Uptake and metabolism of female sex steroids by isolated small neurons and other cell fractions from the rat medial basal hypothalamus

Rat medial basal hypothalami (MBH) and sections of cerebral cortex (CC) were dissociated with trypsin to prepare single cells and subcellular fractions. They were then separated into four fractions on a discontinuous sucrose gradient. The small neurons in Fraction D were highly purified. Fraction A had synaptosomes, myelin and other cell particulates. Fraction B had glial cells, neurons and a few synaptosomes. Fraction C had large neurons and red blood cells. All four fractions contained LHRH, but most (62.5%) of this hormone was present in Fraction A. Dissociated cell suspensions were incubated with ³H]-steroids, with and without a 100-fold excess of unlabeled steroids, then separated on sucrose gradients. In most fractions the total uptake and specific uptake of ³H]-progesterone, ³H]-5α-pregnane-3,20-dione (5α-dihydroprogesterone) and ³H]-l7β-estradiol were greater for the dissociated cells from the MBH than the CC. The dissociated cells and cell particulates in all four fractions from the MBH and CC metabolized progesterone, 5α-dihydroprogesterone and l7β-estradiol.These results indicate that hypothalamic neurons contain small amounts of LHRH and retain the ability to take up and metabolize progesterone, 5α-dihydroprogesterone and 17β-estradiol.