Résumé
The heptapeptide angiotensin-(1-7) is considered to be a biologically active endproduct of the renin-angiotensin system. This angiotensin, which is devoid of the most known actions of angioatensin II such as induction of drinking behavior and vasoconstriction, has several selective effects in the brain and periphery. In the present article we briefly review recent evidence for a physiological role of angiotensin-(1-7) in the control of hydroelectrolyte balance.
Sujets)
Rats , Animaux , Mâle , Angiotensine-III/physiologie , Angiotensine-II/physiologie , Angiotensine-I/physiologie , Angiotensines/physiologie , Consommation de boisson/physiologie , Glomérule rénal/physiologie , Tubules contournés distaux/physiologie , Tubules contournés proximaux/physiologie , Récepteurs aux angiotensines/physiologie , Système rénine-angiotensine/physiologie , Vasopressines/physiologie , Rein/physiologie , Rat WistarRésumé
The present paper reviews mechanisms by which the kidney controls systemic acid-base balance, with emphasis on the role of the distal nephron, and particularly of the cortical distal tubule. These mechanisms are essentially based on H-ion transport along the whole nephron. In proximal tubule cells, approximately 80 of H-ion secretion is mediated by Na+/H+ exchange, and 20 by H(+)-ATPase. In the distal nephron, acid-base transport mechanisms are located mainly in intercalated cells. H-ion secretion is effected by vacuolar H(+)-ATPase in alpha-intercalated cells and, in K-depleted animals, also by the gastric type H/K ATPase. In animals in alkalosis, beta-intercalated cells secrete bicarbonate by an apical Cl-/HCO3- exchanger, while a basolateral H-ATPase transfers H-ions into the interstitium. In cortical distal tubule, these mechanisms have been shown to be present in the intercalated cells of the connecting segment and of the initial collecting duct (the late distal tubule of micropuncture experiments). In the convoluted distal tubule (early distal tubule), most H-ion secretion occurs by means of the Na+/H+ exchanger. These data show that the distal nephron, including the cortical distal tubule, is a nephron segment responsible for a sizeable portion of bicarbonate reabsorption and titratable acid generation, as well as for bicarbonate secretion under appropriate metabolic conditions, being therefore the site of fine regulation of renal mechanisms that maintain acid-base homeostasis.
Sujets)
Animaux , Rats , Équilibre acido-basique/physiologie , Tubules contournés distaux/physiologie , Antiport des ions sodium-hydrogène/physiologie , Proton-Translocating ATPases/physiologie , Hydrogénocarbonates , Concentration en ions d'hydrogène , Néphrons/physiologie , Rat Brattleboro , Rat WistarRésumé
In order to study the mechanism of H-ion secretion in cortical distal tubules of the rat kedney, the luminal pH and transepithelial potential difference (PD) were measured with double-barrelled, pH-sensitive, resin/reference microelectrodes. perfusion of peritubular capillaries with low-sodium solutions increased luminal pH by 0.28 ñ 0.024 units. Perfusion of the lumen with 1 m§ amiloride increased luminal pH by 0.67 ñ 0.01 units. These changes could not be atributed to modification of transepithelial PD. We conclude that early distal acidification is sodium-dependent, possibly owing to the presence of Na+/H+ exchange