظة كركوك

شعبة فاطمة بنت أسد تطلق مسابقتها الإلكترونية (منارة الجود في مهد الصبا) لكتابة القصة للأطفال

المجمع العلمي يقيم برنامجًا قرآنيًا تعليميًا في النجف الأشرف

قسم الشؤون الدينية يقيم مجلسًا عزائيًّا لاستذكار أهل البيت (عليهم السلام)

المزيد

الآخبار الصحية

ما هي أفضل العصائر لصحة القلب وتقوية المناعة والنوم العميق؟

الأطعمة الغنية بالبروتينات النباتية تقلل خطر الأمراض المزمنة

وجع الأوتار قد يخفي خطرا صحيا مرتبطا بالقلب

أزمة "السفينة الموبوءة"..الأرجنتين تحقق في مصدر تفشي "هانتا"

المزيد

الآخبار التكنلوجية

باحثون يحددون تأثير القهوة على الميكروبيوم والمزاج

روسيا.. ابتكار تقنية لمعالجة سبائك التيتانيوم لحماية الطائرات والسيارات

بكين وواشنطن تدرسان إطلاق محادثات رسمية حول الذكاء الاصطناعي

لأول مرة في الولايات المتحدة.. تشغيل مفاعل مصغر نووي يغذي الذكاء الاصطناعي بالطاقة

المزيد

مواضيع ذات صلة

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Placental Lactogen and Placental Growth Hormone

Human Chorionic Gonadotrophin

Polycystic Ovary Syndrome (PCOS)

Estrogen and the Cardiovascular System

Effects of Estrogen on Bone

Uterine Effects of Estrogen and Progesterone

Menopause

Chemistry and Metabolism of Female Steroid Hormones: Feedback Effects on the Hypothalamus and Pituitary

Control of the Ovary by the Hypothalamus and Pituitary

Synthesis of Progesterone and Estrogens

Female Steroid Hormones