The effect of dexamethasone on P450 activities in regenerating rat liver.

The aim of our study was to detect four P450s (CYP1A, CYP2B, CYP2E1, CYP3A) on the basis of selective enzyme activities and protein amount, and to investigate the effect of dexamethasone treatment during liver regeneration. Partial hepatectomy of rats resulted in the loss of CYP1A, CYP2B, CYP2E1, and CYP3A activities. The reduction of enzyme activities and the loss of enzyme protein of CYP2B1/2, CYP2E1, and CYP3A1/2 were the most pronounced. In the case of CYP1A1, only slight decrease was observed. Dexamethasone treatment seems to counteract this loss mainly in the first 12 h.

Hepatic regeneration induces transient acute phase reaction: systemic elevation of acute phase reactants and soluble cytokine receptors.

The growth factors present during liver regeneration partially overlap with the regulators of the hepatic acute phase response. We analysed the acute phase reaction and changes in soluble cytokine receptors after partial hepatectomy, when tissue injury inducing acute phase reaction and major reduction of liver mass occur simultaneously. Three acute phase proteins and mRNAs were determined by ELISA and northern blot hybridisation in rats. Serum levels of IL-6 and three soluble cytokine receptors (sTNF-alpha R I and II, sIL-6R) were detected by ELIBA or dot-blot assay. Time-course profiles of fibrinogen, alpha(2)-macroglobulin and haptoglobin proteins and mRNA are presented. Elevation of IL-6, soluble TNF-alpha receptors and soluble IL-6 receptor levels were also detected. The time-course of changes in haptoglobin concentration and elevation of soluble cytokine receptors is described by this in vivo experimental system. The results show good correlation with (post)transcriptional activation of immediate and delayed early gene products. These data suggest the involvement of both acute phase proteins and soluble cytokine receptors in the regulation of liver regeneration.

Elevated hepatic glucocorticoid receptor expression during liver regeneration in rats.

In rats within the first week of partial hepatectomy reconstruction of the normal histological structure of the liver already starts. To approach the possible role of endogenous glucocorticoids in the process of regeneration we measured the changes in the expression of steroid glucocorticoid receptor gene after various regeneration intervals. After partial hepatectomy, between 0.5 168 hours from the surgery, the gene expression (mRNA) of glucocorticoid receptor was determined by reverse transcription followed by PCR and normalized to that of glycerolphoshate dehydrogenase. Two peaks of glucocorticoid receptor mRNA were detected first, between 3 and 6 hours (first peak) and a second between 24 and 36 hours. Immunoreactive glucocorticoid receptor was detected by immunohistochemistry using monoclonal anti-glucocorticoid receptor. Three days after the surgery immunohistochemical studies showed substantially more immunoreactive GcR protein in the regenerated liver than in the controls. These semiquantitative data provide evidence suggesting elevation of glucocorticoid receptor expression during regeneration of liver at mRNA and protein levels.

Investigation on the formation of the hormone reception mechanism.

The formation of the hormone receptor mechanism is part of the embryonic development. The perinatal age seems to be critical for the maturation of this system, i.e. the development of the proper hormone selectivity, the number of the receptors, their sensitivity to the adequate hormone. Our team tried to get a closer view on this developmental period examining different parameters in different model systems. We were able to show that during the maturation of the hormonal system similar responses could be elicited by the later specific hormones or by the non-specific ones but structurally similar compounds. Also it became evident that one single hormonal treatment, applied during in the perinatal age, could influence the responsiveness to hormones of the adult animals.

Changes in sexual behavior of adult male and female rats neonatally treated with vitamin D3.

1. Neonatal treatment of rats with vitamin D3 resulted in a change of sexual behavior in adulthood. 2. 2.5 mg vitamin D3 completely inhibited the ejaculation of males without any apparent influence on sexual desire. 250 mg vitamin D3 influenced both the desire and ejaculation. 3. Sexual activity of females was depressed by both doses. 4. The experiments demonstrate that vitamin D3, a steroid in structure, given in the critical period of hormonal imprinting may influence steroid hormone-receptor commanded events for life, in a way similar to the effects exhibited by synthetic steroid hormone analogues and benzpyrene in earlier studies.

