Kidney juxtaglomerular apparatus

The novel endocrine glands are the skin, gastrointestinal tract, adipose tissue, kidney (juxtaglomerular apparatus in the cortex which secretes renin that indirectly controls aldosterone secretion, via angiotensin-11), pineal gland, which secretes melatonin, and the heart (cardiac myocytes in the atria, which secrete atrial natriuretic peptide). 

Cyclooxygenase (COX) activity is responsible for the formation of prostaglandins from their arachidonic acid precursor. Two COX isoforms have been identified, COX-1 and COX-2. While COX-1 is constitutively expressed in most tissues, COX-2 is typically only found after induction by proinflammatory stimuli. However, a constitutively expressed and highly regulated COX-2 is found in the kidney, both in the renal medulla and in the renal cortex. Renal cortical COX-2 is located in the area ofthe juxtaglomerular apparatus, and prostaglandins formed by COX-2 regulate the expression and secretion of renin in response to a reduction in NaCl concentration at the macula densa. 

A correlation between the activity of G-6-PDH and extractable renin in rat kidneys has been reported, suggesting that the macula densa cells and also the juxtaglomerular apparatus are parts of a system related to the formation of renin (H6). 

Ito 5 Characteristics of isolated perfused juxtaglomerular apparatus. Kidney Int SuppI 67 546-548,1998... 

Yamada K, SugIsakI Y, Akimoto M, Yamanaka N. FK506-induced juxtaglomerular apparatus hyperplasia and tubular damage In rat kidney-morphologic and biologic analysis. Transplant Proc 1992 24 1396-1398. 

The kidneys have both sympathetic and parasympathetic nerve supplies whose function appears to be predominantly associated with vasomotor activity. The renal lymphatic drainage includes fine lymphatics in the glomerulus, some m close proximity to the juxtaglomerular apparatus, which are associated with removal of material from the glomerular mesangial cells. ... 

Renin is an enzyme of the hydrolase class that catalyzes cleavage of the leucine-leucine bond in angiotensinogen to generate angiotensin I. The enzyme is synthesized as inactive prorenin in the kidney and released into the blood in the active form in response to various metabolic stimuli. The importance of renin in the maintenance of systemic blood pressure was discussed previously (see Juxtaglomerular Apparatus). 

Juxtaglomerular cells function as a baroreceptor-sensing device. Decreased renal artery pressure and kidney blood flow are sensed by these cells and stimulate secretion of renin. The juxtaglomerular apparatus also includes a group of specialized distal tubule cells... 

Fig. 317. Juxtaglomerular apparatus with Goormaghtigh cells (partly split up into their processes) and macula densa from the kidney (block BNh 3372) of a male Wistar rat (No. 2567) 90 min after a single intraperitoneal injection of 5 mg N-benzhydryl-N -p-hydroxybenzylpiperazine HCl per kg body weight. Under pentobarbital anaesthesia (30 mg/kg), the animal was perfused from the abdominal aorta with 2.5% glutaraldehyde in 0.1 M sodium cacodylate buffer (pH 7.4). Postfixation with 1 % osmium tetroxide in sodium cacodylate buffer. Embedded in Epon 812 and sectioned at 50 nm. Lead citrate and uranyl acetate. Plate 2368...

It is not known for certain in which organ erythropoietin is elaborated the kidney has often been suspected of playing this role [26]. The juxtaglomerular apparatus has been claimed as the site of erythropoietin secretion. However, there is no correlation between the disappearance of the vacuole in the cells of the juxtaglomerular apparatus and the appearance of erythropoietin. 

Secondary aldosteronism results in high blood levels of aldosterone in the absence of a primary adrenal defect. Secondary aldosteronism develops when one of the stimuli of aldosterone secretion is overactive. Consequently, at least three types of conditions can lead to secondary aldosteronism excess of renin, ACTH, or potassium. The condition encountered most often clinically is that in which renin is overproduced because of increased secretion by the juxtaglomerular apparatus or, more rarely, because of overproduction of precursors or extrarenal secretion (for example, by tumors). Renal secretion is stimulated when (1) arterial blood flow to the kidney is reduced (stimulation of baroreceptors), either as a result of the reduction in effective blood volume or renal artery obstruction or (2) osmoreceptors are stimulated as a result of hyponatremia. The arterial blood volume can be reduced by factors that decrease the blood volume (reduced water, sodium, or both), passage of fluid from the blood vessels to the extracellular compartment, and pregnancy (see Table 9-1). 

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