摘要:

SummaryStudies have been carried out to assess maturation of myofibrillar and mitochondrial proteins in fetal (113 to 140 days gestation), neonatal (30 min to 21 days postpartum), and adult sheep hearts.Ca++‐activated myosin ATPase activity was ˜20% lower in fetal than in adult left ventricular myocardium (1.13 ± 0.06,n= 12,versus1.36 ± 0.07,n= 9, &mgr;moles P1per g protein per sec;P< 0.025). In fetal and neonatal hearts (but not in adult hearts), myosin ATPase activity was slightly higher (˜14%;P< 0.001) in right ventricular tissue than in left ventricular tissue. In contrast to these small changes in myosin ATPase activity, large changes indicative of maturation of energy metabolism occurred in the creatine kinase system: between 115 days gestation and 21 days postpartum, total creating kinase activity increased nearly 8‐fold (0.2 to 1.6 IU/mg cardiac mass), the MM‐creatine kinase isozyme increased 7‐fold (0.2 to 1.5 IU/mg wet weight), and mitochondrial creatine kinase increased more than 25‐fold (< 0.01 to 0.27 IU/mg wet weight). The total creatine pool, but not the ATP pool, increased (from ˜6 to ˜15 nmoles/g tissue). Neither the concentration nor isozyme distribution of lactate dehydrogenase, a glycolytic enzyme, changed during this 7‐wk period of development.SpeculationWe speculate that changes in biochemical composition of energy‐utilizing and ‐producing proteins, coupled with alterations in the structure and cellular distribution of mitochondria and myofibrils, contribute to the changes in mechanical performance characteristic of the maturing heart.

ISSN:0031-3998    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

SummaryThree children with familial hypomagnesemia from infancy were treated perorally with magnesium for 9 to 12 years. Their somatic and intellectual development have since been normal. Without therapy, the serum magnesium fell from subnormal (about 0.5 mmoles/liter) to very low values (0.2 to 0.3 mmoles/liter) within 1 to 4 wk. We observed a secondary fall in serum calcium and potassium and an increase in sodium and phosphate although serum concentrations of PTH, calcitonin, and 25‐OH‐vitamin D in the blood remained normal. Balance studies confirmed the presence of a defect in the intestinal absorption of magnesium and excluded a defective renal tubular transport system. The subjects continued to require daily magnesium supplements to avoid serious symptoms. Optimal dosage was found to be in the range 0.5 to 0.75 mmoles/kg·day; doses above this caused diarrhoea and a fall in the serum and urine levels of magnesium. Pathophysiologic mechanisms involved in the electrolyte changes that occurred secondarily to the hypomagnesemia are discussed.SpeculationThe pathophysiologic basis for the impaired intestinal absorption of magnesium in this condition is unknown. In fact, the mechanism by which magnesium is normally transported across membranes is also largely unknown. A facilitated transport mechanism seems to be involved. It appears reasonable to believe that errors in enzymes, or perhaps more likely, in specific magnesiumbinding proteins that are involved in the membrane transport form the molecular basis for familial hypomagnesemia.

ISSN:0031-3998    

出版商:OVID    

年代:1981

数据来源: OVID

ISSN:0031-3998    

出版商:OVID    

年代:1981

数据来源: OVID

ISSN:0031-3998    

出版商:OVID    

年代:1981

数据来源: OVID

ISSN:0031-3998    

出版商:OVID    

年代:1981

数据来源: OVID

ISSN:0031-3998    

出版商:OVID    

年代:1981

数据来源: OVID

ISSN:0031-3998    

出版商:OVID    

年代:1981

数据来源: OVID

ISSN:0031-3998    

出版商:OVID    

年代:1981

数据来源: OVID

ISSN:0031-3998    

出版商:OVID    

年代:1981

数据来源: OVID