This paper studies calcitonin (CT) transport across the C-cell-blood (CCB) barrier in normal rats. The efficiency of this transport is expressed as endogenous calcitonin bioavailability (F CT ), i.e., that portion of CT molecules extruded by the thyroid C-cell basal pole that enters the circulating blood. Because currently F CT cannot be estimated directly, a novel methodology was used for its estimation. The essence of this methodology is to assess the CT level before and after the CCB barrier, to study these input-output CT relationships mathematically, and to find the F CT range allowed by the relationships. In this context, the subplasmalemmal granule numerical density in the C-cell basal pole (X) and the CT concentration in the right ventricular blood (Y) were found to be highly correlated: r xy = 0.922, P < 0.001; the covariance coefficient ρ xy = 0.9980, P < 0.0001. Clearly, the overall variance of these input-output relationships in the covariance model ( = 6.32) is explained, specifically, by CT retention (R CT ) variability at the CCB transport stages. The greater the R CT mean value in the studied rats, the greater is the impact of R CT variability on Var xy . The estimated variance caused by R CT (Var CCBR ) makes it possible to determine R CT and F CT (F CT = 100% -R CT ). Thus we estimated Var CCBR as Var CCBR < Var xy -CV RIA 2 , where CV RIA 2 is CT assay variance:= 6.00% (P ≥ 0.95). We then estimated F CT as the value range that does not contradict the Var CCBR obtained: 62% < F CT < 100% (P ≥ 0.95).
Var xy
Var CCBRKey words: calcitonin, C-cell-blood barrier, biological availability, statistical modeling, thyroid gland.The tissue-blood interface is effected by cell-blood (CB) barriers located on the border line between specific organ cells and the blood flowing in close proximity to them. CB barriers ensure a selective supply of substances the cells need, as well as a removal of catabolic wastes into the circulation. A characteristic feature of CB barriers in the endocrine glands is their involvement in hormone transfer to systemic circulation. Therefore these barriers play another very important role that until now has not received due attention, i.e., the role associated with providing the body with the optimum supply of any certain biologically active substance.At the point where the thyroid C-cell comes near the perifollicular blood capillary, a C-cell-blood (CCB) barrier is formed whose phenomenology and ultrastructural parameters we have studied previously [1]. Because of its borderline position, the CCB system can regulate calcitonin (CT) transport to the bloodstream. However, until now the regulatory function of the CCB barrier has not been investigated, which is largely explained by the fact that there are no data on CT kinetics across the CCB barrier. Our paper presents a step forward in this direction, its purpose being to evaluate the efficiency of endogenous CT transport across the CCB barrier in normal rat thyroid.
METHODSMethodology. This section deals with (i) the basic...