Hormonal effects on fatty acid binding and physical properties of rat liver plasma membranes.
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The fluorescent fatty acids, trans-parimaric and cis-parinaric acid, were used as analogs of saturated and unsaturated fatty acids in order to evaluate binding of fatty acids to liver plasma membranes isolated from normal fed rats. Insulin (10-8 to 10-6m) decreased trans-parinaric acid binding 7 to 26% while cis-parinaric acid binding was unaffected. Glucagon (10-6m) increased trans-parinaric acid binding 44%. The fluorescence polarization of trans-parinarate, cis-parinarate and 1,6-diphenyl-1,3,5-hexatriene was used to investigate effects of triiodothyronine, insulin and glucagon on the structure of liver plasma membranes from normal fed rats or from rats treated with triiodothyronine or propylthiouracil. The fluorescence polarization of trans-parinarate, cis-parinarate, and 1,6-diphenyl-1,3,5-hexatriene was 0.3000.004, 0.2510.003, and 0.3020.003, respectively, in liver plasma membranes from control rats and 0.3160.003, 0.2760.003 and 0.3160.003, respectively, in liver plasma membranes from hyperthyroid rats (p<0.025, n=5). Propylthiouracil treatment did not significantly alter the fluorescence polarization of these probe molecules in the liver plasma membranes. Thus, liver plasma membranes from hyperthyroid animals appear to be more rigid than those of control animals. The effects of triiodothyronine, insulin and glucagon added in vitro to isolated liver plasma membrane preparations were also evaluated as follows: insulin (10-10m) and triiodothyronine (10-10m) increased fluorescence polarization of trans-parinaric acid, cis-parinaric acid and 1,6-diphenyl-1,3,5-hexatriene in liver plasma membranes while glucagon (10-10m) had no effects. These hormonal effects on probe fluorescence polarization in liver plasma membranes were abolished by pretreatment of the rats for 7 days with triiodothyronine. Administration of triiodothyronine (10-10m)in vitro increased the fluorescence polarization of trans-parinaric acid in liver plasma membranes from propylthiouracil-treated rats. Thus, hyperthyroidism appeared to abolish the in vitro increase in polarization of probe molecules in the liver plasma membranes. Temperature dependencies in Arrhenius plots of absorption-corrected fluorescence and fluorescence polarization of trans-parinaric acid, cis-parinaric acid and 1,6-diphenyl-1,3,5-hexatriene were noted near 25C in liver plasma membranes from triiodothyronine-treated rats and near 18C in liver plasma membranes from propylthiouracil-treated rats. In summary, hormones such as triiodothyronine, insulin and glucagon may at least in part exert their biological effects on metabolism by altering the structure of the liver plasma membranes. 1982 Springer-Verlag New York Inc.
