Association between serum 25(OH) vitamin D and metabolic disturbances in polycystic ovary syndrome.

BACKGROUND: To assess the relationship between serum 25(OH) vitamin D levels and metabolic parameters together with androgenic hormone levels in women with polycystic ovary syndrome (PCOS). METHODS: This is a single-centre study from the Endocrinology Institute at Firouzgar Hospital in Iran. Seventy-three women aged 15-45 years were recruited from May 2013 to December 2013. Serum 25(OH) vitamin D level, other laboratory biomarkers and anthropometric indexes were measured. Data were analysed with statistical software SPSS version 16.0 for windows and we used specific analytical tests to assess data. RESULTS: Serum 25(OH) vitamin D levels were < 20 ng/ml in 64 patients (79%). Nine patients (12.3%) were diagnosed with metabolic syndrome. A significant difference was found between the women with and without severe vitamin D deficiency with regard to waist circumference, fasting insulin level and HOMA-IR, and abnormal systolic and diastolic blood pressures. The serum 25(OH) vitamin D levels had a reverse but weak correlation with systolic and diastolic blood pressures. CONCLUSION: This study showed an association between serum 25(OH) vitamin D levels and some metabolic parameters; however, there was no significant linear correlation between serum 25(OH) vitamin D levels and metabolic variables, except for systolic and diastolic blood pressure.

Ba2+ ions block K+-induced contractures by antagonizing K+-induced membrane depolarization in frog skeletal muscle fibres.

The effects of Ba2+ ions on twitches, K+-induced contractures, and on intracellularly recorded membrane potentials (Em) and depolarizations of frog skeletal muscle fibres were investigated. Exposure of toe muscles to choline--Ringer's solution with 10(-3) M Ba2+ with Ca2+ (1.08 mM) eliminated or very greatly reduced contractures produced by 60 mM K+. In contrast, not only did the same concentration of Ba2+ ions fail to depress the twitch tension of isolated semitendinosus fibres when added to Ringer's with Ca2+, but it even restored twitches that had been eliminated in a zero Ca2+ Ringer's solution. The resting Em of sartorius muscle fibres in choline--Ringer's solution was reduced about 20 mV by 10(-3) M Ba2+. This Ba2+ ion concentration also antagonized the K+-induced depolarization. Thus in the presence of 1 mM Ba2+, 20 mM K+ hyperpolarized rather than depolarized the fibres and 60 or 123 mM K+ produced only very slowly developing, small depolarizations. These results suggest that the loss of the K+-induced contracture in choline-Ringer's caused by Ba2+ ions is due to an inhibition of the K+-induced depolarization. The latter result is consistent with previous findings of other workers that Ba2+ ions block membrane K+ channels.

Calcium antagonism of an opiate drug effect on an excitable cell membrane.

When frog sartorius muscles are exposed to methadone (2-4 X 10(-4) M) the action potential recorded intracellularly is depressed and eliminated in 3 to 4 hr. This is due to a decrease in the sodium conductance as measured by the maximum rate of rise of the action potential. When the calcium concentration in frog Ringer's solution (normally 1.08 mM) was either lowered to 0.54 mM or raised to 2 mM, the effect of methadone on excitability was unchanged. However, increasing the extracellular calcium to 4 mM decreased the action of methadone. As this would also increase the intracellular calcium concentration, in other experiments the free intracellular Ca+ concentration was raised by adding 0.4 mM caffeine to the Ringer's solution. This also antagonized the depressant action of methadone. The antagonistic action of caffeine was not due to a direct effect of caffeine on sodium conductance because the administration of caffeine by itself caused a 10% depression of the action potential maximum rate of rise and caffeine did not antagonize the action of tetrodotoxin, which is a specific sodium channel blocking agent. Finally, it was shown that the calcium ionophore, A23187, in low concentrations antagonized the depressant actions of methadone and meperidine on action potential production. It was concluded that increasing the intracellular free calcium concentration antagonized the depressant effect on excitability produced by opiate drugs acting on an intracellularly oriented opiate drug receptor.

Taurine stimulation of isolated hamster brain Na+,K+-ATPase: activation kinetics and chemical specificity.

Epileptic foci are associated with locally reduced taurine (2-aminoethanesulfonic acid) concentration and Na+,K+-ATPase (EC 3.6.1.3) specific activity. Topically applied and intraperitoneally administered taurine can prevent the development and/or spread of foci in many animal models. Taurine has been implicated as a possible cytosolic modulator of monovalent ion distribution, cytosolic "free" calcium activity, and neuronal excitability. Taurine may act in part by modulating Na+,K+-ATPase activity of neuronal and glial cells. We characterized the requirements for in vitro modulation of Na+,K+-ATPase by taurine. Normal whole brain homogenate Na+,K+-ATPase activity is 5.1 +/- 0.4 (4) mumol Pi X h-1 X mg-1 Lowry protein. Partial purification of the plasma membrane fraction to remove cytosolic proteins and extrinsic proteins and to uncouple cholinergic receptors yields a membrane-bound Na+,K+-ATPase activity of 204.6 +/- 5.8 (4) mol Pi X h-1 X mg-1 Lowry protein. Taurine activates the Na+,K+-ATPase at all levels of purification. The concentration dependence of activation follows normal saturation kinetics (K1/2 = 39 mM taurine, activation maximum = +87%). The activation exhibits chemical specificity among the taurine analogues and metabolites: taurine = isethionic acid greater than hypotaurine greater than no activation = beta-alanine = methionine = choline = leucine. Taurine can act as an endogenous activator/modulator of Na+,K+-ATPase. Its action is mediated by a membrane-bound protein.

Effect of calcium concentration on isolated hamster brain Na-K-, Mg-dependent ATPase.

In these experiments the effect of different concentrations of calcium on the specific activity of isolated Na-K-ATPase was studied. The result of these investigations showed that calcium at 10(6) and 10(7) M stimulated the Na-K-ATPase activity. These studies also show that at higher calcium concentrations (10(5)-10(3)M), the activity of the enzyme is inhibited. The results from calcium binding to isolated membranes, rich in Na-K-ATPase, strongly suggest the existence of a low-affinity binding site which exhibits a large positive cooperativity. Kd = 2.8 x 10(5) +/- 0.4 x 10(5) M and Hill coefficient of 2.9 +/- 0.2. The calcium concentration (1.9 x 10(5) M sufficient to produce significant (24%) inhibition of the Na-K-ATPase is approximately equal to the Kd observed for calcium binding.