Figure 5.

Time course of inhibition. (a) Surface GH binding. Cultures were incubated in serum-free conditions for 18 hr, treated with insulin or IGF-I for the indicated time periods, and assayed for surface GH binding of cell monolayers. •, insulin; ○, IGF-I. GH binding of the control at time 0 was 1,065 ± 92 cpm/10⁶ cells. Vs. control, ‡, P = 0.001; ∗, P = 0.0005, and †, P < 0.0001. (b) GHR translocation. Cultures were incubated in serum-free conditions for 18 hr, followed by treatment with insulin or IGF-I for the durations as indicated. Cells were then briefly trypsinized, and recovery of surface GH binding was measured 2 hr after trypsinization. □, control; •, insulin; ○, IGF-I. Vs. control at the same time point, ‡, P = 0.02; †, P = 0.007; ∗, P = 0.0006; ¶, P = 0.0002; and §, P = 0.0001.