Effect of nifedipine treatment (imprinting) of rat feti and newborns on the responsiveness of adult rat's uterus. Extension of the imprinting theory.

1. The uterus of adult progeny of rats treated with nifedipine during the late phase of pregnancy react in vitro to oxytocin less and the contractility of ones treated with higher dose (100 micrograms) disappears. 2. There is a more pronounced deficiency or lack of responsiveness in five week old animals treated with nifedipine neonatally. 3. The experiments demonstrate that perinatal imprinting can be developed not only on hormone receptors and enzymes but on ion (Ca2+) channels of the plasma membrane. Consideration of this fact might have an importance in clinical aspects too.

Effect of contraceptive treatment on thymic glucocorticoid receptors and hepatic microsomal enzyme system of adult rats.

Contraceptive steroid treatment accounted for about a 30 per cent decrease in the number of thymic glucocorticoid receptors of adult rats. Neonatal allylestrenol treatment had no influence on that treatment. The activity of the hepatic microsomal (PSMO) enzyme system was not changed by the contraceptive treatment. It appears that contraceptive treatment may account for overlaps on receptors in adulthood.

Impact of single neonatal allylestrenol treatment on the estrus cycle of rats treated with FSH+LH or TSH.

Neonatal allylestrenol treatment administered to female rats significantly increases the duration of estrus phase in the sexual cycle. Treatment with follicle stimulating hormone (FSH) + luteinizing hormone (LH) in adulthood prolongs the duration of estrus even on its own; the effect, however, is more pronounced in those animals who were treated (imprinted) with allylestrenol neonatally. When administered to the control animals, the chemically related thyreotrop hormone (TSH) is either indifferent or it even decreases the estrus index. In animals having received neonatal allylestrenol treatment, however, TSH administration increases significantly the duration of the estrus phase. Either with or without FSH+LH treatment, the ratio of estrogenic to gestagenic phase increases following neonatal allylestrenol treatment. The experiments call attention to the potential functional risks inherent in neonatal allylestrenol treatment. The actual risks, however, seem to be smaller than the effects seen at the receptor level.

Impact of a single insulin treatment (imprinting) applied during liver regeneration on hepatic insulin receptor development, blood glucose level and liver function parameters in adult rats.

Rats subjected to partial hepatectomy (surgical removal of two thirds of the liver) showed no appreciable change in serum cholesterol, bilirubin, albumin, total protein and A/G values at 2, 5, 12 and 21 days after the intervention. The enzyme activities characteristic of liver damage (GOT, GPT, LDH, AP) were high in the control group and low in the insulin-imprinted group at 2 days, tended to normalize in both groups at 5 days and changed slightly at 12 days. The blood glucose level was markedly decreased in the control group and to a lesser degree also in the experimental group at 2 and 5 days of sampling. Insulin treatment (loading) performed at 2 and 5 days accounted for a drop of blood glucose which was followed by normalization within 2 h. Starving value and response to insulin loading uniformly fell into the physiological range at 21 days, whereas at 12 days no normalization occurred in either group within 2 h of insulin loading, although the starving value was physiological. The binding capacity of the insulin receptor was markedly low in the control group as long as 12 days, and tended to normalize by 21 days. In the insulin-imprinted group the binding capacity increased over the control at 2 and 5 days and normalized by 12 days.

Impact of neonatal benzpyrene imprinting on liver microsomal enzyme induction by benzpyrene and phenobarbital in adulthood.

A single neonatal treatment of rats with benzpyrene accounted for a durable induction of the liver microsomal enzyme (PSMO) system. Neonatal treatment with benzpyrene enhanced the inducing action of phenobarbital administrated in adulthood, but did not change the effect of benzpyrene treatment in the adult age. It follows that the imprinting and inducing effects of the neonatal benzpyrene treatment took different trends.