There is a nyctohemeral rhythm of type II iodothyronine 5'-deiodinase activity in rat anterior pituitary | JoVE Visualize

There is a nyctohemeral rhythm of type II iodothyronine 5'-deiodinase activity in rat anterior pituitary

M Murakami¹, K Tanaka, M A Greer

¹Department of Medicine, Oregon Health Sciences University, Portland 97201.

Endocrinology|September 1, 1988

View abstract on PubMed

Summary

Rats exhibit a daily rhythm in type II iodothyronine 5'-deiodinase (5'-D-II) activity in the anterior pituitary, peaking at midnight. This rhythm, absent in hypothyroidism, may influence thyroid-stimulating hormone (TSH) secretion.

Area of Science:

Endocrinology
Molecular Biology
Chronobiology

Background:

Thyroid hormones regulate metabolism and development.
The enzyme type II iodothyronine 5 -deiodinase (5 -D-II) converts prohormone thyroxine to active triiodothyronine (T3).
Thyroid-stimulating hormone (TSH) secretion exhibits a nyctohemeral rhythm, crucial for thyroid hormone homeostasis.

Purpose of the Study:

To investigate the presence and characteristics of nyctohemeral rhythms for 5 -D-I and 5 -D-II in rat tissues.
To determine the influence of hypothyroidism on these enzymatic rhythms.
To explore the potential role of anterior pituitary 5 -D-II rhythm in regulating TSH secretion.

Main Methods:

Measurement of 5 -D-I and 5 -D-II activity in rat anterior pituitary, brown adipose tissue, liver, and kidney.
Comparison of enzyme activity across different time points to identify nyctohemeral rhythms.
Assessment of enzyme activity in hypothyroid rat models.

Main Results:

A significant nyctohemeral rhythm of 5 -D-II was identified in the rat anterior pituitary, with peak activity at midnight.
No nyctohemeral rhythm for 5 -D-II was observed in brown adipose tissue.
No nyctohemeral rhythm for 5 -D-I was detected in the anterior pituitary, liver, or kidney.
Hypothyroidism completely abolished the nyctohemeral rhythm of anterior pituitary 5 -D-II.

Conclusions:

The anterior pituitary exhibits a distinct daily rhythm in 5 -D-II activity.
This rhythm is dependent on thyroid hormone status.
The rhythmic activity of anterior pituitary 5 -D-II may be a key factor in regulating the nyctohemeral pattern of TSH secretion through local T3 feedback.