The progesterone metabolite 5α-pregnane-3α-ol-20-one (3α,5α-THP) is an important modulator of the hypothalamic–pituitary–adrenal axis and stress-induced corticosterone response. Typically, 3α,5α-THP levels are increased in response to acute stress, which may then reduce corticosterone release from the adrenals. Early postnatal stimulation is a developmental stressor that can produce pervasive endocrine effects.
The present studies investigated the effects of early postnatal stimulation on plasma progestin and corticosterone levels and hippocampal progestin levels of rats.
On postnatal days 9 and 10, rats were either left in their home cage undisturbed or injected intraperitoneally as a means of early stimulation (ES). Tissues were collected on either postnatal day 10 (6 h after last handling experience) or adulthood. Plasma corticosterone, progesterone, and 3α,5α-THP and hippocampal progesterone and 3α,5α-THP were measured by radioimmunoassay.
On postnatal day 10, plasma, but not hippocampal, levels of progesterone and 3α,5α-THP were significantly lower among rats exposed to ES than control rats. These effects occurred concomitant with a tendency for plasma corticosterone to be higher among ES compared to control rats. In adulthood, hippocampal 3α,5α-THP was significantly lower among ES vs control rats.
Together, these data suggest that ES may influence immediate secretion of 3α,5α-THP and corticosterone and have pervasive effects in adulthood on the biosynthesis and/or metabolism of progestins in the hippocampus.