Regional changes in ornithine decarboxylase activity and polyamine levels during thyroxine-induced cardiac hypertrophy

Ornithine decarboxylase activities (ODC) and polyamine levels were determined in five cardiac regions of the rat heart, following daily administration of 1 mg/kg of thyroxine, in the right and left atria, the right and left ventricles and the septum. The thyroxine stimulated ODC activity in all five regions of the heart. Enzyme activity in the left atrium and the septum peaked a day earlier than in other regions and the decline of ODC activity was slower. Putrescine in control animals was present in all regions except the right atrium, where its content was below detectable levels. Following the administration of thyroxine, the putrescine content of the left atrium, the right ventricle and the septum declined, while spermidine and spermine levels remained unchanged. In direct contrast to the other regions of the heart, thyroxine stimulated an increase in polyamines, as well as in weight which occurred exclusively in the left ventricle. These findings suggest a causal relationship between increased polyamines and hypertrophy.     

Desensitization of ornithine decarboxylase activity to norepinephrine in the testis of rat

Injection of norepinephrine (NE) at a dose of 10 micrograms per testis caused the testis refractory in terms of ornithine decarboxylase (ODC) activity at 24 h. This desensitization was found to be both time and dose dependent. Injection with follicle stimulating hormone, luteinizing hormone, prostaglandin F2 alpha, cyclic AMP or epinephrine to norepinephrine desensitized testis caused stimulation of ODC activity. This indicates that the refractoriness caused by norepinephrine is specific to this agent alone.     

Increased ornithine decarboxylase activity during meiotic maturation in xenopus laevis oocytes

The activity of ornithine decarboxylase (ornithine carboxylyase E.C. 4.1.1.17) was studied during meiotic maturation induced in vitro by progesterone in follicle cell-free oocytes. Enzyme activity increased 4–6 fold during maturation, preceding germinal vesicle breakdown. The increase in ornithine decarboxylase activity was inhibited by cholera toxin, an agent that blocks meiotic maturation and increases cAMP levels within the cell. It was also prevented by cycloheximide but not by actinomycin D. Treatment of oocytes with D,L-α-difluoromethyl-ornithine, an irreversible inhibitor of ornithine decarboxylase and of putrescine synthesis, effectively abolished enzyme activity without preventing germinal vesicle breakdown. These observations show that the progesterone-induced increase in ornithine decarboxylase activity is not required for completion of meiotic division of the oocyte.     

Modulation of ovarian ornithine decarboxylase activity during follicular differentiation/maturation

The role of gonadotropins and estrogen on the regulation of ovarian ornithine decarboxylase was studied during follicular differentiation/maturation. In intact immature rats follicular differentiation/maturation was initiated with sequential administration of estrogen and follicle stimulating hormone. Ornithine decarboxylase activity in response to human chorionic gonadotropin was markedly enhanced (2-fold) in rats with preovulatory antral follicles when compared to rats with non-ovulatory follicles. This increase could be attributed to the alteration in the turnover of the enzyme. Following follicle maturation the half life of the human chorionic gonadotropin stimulated ornithine decarboxylase was increased from 18 to 62 min. This increase in half life was associated with differentition of follicles. In the estrogen treated group (which does not induce follicular differentiation), the half life of the enzyme remained unaltered. The regulation of ornithine decarboxylase through the formation of protein inhibitor antizyme induced by diamino hexane, was unaltered during follicular differentiation.     

Effect of prostaglandins on ornithine decarboxylase activity in the testis of immature rat

Intratesticular injection of prostaglandin E₂(PGE₂) and F_2α (PGF_2α) caused stimulation of ornithine decarboxylase (ODC) activity in the testis of immature rats. PGE₂ at a dose of 10 μg per testis was maximally effective 2 hours after the injection. Dibutyryl cyclic AMP (cAMP) and 1 methyl, 3-isobutyl xanthine (MIX), a phosphodiesterase inhibitor, also stimulated ODC activity. Simultaneous injection of PGE₂ and FSH or LH caused additional stimulation of ODC activity. Similarly injection of PGE₂ in addition to cAMP or MIX also caused increased stimulation of ODC. Indomethacin (IM, 60 μg/testis) inhibited LH, FSH or cAMP induced ODC activity. However, IM at the same dose inhibited the synthesis of total proteins. These results suggest that PGE₂ and PGF_2α stimulate the activity of ODC. The action of prostaglandins may be independent of the action of gonadotropic hormones. cAMP appears to mediate the action of prostaglandins in the testis of rat.     

