|Prapong, Siriwan - IOWA STATE UNIV., AMES|
Submitted to: Federation of American Societies for Experimental Biology Conference
Publication Type: Abstract Only
Publication Acceptance Date: April 19, 1998
Publication Date: N/A
Technical Abstract: The present study was designed to investigate the expression of calcium ATPase isotypes and 24-hydroxylase in bovine mammary tissue during the periparturient period. Mammary gland biopsies were taken from 9 Jersey cows at approx. -21, -7, 0, +7, +14 d of calving. The total RNA and DNA were extracted and quantitated. Specific primers for PMCA1, PMCA2, and 24-OHase were designed for competitive RT-PCR in order to quantitate the amount of specific transcripts. Nine cows were grouped into normal cows and cows developing periparturient paresis (milk fever), depending on their clinical signs and blood calcium levels. Six of the 9 cows developed milk fever and showed typical signs of recumbence and severe hypocalcemia (less than 5.0 mg/dl) usually within 24 h of calving. Mammary gland 24-OHase expression increased 10-fold in cows with milk fever as compared to a 2-fold increase in cows without clinical signs of disease. These differences could be attributed to the higher (3-4 fold) plasma 1,25-(OH)2D3 levels observed in milk fever cows. The mammary tissue RNA/DNA ratio increased gradually during late pregnancy and remained at approx. 2X that which was observed 3 wk before calving. The mammary tissue PMCA1 mRNA expression paralleled the observed increase in RNA/DNA ratio. However, cows developing milk fever tended to have a lower level of PMCA1 mRNA than normal cows. PMCA2 expression postpartum was approx. 12X higher than that observed prepartum in normal cows. Expression of PMCA2 was significantly lower in cows with milk fever. PMCA2's high expression in the lactating mammary gland suggests that PMCA2 may play an important role in calcium homeostasis of the mammary gland and in calcium homeostasis of the dairy cows during the periparturient period.