Phosphoinositide metabolism in adipocytes from hypothyroid rats.

The effect of hypothyroidism on insulin- and epinephrine-stimulated phosphoinositide metabolism was investigated in rat adipocytes. Insulin-mediated phosphoinositide synthesis was enhanced by hypothyroidism (14.5 +/- 1.5% above basal level, control vs. 22.5 +/- 2.0% above basel level, hypothyroid, P less than 0.05). However, insulin did not stimulate hydrolysis of phosphoinositides to inositol phosphates, neither in control nor in hypothyroid rats. The alpha 1-adrenoceptor agonist (e.g. epinephrine) significantly stimulated the incorporation of myo-[3H]inositol into phosphoinositides (P less than 0.01) and hydrolysis of phosphoinositides (P less than 0.01), but this stimulatory action was unaffected by the hypothyroid state. The results suggest that hypothyroidism has differentiated effects on the hormone-regulated phosphoinositide metabolism and that the presumptive G-protein coupled to the alpha 1-adrenoceptor seems to be unaffected by hypothyroidism.