Effect of catecholamines on ornithine decarboxylase activity in the testis of immature rat

Intratesticular injection of epinephrine and norepinephrine caused stimulation of ornithine decarboxylase (ODC) activity in the testis of immature rat. The effect of epinephrine was time and dose dependant. The minimal effective dose for epinephrine was found to be 100 pg and optimal stimulation was observed with 500 ng of the drug. Maximal stimulation of ODC occurred at 2 h after the treatment and reduced significantly at 4 h reaching to control levels at 6 h. Simultaneous injection of epinephrine with dibutyryl cAMP, luteinizing hormone, follicle stimulating hormone or prostaglandin E₂ caused additional stimulation of the enzyme activity. Injection of epinephrine to norepinephrine treated animals caused additional effect. Both epinephrine and norepinephrine were found to stimulate the enzyme activity in leydig cell and seminiferous tubule fractions. These results suggest that catecholamines are also involved in the regulation of ODC activity in the testis of rat.     

Effect of prostaglandins on ornithine decarboxylase activity in the testis of immature rat

Intratesticular injection of prostaglandin E2 (PGE2) and F2 alpha (PGF2 alpha) caused stimulation of ornithine decarboxylase (ODC) activity in the testis of immature rats. PGE2 at a dose of 10 microgram per testis was maximally effective 2 hours after the injection. Dibutyryl cyclic AMP (cAMP) and 1 methyl, 3-isobutyl xanthine (MIX), a phosphodiesterase inhibitor, also stimulated ODC activity. Simultaneous injection of PGE2 and FSH or LH caused additional stimulation of ODC activity. Similarly injection of PGE2 in addition to cAMP or MIX also caused increased stimulation of ODC. Indomethacin (IM, 60 microgram/testis) inhibited LH, FSH or cAMP induced ODC activity. However, IM at the same dose inhibited the synthesis of total proteins. These results suggest that PGE2 and PGF2 alpha stimulate the activity of ODC. The action of prostaglandins may be independent of the action of gonadotropic hormones. cAMP appears to mediate the action of prostaglandins in the testis of rat.     

Early changes in ornithine decarboxylase activity during Friend leukemia cell differentiation.

Agents such as dimethylsulfoxide, N,N'-dimethylformamide and bisacetyldiaminopentane that induce erythroid differentiation of Friend leukemia cells, cause a rapid increase in ornithine decarboxylase (EC 4.1.1.17) activity in intact cells during the 'latent' period preceding the accumulation of hemoglobin-containing cells. Blockage of erythroid differentiation with 5-bromo-2'-deoxyuridine did not prevent these alterations in enzyme activity. Addition of each chemical inducer in the extracts of these cells stimulate the basal levels of ornithine decarboxylase activity. These data indicate that the chemical inducers of differentiation modify the normal pattern of ornithine decarboxylase activity in this system.     

Human ornithine decarboxylase(ODC)-encoding gene: cloning and expression in ODC-deficient CHO cells

We have cloned a full-length human ornithine decarboxylase (ODC)-encoding gene from a genomic library of human myeloma cells which overproduce ODC due to a selective gene amplification. Correct expression of the cloned gene was assessed by transfecting it into a Chinese hamster ovary (CHO) cell mutant devoid of ODC activity. Transfection with a 10-kb BamHI DNA fragment of the genomic clone, conferred ODC activity to the recipient cells and relieved them of dependence on exogenous polyamines for growth. A set of 40 transformants was isolated, eight of which were further characterized. The transfected ODC gene appeared to be hypomethylated at the cytosine residues in the sequence CpG. The transfectants were all responsive to serum stimulation, but showed different levels of ODC expression depending on both copy number and integration site of the transfected ODC gene. ODC serum induction in the transfectants was sensitive to cycloheximide and polyamine additions, and the half-life of the enzyme was very short, like that in normal CHO cells. These results suggest that the human ODC gene we transfected contains all the elements needed for normal control of ODC expression.     

