Influence of thyroid hormones on transport function and Na+-K+-ATPase activity in the rat choroid plexus

The sympathomimetic stimulation of choroid plexus transport and secretion in rat seems to be mediated by beta-adrenergic receptors. In the present report the effect of induced changes in thyroid function on transport mechanisms in the rat choroid plexus was studied. Following induction of hyperthyroidism (treatment with T3 for 10 days) the tissue/medium ratio (T/M) for choline uptake in choroid plexus in vitro decreased significantly by 68%. The Na+-K+-ATPase activity showed a statistically significant increase of about 16%. Also following cervical sympathectomy, T3 caused a reduction of the T/M for choline, to the same level as in the non-sympathectomized animals, while the effect of T3 on the Na+-K+-ATPase activity was changed into a 22% decrease. Hypothyroidism (administration of PTU in the drinking water) had little or no effect on the uptake and accumulation of choline in the choroid plexus. The Na+-K+-ATPase activity was reduced by 40%, in contrast to the stimulating effect of T3. There is, hence, reason to believe that the transport of choline in the choroid plexus is only partly regulated by adrenergic mechanisms acting via Na+-K+-ATPase. The major effect of T3 on the choline uptake may be exerted by a mechanism different from the ATPase activity and not involving adrenergic receptors.