#VasopressinHormones

#Biology

#EndocrineSystem

Introduction

• Vasopressin or antidiuretic hormone (ADH) or arginine vasopressin (AVP) is a nonapeptide synthesized in the hypothalamus.

• A nonapeptide is a neuropeptide made up of nine amino acids: 

  • Structure: Six amino acids form a ring structure and three form a side chain. 

• Vasopressin, also known as antidiuretic hormone (ADH) or arginine vasopressin (AVP), has several major functions, including:

  • Regulating kidney functioning: Vasopressin primarily affects the kidney's ability to reabsorb water. 

  • Modulating brainstem autonomic function: Vasopressin acts as a central neurotransmitter to modulate brainstem autonomic function. 

  • Regulating social behavior: Vasopressin regulates social behaviors such as affiliation, aggression, monogamy, and paternal behaviors. 

• Vasopressin, also known as arginine vasopressin (AVP) or antidiuretic hormone (ADH), is a nonapeptide with the following structure:

  • Amino acid sequence: Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly-NH2 

  • Disulfide bridge: A disulfide bridge between the cysteine residues at positions 1 and 6 

  • Molecular weight: 1084 Da 

Kidney Functioning

• Vasopressin helps the kidney reabsorb water by increasing the water permeability of the renal collecting duct cells. This is done by :

  • Vasopressin increases the number of AQP2 water channels in the apical membrane of the collecting duct principal cells. This allows water to reabsorb back down its concentration gradient.

  • Vasopressin increases the number of AQP2 water channels in the apical membrane of the collecting duct principal cells. This allows water to reabsorb back down its concentration gradient.

  • Vasopressin activates PKA, which phosphorylates AQP2, and this phosphorylation event is required to increase the water permeability and water reabsorption of the collecting duct cells. It has been established that the phosphorylation of AQP2 induces its apical membrane insertion, rendering the cell water-permeable.

  • The AQP2 gene provides instructions for making a protein called aquaporin 2. This protein forms a channel that carries water molecules across cell membranes. It is found in the kidneys in structures called collecting ducts, which are a series of small tubes that reabsorb water from the kidneys into the bloodstream.

• Water reabsorption regulates blood pressure by increasing or decreasing the amount of water and sodium reabsorbed by the kidneys.

Brainstem Autonomic Function

• Vasopressin (AVP) modulates brainstem autonomic function by acting as a neurotransmitter and neuromodulator: 

  • Neurotransmitter and neuromodulator

    AVP is synthesized in the central nervous system and transported to various areas, where it acts as a neurotransmitter and neuromodulator. 

  • Affects neuronal excitability

    AVP can directly affect neuronal excitability by opening non-specific cationic channels or closing K+ channels. 

  • Influences synaptic transmission

    AVP can influence synaptic transmission by acting postsynaptically or upon presynaptic target neurons or axon terminals. 

Social Behaviour

• Vasopressin (AVP) influences social behaviors through its regulatory effects on the brain, enhancing behaviors like affiliation, aggression, and pair bonding.

• Arginine-vasopressin (AVP) is known to regulate aggressive behavior in certain species, including Syrian hamsters, via specific receptor subtypes like the V1a receptor.

• In males, AVP interacts with various neurochemical signals, including serotonin, which can modulate levels of offensive aggression.