A technique for the organ culture of postnatal and adult rat liver has been developed. Liver slices, 0.3 mm thick, were maintained in Conway units at the interphase between medium and a 95% O2:5% CO2 atmosphere. Postnatal liver in culture for up to 72 h had healthy hepatocytes throughout the explants; if adult liver was used the upper 0.2 mm was healthy after 24 h. These slices incorporated tritiated orotate and leucine into trichloroacetic acid-precipitable material. Incorporation of orotate was shown to be spread over the entire slice of neonatal liver. Culturing did not alter the potassium ion content of postnatal liver. Tyrosine aminotransferase activity in liver slices from postnatal, adult, and adrenalectomized adult rats was stimulated by glucocorticoids and dibutyryl cyclic AMP. Cycloheximide and actinomycin D prevented this response. Further, cortisol exerted a permissive effect on the stimulation of tyrosine aminotransferase activity by dibutyryl cyclic AMP in slices from adrenalectomized rats. Induction of urea cycle enzymes by cortisol was demonstrated in cultures of liver from adrenalectomized adult animals.

The administration of hydrocortisone to 3- to 15-day-old rats increased the levels of hepatic argininosuccinate synthetase (ASS) and arginase. In 13-day-old rat liver expiants maintained in organ culture, ornithine carbamoyltransferase (OTC), carbamoylphosphate synthetase (CPS) and arginase were stimulated by betamethasone. Actinomycin D prevented the responses of the latter two enzymes. Dibutyryl cyclic AMP raised OTC, CPS, ASS and arginase in vitro. The responses of the latter three enzymes were blocked by cycloheximide and puromycin and partially inhibited by actinomycin D. The simultaneous presence of betamethasone and dibutyryl cyclic AMP in the culture medium raised CPS and OTC in an additive manner. The sequential treatment of the cultures with betamethasone followed by dibutyryl cyclic AMP increased CPS and arginase synergistically and amplified the response of ASS to dibutyryl cyclic AMP.