There are four main types of binding proteins in the blood: albumin, globulin, fibrinogen, and lipoproteins. Each type of protein has a different function, but all play a role in keeping the blood circulating properly.
- Albumin is the most abundant protein in the blood plasma and is responsible for maintaining the osmotic pressure of blood.
- Globulin proteins are involved in immune responses and help to transport fats and other substances through the bloodstream.
- Fibrinogen is a clotting protein that helps to stop bleeding by forming clots at injury sites.
- Lipoproteins are responsible for transporting cholesterol and other fats through the bloodstream.
Types of plasma proteins
Hormones that bind to plasma proteins can be divided into two categories: those that bind to albumin and those that bind to globulin. Hormones that bind to albumin include thyroid hormones, steroid hormones, and catecholamines. Hormones that bind to globulin include sex hormones, corticosteroids, and thyroxine-binding globulin.
Plasma protein binding can have a significant impact on the activity of a hormone. For example, the binding of thyroid hormones to plasma proteins decreases their activity because it reduces the amount of hormone that is available to bind to receptor sites.
However, the binding of sex hormones to plasma proteins actually increases their activity because it protects them from being broken down by enzymes in the liver.
In general, plasma protein binding increases the half-life of a hormone and decreases its clearance from the body. This means that hormones that bind to plasma proteins will remain in the bloodstream for a longer period of time and will have a more prolonged effect on the body.
Hormones that bind to plasma proteins are typically more stable and have a longer half-life than those that do not. This is because binding to plasma proteins protects the hormone from being broken down by enzymes in the liver. As a result, hormones that bind to plasma proteins tend to be more potent and have a more prolonged effect on the body.
There are several factors that can influence the amount of hormone that binds to plasma proteins. These include the type of protein to which the hormone binds, the concentration of the hormone in the blood, and the affinity of the hormone for the binding protein.
- The type of protein to which a hormone binds is important because it determines how well the hormone will be protected from breakdown. For example, hormones that bind to albumin are more likely to be degraded by enzymes in the liver than those that bind to globulin.
- The concentration of the hormone in the blood is also important because it determines how much hormone is available to bind to proteins. Finally, the affinity of the hormone for the binding protein influences how tightly the hormone will bind to the protein.
- Hormones that have a high affinity for plasma proteins tend to have a longer half-life and be more potent than those with a low affinity. This is because they are less likely to be broken down by enzymes in the liver. In addition, hormones with a high affinity for plasma proteins tend to bind more tightly to their binding proteins and have a more prolonged effect on the body.
Sex hormone-binding globulin
Sex hormone-binding globulin (SHBG) is a glycoprotein that binds to and transports androgens and estrogens in the blood. Sex hormone-binding globulin (SHBG) is a protein produced by the liver that binds to testosterone and other hormones in the blood, making them unavailable to cells in the body.
SHBG levels are associated with sex hormone levels and may be used as a marker for certain conditions such as testosterone deficiency, hypogonadism, or estrogen excess. In men, SHBG levels may also be used to help diagnose conditions such as testicular cancer or benign prostatic hyperplasia (BPH). In women, SHBG levels may be used to help diagnose conditions such as polycystic ovary syndrome (PCOS), ovarian cancer, or endometriosis.
SHBG levels can be measured using a blood test. The normal range for SHBG is 10-50 nmol/L in men and 18-90 nmol/L in women. Higher than normal SHBG levels may be seen in conditions such as obesity, cirrhosis, or hyperthyroidism. Lower than normal SHBG levels may be seen in conditions such as hypothyroidism, testosterone deficiency, or pregnancy.
SHBG levels can be affected by many factors, including age, sex, hormones, diet, and medications. SHBG levels may also vary throughout the day. SHBG levels should be interpreted using the results of other tests, such as testosterone or estrogen levels, to get a complete picture of an individual’s hormone status.
Causes of increased SHBG levels:
– Use of oral contraceptives or other hormonal medications
– Liver disease
– Thyroid problems
Causes of decreased SHBG levels:
– Diabetes mellitus
– Hypogonadism (testosterone deficiency)
– Use of anabolic steroids or other medications that increase testosterone levels
Thyroid-binding globulin (TBG) is a glycoprotein that binds thyroid hormones in the blood. It is produced by the liver and plays an important role in the regulation of thyroid hormone levels.
TBG is involved in the transport and storage of thyroid hormones, and helps to keep these hormones circulating in the blood. Thyroid hormones are essential for many body functions, including growth, development, and metabolism.
The level of TBG in the blood can be affected by several factors, including:
Certain medications, such as estrogen-containing birth control pills or certain types of hormone therapy
· Liver disease
· Kidney disease
Corticosteroid binding globulin
Corticosteroid-binding globulin (CBG) is a protein that binds to and transports cortisol in the blood. Cortisol is a stress hormone that is released by the adrenal glands in response to stress or injury. CBG helps to regulate the amount of cortisol in the bloodstream and plays a role in maintaining homeostasis.
CBG is produced by the liver and is also known as transcortin. CBG carries various hormones, including cortisol, aldosterone, and progesterone. It has a high affinity for cortisol and can bind up to 80% of the hormone in circulation.
CBG levels are increased in times of stress and decreased in times of relaxation. When cortisol levels are high, CBG binds to the excess hormone and transports it to the liver for metabolism. This prevents cortisol from having prolonged effects on the body and helps to maintain homeostasis.
Causes of decreased CBG levels include:
· -Cushing’s syndrome
· -Nephrotic syndrome
· -Hypovitaminosis (Low B12)
Causes of increased CBG include:
– Estrogen therapy
Albumin is a protein found in blood plasma. Its main function is to maintain the osmotic pressure of blood, but it also plays a role in transporting hormones, lipids, and other molecules through the bloodstream. Albumin is produced in the liver and is constantly being broken down and reassembled in the body.
Because of this, it has a short half-life and must be continually replaced. The albumin in blood can be measured using a simple blood test. An abnormal albumin level may indicate liver disease, kidney disease, or malnutrition.
There are a number of different hormones that bind to albumin in the blood. These include:
Reliability of hormone assessments using the dialysis method
The assessment of hormones by equilibrium dialysis is a reliable and accurate method for determining the levels of various hormones in the body. This method involves the use of a dialysis membrane to separate the hormone molecules from the blood plasma and then measure the amount of hormone that is present in the dialysis chamber.
Equilibrium dialysis is a highly sensitive method for measuring hormones and can be used to measure both free and bound hormone levels. This method is often used to measure levels of testosterone, progesterone, and estradiol. It can also be used to measure other hormones, such as growth hormone and thyrotropin.
Equilibrium dialysis is a laborious and time-consuming method and is not suitable for routine hormone testing. However, it is an excellent method for research purposes and can be used to measure very small changes in hormone levels.
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This was first published on January 8, 2022 and Last Updated on March 16, 2023 by MyEndoConsult