The effects of cigarette smoke compared to 3-methylcholanthrene and phenobarbitone on alkoxyresorufin metabolism by lung and liver microsomes from rats.

The rates of metabolism of phenoxazone and a homologous series of its ethers (alkoxyresorufins) by liver and lung microsomes of rats exposed to cigarette smoke were compared with the metabolism in rats pretreated with 3-methylcholanthrene (3MC) or phenobarbitone (PB). The rate of resorufin production was dependent on the length of the ether side chain. Liver and lung microsomes from control rats differed in their activity profiles (rate of resorufin production plotted against side-chain length), showing highest activity with ethoxy- and benzyloxyresorufin respectively. 3MC and PB selectively induced hepatic microsomal resorufin production with only certain of the substrates and the two agents differed in their selectivity, inducing most greatly with ethoxy- and benzyloxyresorufin respectively. Pulmonary microsomal resorufin production was induced by 3MC with a substrate selectivity similar to that shown for liver, but PB suppressed pulmonary metabolism with all the substrates. A single, short exposure to cigarette smoke induced ethoxyresorufin O-deethylase activity transiently in liver and lung microsomes. Three consecutive daily short exposures to cigarette smoke caused a weak 3MC-like induction of liver microsomal alkoxyresorufin metabolism, but the effect on lung microsomes was like weak 3MC and PB inductions combined. It is concluded that cigarette smoke induces selected cytochrome P-450-linked alkoxyresorufin O-dealkylase activities to a similar extent in both lung and liver and that the effects of cigarette smoke are characteristic of both 3MC-type and non-3MC-type inducers.

Determination of cytochrome P-448 activity in biological tissues.

Three enzymes used for the determination of cytochrome P-448 activity, namely aryl hydrocarbon hydroxylase, biphenyl 2-hydroxylase and ethoxyresorufin O-de-ethylase, were evaluated with respect to their specificity, sensitivity and inducibility. Purified cytochrome P-448 (LM4), but not cytochrome P-450 (LM2), catalysed the O-de-ethylation of ethoxyresorufin in a reaction that was markedly inhibited by 9-hydroxyellipticine. After the administration of 3-methylcholanthrene to rats all three activities were induced, the extent of induction being highest for ethoxyresorufin O-de-ethylase. Administration of very small doses of benzo[a]pyrene (50 micrograms/kg) to rats to induce cytochrome P-448 specifically increased only the O-de-ethylation of ethoxyresorufin. 3-Hydroxybenzo[a]pyrene, the major metabolite determined by the aryl hydrocarbon hydroxylase assay, undergoes further NADPH-dependent oxygenation leading to loss of fluorescence. On the basis of these observations and those by other workers, we conclude that ethoxyresorufin O-de-ethylase provides the most specific, sensitive and reproducible means of determining cytochrome P-448 activity.

Influence of chronic thyroxine treatment on plasma hormone and metabolite concentrations and on responses to insulin, glucagon and thyrotrophin releasing hormone in adult sheep.

Four adult sheep fed twice daily were given daily subcutaneous injections of saline for four weeks, followed by a similar period of daily L-thyroxine (T4) injection (1 mg/day). T4 treatment increased basal plasma concentrations of T4, triiodothyronine (T3), insulin and glucose, together with T3-uptake and the free thyroxine index, while cholesterol and urea concentrations decreased. T4 treatment reduced the rise in prolactin levels after the morning meal. Thyrotrophin releasing hormone (TRH) injection increased plasma T3 only in the control period and T3-uptake only in the T4 treatment period. T4 treatment did not affect the prolactin response to TRH injection or the insulin and glucose responses to glucagon injection. The increase in insulin concentrations after insulin injection and the secondary hyperglycaemia following initial insulin-induced hypoglycaemia were reduced by T4 treatment.

The mutagenicity of 9-hydroxyellipticine and its induction of cytochrome P-448 activity in rat liver microsomes.

Administration of a single dose of the inhibitor of the hepatic mixed function oxidases, 9-hydroxyellipticine (9-OHE), resulted in a marked increase in the cytochrome P-448 catalysed activities of ethoxyresorufin O-deethylase, biphenyl 2-hydroxylase and activation of benzo[a]pyrene to mutagens. In contrast there was no effect on the cytochrome P-450 catalysed benzphetamine N-demethylase activity. The inductive effect was prevented by simultaneous administration of the protein synthesis inhibitors cycloheximide and actinomycin D. It is concluded that 9-OHE may also act as an inducer of the hepatic microsomal mixed function oxidases, selectively inducing the synthesis of cytochrome P-448. Therefore, 9-OHE, like other inhibitors of this enzyme system, exhibits a biphasic effect, its inhibitory phase being followed by one of enzyme induction. 9-OHE was a direct mutagen in the Salmonella typhimurium strains TA 98 and TA 100.

Plasma growth hormone levels in normal and testosterone implanted growing turkeys.

The growth of normal and testosterone implanted female turkeys was followed between 2 and 16 weeks of age and the concentration of immunoreactive growth hormone (GH) in the peripheral plasma measured. The testosterone treated birds were larger than the controls between 3 and 11 weeks of age. In both groups the plasma GH levels were inversely correlated with the bird's age and body weight and directly correlated with the percentage weekly weight gain Plasma GH concentrations in the testosterone treated birds were higher than in the controls at 4 weeks of age and lower at 3, 6, 7, 8, and 9 weeks of age. Significant differences between the groups in percentage weekly weight gain were not consistently associated with corresponding differences in plasma GH level.

