It has been shown previously that liver regeneration after partial hepatectomy in rats is delayed if the liver is subjected to either concurrent ischaemia, flushing with cold solution, or grafting. We have shown recently that treatment with CsA preoperatively overcomes the suppressive effect of flushing and returns the regenerative response to a normal time scale. The present study was designed to investigate whether administration of FK506 would also return the observed delayed regenerative response to normal.Long-Evans rats weighing 250–350 g were subjected to standard 68% partial hepatectomy. Group 1 had no further treatment; in group 2, the liver remnant was flushed with 10 ml cold (4°C) Ringers lactate solution, and in group 3, FK506 (1 mg/kg/day) was administered by intramuscular injection for 3 days before the partial hepatectomy and flushing as in group 2; a final dose was given after completion of the procedures. Animals were killed in sets of 6 per group at 4, 24, 48, 72, and 96 hr after surgery and blood samples were taken for measurement of plasma aspartate aminotransferase. Liver biopsies were analyzed for measurement of thymidine kinase and ornithine decarboxylase activity and for counting of mitotic figures. While the highest recorded thymidine kinase activity occurred in group 1 at 24 hr, this was delayed to 48 hr in both groups 2 and 3 and counts remained high up to 96 hr in group 3. Mitotic indices were only significantly elevated (compared with group 1 at 96 hr), while ornithine decarboxylase activity did not correlate with these changes being significantly lower than in groups 2 and 3 at 4 hr and in group 3 also at 24 hr. Plasma aspartate aminotransferase was also significantly higher in group 3. It is concluded that the administration of FK506 preoperatively to rats subjected to partial hepatectomy and flushing did not restore the delayed regenerative response to normal but enhanced the response (as measured by thymidine kinase but not by mitotic indices) which commenced at 48 hr and was still present at 96 hr.
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