The oestrogenic activity of bovine colostrum

Insulin-like growth factors (IGFs), IGF binding proteins, and other endocrine factors in milk: role in the newborn

The role of colostrum and milk in the neonate has been chiefly recognized as a comprehensive nutrient foodstuff. In addition, the provision of colostrum-the first milk-for early immune capacity has been well documented for several species. Colostrum is additionally a rich and concentrated source of various factors that demonstrate biological activity in vitro. Three hypotheses have been proposed for the phenotypic function of these secreted bioactive components: (1) only mammary disposal, (2) mammary cell regulation, and (3) neonatal function [gastrointestinal tract (GIT) or systemic]. Traditionally, it was assumed that the development of the GIT is preprogrammed and not influenced by events occurring in the intestinal lumen. However, a large volume of research has demonstrated that colostrum (or milk-borne) bioactive components can basically contribute to the regulation of GIT growth and differentiation, while their role in postnatal development at physiological concentrations has remained elusive. Much of our current understanding is derived from cell culture and laboratory animals, but experimentation with agriculturally important species is taking place. This chapter provides an overview of work conducted primarily in neonatal calves and secondarily in other species on the effects on neonates of selected peptide endocrine factors (hormones, growth factors, in part cytokines) in colostrum. The primary focus will be on insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) and other bioactive peptides, but new interest and concern about steroids (especially estrogens) in milk are considered as well.

A double antibody radioimmunoassay for free and conjugated estradiol-17 beta in cow's milk

A radioimmunoassay for free estradiol-17 beta, conjugated estradiol-17 beta or total (free + conjugated) estradiol-17 beta in defatted milk of cows is described. Conjugated estradiol-17 beta was hydrolyzed by enzymes of Helix pomatia juice. Estrogens were extracted with dichloromethane; no other purification step was required before radioimmunoassay because of the high specificity of the antiserum. Immunoprecipitation was used to separate bound and free estradiol-17 beta. Concentrations measured were corrected for procedural losses on a per sample basis. The assays were shown to be accurate and specific. The sensitivity was 1.3pg/ml for the assay of free estradiol-17 beta (5ml of milk extracted) and 2.9pg/ml for conjugated or total estradiol-17 beta (2 ml of milk hydrolyzed and extracted). Estrogens were measured in the milk of cyclic cows and in cows stimulated with pregnant mare serum gonadotropin (PMSG). A preovulatory increase was clearly observed. Wether or not the ovary was stimulated by PMSG, concentrations of estrogens were higher and the relative increase during the preovulatory peak was greater for conjugated estradiol-17 beta than for the free form. The assay of conjugated or total estradiol-17 beta in defatted milk should be a practical method for assessing preovulatory growth of follicles in cows.

Oestrogens in milk

The steroid oestrogens oestradiol-17 beta, oestrone and oestradiol-17 alpha have all been adequately identified in various body fluids and tissues of cattle. There is also good evidence for the presence of oestrone sulphate. Oestriol (or similar triols) may also be present. The oestrogens found in the systemic plasma of cattle are present in milk in similar concentrations; whether their passage into milk involves metabolism by the mammary gland is uncertain. Oestrone sulphate, at least at relatively high levels of secretion, is believed to be found only in pregnant cattle and measurement of its concentration in milk is in use as a practical test for pregnancy. A close correlation has been found between the concentrations of oestradiol-17 beta in systemic plasma and milk of non-pregnant cows and levels of this oestrogen in milk may, together with those of progesterone, now be used in studies of post-partum ovarian function.

Measurement of estrogens in cow's milk, human milk, and dairy products

Free natural estrogens in raw and commercial whole milk were quantitated by radioimmunoassay. The ranges of concentration of estrone, estradiol 17-beta, and estriol were 34 to 55, 4 to 14, and 9 to 31 pg/ml. Proportions of active estrogens (estrone and estradiol) in the fat phases of milk by radioactive tracer on separated milk were 80% and 65%. These findings were supported by radioimmunoassay of skim milk and butter. Equilibrium dialysis of skim milk with hydrogen 3 labeled estrogens showed that 84 to 85% of estrone and estradiol and 61 to 66% of estriol were protein bound. Whey proteins demonstrated a greater binding capacity than casein. This result was confirmed by radioimmunoassay of dry curd cottage cheese and whey. The concentrations in curd were 35, 11, and 6 pg/g. In whey they were 4, 2, and 3 pg/ml. The quantity of active estrogens in dairy products is too low to demonstrate biological activity. Butter was highest with concentrations of 539, 82, and 87 pg/g. Human colostrum demonstrated a maximum concentration of 4 to 5 ng/ml for estrone and estriol and about .5 ng/ml for estradiol. By the 5th day postpartum, they decreased to become similar to cow's milk.

Hormone induced lactation in the bovine III. Dynamics of injected and endogenous hormones

Three lactations were induced in two cows in two trials by twice daily subcutaneous injections for seven days. Each injection contained .05 mg/kg body weight of estradiol-17beta and .125 mg/kg body weight of progesterone. Included with the hormones in trial 1 was a combination of 233 muCi of [6,7-hydrogen-3] estradiol-17beta and 12 muCi of [4-carbon-14] progesterone. During trial 2,2050 muCi of [2,4,6,7 hydrogen-3] estradiol-17beta were incorporated with the hormones for one cow and 2344 muCi of [1,2,6,7 hydrogen-3] progesterone for the other. Radioactivity from hydrogen-3 and carbon-14 was detected in urine and feces but not in mammary secretion during trial 1. Isotope recovery from [hydrogen-3] estradiol-17beta was too low to quantify. By day 17, 90% of the carbon-14 from progesterone was accumulated in feces and 8.0% in urine. For trial 2, recoveries of radioactivity by day 28 from urine, feces, and mammary secretions were, respectively, 32.4, 56.2, and less than .002% from [hydrogen-3] estradiol-17beta and 6.0, 87.7, and .25% from [hydrogen-3] progesterone. Estrogen and progesterone in plasma averaged 1.83 and 2.61 ng/ml during days 2 to 7. Estrogen decreased more rapidly than progesterone post-treatment, but both had decreased by days 16 to 19 when average prolactin of plasma increased. Quantitative measures of estradiol 17-beta and progesterone absorption, whether in plasma or excreta, were correlated.