Plasma growth hormone pattern regulates epidermal growth factor (EGF) receptor messenger ribonucleic acid levels and EGF binding in the rat liver.

Abstract

It has recently been shown that GH increases the number of available hepatic receptors for epidermal growth factor (EGF). In the present study the effects of the sexually dimorphic plasma GH pattern (higher pulsatility in male rats) on hepatic EGF binding and EGF receptor mRNA concentration were investigated. The specific binding of [125I]EGF to purified liver membranes was about 2-fold higher in male rats than in females on days 35, 50, and 80 of life. EGF receptor mRNA levels, as determined by an RNase protection solution hybridization assay, were higher in males only on days 47-50. Hypophysectomy on day 50 reduced the EGF receptor mRNA concentration to a level that did not differ between male and female rats. In hypophysectomized rats of both sexes, intermittent GH treatment (sc injections every 12 h for 7 days) enhanced hepatic EGF receptor mRNA concentrations to normal male levels, while continuous GH administration was less effective. Northern blot analysis indicated that transcripts with apparent sizes of 9.5 and 6.6 kilobases were dependent on the plasma GH pattern. Intermittent iv GH replacement therapy for 5 days given at 3-h intervals by an automatic iv infusion system increased the hepatic EGF receptor mRNA concentration as well as specific EGF binding, whereas continuous iv GH infusion was ineffective. These results show that a pulsatile plasma GH pattern, similar to that of male rodents, is markedly more effective in enhancing hepatic EGF receptor mRNA levels and EGF binding than a continuous feminine GH pattern. These results are consistent with a pretranslatory stimulation of EGF receptor synthesis by pulsatile GH.