Resumo

MORALES, Carlos A  e  RODRIGUEZ, Nélida. Thyroid hormones in reproduction and lactation of milk cattle. Rev Colom Cienc Pecua [online]. 2005, vol.18, n.2, pp.136-148. ISSN 0120-0690.

Besides the interest on the actions that exert the thyroid hormones (TH) on the maintenance of basal metabolism and on the functions of organs in mammals and nonmammals, they are of particular importance in the physiology of reproduction and lactation in milk cattle. Although the review tries to emphasize on reproductive aspects and lactation, it collects in addition, updated and inescapable information, regarding TH synthesis, molecular bases of their action mechanisms, metabolism and excretion, and some data about the actions exerted in other systems. Within the main conclusions, it is remarkable, the negative correlation between milk production and blood concentration of TH, point in which agree multiple works. It is important the elucidation regarding the concept of hypothyroid state of nursing animals, as a protective mechanism that diminishes the systemic metabolic demands, accompanied by a euthyroid state on the mammary gland. In the reproductive aspect, this article reviews the discoveries of TH direct actions on the ovarian cells, surpassing the concept of their merely permissive actions. Latest advances in molecular biology, when explain the chemistry of TH receptors, its mechanisms of action and signaling routes, promise to facilitate the understanding of many of their actions to be applied to the fields of clinic and production. This article also reviews some evidences on the TH nongenomic actions. Finally, several works support the importance of nutrition, in order to hold the euthyroid state.

Palavras-chave : lactation; thyroid hormones; thyroxine; reproduction.

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