Comparative effects of calcitriol and parathyroid hormone on serum aluminum in vitamin D-depleted rabbits fed an aluminum-supplemented diet.

Under normal circumstances, the body barriers effectively limit the entry and retention of dietary aluminum. However, both parathyroid hormone (PTH) and calcitriol (physiologically active hormonal form of vitamin D3) have been reported to produce elevation of serum aluminum in animals fed an aluminum-supplemented ration. To compare the effects of calcitriol with those of PTH with reference to their putative effect to enhance aluminum absorption, an experiment was designed wherein the serum levels of both PTH and calcitriol would be changing markedly during a short time-frame. To condition the rabbits used for this comparison, they were fed a vitamin D-free diet, which caused the level of calcitriol and its precursors to decline rapidly. The calcitriol deficit together with the ensuing lack of calcium absorption resulted in a state of secondary hyperparathyroidism. Vitamin D-depletion was shown to be complete by the high level of serum PTH and a low (unmeasurable) level of serum calcitriol. To enable comparison of PTH with calcitriol, exogenous calcitriol infusion (60 IU/day) was started by osmotic pump simultaneously with the beginning of an aluminum (aluminum lactate) supplemented diet. Aliquots were collected for both serum PTH and serum calcitriol at intervals during the 7 day study. A rising serum aluminum level was highly correlated with the rising serum calcitriol level in the rabbits (r = 0.903, p = 0.036) during the first 4 days of the infusion. The mean serum aluminum levels rose nearly 13 parts per billion (ppb) in the 7 day period. Declining serum PTH (due to feedback mechanisms of calcitriol suppressing PTH synthesis) showed a negative correlation of serum aluminum and serum PTH (r = -0.959, p = < 0.01) during the first 4 days of infusion. Control rabbits (vitamin-D depleted) fed aluminum-supplemented rations have shown only a minimal transient rise in serum aluminum level which returned to the pre-test level by the end of the week. To test for any effect of PTH on serum aluminum in the absence of calcitriol, five rabbits were implanted with osmotic pumps infusing PTH (mean 6.0 U/hr) and started on an aluminum supplemented diet. These rabbits, having previously been depleted of vitamin D were already in a state of nutritional secondary hyperparathyroidism as shown by their elevated pretest PTH levels. During the 7 day infusion, the serum aluminum rose only a mean of approximately 1 part per billion (ppb).(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of calcitriol infusions on serum aluminum in vitamin D-depleted rabbits fed an aluminum-supplemented ration.

Three dosages of calcitriol (10, 30 and 60 IU/day) were given to rabbits by subcutaneously implanted osmotic pumps. The purpose was to compare the dosages with regard to their putative effect in elevating serum aluminum levels by mechanisms such as enhancing intestinal absorption, diminishing renal excretion, or others. To establish uniform levels of endogenous calcitriol and its precursors, all rabbits had been depleted of vitamin D. The depletion was demonstrated by their serum calcidiol and calcitriol levels declining to unmeasurable levels, following the regimen of a vitamin D-free diet. The 8 rabbits were then placed on an aluminum-supplemented (aluminum lactate) ration. The amount of feed (and aluminum) consumed was determined at daily intervals. Serum aluminum levels were determined at intervals during the 7 days on this regimen. In a second test, the same 8 rabbits received the same regimen but in addition were infused with 10, 30 or 60 IU calcitriol per day. It was found that the aluminum-fed rabbits receiving 60 IU/day and 30 IU/day calcitriol infusions showed statistically significantly elevated serum aluminum levels as compared to their levels without calcitriol (p = 0.0208 and p = 0.434, respectively). Rabbits receiving pumps delivering 10 IU/day while receiving the aluminum-supplemented ration showed no rise in serum aluminum with time or treatment during the 7 day study. Likewise rabbits receiving aluminum-supplemented rations without calcitriol showed only an early minimal rise in mean serum aluminum which returned to the pre-test level by the end of a week in spite of continued consumption of aluminum-supplemented rations.

Digital modulator and synchronous demodulator system: an alternative to the analog phase detector.

A digital modulator and synchronous demodulator system has been developed which more effectively recovers signals buried in noise than does its analog counterpart. Circuitry of integrated design is described for controlling the modulation in physical measurements and the simultaneous, synchronous demodulation and conversion of the signal into a binary number. This system is especially useful when interfaced with a laboratory computer. The square wave which produces the modulation has purposely lengthened transition times to minimize modulation transients. Demodulation is accomplished by feeding the amplified AM signal into a voltage-controlled oscillator and counting the resulting pulses with counters gated, by the modulation reference circuitry, to count up and down on alternate half-cycles. The number accumulated by the counters is proportional to the true integral of the demodulated signal over a preset number of modulation cycles. The period of the modulation cycle is, in turn, determined by a quartz crystal oscillator. The demodulator can be gated to ignore excessively noisy portions of the modulated signal. Four demodulators with relative gains in ratios of eight operate simultaneously to provide a large dynamic range of more than 10(6). Application of this system to a computer-controlled microwave spectrometer is described. A sample spectrum is given to illustrate the wide dynamic range.