Progesterone’s primary function during the menstrual cycle is to induce a secretory endometrium ready for implantation of a fertilized egg.

Levels therefore increase during the luteal phase of the cycle after ovulation.

If no implantation occurs, progesterone returns to follicular phase levels. If a pregnancy results, progesterone continues to rise to very high levels and carries out a variety of functions necessary to sustain the pregnancy.

In some patients with infertility, ovulation may occur but luteal phase levels of progesterone are inadequate. Luteal phase deficiency is a result of inadequate progesterone production by the corpus luteum.

During menopause, ovarian progesterone production dwindles, resulting in postmenopausal levels similar to those seen in men.

Progesterone has wide-ranging physiological effects, including neuroprotection, maintenance of skin elasticity, and development of bone tissue. Progesterone also counteracts the proliferative effects of estrogen on the endometrium. When samples are collected after transdermal application of progesterone, saliva progesterone levels are higher than serum, indicating distribution of progesterone to tissues.

Proinsulin is the precursor of insulin and C-peptide. Following synthesis, proinsulin is packaged into secretory granules, where it is processed to C-peptide and insulin by prohormone convertases and carboxypeptidase E.

Only 1% to 3% of proinsulin is secreted intact. However, because proinsulin has a longer half-life than insulin, circulating proinsulin concentrations are in the range of 5% to 30% of circulating insulin concentrations on a molar basis, with the higher relative proportions seen after meals and in patients with insulin resistance or early type 2 diabetes. Proinsulin can bind to the insulin receptor and exhibits 5% to 10% of the metabolic activity of insulin.

Prolactin: Functions, Normal Ranges, and Clinical Significance

Prolactin is a hormone produced by the pituitary gland that plays a vital role in reproductive health and various physiological processes.

Functions of Prolactin

• In Women: Primarily responsible for breast development and milk production, with levels rising during pregnancy and peaking at delivery.
• In Men: Contributes to reproductive function, though its role is less pronounced.
• In Both Genders: Can fluctuate due to nipple stimulation, breastfeeding, and physical or emotional stress.

Normal Prolactin Ranges (ng/mL)

Prolactin Levels During Puberty (Tanner Stages) (ng/mL)

When prolactin levels exceed normal ranges, a condition called hyperprolactinemia may develop, potentially indicating underlying health conditions that require medical evaluation. Monitoring prolactin levels is crucial for diagnosing and managing hormonal imbalances that affect fertility, metabolism, and overall endocrine health.

Prolactin is a hormone produced by the pituitary gland that causes breast development in women and milk production in pregnant women. Prolactin does not have known biological function in men.

Proline is a nonessential amino acid. It contains a secondary α-imino group and is sometimes called an α-imino acid. Proline, and its metabolite hydroxyproline, constitute a third of the total amino acids found in collagen. Lysine, proline, hydroxyproline, and vitamin C are all important in the synthesis of collagen for skin, bones, tendons, and cartilage. Proline is abundant in meat, bone meal, poultry, salmon, wheat, barley, and corn. In addition to dietary sources, proline can be synthesized from glutamate/glutamine, arginine, and ornithine. It can also be synthesized within enterocytes from degradation of small peptides.

Proline is a nonessential amino acid. It contains a secondary α-imino group and is sometimes called an α-imino acid. Proline, and its metabolite hydroxyproline, constitute a third of the total amino acids found in collagen. Lysine, proline, hydroxyproline, and vitamin C are all important in the synthesis of collagen for skin, bones, tendons, and cartilage. Proline is abundant in meat, bone meal, poultry, salmon, wheat, barley, and corn. In addition to dietary sources, proline can be synthesized from glutamate/glutamine, arginine, and ornithine. It can also be synthesized within enterocytes from degradation of small peptides.

Proline is a nonessential amino acid. It contains a secondary α-imino group and is sometimes called an α-imino acid.

Proline, and its metabolite hydroxyproline, constitute a third of the total amino acids found in collagen. Lysine, proline, hydroxyproline, and vitamin C are all important in the synthesis of collagen for skin, bones, tendons, and cartilage.

Proline is abundant in meat, bone meal, poultry, salmon, wheat, barley, and corn.

Proline is a nonessential amino acid. It contains a secondary α-imino group and is sometimes called an α-imino acid. Proline, and its metabolite hydroxyproline, constitute a third of the total amino acids found in collagen. Lysine, proline, hydroxyproline, and vitamin C are all important in the synthesis of collagen for skin, bones, tendons, and cartilage. Proline is abundant in meat, bone meal, poultry, salmon, wheat, barley, and corn. In addition to dietary sources, proline can be synthesized from glutamate/glutamine, arginine, and ornithine. It can also be synthesized within enterocytes from degradation of small peptides.

Proline is a nonessential amino acid, which means that it is manufactured from other amino acids in the liver; it does not have to be obtained directly through the diet.

Proline is the precursor to hydroxyproline, which is a major amino acid found in the connective tissue of the body – collagen.

Proline is a nonessential amino acid. It contains a secondary α-imino group and is sometimes called an α-imino acid.

Proline, and its metabolite hydroxyproline, constitute a third of the total amino acids found in collagen. Lysine, proline, hydroxyproline, and vitamin C are all important in the synthesis of collagen for skin, bones, tendons, and cartilage.

Proline is abundant in meat, bone meal, poultry, salmon, wheat, barley, and corn.

Proline is a nonessential amino acid. It contains a secondary α-imino group and is sometimes called an α-imino acid. Proline, and its metabolite hydroxyproline, constitute a third of the total amino acids found in collagen. Lysine, proline, hydroxyproline, and vitamin C are all important in the synthesis of collagen for skin, bones, tendons, and cartilage. Proline is abundant in meat, bone meal, poultry, salmon, wheat, barley, and corn. In addition to dietary sources, proline can be synthesized from glutamate/glutamine, arginine, and ornithine. It can also be synthesized within enterocytes from degradation of small peptides.

Proline is a nonessential amino acid. It contains a secondary α-imino group and is sometimes called an α-imino acid. Proline, and its metabolite hydroxyproline, constitute a third of the total amino acids found in collagen. Lysine, proline, hydroxyproline, and vitamin C are all important in the synthesis of collagen for skin, bones, tendons, and cartilage. Proline is abundant in meat, bone meal, poultry, salmon, wheat, barley, and corn. In addition to dietary sources, proline can be synthesized from glutamate/glutamine, arginine, and ornithine. It can also be synthesized within enterocytes from degradation of small peptides.

Proline is a nonessential amino acid. It contains a secondary α-imino group and is sometimes called an α-imino acid.

Proline, and its metabolite hydroxyproline, constitute a third of the total amino acids found in collagen. Lysine, proline, hydroxyproline, and vitamin C are all important in the synthesis of collagen for skin, bones, tendons, and cartilage.

Proline is abundant in meat, bone meal, poultry, salmon, wheat, barley, and corn.

Collagen Catabolism: Collagen contains proline, hydroxyproline, and glycine.

→ Sarcopenia (low muscle mass) was associated with higher plasma proline.

→ Proline was significantly lower in esophageal cancer patients compared to the healthy controls.

→ Hydroxyproline and proline together constitute around 25% of residues and allow for stability and twisting of collagen.

→ Dietary intake increases levels of proline and hydroxyproline.

→ Proline and hydroxyproline both negatively correlated with a higher likelihood of anxiety, depression, and psychoses.

Proline is a nonessential amino acid, which means that it is manufactured from other amino acids in the liver; it does not have to be obtained directly through the diet.

Proline is the precursor to hydroxyproline, which is a major amino acid found in the connective tissue of the body – collagen.