SEXUAL DIMORPHISM IN THE REGULATION OF CELL TURNOVER DURING LIVER HYPERPLASIA

A sexual dimorphism occurs in liver cell proliferation following parti al hepatectomy, female liver regenerating faster than male, while a co ntinuous ex cess of choline to females shifts their growth pattern tow ard that of males (L. Tessitore, P. Pani and M.U. Dianzani, Carcinogen esis, 13 (1992) 1929). In this study we have investigated (a) if the s ame sexual modulation occurs in a different type of liver growth, hype rplasia induced by a direct mitogen and (b) if the pre-administration of choline to females is able to modulate this dimorphism. Liver hyper plasia induced by lead nitrate, a potent mitogen, has also shown a pec uliar sexual dimorphism in all phases of the proliferative process. In contrast with liver regeneration after partial hepatectomy, the mitog enic action of lead nitrate was less effective and was delayed in fema les as compared with males, by evaluating liver weight, protein accumu lation, DNA synthesis and mitotic index. These results were also confi rmed by the trend of liver regression by apoptosis. The apoptotic inde x was higher in males than in females. A prolonged administration of a n excess of choline has partially filled these sexual differences, sin ce choline has moved, in females, all the observed parameters (liver w eight, protein accumulation, DNA synthesis, mitotic and apoptotic inde xes) to values closer to those observed in males.