Parathyroid hormone-related protein (PTHrP) derived from the lactating mammary gland of cattle

乳牛の乳腺組織ではPTHrPが合成・分泌され,またそのレセプターであるPTH/PTHrPレセプターが発現していることから,PTHrPが乳腺組織において何らかの作用を有する可能性が考えられた。そこで本研究では,乳汁中のPTHrP濃度とCa濃度との関連を検討した。最初にMBP-ウシPTHrP[1-141]を合成し,スタンダードとして用いて血漿中ならびに乳汁中PTHrP濃度を測定した。まず,周産期のジャージー種乳牛1頭を用いて,PTHrPの乳腺組織からの分泌,ならびにCaの乳腺組織への取り込みについて検討した。すなわち,腹大動脈と腹皮下静脈(乳静脈)から血液を採取し,PTHrP濃度とCa濃度を測定し,動静脈差を求めた。血清Ca濃度はこれまでの報告と同様に分娩前後に一過性の減少が認められたが,その低下時にCa濃度の動静脈差は認められず,乳腺への取り込みは明らかではなかった。一方,血漿中PTHrP濃度はいずれの時期においても検出限界以下(0.57pM)で,動静脈差を検討することはできなかった。ついでホルスタイン種泌乳牛9頭について血漿中PTHrPの動静脈差を検討するとともに,乳汁中のPTHrPとCa濃度について検討した。その結果,血漿中PTHrP濃度は動静脈共に周産期のそれと同様,検出限界以下であった。一方,乳汁中のPTHrP濃度は著しく高く,28.4±7.6nM(平均±標準偏差)であり,90%以上が乳腺組織由来であることが明らかとなった。また乳汁中Ca濃度は98.7±13.3mg/dl(平均±標準偏差)であり,乳汁中のPTHrP濃度との間には有意な正の相関(P<0.01)を認め,乳腺組織由来のPTHrPが,乳汁へのCa輸送に関与している可能性が示唆された。To investigate the roles of PTHrP derived from the mammary gland of cattle, plasma PTHrP and Ca levels, and their arterial-venous differences were examined in a Jersey cow during the periparturient period. Levels of Ca in both abdominal aorta and subcutaneous vein of abdomen blood slightly decreased around the parturition and at 24 days after parturition, however, no remarkable arterial-venous differences were observed. Plasma PTHrP levels in both arterial and venous samples were below the detection limit (0.57pM) during the experimental period. Milk PTHrP and Ca levels were measured in 9 Holstein dairy cows. Although plasma PTHrP levels in all arterial and venous samples were also below the detection limit, milk PTHrP and Ca levels were high, ranging from 14.9nM to 41.2pM and from 77.2mg/dl to 120mg/dl, respectively. In addition, a significant positive correlation (P<0.01) was observed between milk PTHrP and milk Ca levels. In conclusion, we collected blood from one Jersey cow with time around parturition and from 9 Holstein cows those had different lactation stages and milk production, secreted plasma PTHrP from the lactating mammary gland would not detect even in subcutaneous veins of abdomen which lies downstream of the mammary gland. However, milk concentration of PTHrP was remarkable high and almost (90%<) derived from the mammary gland in cattle. We could not demonstrate that the lactating mammary gland secrete PTHrP into a peripheral circulation in cattle, though milk contains large amount of PTHrP as a protein and the meaning stay to be elucidated.P(論文)特集application/pdfFEATURE ARTICLESdepartmental bulletin pape