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Recently reports have indicated that both cimetidine and ranitidine delay cell proliferation in rats following 70% partial hepatectomy and result in an increased mortality following this procedure. The present study was designed to determine whether three H2 blocking agents (cimetidine, ranitidine, famotidine) and a new, powerful antisecretory drug (omeprazole) specifically influence hepatocyte proliferation in primary culture. Hepatocytes were isolated from livers of normal male rats by the standard collagenase perfusion technique. Hepatic DNA synthesis and percent of labelled nuclei were determined after 48 h incubation. Hepatocytes in culture were incubated with the H2 blocking agents and omeprazole or with different concentrations of serum obtained from sham-operated or 70% hepatectomized rats treated or not with the same agents. Rats were injected intraperitoneally at 8:00 a.m. on two consecutive days. In hepatectomized rats, the first dose was injected at 8:00 a.m. immediately after surgery, the second, 24 h later. The serum of sham-operated or 70% hepatectomized rats that did not receive drugs served as control. No changes in DNA synthesis, percentage of labelled nuclei and transaminase were detected when the agents were added to the hepatocytes in culture at concentrations within the effective pharmacological dosage and 30 times higher. Similarly, no changes in these parameters were obtained when different concentrations of serum obtained from sham-operated rats treated with H2 blocking agents or omeprazole were added to the basal culture medium. However, a significant inhibition of DNA synthesis and of percentage of labelled nuclei was observed when hepatocytes were incubated in the presence of serum from 70% hepatectomized rats that had been treated with cimetidine or with ranitidine. The serum of 70% hepatectomized rats treated with famotidine and omeprazole had no effect on hepatocyte proliferation in vitro. No effect on transaminase was found in these conditions.

Mammalian liver is a sex steroid-responsive tissue. The effects of these hormones presumably are mediated by hepatic estrogen receptors (ER) and androgen receptors (AR). Serum levels of sex hormones display circadian rhythms. Further, estrogens and androgens are commonly administered; administration of these agents is associated frequently with liver disease. Therefore, we investigated whether the cytosolic and nuclear sex steroid receptors also display a similar circadian rhythm, and whether variations occurred in the distribution of receptors between cytosolic and nuclear compartments. Animals were killed every 4 h from midnight till the following midnight; cytosolic and nuclear levels of both ER and AR were measured. Cytosolic ER reached a maximum level at 4 AM, and a minimum at 8 PM and midnight of both days. Nuclear ER was highest at 8 AM and lowest at 4 PM and 8 PM, a pattern which parallels variations in serum estradiol levels. Cytosolic AR was highest at 8 PM and lowest at midnight and 4 AM. Nuclear AR was highest at 4 AM and lowest at 4 PM and 8 PM. The highest level of nuclear AR does not correspond to the maximum serum testosterone level, which occurred at 4 PM. The total hepatic content of both ER and AR was not constant over the 24-h period, but varied considerably with time of day. These studies suggest that both ER and AR show a distinct circadian rhythm in subcellular compartmentalization, and that total hepatic content of ER and AR varies significantly during a 24-h period.

Sex hormone receptors were quantitated in normal male rat liver and in regenerating liver at several different times after partial (70%) hepatectomy. Both estrogen and androgen receptor content were altered dramatically by partial hepatectomy. Total hepatic content and nuclear retention of estrogen receptors increased, with the zenith evident 2 days after partial hepatectomy, corresponding to the zenith of mitotic index. Serum estradiol increased after 1 day, and reached a maximum at 3 days after surgery. In contrast, total and nuclear androgen receptor content demonstrated a massive decline at 1, 2, and 3 days after resection. Serum testosterone displayed a parallel decline. In addition, hepatic content of two androgen-responsive proteins was reduced to 15% and 13% of normal values during this period. The activity of these various proteins during regeneration of male rat liver is comparable to that observed in the liver of normal female rats. Taken together, these results indicate that partial hepatectomy induces a feminization of certain sexually dimorphic aspects of liver function in male rats. Furthermore, these data provide evidence that estrogens, but not androgens, may have an important role in the process of liver regeneration.