Increased glomerular angiotensin II binding in rats exposed to a maternal low protein diet in utero

Abstract

In the rat, protein restriction during pregnancy increases offspring blood pressure by 20-30 mmHg. We have shown in an earlier study that this is associated with a reduction in nephron number and increased glomerular sensitivity to angiotensin II (Ang II) in vivo. Hence, we hypothesized that exposure to a maternal low-protein diet increases glomerular Ang II AT1 receptor expression and decreases AT2 receptor expression. To test this hypothesis, pregnant Wistar rats were fed isocalorific diets containing either 18% (control) or 9% (LP) protein from conception until birth. At 4 weeks of age, the kidneys of male offspring were harvested to measure cortical AT1 and AT2 receptor expression, 125I-Ang II glomerular binding, tissue renin activity, tissue Ang II and plasma aldosterone concentrations. AT1 receptor expression was increased (62%) and AT2 expression was decreased (35%) in LP rats. Maximum 125I-Ang II (125I-Ang II) binding (Bmax) was increased in LP rats (control n = 9, 291.6 +/- 27.4 versus LP n = 7, 445.7 +/- 27.4 fmol (mg glomerular protein)(-1), P < 0.01), but affinity (KD) was not statistically different from controls (control 2.87 +/- 0.85 versus LP 0.84 +/- 0.20 pmol 125I-Ang II, P = 0.059). Renal renin activity, tissue Ang II and plasma aldosterone concentrations did not differ between control and LP rats. Increased AT1 receptor expression in LP rat kidneys is consistent with greater haemodynamic sensitivity to Ang II in vivo. This may result in an inappropriate reduction in glomerular filtration rate, salt and water retention, and an increase in blood pressure.

Figure 1. Renal AT₁ receptor expression

A, typical immunoblot for the AT₁ receptor in the renal cortex of 4-week-old control (C) and low-protein (LP) rats. B, renal cortical AT₁ receptor expression in 4-week-old control (open bars, n = 5 from 5 litters) and LP rats (filled bars, n = 5 from 5 litters). Data normalized to the control bands and presented as means ±s.e.m. Statistical comparisons were by Student's unpaired t test. *P < 0.05 control versus LP.

Figure 2. Renal AT₂ receptor expression

A, typical immunoblot for the AT₂ receptor in the renal cortex of 4-week-old control and LP rats. B, renal cortical AT₂ receptor expression in 4-week-old control (open bars, n = 5 from 5 litters) and LP rats (filled bars, n = 5 from 5 litters). Data normalized to the control bands and presented as means ±s.e.m. Statistical comparisons were by Student's unpaired t test. *P < 0.05 control versus LP.

Figure 3. Glomerular ¹²⁵I-angiotensin II binding curves

A, saturation curves of ¹²⁵I-Ang II binding to glomeruli isolated from 4-week-old control and LP rats. Binding curves are shown for ¹²⁵I-Ang II alone (Δ, control n = 9 from 6 litters, •, LP n = 7 from 6 litters), ¹²⁵I-Ang II and losartan (▵, control n = 7 from 5 litters, ▴, LP n = 7 from 5 litters) and ¹²⁵I-Ang II and PD123319 ( ▿, control n = 7 from 5 litters, ▾, LP n = 7 from 5 litters). B, Scatchard plots for ¹²⁵I-Ang II binding alone. Correlation coefficients for the Scatchard plots were significant for both control (r =−0.771, P < 0.05) and LP rats (r = −0.916, P < 0.01).

Figure 4. Renin–angiotensin–aldosterone system activity

A, renal renin activity (micrograms of angiotensin I per gram kidney weight per hour) in kidneys from 4-week-old control (open bars, n = 9 from 5 litters) and LP (filled bars, n = 7 from 5 litters) rats. B, renal Ang II concentrations (picomoles per gram kidney weight) in kidneys from 4-week-old control (open bars, n = 5 from 5 litters) and LP (filled bars, n = 5 from 5 litters) rats. C, plasma aldosterone concentrations (picomoles per litre) in 4-week-old control (open bars, n = 5 from 5 litters) and LP (filled bars, n = 5 from 5 litters) rats. Statistical comparisons were by Student's unpaired t test.