Membrane bound Progesteron Receptors (mPRs, PAQR receptor family) are 7-TM proteins expressed on the plasma membranes of cells and bind progestins in a specific, displaceable, high affinity, limited capacity manner, characteristic of steroid membrane receptors and activate G-proteins in several cell types. The mPRs however, do not belong to the GPCR superfamily, nore do they belong to the family of nuclear receptors N3RC like the progesterone receptor (PR). In contrast, mPRs are members of the progestin and adipoQ receptor (PAQR) family. Noteworthy, the Axon ligands™ DiMNF and Stemregenin 1 (Axon 1935 and Axon 1865, respectively) modulating the activity of the aryl hydrocarbon receptor (AHR) are listed and discussed in the section of transcription factors as well, since their biological target has been defined as a class 1 transcription factor[1].