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Effect of hypergravity on expression of receptors associated with lactogenesis in rat mammary gland from pregnancy to lactation.  M.K. VanKlompenberg, O.V. Patel, H. Dover and K. Plaut; Dept. of Animal Science, Michigan State Univ., E. Lansing, MI.

   Prolactin (PRL), the key hormone responsible for lactogenesis, has multiple receptor isoforms in rats; two of the principle forms are the long (L) and short (S).  Glucocorticoids (GC) that are essential for transition from pregnancy to lactation also exert their cellular effect through their specific receptor.  Alteration in gravitational force has a detrimental effect on lactogenesis and neonatal survival.  Therefore, the objective of this study was to see how hypergravity affects mRNA expression of the two forms of PRL receptors and GC receptor in the rat mammary gland during pregnancy and lactation.

   Rats were placed on a centrifuge at 2 g (HG) starting at gestation day 11(G11) until parturition day 1(P1), while a group of stationary control (SC) rats were housed in the same room at 1g.  On G20 (SC:n=5, HG:n=5) or P1(SC:n=4, HG:n=4), rats were euthanized and mammary tissue collected and stored at -80^oC.  RNA was extracted from the mammary tissue using Trizol®.  RNA was reverse transcribed to cDNA, and receptor abundance was quantified using qPCR.  Relative expression among groups was determined using the ΔΔct method and statistics were run using SAS. 

   The PRL(L) receptor mRNA abundance was 7 fold less in HG G20 compared to SC G20 (p<.001).  The same receptor increased 5 fold from pregnancy to lactation in SC (p<.001) but only 2 fold in HG (p<.01).   The abundance of PRL(S) receptor was slightly less in HG than SC (P <.05).  PRL(S) receptor mRNA increased from pregnancy to lactation approximately 4 fold (p<.001).  The mRNA levels of GC receptor showed a 4 fold decrease at HG G20 compared to SC G20 (p<.01).  The latter receptor increased 3 fold between pregnancy and lactation (p<.001). 

   Hypergravity decreases mRNA levels of both long and short form PRL receptors and the GC receptor at days G20 and P1. 

(Supported by NASA: NNA05CP91A)