Like the M 1 and M 3 muscarinic receptor, M 5 receptors are coupled with G proteins of class Gq that upregulate phospholipase C and, therefore, inositol trisphosphate and intracellular calcium as a signaling pathway.
Radioactive iodine is a very effective type of treatment for cancer of the thyroid gland. Thyroid cells absorb iodine. The radioactive iodine from the drink or capsule is absorbed into your body and picked up by the thyroid cancer cells wherever they are. So it can kill the cancer cells even if they have spread.
Japanese women (who have a very high iodine intake thanks to all the seaweed in their diet) have lower rates of breast cancer than women in most other parts of the world. In some rat studies, feeding iodine or seaweed has a suppressive effect on breast tumors.