Evidence for persistent binding of biologically active thyrotropin to thyroid in vitro

Area of Science:

• Endocrinology
• Molecular Biology
• Cellular Signaling

Background:

• Hormone inactivation and dissociation rates vary across target tissues.
• Understanding hormone-target tissue interaction duration is crucial for deciphering signaling mechanisms.

Purpose of the Study:

• To investigate the binding characteristics of biologically active thyroid-stimulating hormone (TSH) to thyroid slices.
• To compare the persistence of TSH binding with that of prostaglandin E1 (PGE1) on thyroid tissue.

Main Methods:

• Canine thyroid slices were incubated with bovine TSH, followed by washing and incubation in hormone-free media.
• Subsequent incubations assessed cyclic adenosine monophosphate (cAMP) levels, protein kinase activity, and glucose oxidation.
• Experiments were repeated with human, bovine, and porcine thyroid slices.

Main Results:

• Biologically active TSH showed persistent binding to thyroid slices, evidenced by sustained increases in cAMP and glucose oxidation.
• This persistent binding was abolished by trypsin and reduced by TSH antiserum.
• Comparable persistent binding was not observed for PGE1 on thyroid, glucagon on liver, or parathyroid hormone on renal cortex.

Conclusions:

• Biologically active TSH exhibits prolonged binding to thyroid tissue, suggesting a unique interaction mechanism.
• The duration of TSH-PGE1 interaction with thyroid differs, potentially due to TSH's gradual dissociation or PGE1's rapid inactivation.