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 con centrations of tachykinins compared to other laboratory rodents. In th is investigation we studied the relative quantities of neurokinin A (N KA), neuropeptide gamma (NPG), and neuropeptide K (NPK) present in ext racts of anterior pituitaries from this species. The anterior pituitar y 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 beta-preprotachykinin A, whic h is a precursor of substance P, NKA, and NPK. This fact proves that t he anterior pituitary gland of the Siberian hamster has the ability to synthesize tachykinins. Animals exposed to short photoperiods had hig her concentrations of tachykinins in the pituitary gland, and triiodot hyronine markedly depressed the stores of these peptides in the anteri or pituitary In some groups of animals, the somatostatin analog octreo tide induced a small, but significant decrease of the levels of NKA in the pituitary. The present results, together with previously publishe d findings, indicate that thyroid hormones and estrogens are the most active endogenous substances to suppress the levels of anterior pituit ary tachykinins in the Siberian hamster.