Diurnal rhythms of rat liver serine dehydratase, D-site binding protein, and 3-hydroxy-3-methylglutaryl coenzyme A reductase mRNA levels are altered by destruction of the suprachiasmatic nucleus of the hypothalamus.

It is generally accepted that a clock generating biological rhythms exists in the suprachiasmatic nuclei (SCN) of the hypothalamus in rodents. We have examined if diurnal variations of rat liver serine dehydratase (SDH), D-site binding protein (DBP), and 3-hydroxy-3-methyl-glutaryl coenzyme A reductase (HMGR) mRNA levels, each of which exhibits low values during the daytime (06:00-18:00) and high values during the dark period, are controlled by the SCN. The SCN were destructed electrolytically, and, 2 weeks later, rats were sacrificed at 06:00, 12:00, 18:00, and 24:00. Completeness of SCN lesions was assessed by the alteration of spontaneous locomotor activity and histological examination of the brains. The SDH and DBP mRNA levels in SCN-lesioned rats were very low at 06:00 and almost eliminated at 18:00, whereas the HMGR mRNA level at 06:00 was low at 06:00 and slightly increased at 18:00 compared to the control values. When determined at 12:00 and 24:00, the SDH, DBP, and HMGR mRNA levels in sham-operated rats were higher at 24:00 than at 12:00, whereas those in SCN-lesioned rats were higher at 12:00 than at 24:00. The hepatic beta-actin and glycine N-methyltransferase mRNA levels showed no significant diurnal variation and were not affected by SCN lesions. These results indicate that the SCN also play a pivotal role in determining rhythmic gene expression in liver.