Lipophilic Hormones

Due to lipophilia, steroid hormones and thyroid hormones T3 and T4 are bound in the blood to larger transport proteins, usually specific for the respective hormone, thus protecting them from rapid degradation and excretion. Since only the free, unbound hormone is bioactive and there is a balance between the bound and free parts, the protein-bound hormone can also serve as a circulating storage form. Accordingly, the half-lives of these hormones are hours to days, and the steroid hormones penetrate the cell unhindered. There they find the specific cytoplasmic binding protein or receptor protein suitable for them. Binding with this intracellular receptor is a prerequisite for hormone action. The hormone-receptor protein complex - H-R protein complex - then migrates through the pores of the nuclear membrane into the cell nucleus -translocation - and attaches itself to specific regions of the DNA. This releases a specific portion of the nucleotide sequence of DNA for transmission into m-RNA - messenger RNA - transcription. The m-RNA then migrates via the endoplasmic reticulum into the cytoplasm where it is translated at the ribosomes into a protein or enzyme - translation.