A RIA procedure for measuring progesterone (PROG), 5 alpha-pregnane-3,20-dione (5 alpha-DH PROG), and 3 alpha-hydroxy-5 alpha-pregnan-20-one (3 alpha,5 alpha-TH PROG) has been developed and validated by GLC/mass spectrometry. Measurements were made in intact and adrenalectomized (ADX) male rats, in cyclic, pregnant, spayed, and spayed-ADX females, and in both males and spayed females injected with PROG. The predominant contribution of the ovary to the concentrations of 3 alpha,5 alpha-TH PROG in plasma and brain, was indicated by its larger levels in females, in particular during pregnancy, and by its presence in ovarian tissue and disappearance after ovariectomy. An additional adrenal origin in both males and females was shown. Neither PROG nor 5 alpha-DH PROG disappeared from brain, contrary to plasma, after combined adrenalectomy and gonadectomy, thus suggesting that PROG might be synthetized de novo in brain. However, the concentrations of 3 alpha,5 alpha-TH PROG in plasma and brain of female rats were positively correlated with the concentrations of PROG in plasma, indicating that plasma PROG was the major precursor of 3 alpha,5 alpha-TH PROG. The direct formation of 3 alpha,5 alpha-TH PROG from PROG in brain was strongly suggested by the increased 3 alpha,5 alpha-TH PROG/PROG ratios in brain vs. plasma, when measured in control females, and after injection of PROG to both males and OVX females. It was previously reported that 3 alpha,5 alpha-TH PROG is a sedative/anxiolytic steroid, as a result of its binding to gamma-aminobutyric acid (GABA)A receptors and allosteric potentiation of GABAcergic neurotransmission. Its concentrations in brain reach indeed the neuroactive range in cyclic and pregnant females, and are compatible with a physiological role of this neurosteroid.

Five steroids-38-hydroxypregn-S-en-20-one (pregnenolone; P), 3fi-hydroxy-5a-pregnan-20-one (3.3-AP), 3a-hydroxy-5a-pregnan-20-one (3a-AP), 3.-hydroxyandrost-5-en-17-one (dehydroepiandrosterone; D), and 3fi-hydroxy-5a-androstan-17-one (EpiA)-were extracted from the brains of adult male rats, rabbits, and dogs. The steroids exist in this organ as uncoajugated compounds and as sulfates, lipoidal esters, and sulfolipids. The techniques for separating these four classes ofsteroids from each other and for separating the five steroids from each other are described. In all cases, the steroids were identified by their retention time (Re) on HPLC, theirRt by gas chromatography, and by selected ion monitoring of their mass spectra. The latter were also used for quantification. In their reaction toward organic bases, the sulfolipid conjugates resemble previously described sulfolipids of cholesterol and sitosterol. These conijugates are relatively abundant in brain, particularly those of P and D, and this suggests that, in the search for the physiological significance of these brain constituents, these conjugates warrant attention.also seem to indicate that the above-mentioned steroids may be present in brain in amounts somewhat larger than those previously reported. Furthermore, until now only the sulfate and lipoidal esters of both P and D have been detected in the brain. Our findings reveal that another steroidal conjugate(s), still to be characterized, is also present. In particular, evidence is given here that indicates that steroidal conjugates comparable in nature to those that we previously described (11) for cholesterol and sitosterol are also present in substantial amounts in brain. We have designated this conjugated form a sulfolipid, with the possible structure StO-SO2-OL (where St is a steroid and L is a lipid moiety), because this nonpolar conjugate, when treated with an organic base such as triethylamine, can cleave to give either a product that behaves like the sulfuric acid ester of a steroid or an unconjugated steroid, like P. Although their exact structures have yet to be determined, the abundance of these conjugates in brain suggests that their relationship to brain function warrants corsideration.The most recent facet of steroid hormone biochemistry to evoke intense interest, astonishing activity, and discoveries that presage previously unforeseen scientific advances is that which deals with the relationship between steroids and neuronal-especially brain-function. One ofthe factors that has been responsible for stimulating the interest in this chapter of biochemistry has been the detection of steroids in brain (neurosteroids) by Baulieu and his colleagues (1). Another impetus for the development was the finding of Majewska et al. (2) that certain steroid derivatives are potent modulators of the Cl-channel associated with the type A receptor for y-aminobutyric acid. More recent findings have shown that other ion channels, particularly those associated with N-methyl-D-aspartate receptors, may also ...

Dehydroepiandrosterone (