Avances en el conocimiento de las proteínas de la leche materna / Advances in the knowledge about human milk proteins

La glándula mamaria y la leche materna son el resultado de millones de años de una evolución que llevó a una composición óptima para el crecimiento y desarrollo de recién nacidos y lactantes; la leche materna favorece el crecimiento, la adaptación y la supervivencia de su organismo y de sus órganos inmaduros. Análisis recientes han demostrado en ella la presencia de 1606 proteínas que en su mayoría son sintetizadas en los acinos de la glándula mamaria aunque otras proteínas y péptidos provienen de órganos como el sistema linfático y el aparato digestivo. La composición de la leche materna incluye enzimas que modifican sus proteínas y originan péptidos antimicrobianos, antihipertensivos y estimuladores del metabolismo. Esta actividad proteolítica actúa en sitios específicos de las cadenas peptídicas de la proteína de la leche. La activación extemporánea de estos enzimas en los acinos es regulada por péptidos inhibidores y activadores que previenen procesos inflamatorios. Algunos enzimas de la leche actúan en el tubo digestivo de recién nacidos y lactantes y complemen tan la menor concentración y actividad de sus propios enzimas digestivos. Así, la enteroquinasa de la leche estimula la liberación de enzimas pancreáticos (mediada por el estímulo de la colecistoquinina-pancreozimina); la lipasa activada por las sales biliares complementa la baja producción de lipasa pancreática. Estas actividades probablemente facilitan la nutrición de los prematuros, cuyo tubo di gestivo es más permeable a las proteínas parcialmente hidrolizadas y cuyas actividades enzimáticas y factores defensivos locales no han alcanzado su plena madurez. Esto también puede estimular en ellos la tolerancia inmunológica. En este artículo se presentan los aspectos fisiológicos relevantes de la leche materna, y los avances en el conocimiento de su composición, para el cabal conocimiento del pediatra de esta importante materia.

The mammary gland and maternal milk are the product of millions of years of evolution that resul ted in an optimal composition that sustains the growth and development of newborns and infants. Maternal milk supports the growth, adaptation and survival of this immature organism. Recent studies have detected 1606 different proteins in human milk, most of them synthesized in the acini of the glandular tissue while others originate from distant organs such as the lymphoid tissue and the digestive tract. Maternal milk enzymes modify its proteins and liberate peptides with antimicrobial, antihypertensive or stimulatory activities. This proteolytic activity occurs at specific sites in peptide chains. To prevent the extemporaneous activation of these proteolytic enzymes, that would result in inflammatory processes, maternal milk also contains inhibitory peptides that together with the stimulatory peptides conform a complex regulatory system. Some enzymes in maternal milk main tain their activity in the gastrointestinal tract of infants and compensate for the decreased activity of digestive tract enzymes in newborns. Thus, the milk enterokynase stimulates the release of pancreatic proteases as it induces the liberation of cholecystokynin/pancreozymin. The bile salt-activated lipase of human milk is activated in the duodenum by the infants' bile salts and partially compensates for the low levels of pancreatic lipase in newborns. These milk enzymes probably contribute to the nutrition of premature infants as they increase the availability of amino acids and peptides in their upper gastrointestinal tract; furthermore, as their intestinal epithelium is more permeable to peptides and partially digested protein this may help induce immune tolerance. The most relevant issues in the physiology and composition of the maternal milk are presented in this review.

Vascular endothelial growth factor [Vegf] localization in the mammary gland at various stages of its physiological cycle; a histological and immunohistochemical study

Vascular Endothelial Growth Factor [VEGF] is a potent angiogenic and vascular permeability enhancing factor under both physiological and pathological conditions including tumor angiogenesis. To study the localization and intensity of VEGF in the mammary gland at various stages of its physiological cycle. Mammary glands from sixty female albino rats were divided intosix groups [10 rats each]: Group I nulliparous, group II early pregnancy, group III late pregnancy, group IV lactating, group V early involution and group VI late involution. Human specimens from five females of variable age [childbearing and post-menopausal] were examined. Animal specimens were subjected to histological study while all specimens were subjected to immunohistochemical detection of VEGF. Morphometric analysis was performed for area% and optical density of positive VEGF reaction. VEGF was detected in epithelial lining of ducts and acini, endothelium of blood vessels as well as some stroma cells and macrophages. It was detected in resting nulliparous rat mammary gland with an increase during early pregnancy that became remarkable in late pregnancy and reached its maximum during lactation. Furthermore, VEGF was also detected in milk within lactating mammary acini. During involution, VEGF decreased progressively and reached a minimum in late involution. Human specimens showed stronger VEGF reaction during childbearing period than in post-menopause. The localization of VEGF in the endothelial cells of blood vessels, epithelium of mammary gland ducts and acini as well as some stroma cells and macrophages denoted that it is secreted by those cells. The increased VEGF in pregnancy and lactation indicates that it plays an important role in the development and function of the manunary gland