WEINSTEIN, R.B.*; LECESNE, C.; DURANDO, B.; LAYTON, C.; RUDINSKY, S.; TISCHLER, M.E.: Comparison of human insulin and its analogs on stimulation of in situ protein synthesis in rat soleus muscle

Insulin analogs can be used to discriminate between metabolic and mitogenic (growth-related) pathways. This study compared the stimulatory effects of human insulin (HI) and two recombinant analogs (X2 and H2) on protein synthesis in rat soleus muscle in situ. Protein synthesis was measured as incorporation into protein of [³H]phe injected into contralateral muscles with or without insulin. Maximal stimulation occurred at 1.0E-5 M for HI and 1.0E-6 M for X2 and H2. At these concentrations, HI had a larger effect (34%) than either X2 (25%) or H2 (20%). The ED50 values for HI, X2 and H2 were 3.0E-7 M, 3.2E-7 M, and 1.0E-9 M, respectively. The relative ED50 values for phe incorporation were consistent with values we had previously determined for in situ glucose uptake, an indicator of metabolic potency. The biological potency of each analog can be expressed as a ratio of ED50HI/ED50analog. X2 is less potent than HI for both metabolic (0.19) and growth-related (0.94) pathways whereas H2 is more potent than HI for both metabolic (20) and growth-related pathways (300). These data also indicate that X2 and H2 have a greater capacity to stimulate a growth-related than a metabolic pathway. The biological potencies measured in our studies are consistent with previously measured relative insulin receptor dissociation rate constants, which are inversely proportional to in vitro biological potencies. In addition, our in situ data agree qualitatively with the relative capacities of HI and its analogs to stimulate metabolic and mitogenic pathways in vitro. These data show that our approach for studying insulin responsiveness in muscles in situ may be a useful tool for investigating insulin signaling in vivo. Supported by NASA Grant NAG2-1187.