Exposure to a low protein diet during pregnancy results in an increase in offspring blood pressure as early as 4 weeks of age. Previously we have reported that in utero protein restriction is associated with a reduction in glomerular number and increased AT₁ receptor expression (Sahajpal & Ashton, 2002). These jointly enhance renal haemodynamic sensitivity in rats exposed to low (9 %) protein, resulting in a significantly greater reduction in GFR than in control (18 %) rats (Sahajpal & Ashton, 2001). We now report differences in glomerular angiotensin II (Ang II) binding in preparations isolated from the renal cortex of rats exposed to 9 and 18 % protein diets.

In utero protein restriction was induced by feeding female Wistar rats a diet containing 9 % protein compared with an isocalorific 18 % protein diet for control animals, from the day of conception until birth. Immediately after birth, dams and pups were fed with a standard maintenance diet. At 4 weeks of age the offspring were humanely killed and kidneys were harvested, decapsulated and chilled in ice-cold phosphate-buffered saline, pH 7.4 (PBS). Cortical tissue was minced, washed through grade sieves with PBS, and centrifuged at 120 g at 4°C for 5 min. The pellet was resuspended in PBS, passed under pressure through a 23-gauge needle to remove Bowman’s capsule and recentrifuged for a further 5 min. The final yield was > 80 % glomeruli.

Glomerular binding of Ang II was determined by incubating 20 mg of glomerular protein with ¹²⁵I-labelled Ang II (1 X 10^-10 to 1 X 10^-7 M) for 45 min in BSA-coated tubes. Non-specific binding was determined by the addition of unlabelled Ang II (5 X 10^-5 M) to the incubation medium. After incubation, all tubes were centrifuged at 10 000 g for 10 min and the supernatant was aspirated. Each sample was then washed in PBS, recentrifuged and bound activity in the pellet counted in a gamma counter.

Binding of ¹²⁵I-labelled Ang II by glomeruli from the 9 % protein rats was significantly greater than that by glomeruli from the control 18 % protein rats (18 %, n = 9, 159 ± 49 vs. 9 %, n = 7, 452 ± 75 fmol (mg protein)^-1, mean ± S.E.M., unpaired t test, P < 0.01). The binding affinity constant (K_D) was comparable between both groups (18 %, n = 9, 1.82 ± 1.06 vs. 9 %, n = 7, 0.99 ± 0.26 pmol ¹²⁵I-labelled Ang II).

These data show that rats exposed to low protein in utero have more Ang II binding sites in their glomeruli, although the affinity of these receptors remains unchanged. This supports our previous observation that protein restriction results in a significant increase in AT₁ receptor protein expression (Sahajpal & Ashton, 2002). Increased sensitivity to Ang II coupled with fewer glomeruli may account for the elevated blood pressure observed in these rats.

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