THE EFFECT OF NEONATAL THYROIDECTOMY ON THE DEVELOPMENT OF THE ADENOSINE 3′,5′‐MONOPHOSPHATE SYSTEM IN THE RAT BRAIN

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Abstract
Abstract— The effect of neonatal thyroidectomy on the cyclic AMP system in the developing rat brain was examined. Administration of 131I at birth led to a 16 per cent reduction in brain weight and a 70 per cent reduction in body weight by 40 days of age. The level of cyclic AMP in the brain increased 5‐fold between birth and 40 days of age and this increase was partially reduced by early thyroidectomy. A similar increase in the activity of adenyl cyclase and phosphodiesterase was observed during development, but thyroidectomy produced no detectable changes in the activity of either enzyme. The activity of the cyclic AMP‐dependent protein kinase was already maximal at birth and also was unaffected by thyroidectomy.Norepinephrine increased levels of cyclic AMP 4‐ to 5‐fold in brain slices prepared from adult rats, but was without effect on slices prepared from newborn or 3‐day‐old rats. The response to norepinephrine in thyroidectomized rats did not differ from that in control rats at any of the ages examined. Our findings indicate that neonatal hypothyroidism does not deleteriously affect the development of the cyclic AMP system in the rat brain.