INFLUENCES OF HYPOTHYROIDISM ON LIPID-COMPOSITION AND INOSITOL LIPID-LINKED RECEPTORS RESPONSIVENESS AND PROTEIN-KINASE-C (PKC) ACTIVITY INTHE CEREBRAL-CORTEX OF LEWIS RATS

The influence of hypothyroidism (HO) induced by treatment with propylt hiouracil on lipid composition, receptor responsiveness of M1-muscarin ic receptors (M(1)AChRs) and metabotropic glutamate receptors (mGluRs) as well as on protein kinase C (PKC) activity was investigated in the cerebral cortex of Lewis rats. HO did not influence the lipid composi tion. There was a significant 2-fold increase of efficacy and 6-fold d ecrease of potency of carbachol-induced inositol phosphate (IF) accumu lation in HO, with respect to control rats. The efficacy of trans-(1S, 3R)-1-amino-1,3-cyclopentanedicarboxylic acid (ACPD)-induced IP accumu lation was also higher in HO (by 50%), without differences in EC50 val ues. The activities of soluble calcium-dependent and calcium-independe nt PKC were higher in HO than in control rats (both roughly 30%); memb rane-associated PKCs were not modified. The data indicate that HO indu ces an increased responsiveness of M(1)AChRs and mGluRs and a rise in the soluble PKC activity that could be available and ready for translo cation.