Administration of dopamine to rats disorganizes the rhythm of protein synthesis in hepatocytes.

Dopamine was injected intravenously (9 µg/kg) or intraperitoneally (15 µg/kg) to Wistar rats (3-4 months, 300-400 g). Hepatocytes were isolated 40 min after dopamine injection. Dense cultures were maintained on collagen-coated glasses. By the 5th hour, the circaholarian rhythm of protein synthesis in hepatocytes cultures was absent in the dopamine group, but was present in cultures from animals receiving physiological saline (NaCl). The rhythm-disorganizing effect of dopamine was reversible. The rhythm was observed in cultures of hepatocytes isolated 1 day after dopamine treatment. The effect of dopamine was abolished by melatonin. The protein synthesis rhythm was revealed in 5-h cultures of hepatocytes from rats receiving melatonin (32 ng/kg) 40 min after intraperitoneal injection of dopamine. The results of our in vitro experiments with addition of dopamine into the medium of cultured hepatocytes [1] suggest that dopamine in vivo produces a direct effect on liver cells. The observed changes are discussed taking into account the biochemical mechanisms for a direct cell-cell interaction and previously unknown properties of catecholamines.

Effect of protein synthesis rhythm-organizing signal persists for a day after single administration of melatonin to rat.

Melatonin administered to rat intraperitoneally organizes ultradian rhythm of protein synthesis in hepatocytes that persists for 1 day after exposure to the synchronizing signal. Hepatocytes were isolated 1 day after melatonin administration and cultured on coverslips in a serum-free medium. In 24 h in culture, the kinetics of protein synthesis was analyzed. In our previous experiments, we detected a rhythm in cells isolated in 1.5 h, but not in 3 days after melatonin administration to the rat. We have found that synchronization of oscillations of the protein synthesis intensity in vivo persists over 1 day after rat exposure to melatonin. Phenylephrine, an efficient synchronizer of protein synthesis in vitro, does not organize the rhythm in vivo.