Tubuloglomerular feedback.

The macula densa, a plaque of specialized tubular epithelial cells located in the distal tubule, monitors the NaCl concentration of the tubular fluid and sends an as of yet unidentified signal to control glomerular hemodynamics. In this mechanism, called tubuloglomerular feedback (TGF), an increase in NaCl concentration at the macula densa constricts the glomerular afferent arteriole and thus decreases the single-nephron GFR. Along with the myogenic response, TGF significantly contributes to renal autoregulation. In addition, the macula densa also controls the rate of renin release, and hence the level of angiotensin II. Studies indicate that an appropriate interaction between TGF and the renin-angiotensin system is essential for body fluid and electrolyte homeostasis in the face of rather big variations in daily salt intake. Thus, alterations in TGF may play an important role in the pathogenesis/pathophysiology of various diseases such as hypertension, diabetes mellitus and congestive heart failure.