Submitted to: Joint Abstracts of the American Dairy Science and Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: February 21, 2005
Publication Date: May 20, 2005
Citation: Capuco, A.V., Connor, E.E., Wood, D.L. 2005. Transcriptioal regulation of mammary gland sensitivity to thyroid hormones duirng the transition from pregnancy to lactation [abstract]. Journal of Dairy Science. 83(1):120.
Thyroid hormones are galactopoietic and appear to assist in establishing the mammary gland's metabolic priority during lactation. Expression patterns for genes that can alter tissue sensitivity to thyroid hormones and thyroid hormone activity were evaluated in the mammary gland and liver of Holstein cows at dry-off, 7, 25, 40 and 53 days into the dry period, and 14 and 90 days into lactation. Transcripts for the three isoforms of iodothyronine deiodinase, type I (DIO1), type II (DIO2) and type III (DIO3) and transcripts for the thyroid hormone receptors alpha1 (TRa1), alpha2 (TRa2) and beta1 (TRb1) were evaluated. Tissues for this purpose were obtained at slaughter from 3 to 6 cows per physiological state. The DIO3 is a 5-deiodinase that produces inactive iodothyronine metabolites, whereas DIO1 and DIO2 form the active thyroid hormone, triiodthyronine, from the relatively inactive precursor, thyroxine. Low copy numbers of DIO3 transcripts were present in mammary gland and liver during all physiological conditions. DIO2 was the predominant isoform expressed in mammary gland and DIO1, the predominant isoform expressed in liver. Quantity of DIO1 mRNA in liver tissues did not differ (P>0.05) with physiological state, but tended to be lowest during lactation. Quantity of DIO2 mRNA in mammary gland increased during lactation (P<0.05), with copy numbers at 90 d of lactation 6-fold greater than at days 25 and 40 of the dry period. When the ratios of DIO2/DIO3 were evaluated, the increase was even more pronounced (>100-fold). Quantity of TRb1 mRNA increased during lactation, whereas TRa1 and TRa2 did not vary with physiological state (P>0.05). Data support a role for increased expression of mammary TRb1 and DIO2 as means to increase thyroid hormone activity in the mammary gland during lactation.