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Endocrine regulation of thymic biosynthetic polyamine decarboxylases in adult rat
Abstract:
The activities of ornithine and S-adenosyl-L-methionine decarboxylase were assayed in the thymuses of adult rats killed at 7-day intervals up to 6 wk after either pinealectomy or sham pinealectomy. The absence of the pineal gland markedly influenced the ornithine decarboxylase activity in the thymus, in which the level of the enzyme was decreased permanently by the 4th wk after the operation (P less than 0.05). The time course of the changes in S-adenosyl-L-methionine decarboxylase activity in the thymus during the entire period investigated was also significantly (P less than 0.05) modified by pinealectomy but did not show any stable trend. Adrenalectomy significantly raised (P less than 0.001) for ornithine decarboxylase; P less than 0.01 for S-adenosyl-L-methionine decarboxylase) the basal levels of the thymic biosynthetic polyamine decarboxylases. A pharmacological dose of corticosterone or cortisol produced a rapid and significant decrease in ornithine and S-adenosyl-L-methionine decarboxylase activities (P less than 0.02) in the thymus, whereas the injection of either D-aldosterone or ACTH was ineffective. Therefore, the thymic biosynthetic polyamine decarboxylases that in this organ are known to be located only in the lymphocytes appear to be regulated in opposing ways by the pineal gland and by the adrenal cortex.
Insights
Pinealectomy permanently reduces ornithine decarboxylase activity in rat thymus. Both pinealectomy and adrenalectomy significantly alter thymic polyamine decarboxylase activities, suggesting opposing regulatory roles.
Area of Science:
- Endocrinology
- Immunology
- Biochemistry
Background:
- The thymus plays a crucial role in immune function.
- Polyamine metabolism is essential for cell growth and differentiation.
- The pineal gland and adrenal cortex are known endocrine regulators.
Purpose of the Study:
- To investigate the impact of pinealectomy and adrenalectomy on thymic polyamine decarboxylase activities in adult rats.
- To explore the regulatory relationship between the pineal gland, adrenal cortex, and thymic lymphocytes.
Main Methods:
- Assaying ornithine decarboxylase (ODC) and S-adenosyl-L-methionine decarboxylase (SAMDC) activities in rat thymuses.
- Performing pinealectomy, sham pinealectomy, and adrenalectomy surgeries.
- Administering pharmacological doses of corticosterone, cortisol, D-aldosterone, and ACTH.
Main Results:
- Pinealectomy led to a permanent decrease in thymic ornithine decarboxylase activity by 4 weeks post-operation.
- Pinealectomy significantly modified the time course of S-adenosyl-L-methionine decarboxylase activity without a stable trend.
- Adrenalectomy significantly increased basal levels of both ODC and SAMDC in the thymus.
- Corticosterone and cortisol rapidly decreased thymic ODC and SAMDC activities, while D-aldosterone and ACTH were ineffective.
Conclusions:
- The pineal gland and adrenal cortex exert opposing regulatory effects on thymic biosynthetic polyamine decarboxylases, primarily located in lymphocytes.
- These findings highlight the intricate interplay between the pineal and adrenal systems in modulating thymic function and immune cell activity.