Exploring the magnesium-deficient weanling rat as an animal model for the sudden infant death syndrome: physical, biochemical, electrocardiographic, and gross pathologic changes

Citation study of peripheral theories in an expanding research front

In most research fields, particular theories and lines of study tend to become dominant. Thomas Kuhn has shown that 'scientific revolutions' nevertheless occur. Citations in an ex panding research area are analysed with particular reference to a few theories which conflict with the mainstream of scientific thought on the topic. The progress of these theories past editors and referees into the primary literature and, if they make it, into citations and reviews is examined. The example used concentrates on mechanisms rather than the validity or other wise of the theories reported.

Exposure of piglet coronary arterial muscle cells to low concentrations of Mg2+ found in blood of ischemic heart disease patients result in rapid elevation of cytosolic Ca2+: relevance to sudden infant death syndrome

Exposure of cultured piglet primary neonatal coronary arterial smooth muscle cells to concentrations of ionized Mg2+ ([Mg2+]o (i.e., 0.48, 0.3, 0.15 mM) found in blood of patients presenting with ischemic heart disease and in hypoxic neonates resulted in concentration-dependent elevation in intracellular free Ca2+ ions ([Ca2+]i; the lower the [Mg2+]o, the higher the [Ca2+]i rise. The lowest concentration of [Mg2+]o tested, i.e., 0.15 mM, resulted in a clear rounding-up (i.e., contraction) of many of the coronary smooth muscle cells; reintroduction of normal 1.2 mM [Mg2+]o failed to restore either normal [Ca2+]i or cell shape.

In vivo assessment of prevention of white-noise-induced seizure in magnesium-deficient rats by N-methyl-D-aspartate receptor blockers

The behavioral changes associated with seizures induced by auditory stimulation in magnesium (Mg)-deficient rats originate in deep brain structures and secondarily project to neocortex. In the present study, we examined the roles of N-methyl-D-aspartate (NMDA) receptors in this seizure model. The intraperitoneal administration of the competitive NMDA receptor blocker DL-2-amino-7-phosphonoheptanoic acid (36 and 72 mg/kg) and the non-competitive NMDA receptor blocker MK-801 (1.35 and 2.7 mg/kg), completely prevented the induction of seizure and bradyarrhythmia or sudden death resulting from seizure. Therefore, the white-noise-induced seizures in Mg-deficient rats are linked to increased neuronal excitability via the NMDA receptor.

Effects of hypomagnesemia on reactivity of bovine and ovine platelets: possible relevance to infantile apnea and sudden infant death syndrome

Blood platelet function and possible involvement in death of hypomagnesemic ruminants was investigated with 26 Angus cows, 15 mature Hampshire wethers, eight Finnish-Hampshire ewes, and 36 growing Dorset lambs. Hypomagnesemia was induced by feeding vegetative spring tall fescue to 13 cows and semipurified diets low in Mg to nine wethers, four ewes, and 18 lambs. In comparison with controls, dietary treatments reduced plasma Mg concentrations 55% in cows, 36% in wethers, 66% in ewes, and 78% in lambs. Hypomagnesemia reduced in vitro reactivity of cow and lamb platelets to thrombin, ADP, and platelet active collagen, but in vitro tests may not accurately reflect in vivo platelet reactivity. Microscopic examination of platelet-rich plasma revealed a threefold increase in clumped platelets from four hypomagnesemic ewes compared to four normomagnesemic ewes. This suggests that in vivo activation and exhaustion of platelets may have contributed to reduced in vitro platelet reactivity. Six of 18 hypomagnesemic lambs died spontaneously in tetany after 2-12 months on low-Mg diets. Heart and lung lesions were markedly similar to pathological changes induced in other lambs by intravascular activation of platelets with 500 micrograms of vascular collagen fibrils per kg body weight injected intravenously. These results suggest the possibility of abnormal blood platelet activation as a significant mortality risk factor in severe hypomagnesemia.

Magnesium therapy in premature neonates with apnea neonatorum

Apnea, bradycardia, and neuromuscular hyperirritability have been associated with magnesium (Mg) deficiency in young human infants and weanling animals. This is a retrospective review of a clinical experience of Mg therapy among 200 premature neonates who showed physical and clinical chemical changes compatible with Mg deficiency. The 200 infants all had idiopathic apnea neonatorum, and 93% also had the respiratory distress syndrome (RDS). This review was conducted to learn whether Mg therapy was associated with a significant reduction in apnea. The author suggested that the dose of Mg be 0.4 mEq/kg body weight/day, as 50% MgSO4.7H2O intramuscularly (IM) for 5 days; or as 1.0 mEq/kg/day, as 10% MgCl2.6H2O by mouth for 2 or more weeks, with appropriate monitoring of plasma Mg values in all infants. Sixty-one infants received a minimum of 5 days of Mg by either route (mean, 11.4 +/- 0.9, Group A); five received 3-4 doses IM (mean, 3.6 +/- 0.2, Group B); and 134 received 0-2 doses IM (0.5 +/- 0.1, Group C). Group A infants Mg-treated before Day 20 showed earlier cessation of apnea and bradycardia than those treated after Day 20. In Group A patients, 7 dose-days [corrected] of Mg therapy was associated with continuation of apnea; 14 dose-days [corrected], with cessation of apnea. Compared with Group A, Group C continued to develop apnea (P less than .003) and bradycardia (P less than 0.03) over longer periods of time. Group A infants showed no record of death or of hospital readmission for recurrent apnea, while 32 of 134 Group C infants had one or both of those unfavorable outcomes (P less than 0.001), with four of the five deaths in Group C (NS) as the sudden infant death syndrome (SIDS). In conclusion, Mg was associated with a reduction of apnea in this population. Emphasis was placed on the need to closely observe infants receiving supplementary Mg, with monitoring of plasma Mg levels.