Regulation of heart insulin receptor tyrosine kinase activity by magnesium and spermine.

Insulin action and aspects of the insulin-signaling pathway have been studied in the heart although the direct regulation of the heart's insulin receptor has not been explored. This study describes the first purification and characterization of the mammalian (rabbit, rat and bovine) heart insulin receptor. The rabbit heart IR showed maximum insulin binding of 18 microg/mg (approximately 1 mole insulin/mole (alpha2beta2) receptor) and a curvilinear Scatchard plot with a high affinity KD for insulin binding of approximately 4 nM at optimal pH (7.8) and NaCl concentration (150 mM). The insulin receptor tyrosine kinase activity was stimulated by insulin, Mg2+ (half-maximum response at approximately 5.6-10.6 nM and approximately 8.5 mM, respectively) and by the physiological polyamines, spermine and spermidine. The stimulation by Mg2+ and the polyamines occurred with and without insulin. These characteristics of the heart insulin receptor provide a mechanism for regulating the activity of the receptor's tyrosine kinase activity by the intracellular free Mg2+ concentration and the polyamines in the absence and presence of insulin.

Pharmacokinetics of subcutaneous selenium in adult llamas.

Selenium (Se) deficiency disease has been described in camelids and only clinical data is available for administration of parenteral Se supplements. This study investigated the pharmacokinetic effects of subcutaneous Se injection (0.1 mg/kg) in llamas fed a diet adequate in Se. Absorption of Se was rapid with peak whole blood Se concentration at the first sampling time. Significant differences in whole blood Se concentration from before injection of Se were not found past 2 days after Se injection. Parenteral Se is unlikely to have a long-term effect on whole blood Se concentration in llamas fed adequate dietary Se.