Enzyme-inducing effects of bicalutamide in mouse, rat and dog.

1. Bicalutamide, a non-steroidal antiandrogen, produced dose-related increases in total cytochrome P450 (P450) and aldrin epoxidase, but had no effect on ethoxyresorufin O-deethylase, when administered for 10 weeks at 0, 25, 75 and 150 mg/kg/day to the male dog. 2. In the male and female mouse, bicalutamide, administered orally at 75 mg/kg/day for 3 months, produced marked induction of total P450, ethoxycoumarin O-deethylase, pentoxyresorufin O-dealkylase and aldrin epoxidase. Immunoblotting showed that bicalutamide produced substantial induction of CYP2B isoforms, with lower increases in CYP3A. Immunohistochemistry of mouse liver sections also showed marked increases in the level of CYP2B isoforms, with an increase in the extent of distribution from centrilobular to panlobular; CYP3A isoforms were also increased, but to a lesser degree. 3. Bicalutamide, administered as 14 daily oral doses (250 mg/kg) to groups of male rats, produced increases primarily in ethoxycoumarin O-deethylase and erythromycin N-demethylase, together with smaller increases in ethoxyresorufin O-deethylase and pentoxyresorufin O-dealkylase; these changes were reversible within 7 days. Immunoblotting of microsomes and immunocytochemistry of liver sections showed that bicalutamide markedly induced CYP3A1, but had little effect on CYP2B1 in rat. Compared with dexamethasone, bicalutamide is a more selective inducer of CYP3A1 in rat. 4. Bicalutamide, administered to rats as 14 daily oral doses of 10 mg/kg, induced its own metabolism by stimulating both aromatic hydroxylation and direct glucuronidation. This effect was apparently offset by a concomitant decrease in hydrolysis of bicalutamide, resulting in no marked change in total amounts of dose eliminated over 2 days. 5. Although the secondary effects of enzyme induction result in thyroid hypertrophy and adenoma in rat and hepatocellular carcinoma in mouse following chronic administration of bicalutamide, these changes are considered to have little clinical relevance. In any case, bicalutamide does not produce enzyme induction in man at clinically relevant dose levels.

Expression of growth factors and growth factor receptors in the liver of C57BL/10J mice following administration of phenobarbitone.

Liver enlargement is a common feature of non-genotoxic rodent hepatocarcinogens administered at high doses. In the present study, the expression of growth factors and growth factor receptors was investigated in the C57BL/1OJ mouse during liver enlargement induced by the non-genotoxic rodent hepatocarcinogen, sodium phenobarbitone (PB). Male mice were dosed 0-2500 p.p.m. PB in the diet for 1, 4 and 13 weeks. There was a dose and time dependent increase in liver weight. Hepatocyte replication, assessed by incorporation of bromodeoxyuridine, was increased in a dose-dependent manner at week 1 only (18-fold increase at 2000 p.p.m.) and was predominantly localized in the centrilobular region. At week 1, PB (2500 p.p.m.) caused transient increases in transforming growth factor alpha (TGFalpha) and epidermal growth factor receptor (EGFR) and decreases in transforming growth factor beta1 (TGF-beta1) and mannose-6-phosphate receptor (M6PR) in centrilobular hepatocytes which correlated with the replication in this region. At week 1, there was an increase in both hepatocyte growth factor (HGF) and hepatocyte growth factor receptor (HGFR) which colocalized in centrilobular hepatocytes; in some mice or periportal hepatocytes in other mice. After 13 weeks, HGF and HGFR were localized in the cytoplasm of centrilobular hepatocytes of all mice but exhibited a differential intracellular distribution across the lobule. At 2500 p.p.m. PB, EGFR and HGFR mRNA were essentially unchanged over the 13 week dosing period whilst M6PR mRNA was increased 2- to 4-fold. At 2500 p.p.m. PB, EGFR protein levels from immunoblots showed a consistent decrease over the 13 weeks whilst M6PR and HGFR protein levels were essentially unchanged. The protein level and mRNA data for EGFR suggest post-transcriptional modification. Thus, phenobarbitone caused transient replication of hepatocytes and modulation of growth stimulatory and inhibitory factors and their associated receptors in terms of overall levels and regional distribution in the liver.

The effects of ZENECA ZD8731, an angiotensin II antagonist, on renin expression by juxtaglomerular cells in the rat: comparison of protein and mRNA expression as detected by immunohistochemistry and in situ hybridization.

Changes in the mRNA and protein expression of renin-secreting cells in the juxtaglomerular apparatus (JGA) were examined in the rat following administration of ZENECA ZD8731, an angiotensin II receptor antagonist. Doses of 0 or 90 mg/kg were administered daily by gavage for 26 wk. JGA hypertrophy was apparent in histological sections. Immunohistochemistry demonstrated an increase in the number of renin-containing cells in both the afferent arterioles and the interlobular arteries. Similarly, renin mRNA expression, demonstrated by in situ hybridization, had extended to more proximal segments of the afferent arterioles and was also present in efferent arterioles and interlobular arteries. In conclusion, JGA hypertrophy occurred as a result of antagonism of the angiotensin II receptor. Associated with JGA hypertrophy was increased expression of both renin and renin mRNA, indicative of stimulated renin synthesis caused by an exaggerated pharmacological response of renin-secreting cells to the loss of feedback inhibition by angiotensin II.

A quantitative study of neuropeptide immunoreactive cell bodies of primary afferent sensory neurons following rat sciatic nerve peripheral axotomy.

Following peripheral axotomy, fluoride resistant acid phosphatase (FRAP) and most neuropeptides are depleted in the central terminals of axotomised nerves and reduced in their corresponding cell bodies (DRG) but vasoactive intestinal polypeptide (VIP) increases. The increase in VIP probably results from a change in gene expression in other ganglion cells which do not normally express VIP. A quantitative study was performed to investigate the proportion of DRG cells immunoreactive for different peptides at increasing times after sciatic nerve section. Retrograde fluorescent neuronal labelling of sciatic nerve cell bodies by injection of fast blue into the proximal stump was combined with unlabelled antibody immunohistochemistry for CGRP and VIP. The proportion of cells immunoreactive for these peptides was quantified between two and fourteen days post-axotomy. The number of VIP immunoreactive profiles increased significantly in the first 4 days post-axotomy, followed by a slight decrease before rising again. In contrast, the number of and CGRP-immunoreactive cell profiles declined to zero by 14 days post-axotomy. 4 days post-axotomy 50% of VIP positive cells were also immunoreactive for CGRP. There was neither colocalisation between VIP and FRAP nor between CGRP and FRAP. It is concluded that many peptidergic DRG cell bodies switch their expression of peptide to VIP after injury, whereas non-peptide-containing subpopulations do not.