Multiple species of ornithine decarboxylase in mouse kidney. Effect of testosterone.

Multiple species of ornithine decarboxylase were separated by chromatography of mouse kidney extract on DEAE-Sepharose CL-6B. The elution patterns of ornithine decarboxylase activity and immunoreactive enzyme protein in the kidneys of untreated and testosterone-treated male mice did not differ otherwise than in order of magnitude. The immunoblots of the chromatography fractions neither revealed any differences in enzyme subunit size between two experimental groups. These findings suggest that the stabilization of ornithine decarboxylase by androgens is not due to the molecular changes of enzyme protein.

The effect of testosterone on the half-life of ornithine decarboxylase-mRNA in mouse kidney.

The effect of testosterone on half-lives of ornithine decarboxylase and its mRNA in mouse kidney was studied. In addition to the prolongation of enzyme protein half-life by androgens, excess of testosterone increases in vivo the half-life of its mRNA to about 3-fold as manifested by the change of enzyme half-life in testosterone-treated animals after alpha-amanitin or actinomycin D. These results suggest that the accumulation of ornithine decarboxylase in mouse kidney by androgens is partly due to the stabilization of its mRNA.

Possible involvement of humoral regulation in the effects of elevated cerebral 4-aminobutyric acid levels on the polyamine metabolism in brain.

It has been reported in several recent studies that the manipulation of cerebral 4-aminobutyric acid (GABA) level results in unexpected changes in the cerebral polyamine metabolism in vivo. The mechanisms behind these interactions have remained unknown. The present results show that the changes in polyamine metabolism are not limited to the brain, but are observable also in the liver, which served as a peripheral reference tissue. Different types of responses in the activities of the polyamine-synthesizing enzymes, ornithine decarboxylase and adenosylmethionine decarboxylase, were observed after increasing the cerebral GABA concentration of mice with varying doses of two GABA transaminase inhibitors, gabaculine and ethanolamine-O-sulphate. The time course of the significant changes in the enzyme activities showed significant correlation between the brain and liver. The possibility of direct effects of the drugs on liver was excluded by injecting them intracerebroventricularly, and by performing control experiments with equal doses given peripherally. It is concluded that the observed changes in the polyamine metabolism of liver are produced through centrally mediated humoral regulation, and that the corresponding changes in the brain are obviously due to the same factor or factors, since they are significantly correlated to the changes in liver.

The inverse changes of mouse brain ornithine and S-adenosylmethionine decarboxylase activities by chlorpromazine and imipramine. Dependence of ornithine decarboxylase induction on beta-adrenoceptors.

Intraperitoneal injection of chlorpromazine and imipramine increases mouse brain ornithine decarboxylase but decreases S-adenosyl-L-methionine decarboxylase activity. Maximal effect was obtained 6-8 hr after treatment at which time single dose of chlorpromazine (50 mg/kg) stimulated ornithine decarboxylase activity 7-fold and decreased S-adenosylmethionine decarboxylase activity to 50% from the control level. Correspondingly, ornithine decarboxylase activity was 5.5 times higher than the control value and S-adenosylmethionine decarboxylase activity about 40% from that after imipramine injection (80 mg/kg). The possible dependence of the enzyme responses on adrenergic receptors was studied using alpha-adrenoceptor antagonist, phentolamine, and beta-adrenoceptor antagonist, propranolol, concurrently with chlorpromazine and imipramine. The stimulation of ornithine decarboxylase but not the inhibition of S-adenosylmethionine decarboxylase could be abolished by propranolol (10 mg/kg), whereas phentolamine (10 mg/kg) slightly increased ornithine decarboxylase activity even when given alone. This suggests that beta- but not alpha-adrenergic mediation is involved in the stimulation of mouse brain ornithine decarboxylase activity and that brain ornithine and S-adenosylmethionine decarboxylase activities are independently regulated. When chlorpromazine and imipramine were tested in vitro, both of them turned out to have an inhibitory effect on S-adenosylmethionine decarboxylase. The former caused 50% inhibition at a concentration of 1 mM and the latter at 2 mM. Preliminary tests suggest that the type of inhibition is noncompetitive for both of them.

Inhibition of polyamine synthesis blocks urinary secretion of beta-glucuronidase from mouse kidney.

The effect of inhibition of polyamine synthesis on castrated male mouse kidney beta-glucuronidase induction and secretion by testosterone was studied. Inhibition of the activities of polyamine synthesis key-enzymes, L-ornithine and S-adenosyl-L-methionine decarboxylases, was performed with the combined treatment of 2-difluoromethylornithine and methylglyoxal' bis(guanylhydrazone). Blockage of polyamine synthesis did not affect testosterone-induced increase in renal beta-glucuronidase but blocked its secretion into the urine. After withdrawal of inhibitor-treatment beta-glucuronidase secretion normalized, and repeated testosterone administration produced undisturbed beta-glucuronidase secretion peak in urine suggesting that blockage of beta-glucuronidase secretion was not due to the tissue damage produced by inhibitors. These results indicate that the stimulation of renal polyamine synthesis by testosterone is not necessary for the induction of beta-glucuronidase but is required for the urinary secretion of this protein.

Developmental changes in mouse brain polyamine metabolism.

Mouse brain ornithine decarboxylase (ODC) activity is high at the time of birth, whereas S-adenosyl-L-methionine decarboxylase (SAM-DC) activity is low. ODC activity, and putrescine, spermidine and spermine concentrations decline rapidly during postnatal development to the low level characteristic of mature brains, while SAM-DC activity behaves in the opposite manner. The fluctuations in mouse brain polyamine metabolism are in accord with those found in the rat. The apparent Km values of ODC and SAM-DC for their substrates decline parallel with the decrease of substrate and product concentrations during ontogeny suggesting substrate and/or product dependent regulation of polyamine synthesis in the developing brain.