Question

Written form: What do you think would happen if the receptors on a target cell become resistant to the hormone? Do you know any disease related to this?

Answer 1

Hormone after releasing from the endocrine glands it reaches to the target organ through blood for their physiological actions. At first hormone has to bind with the receptor of that particular target organ, there are four types of receptor in the body for binding with different hormones. Receptor kinase (for insulin, growth factors), receptor linked kinases ( growth hormone, prolactin, cytokine), G-protein coupled receptor (glucagon, parathyroid hormone, epinephrine), ligand gated ion channel ( some neurotransmitter like GABA, acetylcholine binds). These are membrane bound receptor, but some hormones also binds with nuclear receptors.

So the hormone either binds with membrane receptor or with intracellular receptor and regulate the gene expression. So receptor binding is important for hormones for exhibit their physiological actions. So, if any receptor on target cells is resistance to any specific hormone then the hormone couldn't exhibit its physiological actions in our body. The plasma levels of that specific hormone is remain high but couldn't binds with the receptor of target cell. In this time the hormone-receptor complex couldn't be formed and no gene expression is occured and no mRNA is formed for their actions.

Example: Type 2 diabetes or non-insulin dependent diabetes mellitus is a genetic disorder in which the insulin receptor in the responsive (target) cells is resistance to insulin hormone. In this case the plasma levels of insulin is normal or increased but there is no action of insulin hormone in the body. In normal conditions insulin binds with receptor on membrane and exhibit its physiological actions through the tyrosine kinase activity of the membrane receptor. Insulin after increases the glucose uptake in target cells by translocating glucose transporter (GLUT4) in the membrane in this way insulin helps to absorb glucose from blood to the tissue for cellular metabolism. But in case of insulin resistance the hyperglycemia is occured where the blood glucose levels is increased, because the insulin hormone couldn't binds with their receptor or the receptor is resistance to insulin. The tyrosine kinase domain of insulin receptor has sometimes have mutations so that it couldn't initiate the downstream consequences of insulin binding and the receptor become resistance to insulin. So if a target cells is resistant to its specific hormone then the physiological actions of that hormone couldn't be exhibited in our body.