To determine whether the filtration rate of juxtamedullary nephrons is regulated by tubuloglomerular feedback (TGF), we developed two micropuncture techniques suitable for the papilla of young rats. One consisted of measuring the tubular flow in descending limbs of Henle loops (VDLH) while the ascending limbs of the loop of Henle (ALH) were perfused at various rates with three different solutions: modified Ringer, artificial Henle loop solution, and Ringer containing 10(-4) M furosemide. SNGFR was also measured in several juxtamedullary nephrons. The other protocol consisted of measuring the tubular stop-flow pressure (PSF) in descending limbs of the loop of Henle upstream to a wax block. Distal to the block Ringer was perfused at various rates through ALH. Our results provide the first evidence of a TGF response in juxtamedullary nephrons. VDLH and SNGFR decreased during Ringer perfusion to 42 +/- 4 and 44 +/- 4% of their values at zero perfusion. The same pattern was observed using Henle loop solution as perfusate, whereas with furosemide VDLH did not change. The maximal decrease in PSF was 14.1 +/- 1.4 mmHg. The perfusion rate necessary to induce a half-maximal PSF decrease was 9.1 +/- 0.9 nl/min. Similar micropuncture techniques were used in proximal tubules of surface nephrons in these rats, which in comparison to the deep nephrons showed smaller feedback responses. The mechanism seems to be active at physiological nephron flow rates in both nephron populations. Thus, TGF can exert its effect on GFR of the whole kidney by acting in both deep and surface nephrons.