Thyroidal regulation of lingual lipase development in suckling rats

Rat lingual lipase undergoes maturational increases during postnatal development. The role of thyroxine (T4) in the control of lingual lipase during development was evaluated. T4 given at an early suckling stage (starting day 4 or 5) moderately increased lingual lipase (20-30%) compared to age-matched controls. A similar dose of T4 given later (age > 2 weeks) was ineffective. The T4-sensitive period coincides with a time of low circulating T4, suggesting a role of T4 in modulating the development of lingual lipase in rat pups. Since simultaneous treatment with U486, a type II glucocorticoid receptor antagonist only partially blocked the T4 induction of lingual lipase, T4 appeared to have a direct action on the lingual gland. Pups of propylthiouracil (PTU)-treated dams (previously found to be hypothyroid) showed a delay in the maturation of lingual lipase compared to age-matched pups whose dam was not given PTU. Pups were most sensitive to PTU in the early suckling stage. PTU-induced delayed maturation of lingual lipase was a result of hypothyroidism, since T4 replacement when given early (at the age of 5 days) abolished most of the effect of PTU. When T4 was given later (at the age of 10 days), recovery was much less. This suggests the presence of an early period that is critically dependent on T4 for the full expression of lingual lipase in the rat tongue serous glands.(ABSTRACT TRUNCATED AT 250 WORDS)