Nutrient sources:

• Milk Fat Globule -

Fat Soluble Vitamins

Steroid Hormones

Progesterone less than 1 to more than 30 ng/ml whole milk

Estrogens Estradiol-17ß - peaks in colostrum is ~.6 ng/ml, then declines

Estrone -peaks in colostrum is 2 ng/ml, then declines

Corticosteroids ~3 ng/ml at parturition, .2 - .5 ng/ml in milk

Androgen Low concentrations

• Casein - Provides a balanced source of amino acids.

In addition to a nutritional source of amino acids, partial digestion of ß-casein;yields casomorphins - Tyr-Pro-Phe-Pro-Gly-Pro-Ile

These pepides have opioid activity in several assays

Generally are protease resistant

Have been identified in calf blood after milk ingestion

May regulate development of the intestinal mucosal immune system in the neonate

• Other immunomodulatory activitieshave been identified in peptides generated by proteolytic hydrolysis of ß-lactoglobulin and a-lactalbumin.
• Enzymes

Milk and colostrum contain many enzymes. There is considerable species variation. Some have fairly high activities in some species.

High in cow milk, low in human milk : Lactoperoxidase, Xanthine oxidase, Ribonuclease, and Alkaline Phosphatase

High in human milk, low in cow milk : Lipase activity (bile salt activated), Lysozyme, and Protease activity

Milk and colostrum also contain plasmin and plasminogen, and plasminogen activator activity, as well as trypsin inhibitor activity (Cow has high TIA in colostrum and during mastitis, low in milk; Human milk has ~.7 mg/ml in colostrum, ~.05 mg/ml in mature milk)

• Carrier Proteins in Colostrum and Milk
• Vitamin-binding proteins for Folate and B12
• Mineral-binding proteins Fe - lactoferrin, transferrin; Ca - casein and a- lactalbumin; Cu - lactoferrin
• Lipid-binding proteins, such as ß-lactoglobulin; binds fatty acids, retinol (?) and serum albumin binds fatty acids

• Hormone-binding proteins, such as Corticosteroid-binding globulin and IGF-binding proteins

• Growth Factors

A range of growth factor activities have been identified in milk, including, IGF-I which is in milk at about 25 - 50 ng/ml, and IGF-II which is in milk at about 80 - 120 ng/ml.

EGF is in HUMAN milk at about 50 ng/ml (it is the major growth factor activity in human milk); in mouse milk, EGF is at about 150 - 400 ng/ml milk. EGF stimulates enterocyte (crypt cell) proliferation. It is effective when administered orally. Effects are probably indirect, because it is ineffective in vitro. TGF-a is in milk. It is similar in activity to EGF. NGF (nerve growth factor) has been identified at least in mouse milk.

• Hormones in Milk

A wide range of hormones have been identified in milk, including:

• Other Factors

Numerous other bioactive factors have been identified in milk, including:

Erythropoietin

MDGF1 (mammary derived growth factor 1) Isolated from human milk, mammary tumors Stimulates growth of mammary cells and production of collagen mRNA. Receptors on mammary and kidney cells.

HMGF I and HMGF II (Human milk growth factors)

CBGF (Colostric basic growth factor), similar to PDGF

Calcitonin-like peptide is in milk at about 600 pg/ml. It is an inhibitor of PRL release. Passive immunization of rat pups with anti-CT increases serum PRL. No CT-like RNA in the rat mammary gland.

Parathyroid hormone-like peptide mRNA is expressed in the rat mammary gland only during lactation It is only expressed for about 2 - 4 hr after suckling.

CAMP

CGMP

Prostaglandins

Neurotensin

Bombesin (Gastrin-releasing peptides). Bombesin stimulates proliferation of fibroblasts and bronchial epithelial cells, in vitro. In vivo, induces gastric cell hyperplasia and increased pancreatic DNA content Other effects - Hypertension, satiety, change in sugar metabolism, hypothermia, modulation of levels of gastrointestinal-associated peptide hormones, increased gastric acid secretion.