Rationale: To establish relationship, if any, between renal morphology and renal haemodynamic response to amino acids.
Design and methods: We investigated the correlation between renal haemodynamic regulation and morphology in a group of 15 patients with primary IgA nephropathy (IgAN) (age 26 +/- 2 years, BMI 24.4 +/- 1, GFR 64 +/- 5 ml/min, RPF 377 +/- 34 ml/min, FF 0.17 +/- 0.02). Twelve normal subjects (age 30 +/- 3 years, BMI 24 +/- 1, GFR 82 +/- 6 ml/min, RPF 421 +/- 42 ml/min, FF 0.19 +/- 0.02) were studied as controls. IgA patients were divided into two groups according to the histological staging of glomerular lesions: group I (n = 7) stage II, and group II (n = 8) stage III-IV.
Results: In the basal state GFR was similar in the two groups and averaged 64 +/- 9 and 64 +/- 6 ml/min respectively. In contrast, FF was significantly lower in group II (0.14 +/- 0.01) (P < 0.05) in comparison to group I (0.21 +/- 0.03) and controls (0.19 +/- 0.02). In order to evaluate the renal functional reserve, all study groups underwent to an intravenous amino-acid infusion designed to increase plasma amino acid levels twofold (total from 2096 +/- 145 to 4301 +/- 221 mumol/l in IgA nephropathy patients and from 2272 +/- 83 to 3844 +/- 238 mumol/l in controls). In response to amino-acid infusion, GFR rose significantly in group I (GFR 20 +/- 2% and RPF 37 +/- 4% versus basal) and controls (GFR 20 +/- 2% and RPF 20 +/- 3% versus basal) (both P < 0.01 vs basal). In contrast, in patients with more severe glomerular lesions (group II) neither GFR nor RPF rose significantly (GFR -1 +/- 4% and RPF -8 +/- 6% versus basal) (P NS versus basal, P < 0.01 versus group I and controls).
Conclusions: The data show that in IgA nephropathy: severe forms of glomerular lesions are associated with a complex alteration of glomerular haemodynamic regulation, characterized by lower basal FF and loss of haemodynamic response to hyperaminoacidaemia.