Twentyfour-hour zinc (Zn) kinetics concordant with the nine-day kinetics was developed to show the validity of the 24-h spot plasma Zn pool as a practical indicator of the so-called rapidly exchangeable Zn pool size (EZP). We compared kinetic parameters after iv dose of 67Zn derived from 0 -9 days (9-d model) and from 0-24 hours (24-h model) plasma collections in six subjects (5 men and 1 woman, age 24-64 y, BMI 23.2-30.4). Plasma Zn isotope ratios (IR) were measured by inductively coupled plasma mass spectrometry. After baseline subtraction the plasma Zn IR was divided by the natural Zn IR to give the normalized IR (NIR). The tri-exponential function explained (R2=0.99> NIR from 0-9 days = K1 exp(-g1 t) + K2 exp(-g2 t) + K, exp (-g3 t), where t is time in days. Since the change of the third term during 24 hours was about 10%, NIR from 0-24 hours was fitted (R2= 0.98 -0.99) by the above function when g3 was constrained as 0. The estimated coefficients from the 9-d and 24-h kinetic models were similar except for g2. The sum of three pools as a norm of EZP was calculated from the 0 - 9 day data using the three-pool models (mammillary and catenary; Ramakrishnan. Math. Biosci. 1984;72:373) with a single outlet, which account for the loss of tracer from the system and the quasi-equilibrium between pools. We have shown the mathematical equivalency of the sum of three pools between the mammillary and catenary models, indicating that EZP is invariant by other models. The 24-h spot plasma Zn pool was highly correlated (r 0957) with the sum of three pools, suggesting that the 24-h spot plasma Zn pool is a practical indicator of EZP.
|Original language||English (US)|
|State||Published - Dec 1 1997|
ASJC Scopus subject areas
- Molecular Biology