Thyroid hormone status regulates preprotachykinin-A gene expression in male rat anterior pituitary

Substance P (SP) and substance K (SK) are mammalian tachykinin peptides derived from a single preprotachykinin-A (PPT-A) gene and are widely but selectively distributed in neural and endocrine tissues. SP is present in the rat anterior pituitary, and its content there varies with the thyroid status of the animal. The present studies were undertaken to determine whether the PPT-A gene is expressed in the anterior pituitary and if so, whether PPT-A messenger RNA (mRNA) abundance is regulated by thyroid hormone status. Male rats were surgically or chemically thyroidectomized or made hyperthyroid by thyroid hormone (T3) injection. Total RNA was isolated from individual anterior pituitaries, and PPT-A mRNA abundance was determined by dot blot procedures. In parallel groups of rats, anterior pituitaries were extracted for measurement of SP and SK by specific RIAs. Surgical or chemical thyroidectomy increased PPT-A mRNA abundance 4 to 6-fold and increased both SP and SK content in the anterior pituitary. Administration of T3 to thyroidectomized rats reversed the increase in both PPT-A mRNA abundance and SP and SK content in the adenohypophysis. T3 administration to euthyroid rats also decreased PPT-A mRNA abundance and SP and SK content in the anterior pituitary. The coordinate presence of PPT-A mRNA with SP and SK in the anterior pituitary strongly suggests that these peptides are synthesized within this gland.