Tachykinins and their gene expression in the anterior pituitary of the siberian hamster-Effects of photoperiod, thyroid hormones, and analogs of hypothalamic hormones.

The anterior pituitary gland of the Siberian hamster contains high concentrations of tachykinins compared to other laboratory rodents. In this investigation we studied the relative quantities of neurokinin A (NKA), neuropeptide gamma (NPG), and neuropeptide K (NPK) present in extracts of anterior pituitaries from this species. The anterior pituitary extracts, purified by HPLC, contained similar quantities of NKA and NPG, and lower quantities of NPK. The anterior pituitary gland of the Siberian hamster contained mRNA encoding β-preprotachykinin A, which is a precursor of substance P, NKA, and NPK. This fact proves that the anterior pituitary gland of the Siberian hamster has the ability to synthesize tachykinins. Animals exposed to short photoperiods had higher concentrations of tachykinins in the pituitary gland, and triiodothyronine markedly depressed the stores of these peptides in the anterior pituitary. In some groups of animals, the somatostatin analog octreotide induced a small, but significant decrease of the levels of NKA in the pituitary. The present results, together with previously published findings, indicate that thyroid hormones and estrogens are the most active endogenous substances to suppress the levels of anterior pituitary tachykinins in the Siberian hamster.