[Dynseli]

REGULATION OF RECEPTOR NUMBERS

The half-life of steroid hormone receptors ranges from 2 to 4 hours for ERα 4 hours for AR, 7 to 10 hours for PR, and 19 hours for GR. The relatively long half-life of the steroid hormone receptors strongly suggests that the receptor proteins are recycled before eventual degradation.

The half life of the receptors, or the hormones on the receptors? If that's a direct quote from a paper, I don't get it. If the half-life of a receptor is that short, how does anyone have enough receptors? Or I misunderstood it, or there's something more...

Steroid hormones generally autoregulate their receptor levels. Desensitization or downregulation of receptor numbers, measured by decreased ligand binding capacity, occurs in response to exposure to high levels of ligand and involves the reduction in receptor mRNA levels, decreasing the number of available receptors. The receptor gene may be negatively regulated by the hormonal ligand itself through its receptor protein interacting with specific HREs in the gene. Upregulation or self-priming may occur in an analogous fashion. Steroid hormones can regulate receptor levels for other hormones (e.g. E2 increases PR levels in estrogen-responsive tissues). Progesterone can downregulate its own receptors, as well as ERα and ERβ. This increase or decrease in receptor levels in homologous or heterologous regulation can be caused by alterations in receptor gene transcription or decay rates for receptor mRNA or protein.

I thought progesterone antagonized yet upregulated ER α and β, even though I found nothing solid on this. Perhaps there's more to understand here.