Characteristics of isolated perfused juxtaglomerular apparatus

Tubuloglomerular feedback (TGF), which operates between the tubule and the parent glomerulus, is important to renal autoregulation and homeostasis of body fluid and electrolytes. The juxtaglomerular apparatus (JGA) has long been suggested as the anatomical site of TGF. To study the function of the JGA directly, we developed an in vitro preparation in which both the afferent arteriole (Af-Art) and macula densa (MD) of a microdissected rabbit JGA are microperfused simultaneously. We see that increasing the [NaCl] of the MD perfusate constricts the afferent arteriole in the segment close to the glomerulus. This constriction is blocked by furosemide, a loop diuretic known to inhibit TGF. On the other hand, microperfusion of Af-Arts alone showed the myogenic response to exist in the more proximal segments. Such an anatomical relationship between the myogenic response and TGF may enable the kidney to achieve its extremely efficient autoregulation.