Fig. 6. Using the model to interpret real data. The open symbols show measured GH release from isolated, dispersed somatotrophs in vitro during an infusion with 100 nm GHRP6 for 60 min (from time 0). The model assumes that desensitization is a smooth, continuous process, directly associated with the process of receptor activation that leads to GH release, but this is not readily apparent from the observed data. Indeed the measured data at first sight appear consistent with the interpretation that there are successive phases of sensitization and desensitization, or with the interpretation that there is a lag before the onset of desensitization. The authors have used the model described in the text to generate the best model fit to the observed data, and this fit is indicated by the thin line. The thick line denotes the rate of release of GH, which would result in the fitted GH concentration curve, confirming that the observed data are indeed consistent with rapid, smooth desensitization of the GH release mechanism.
This fitted curve only fixes A, B, K, and X. The estimates and their standard errors are A = 0.98 (se 0.59), B = 18.5 (se 3.5), K = 0.15 (se 0.05), and X = 0.49 (se 0.18). From these figures, under certain assumptions, can be estimated kb kb, and kr (in the absence of SRIF) and equilibrium levels of free receptor. Furthermore, within the limitations of the data, the model fits adequately.
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