Diurnal variation in growth hormone receptor messenger ribonucleic acid in liver and skeletal muscle of lit/+ and lit/lit mice.

The present study investigated the diurnal variation in GH receptor (GHR) mRNA in liver and skeletal muscle of 3-month-old GH-deficient and -sufficient mice using quantitative real-time RT-PCR. lit/lit (GH deficient) or lit/+ (GH sufficient) mice were fed ad libitum and lights were on between 0600 and 2000. Tissues were collected at 0800-1000, 1200-1400 and 2000-2200. Hepatic GHR mRNA levels of lit/+ mice at 0800-1000 were significantly lower than those at 1200-1400 and 2000-2200. There was no significant variation in hepatic GHR mRNA of lit/lit mice. In skeletal muscle, GHR mRNA levels of both lit/+ and lit/lit mice at 1200-1400 were significantly higher than those at 0800-1000 and 2000-2200. There was also a diurnal change in hepatic IGF-I mRNA levels of lit/+ but not of lit/lit mice; the levels were lowest at 0800-1000 in lit/+ mice. On the other hand, there was no variation in IGF-I mRNA levels in skeletal muscle. These results suggest that 1) there is a diurnal variation in GHR expression in liver and skeletal muscle and the pattern of the variation is tissue specific; 2) GH deficiency blunted the diurnal variation in GHR mRNA in liver but not that in skeletal muscle; 3) IGF-I mRNA expression in liver is more closely related to GHR mRNA expression than that in skeletal muscle.