IMMUNOREACTIVE SUBSTANCE-P AND NEUROKININ-A IN THE HYPOTHALAMUS AND ANTERIOR-PITUITARY GLAND OF SIBERIAN-HAMSTERS AND SYRIAN-HAMSTERS AND OF RATS

In this investigation the concentrations of immunoreactive substance P and neurokinin A in the hypothalamus and anterior pituitary of the Siberian hamster were compared with those in the rat and Syrian hamster. The concentrations of immunoreactive neurokinin A in the hypothalamus of Siberian hamsters were significantly higher than those of: rats and Syrian hamsters, while male Siberian hamsters had similar amounts of substance P in the hypothalamus to those of male Syrian hamsters, but had higher amounts than those in male rats. However, female Siberian hamsters had significantly higher hypothalamic concentrations of both substance P and neurokinin A than did female Syrian hamsters and rats. In the anterior pituitary glands of Siberian hamsters, concentrations of substance P and neurokinin A were markedly higher than they were in rats and even more so than in Syrian hamsters. Ovariectomy further increased tachykinin concentrations in the anterior pituitary gland of female Siberian hamsters, and this was completely prevented by oestradiol replacement. Female Siberian hamsters kept under conditions of reduced photoperiod had significantly higher tachykinin concentrations in the anterior pituitary than did animals kept under daily photoperiods of 16 h light:8 h dark. The incubation of anterior pituitaries from female Siberian hamsters with a neurokinin A receptor antagonist resulted in a partial blockade of the LH and FSH release in response to LHRH. Thus, the high concentration of tachykinins present in the anterior pituitary of the Siberian hamster may have a local role in modulating the secretion or release of gonadotrophins.