Epidermal growth factor reactivity in rat milk.

Area of Science:

• Biochemistry
• Developmental Biology
• Lactation Biology

Background:

• Epidermal Growth Factor (EGF) is crucial for cell growth and development.
• EGF's presence and form in lactational secretions are not fully characterized.
• Investigating EGF in rat whey provides insights into its role during neonatal development.

Purpose of the Study:

• To characterize the concentration, molecular form, and origin of EGF in rat whey.
• To compare rat whey EGF with salivary gland EGF.
• To understand the stability and potential binding proteins of EGF in rat milk.

Main Methods:

• Quantification of EGF immunoreactivity in rat whey across lactation.
• Gel chromatography (S-200) and gel filtration to determine molecular weight and size.
• Immuno-affinity chromatography for partial purification.
• Binding studies using radiolabeled EGF and antibodies.
• Incubation of rat milk to assess EGF stability.

Main Results:

• EGF concentration in rat whey significantly increases from lactation day 1 to day 19.
• The predominant form of EGF in whey is an 80 kDa complex, not the 6 kDa free form.
• Sialoadenectomy did not affect whey EGF levels, and whey lacked EGF binding proteins.
• Incubation of milk degraded the 80 kDa form into 35 kDa and 6 kDa forms.
• Whey EGF showed different antibody binding compared to submandibular EGF but similar receptor binding.

Conclusions:

• EGF in rat whey exists primarily as a large complex (80 kDa) that changes during lactation.
• This whey EGF is unlikely to originate from the submandibular salivary glands.
• The 80 kDa complex is unstable and can be degraded into smaller forms in rat milk.