Early changes in ornithine decarboxylase activity during friend leukemia cell differentiation

Agents such as dimethylsulfoxide, N,N′-dimethylformamide and bisacetyldiaminopentane that induce erythroid differentiation of Friend leukemia cells, cause a rapid increase in ornithine decarboxylase (EC 4.1.1.17) activity in intact cells during the ‘latent’ period preceding the accumulation of hemoglobin-containing cells. Blockage of erythroid differentiation with 5-bromo-2′-deoxyuridine did not prevent these alterations in enzyme activity. Addition of each chemical inducer in the extracts of these cells stimulate the basal levels of ornithine decarboxylase activity. These data indicate that the chemical inducers of differentiation modify the normal pattern of ornithine decarboxylase activity in this system.     

Developmental regulation of ENaC subunit mRNA levels in rat kidney

To assess therole of distal nephron apical Na channel (ENaC) gene expression in Nawasting by the immature kidney, ENaC -, -, and -subunit mRNAlevels were examined in the rat by RT-PCR. In microdissected nephronsegments, all three ENaC subunit mRNAs were detected in the distalconvoluted tubule, connecting tubule, cortical collecting duct, andouter medullary collecting duct. The inner medullary collecting ductand all other nephron segments were consistently negative. The mRNAlevels were quantified in kidneys at different developmental stages bymultiplex RT-PCR with "primer dropping," with endoplasmicreticulum-specific cyclophilin mRNA as an internal standard. All threeENaC mRNA levels were low or undetectable on gestationalday 16 and only slightly higher 3 daysbefore birth. A sharp rise was observed between 3 days before and1-3 days after birth; the levels at postnataldays 1-3 were already similar tothose of adult kidneys. The results suggest that ENaC subunit geneexpression is not a limiting factor in the full-term newborn ratkidney, but low levels of expression may limit distal Na absorption inmore immature kidneys, such as those of very premature human infants.

     

Steroid regulation of kidney histidine decarboxylase and ornithine decarboxylase levels in mouse kidney: effects of the mutation testicular feminization, Tfm

1. Testosterone represses kidney histidine decarboxylase levels in both normal male and female mice. Tfm/Y mutant mice lack an androgen receptor and are phenotypically female. It has been suggested that the testosterone induction of HDC levels in these animals is a result of aromatisation to oestrogens in the absence of the androgen receptor; the oestrogens then induce the enzyme. 2. It is shown that the induction of HDC in Tfm/Y mice is specific to testosterone and not other androgens and can be mimiced by low doses of beta-oestradiol in normal female mice. 3. Analysis of Tfm/+ mice indicates that the testosterone induction effect is a function of individual kidney cells.     

Developmental regulation of hormone-sensitive lipase mRNA in the rat: changes in steroidogenic tissues.

The hydrolysis of triglycerides and cholesteryl esters stored within cells is mediated by the enzyme, hormone-sensitive lipase. In adipose tissue and heart, hormone-sensitive lipase primarily hydrolyzes stored triglycerides to free fatty acids, while in steroidogenic tissues, it principally converts cholesteryl esters to free cholesterol for steroid hormone production. To determine whether hormone-sensitive lipase is under tissue-specific, developmental regulation, the steady state levels of hormone-sensitive lipase mRNA were determined in normal rats from late fetal life through 2 years of age. Hormone-sensitive lipase mRNA levels did not appear to vary in adipose tissue from epididymal fat pads obtained from animals between 3 weeks and 2 years of age. In heart, hormone-sensitive lipase mRNA levels were lowest in the fetus increased rapidly within the first day postnatally, and then gradually increased to stable adult levels by 2 months that were 3-fold higher than observed in fetal rats. Steady state mRNA levels of hormone-sensitive lipase in the adrenals were lowest in fetal rats, increased 4-fold during the first day and peaked at levels that were 9-fold higher by the end of the first week. Thereafter, levels fell and remained 3- to 4-fold higher than at birth throughout adult life. Hormone-sensitive lipase mRNA was undetectable in testes before 4 weeks of age and increased 25-fold to stable adult levels between 4 and 12 weeks. Thus, hormone-sensitive lipase is differentially expressed and regulated in a tissue-specific fashion during development and aging.