Cell & Developmental Biology
Open Access

A Perspective on Intracellular Messenger Mediating Hormonal Actions

Hali Sinha^{* *}Correspondence: Hali Sinha, Centre for Stem Cell Research, Christian Medical College Campus, Vellore, India, Email:

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Description

Hormones work together in complex networks to maintain homeostasis and ensure the proper functioning of various systems and processes in the body. They play a significant role in regulating numerous physiological processes, including growth and development, metabolism, immune function, mood, and reproduction. Hormonal actions in the human body are diverse and can affect nearly every aspect of our health and well-being. Few examples of hormonal actions:

• Hormones such as insulin, glucagon, and thyroid hormones play a vital role in regulating metabolism, and controlling the use and storage of energy from food.

• Growth Hormone (GH) and insulin-like growth factor (IGF-1) are essential for the growth and development of tissues and bones, especially during childhood and adolescence.

• Hormones like estrogen and progesterone in females and testosterone in males regulate the reproductive system, including the menstrual cycle, pregnancy, and fertility.

• Neurotransmitters like serotonin, dopamine, and norepinephrine, which have hormonal functions, play a significant role in mood regulation and emotional well-being.

• Hormones like Human Chorionic Gonadotropin (HCG) play a significant role in maintaining pregnancy, while prolactin is involved in milk production during lactation.

• Hormones like estrogen and testosterone are responsible for the development of secondary sexual characteristics, such as facial hair in males and breast development in females.

Hormonal actions at cellular level

Hormonal actions at the cellular level involve how hormones interact with target cells to regulate various physiological processes. When a hormone is released into the bloodstream, it travels to its target tissues or cells, where it binds to specific receptors. This binding triggers a series of cellular responses, leading to various physiological effects. When a hormone binds to its receptor on the cell surface or inside the cell, it initiates a signaling cascade, which may involve secondary messengers like cyclic AMP (cAMP), calcium ions (Ca2+), or protein kinases. The signaling cascade activated by hormone-receptor binding leads to specific cellular responses. These responses can vary widely depending on the type of hormone, the target tissue, and the receptors involved. Examples of cellular responses include:

Gene expression: Some hormones, like steroid hormones (e.g., cortisol or estrogen), enter the cell and bind to nuclear receptors, influencing gene transcription and protein synthesis.

Enzyme activation/inhibition: Hormones can activate or inhibit specific enzymes within the cell, altering metabolic pathways.

Ion transport: Hormones can affect ion channels, leading to changes in membrane potential and cellular excitability.

Cell growth and differentiation: Certain hormones play a role in cell growth, proliferation, and differentiation.

Hormonal actions at cyclic AMP (cAMP)

The process begins when a hormone, such as epinephrine or glucagon, binds to a G Protein-Coupled Receptor (GPCR) on the cell membrane. GPCRs are a large family of cell surface receptors involved in transmitting signals from the extracellular environment to the inside of the cell. When the hormone binds to the receptor, it causes a conformational change in the receptor, leading to the activation of a G protein associated with the receptor. The activated G protein, specifically the alpha subunit (Gα), activates an enzyme called adenylyl cyclase. Adenylyl cyclase is responsible for converting Adenosine Triphosphate (ATP) into cyclic AMP (cAMP).

Adenylyl cyclase catalyzes the conversion of ATP to cAMP, leading to an increase in intracellular cAMP levels. Cyclic AMP serves as a second messenger by binding to and activating Protein Kinase A (PKA). PKA is a protein kinase enzyme that phosphorylates target proteins by adding phosphate groups. Active PKA then phosphorylates specific target proteins within the cell. Phosphorylation of target proteins by PKA leads to a variety of cellular responses, depending on the specific target and cell type. Some common responses include:

• Modulation of ion channels, affecting membrane potential and cellular excitability.

• Regulation of gene transcription by phosphorylating transcription factors or other regulatory proteins.

The cAMP signaling pathway is tightly regulated to prevent prolonged activation. Cyclic AMP is degraded by an enzyme called Phosphodiesterase (PDE), which converts cAMP into AMP (Adenosine Monophosphate). This degradation reduces cAMP levels and terminates the signaling cascade.

Conclusion

Understanding hormonal actions at the cellular level is essential for comprehending how hormones regulate various physiological processes and contribute to overall health and homeostasis. Dysregulation of hormonal signaling can lead to a wide range of health disorders and conditions. Hormones that use the cAMP signaling pathway include epinephrine, glucagon, and many others. Each hormone binds to its specific receptor, initiating a cascade of events that ultimately lead to the activation or inhibition of various cellular processes. The cAMP signaling pathway is just one of several intracellular signaling pathways that hormones can use to exert their effects within cells. Different hormones and receptors can activate distinct signaling pathways, allowing for fine-tuned regulation of cellular responses.