SUBSTANCE-P AND NEUROKININ-A VARIATIONS THROUGHOUT THE RAT ESTROUS-CYCLE - COMPARISON WITH OVARIECTOMIZED AND MALE-RATS .1. PLASMA, HYPOTHALAMUS, ANTERIOR AND POSTERIOR PITUITARY

The concentrations of Substance P and Neurokinin A were measured in pl asma, and the hypothalamo-pituitary complex of 4-day-cycling female, o variectomized and male rats, Estrous cycle-related fluctuations were r ecorded for these two neurokinins. The patterns of plasma concentratio ns of Substance P and Neurokinin A, however, were not similar througho ut the rat estrous cycle, The plasma concentration of Substance P incr eased on proestrus at 19.00 hr, while Neurokinin A decreased, The plas ma concentration of Substance P was positively correlated with plasma 17 beta-estradiol levels, In the ovariectomized rat, the absence of ov arian steroids led to low levels of plasma Neurokinin A, but the plasm a concentration of Substance P did not show any change as compared to the estrous cycle, In the male rat, a similar observation was made in the presence of a testosterone environment, The largest variations in tissue concentration of both peptides were observed in the anterior pi tuitary, Substance P and Neurokinin A contents were higher throughout the proestrous day than the 3 other days, However, the level fell at 1 8.00 hr on proestrus, and there were similar falls in the hypothalamic contents of Substance P and Neurokinin A at 19.00 hr, In the ovariect omized rat, with no gonadal steroids, the hypothalamic and/or anterior pituitary levels of Substance P were in the same range as during the estrous cycle, However, the hypothalamic levels of Neurokinin A were l ower and Neurokinin A was undetectable in the anterior pituitary, Subs tance P and Neurokinin A concentrations in the posterior pituitary wer e stable throughout the estrous cycle, with the exception of rises for both peptides on estrous day, Substance P levels were much lower in o variectomized and male rats, These results describe large fluctuations in hypothalamic and pituitary Substance P and Neurokinin A contents t hrough the estrous cycle in the female rat, They also strongly suggest the involvement of gonadal steroids in the differential regulation of Substance P and Neurokinin A in the female and male rat. (C) 1996 Wil ey-Liss, Inc.