Five rats were given twice daily intraperitoneal injections of hypertonic dialysis fluid for 6 weeks. The structure of the hepatic peritoneum of this group was compared with that of a control group by applying morphometric techniques to transmission electron micrographs. The experimental group showed marked mesothelial hyperplasia with doubling of the number of cells and a significant increase in the length of intercellular junction per unit area of peritoneum. Since cell volumes in the two groups were similar, the increase in cell density in the experimental animals was the result of the cells assuming a more cuboidal shape. Experimental animals also showed an increase in the number of microvilli, pinocytotic vesicles and rough endoplasmic reticulum per unit area of peritoneum. Chronic exposure to dialysis fluid has profound effects on the number, shape and composition of peritoneal mesothelial cells in the rat.
Eleven rats were given twice-daily intraperitoneal injections of 20 mL of dialysis fluid containing 4.5% glucose for 6 weeks. The peritoneal ultrafiltration capacity of this group was compared with that of a control group of 10 rats that had received no injections by measuring the volume and glucose concentration of the dialysate remaining in the peritoneal cavity 2 hours after injection. Animals that had received injections of dialysis fluid showed significant loss of peritoneal ultrafiltration: volume of dialysate remaining in the control group was 31 (13–35) mL, and in the experimental group was 25 (11–45) mL, with p<0.02 (Mann-Whitney). This was associated with enhanced glucose absorption: glucose absorbed by the control group was 382 (312–706) mg, and 595 (435–738) mg in the experimental group (p<0.002, Mann-Whitney).
This paper reviews the structure, function, and clinical significance of peritoneal mesothelium, once thought to be a passive membrane, but now known to play an active role in exchanges between the peritoneal cavity and the blood. The advent of continuous ambulatory peritoneal analysis (CAPD) has revived interest in the peritoneum, whose ultrastructure is much changed by CAPD.
Studies of the healing of mesothelium have shown that the new mesothelium develops from subperitoneal perivascular connective tissue cells, and not by a process of centripetal growth from the wound margins as in the healing of other epithelial surfaces.
Peritoneal mesothelial cells possess fibrinolytic properties, which may be important in preventing fibrinous adhesions from being converted to permanent fibrous adhesions, which may cause intestinal obstruction. Mesothelium also produces prostacyclin. These properties have led to the use of mesothelium as a substitute for endothelium, both for coating prosthetic vascular grafts, and also in peritoneal tube grafts for replacing segments of vein. The resurgence of interest in the peritoneal mesothelium provides a stimulus for clinician and anatomist to cooperate in further exploration of its clinical potential.
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