The effects of neonatal capsaicin treatment on growth and subsequent reproductive function in the rat.

The results of the present study describe the following effects of neonatal capsaicin treatment on growth and reproductive function in the rat. Neonatal capsaicin treatment in the rat resulted in a retardation of body growth through adulthood most pronounced at 35 days of age. Capsaicin-treated rats had normal estrous cycles, but mated significantly less frequently than age-matched controls. Confirmed matings in capsaicin-treated female rats resulted in significantly fewer pregnancies compared to controls. Male rats treated with capsaicin as neonates produced significantly fewer pregnancies when mated with untreated females compared to controls. Ovulation, sperm transport, and fertilization occur normally in capsaicin-treated rats. The decidual response was markedly diminished in mated capsaicin-treated rats. These findings led to the conclusion that the neurohormonal reflex, which is normally initiated through the stimulation of the cervix by copulation, and which ultimately stimulates secretion of pituitary luteotropic hormones, did not occur in capsaicin-treated rats. Thus, ovarian progesterone secretion was not facilitated resulting in inadequate hormonal support for implantation, pregnancy or pseudo-pregnancy. These data further suggest that the sensory limb of this neurohormonal reflex may consist of capsaicin-sensitive, possibly substance P containing, primary afferent fibers.