Variations in plasma prolactin, thyroid hormones, gonadal steroids and growth hormone in turkeys during the induction of egg laying and moult by different photoperiods.

1. Concentrations of prolactin, growth hormone, testosterone, progesterone, thyroxine and triiodothyronine were measured in the blood plasma of female turkeys during successive periods of egg laying, a decline in lay, a moult induced by a short photoperiod (6 light: 18 dark) and a resumption of egg laying induced by a long photoperiod (16L:8D). 2. Concentrations of prolactin, growth hormone, testosterone and progesterone were higher in laying birds than in birds which were moulting or not laying. 3. The concentration of testosterone, but not of the other hormones studied, increased significantly during the period of profuse moult. 4. Concentrations of the thyroid hormones did not change with the varying physiological condition of the birds. However, the concentration of thyroxine was depressed by the long photoperiod.

Effect of photoperiod on gonadotrophin concentrations in domestic turkeys.

1. Circulating immunoreactive luteinising hormone (LH) and follicle stimulating hormone (FSH) concentrations have been measured during photoperiodically-induced changes in the reproductive state of turkeys. 2. In a period of sexual quiescence on short photoperiods (6L: 18D) LH concentrations were higher during the hours of darkness in both sexes. 3. Transfer to long photoperiods (16L: 8D) stimulated a rapid increase in LH and FSH concentrations. This was maintained for between 2 to 3 months when the concentrations of both gonadotrophins decreased as the birds became photorefractory. 4. Return to short photoperiods had no immediate effect on the concentrations of LH and FSH in females. The concentration of LH was increased during the 3rd week of short photoperiods when the hens were moulting. 5. LH concentrations fluctuated during the ovulatory cycle and were highest about 6 h before ovulation.

Gonadotrophin concentrations during growth and maturation in domestic turkeys.

1. Circulating immuno-reactive-luteinising hormone (LH) and follicle stimulating hormone (FSH) were measured between hatching and either 17 or 30 weeks of age in turkeys. 2. In one experiment both sexes were reared together. The pattern of changes in gonadotrophin concentration with age consisted of high LH concentrations at 3 to 8 and 16 to 19 weeks old and FSH peaks between weeks 3 and 10 and at weeks 18 and 19. 3. In two separate experiments male and female birds were reared separately for 17 weeks. In these turkeys the LH concentration was high for 3 weeks following hatching and also after 10 weeks, while FSH was elevated at weeks 10 and 15 in females and at weeks 7 and 13 in males. 4. There were lower plasma LH concentrations in turkeys which had received testosterone implants while the FSH concentration was elevated. 5. Pinealectomy in female turkeys led to increased FSH concentrations at 2 weeks but depressed FSH concentrations thereafter.

Plasma growth hormone concentrations during growth in turkeys.

The concentrations of circulating GH were low in 1-week-old birds (male plasma pool 30 ng/ml, female 32 ng/ml), reached a maximum at 7 weeks in male birds (142 +/- 26 SEM ng/ml) or 4 weeks in females (185 +/- 32 ng/ml) and then decreased to 17-3 +/- 2-8 ng/ml in males and 8-7 +/- 0-6 ng/ml in females at 17 weeks. 2. Significant inverse correlations between GH concentration and age or body weight were found (male, r = -0-693), female, r = -0-623). 3. In males, but not females, the weekly increase in body weight was correlated with the plasma GH concentration (r = 0-291).

The effect of luteinizing hormone releasing hormone and steroids on the release of LH and FSH from incubated turkey pituitary cells.

The secretion of immunoreactive luteinizing hormone (IR-LH) and follicle stimulating hormone (IR-FSH) by turkey pituitary cell suspensions has been investigated. No significant effects of synthetic ovine luteinizing hormone-releasing hormone (LH-RH) on gonadotrophin release were found with cells from 17 to 19 weeks old birds, though IR-LH secretion was elevated with tissue from young (13 weeks) birds. Although IR-FSH secretion was increased in the presence of progesterone alone, effects of oestradiol and testosterone on IR-FSH release and of oestradiol, progesterone and testosterone on LH-RH release were observed when the steroid treatment was combined with that of LH-RH.

An homologous radioimmunoassay for chicken follicle-stimulating hormone: observations on the ovulatory cycle.

A highly purified FSH preparation has been used to develop a specific homologous radioimmunoassay for chicken FSH which is sufficiently sensitive and precise to measure the hormone in small sample (10-100 microliter) of plasma. The assay was used to measure plasma FSH in the chicken and turkey. The FSH concentration was higher in sexually mature chickens than in juvenile birds and further elevated after castration or ovariectomy. In turkeys, it was lower in birds held on a short daily photoperiod than in birds held on a long daily photoperiod. FSH rose in sexually quiescent female turkeys after injection of synthetic LH-releasing hormone and was increased in laying hens after injection of progesterone. No major changes were observed in FSH concentration during the chicken ovulatory cycle, although there was a small increase 15 and 14 h before ovulation.