Vascular and interstitial changes in the peritoneum of CAPD patients with peritoneal sclerosis

Objective:To analyze morphological changes in the peritoneum of peritoneal sclerosis (PS) patients. Emphasis was put on vascular abnormalities, becaus e the continuous exposure to glucose-based dialysis solutions could cause d iabetiform changes and because longitudinal transport studies suggested the development of a large peritoneal vascular surface area. Design: Peritoneal biopsies from continuous ambulatory peritoneal dialysis (CAPD) patients were investigated in two studies. Diabetic patients were ex cluded. In study 1, 11 PS biopsies were compared to three control groups va rying in duration of CAPD treatment: 0 months (n = 15), 2 - 25 months (n = 7), and > 25 months CAPD (n = 7). The second study was a case-control study , comparing six biopsies from the long-term control group to six PS biopsie s, matched for age and duration of CAPD. All biopsies were scored for prese nce and type of fibrosis [Picro Sirius red, type IV collagen, alpha-smooth muscle actin (alpha SMA)] and for neoangiogenesis (factor VIII). Thickening of vascular walls by type IV collagen and vasodilation of capillaries were measured by computer-aided planimetry. Results: In study 1 the presence of sclerosing fibrosis, deposition of inte rstitial type IV collagen, and the number of myofibroblasts (alpha SMA-posi tive cells) was greater in the PS biopsies than biopsies from all control g roups (p < 0.002). Moreover, the number of vessels per field was higher in PS biopsies (p < 0.01). Vascular wall thickening of small arteries (p < 0.0 08) and vasodilation of capillaries were found in PS biopsies compared to a ll control groups (p (0.007). The second study revealed differences in the presence of sclerosis but not in the extent of fibrosis between PS biopsies and their controls. The number of vessels per field in PS biopsies was hig her compared to controls (p = 0.04). Also, thickening of the vascular wall was more marked in PS biopsies (p = 0.03). Vasodilation of capillaries was greater in PS biopsies than in controls (p = 0.07). Conclusion: Fibrosis of the peritoneum may precede peritoneal sclerosis. Th e deposition of type IV collagen and the presence of myofibroblasts in the interstitial layer could be part of a pathologic process similar to the sca rring in diabetic nephropathy. Neoangiogenesis and thickening of the vascul ar wall by type IV collagen are consistent with glucose-induced microangiop athy. These abnormalities and the vasodilation of the capillaries can expla in the high dialysate-to-plasma ratios or mass transfer area coefficients o f low molecular weight solutes that can be found in long-term CAPD patients .