Abundance of the alpha-subunits of Gi1, Gi2 and Go in synaptosomal membranes from several regions of the rat brain is increased in hypothyroidism.

1. Rats (4 weeks old) were made hypothyroid by treatment with propylthiouracil together with a low-iodine diet for a further period of 4 weeks. Synaptosomal membranes were obtained from six anatomical regions of the brain. 2. The abundances in these membranes of the G-protein alpha-subunits Gi1 alpha, Gi2 alpha and Go alpha were measured by quantitative immunoblotting. 3. Hypothyroidism significantly increased the abundances of all three G-protein subunits in membranes from the cerebral cortex and the striatum. In the medulla oblongata and the hippocampus the abundances of Gi2 alpha and Go alpha were increased significantly. By contrast, in the cerebellum only Go alpha was increased, and in the hypothalamus only Gi2 alpha was increased. 4. It is suggested that this up-regulation of G-protein abundances may modify signalling pathways and may contribute to the functional changes that are observed in the central nervous system in hypothyroidism.