Triiodothyronine (T₃), insulin and characteristics of 5'-monodeiodinase (5'-MD) in mare's milk from parturition to 21 days post-partum

Abstract

-It is generally accepted that hormones and tissue growth factors are supplied from mother to neonate via mammary secretion. Among the protein hormones, insulin and prolactin are considered as the most important milk components for neonates. The significance of the thyroid hormones, namely triiodothyronine (T 3 ) generated locally by 5'-monodeiodinase (5'-MD) in the mammary tissues, for the mammary gland itself and for suckling neonates is still under consideration. In the present study the activity of the 5'-MD and the concentrations of T 3 and insulin in mare's colostrum and milk during the first 21 days of lactation were measured. Post partum, T 3 increased to its highest concentration around day 4 ( 1.14 ± 0.08 nmol/L), then progressively decreased until day 7, reaching a relatively stable concentration of 0.71 ± 0.06 nmol/L (overall mean for days 7-21 The colostral insulin concentration, highest on the day of parturition (401.0 ± 24.9 pU/mL), decreased to a nadir value (25.0 ± 3.4 ( l U/mL) on day 5, after which it tended to increase. The mare's milk showed the presence of PTU-sensitive (type I) and PTU-insensitive (type II) 5'-monodeiodinases (5'-MD). Contrary to the classical type II 5'-MD, the mare's milk isoenzyme was inhibited non-competitively by aurothioglucose. A significant relationship (r = 0.962, P < 0.01) between T 3 concentration and 5'-MD activity, from the 1 st to the 6th lactational day was found, which may indicate a dependence of T 3 concentration on the milk 5'-MD activity.

Enhanced or Reduced Fetal Growth Induced by Embryo Transfer into Smaller or Larger Breeds Alters Post-Natal Growth and Metabolism in Pre-Weaning Horses

“…Similarly, increased milk production in draft mares could account for the growth advantage in P-D foals, since milk yields are known to be breed specific [61] and to be increased with the mare's size [61]. Hormones and growth factors such as T 3 [62], leptin [63], IGF-1 and insulin [64] and thyroid stimulating hormone (TSH) [49] are also supplied through the mare's colostrum. In Quarter horses, milk leptin, IGF-1 and TSH concentrations were at their maximum the day of parturition and reached minimum at 2 months postpartum (leptin and TSH) or became undetectable by 12 days postpartum (IGF-1) [49].…”

Deiodinase type 1 activity is expressed in the prostate of pubescent rats and is modulated by thyroid hormones, prolactin and sex hormones

“…Moreover, we and other authors have found deiodinase activity in seminal plasma (Brzezinska et al 2000, B Anguiano, unpublished observation) and in other types of secretions, such as milk (Slebodzinski et al 1998 …”

The Pattern of Expression and Role of Triiodothyronine (T3) Receptors and Type I 5′-Deiodinase in Breast Carcinomas, Benign Breast Diseases, Lactational Change, and Normal Breast Epithelium

“…8 In animal studies, it was shown that deiodinases initiate the breast in late pregnancy for lactation through various galactopoietics actors including increasing intramammary T3 to support lactogenesis. 11,13 It has also been reported that human lactating mammary glands expresses both D1 and D2 enzymes. 21 This is the first study to analyze the expression of deiodinase 1 at the level of RNA by RT-PCR, which is the most sensitive technique for mRNA detection in formalinfixed, paraffin-embedded tissues of different breast pathologic lesions in contrast with normal and lactating mammary tissues.…”

“…Animal studies have shown that thyroid hormones are necessary for a galactopoietic response to prolactin and somatotropin, and demonstrated that such hormones increased the 5 0 -deiodinase activity specifically in the mammary gland. In addition, there seems to be enhanced local conversion of T4 to T3 within the mammary gland during lactation 11,13 and increased expression of THR-a1, -a2, and -b1 which may alter signaling and increase the sensitivity of lactating mammary tissue to thyroid hormones. 11 The study of such receptors is therefore critically important in the process of evaluation of signaling pathways that affect cell growth and carcinogenesis.…”

“…This protective effect seems greater for women who had extended periods of breastfeeding during their lifetime. [12][13][14] Postmenopausal women with breast cancer have a significantly increased thyroid hormone/estradiol ratio. Such imbalance may confer a tumor growth-promoting effect.…”