Parathyroid Hormone Secretion in Sheep Fed a Low Magnesium and/or High Potassium Diet

Research Project

Project/Area Number	61560329
Research Category	Grant-in-Aid for General Scientific Research (C)
Allocation Type	Single-year Grants
Research Field	畜産化学
Research Institution	Kitasato University
Principal Investigator	TERASHIMA Yoshiaki Kitasato University, 獣医畜産学部, 教授 (30050529)
Project Period (FY)	1986 – 1987
Project Status	Completed (Fiscal Year 1987)
Budget Amount *help	¥1,300,000 (Direct Cost: ¥1,300,000) Fiscal Year 1987: ¥300,000 (Direct Cost: ¥300,000) Fiscal Year 1986: ¥1,000,000 (Direct Cost: ¥1,000,000)
Keywords	Sheep / Parathyroid gland PTH / Ca mobilization / hypomagnesemia / Grass tetaney / グラステタニー / 無機物代謝異常
Research Abstract	Hypomagnesemia (grass tetany) in ruminants has been shown to be associated with consumption of early spring forages which are sometimes characterized by low magnesium (Mg) and high potassium (K) contents. In ruminats, hypomagnesemia and hypocalcemia are almost always combined in clinical cases of tetany. Several reports suggest that hypomagnesemia may be involved in an impared ability to mobilize calcium (Ca) from reserves (bone). As parathyroid hormone (PTH) is deeply associated with Ca metabolism, hypomagnesemic animals may disturbe PTH secretion and Ca mobilization. The present experiment was designed to determine PTH secretion and the Camobilization in hypomagnesemic sheep induced by a low Mg and/or high potassium(K) diet. 1. A semi-purified diet containing 0.26%Mg-0.74%K(control), 0.07%Mg-0.75%K(low Mg), 0.24%Mg-4.90%K(highK) or 0.05%Mg-5.00%K(low Mg/high K) was fed once daily for 8 days. Intravenous EDTA infusion (0.134 mmol/Kg BW/30 min)was performed in each diet-sheep to determin … More e PTH secretion. Plasma ionized Ca concentrations decreased linearly during the EDTA infusion in all groups and the rate of decrease in ionized Ca level tended to be greater in hypomagnesemic animals fed the low Mg and/or high K diet. Parathormogenic index(increased plasma PTH after EDTA infusion/ decreased ionized Ca after EDTA infusion) was 0.263, 0.402 and 0.413 in a low Mg/high k, low Mg and high K diet-fed sheep, respectively. They were significantly lower than those of the control (1.721) sheep. PTH stimulation index(maximum plasma PTH after EDTA infusion/basal PTH) had a similar tendency of parathormogenic index. These results suggest that hypomagnesemic animals may have depressed PTH secretion. 2. Four sheep were subjected to four diet (control, low Mg, high K and low Mg/high K) treatements for 7-10 days in a 4x4 latin square design to determine Ca mobilization in hypomagnesemic sheep fed on a low magnesium and/or high potassium diet. Intravenous EDTA infusion (0.26 mmol/kg BW/60 min) was conducted to determine Ca mobilization. The mean Ca mobilization rates in the control, low Mg, high K and low Mg/high K diet-fed sheep during EDTA infusion were 4.98,3.83, 3.23 and 3.58 mmol, respectively. These results suggest depressed Ca mobilization in hypomagnesemic sheep. Less