Anti-implantation role for substance P and neurotensin in rat.

Substance P (SP) and neurotensin (NT), two structurally related peptides with contrasting biological actions, have been shown to have some role in peripheral reproductive processes. Intrauterine microinjection of SP or NT on day 4 or 5 of pregnancy in the rat significantly reduced the number of viable fetuses, weight and glycogen content of the uterus. The number of viable fetuses, uterine weight or glycogen content were not modified when SP/NT was microinjected on day 8, 9, 10 or on day 14, 15 and 16. The results indicate that the peptides possibly exert a direct local alteration in uterine vascular permeability causing failure in implantation.