ABSTRACT

In an effort to understand the physiological functions of cytochrome P-450 in the central nervous system and pituitary gland, we evaluated changes in the level of the enzyme as a function of the endocrine status of rats and the ability of these tissues to synthesize or degrade steroids. The P-450 content of microsomes prepared from the hypothalamic preoptic area (HPOA), the olfactory lobes and the cerebrum was 0·040 ± 0·009 and in the pituitary gland 2·2 ± 0·6 (s.d.) nmol/g tissue. The P-450 content of the HPOA and olfactory lobes, but not of the rest of the cerebrum, was influenced by the endocrine status of rats. In microsomes it increased five- to tenfold over control levels during late pregnancy in the olfactory lobes and during lactation in the HPOA, and in both brain regions treatment of rats with 5α-dihydrotestosterone (DHT) caused an eight- to tenfold increase in the P-450 content. Androstenedione was not a good substrate for brain P-450. The level of androstenedione 19-hydroxylase in the olfactory lobe microsomal fraction was 0·50± 0·06 nmol 19-hydroxyandrostenedione formed/g tissue per h. This activity was tenfold lower in other brain areas and was not detectable in the pituitary gland. The rate of aromatization of androstenedione to oestradiol in the HPOA and olfactory lobe of lactating rats was 0·46 ± 0·14 and 0·38 ± 0·05 pmol/oestradiol formed/g tissue per h respectively. 5α-Androstane-3β,17β-diol (A-5α-3β,17β-diol) was a much better substrate for P-450 throughout the brain and pituitary gland. Catalytic activity was 125 ± 46 and 307 ±108 nmol triols formed/g tissue per h in the brain and pituitary gland respectively. The P-450 responsible for this catalytic activity was isolated and its substrate specificity examined. In addition to A-5α-3β,17β-diol, 5-androstene-3β,17β-diol, dehydroepiandrosterone and DHT were also substrates, with turnover numbers of 27, 8, 12 and 1 mol product/mol P-450 per min respectively. None of these catalytic activities was induced in the rat brain during pregnancy, lactation or DHT treatment. The enzyme was also present in the brains of mice but not guinea-pigs.

The yield of P-450 from the mitochondrial fraction of the HPOA and olfactory lobes in control rats was 0·01–0·02 nmol/g tissue. This increased tenfold during pregnancy. Immunological evidence for the presence of the cholesterol side-chain cleavage enzyme P-450 SCC was found in the HPOA and olfactory lobes of pregnant but not of control rats. However, no SCC catalytic activity was detectable in these brain mitochondrial P-450 fractions. From these studies we conclude that there is a major influence of the endocrine system on the content and quality of P-450 in the brain. However, the function and substrate specificities of these P-450s as well as of those in the pituitary gland remain to be characterized.

Journal of Endocrinology (1989) 122, 341–349

Abstract

Glucocorticoids are among the most potent anti-inflammatory agents that can be used in the treatment of rhinitis. Their mechanisms of action are multiple and complex and a number of reports describe significant systemic effects of locally administered glucocorticoids. In order to evaluate the short-term systemic effects of intranasally administered glucocorticoids, 14 normal healthy subjects were treated with two doses of either budesonide (BUD) or fluticasone propionate (FP) for 2 weeks. Before treatment, at regular intervals during the treatment, 1 week and finally 6 weeks after termination of treatment, the effects on glucocorticoid receptor (GR) and methallothionein (MTIIa) mRNA expression levels were examined in peripheral lymphocytes using a solution hybridization assay. Serum cortisol, osteocalcin and urinary cortisol levels were also determined. An insulin tolerance test (ITT) was performed at the end of the second week of treatment and at the end of the 6-week washout period with no statistically significant change in cortisol response. In peripheral lymphocytes, GR mRNA levels were significantly down-regulated. MTIIa mRNA levels increased significantly. Serum osteocalcin decreased significantly during treatment with both BUD and FP. Serum cortisol decreased after 1 week of treatment whereas urinary cortisol was not affected until the second week of treatment. In conclusion, intranasal glucocorticoids at clinically recommended doses have not only significant systemic effects on adrenal function, but also have an effect on specific gene expression in peripheral lymphocytes. These effects are receptor-dependent, reversible, and according to serum and urinary cortisol levels and ITT, leave the hypothalamic-pituitary-adrenal function intact. Finally, these short-term systemic effects were not associated with any of the noticeable side-effects usually observed during long-term treatment with glucocorticoids.

Journal of Endocrinology (1995) 144, 301–310