Stimulation by insulin of ornithine decarboxylase activity in cultured mammary tissue

Nerve growth factor increases activity of ornithine decarboxylase in rat brain

Intraventricular administration of nanogram quantities of nerve growth factor to adult rats results in a marked increase in the activity of ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) in the brain. The increase occurs in all major brain regions and the activity is maximal by 7.5 hr after administration. The enzyme response to nerve growth factor increases in magnitude during maturation; the relative increase in ornithine decarboxylase activity in adult animals is much greater than that in young. Neither insulin nor bovine growth hormone was able to increase ornithine decarboxylase activity to the same extent as did nerve growth factor. When brain was separated into neuronal- and glial-enriched fractions, induction of ornithine decarboxylase was found in both, but a greater increase was observed in the glial fraction.

Insulin regulates milk protein synthesis at multiple levels in the bovine mammary gland

The role of insulin in milk protein synthesis is unresolved in the bovine mammary gland. This study examined the potential role of insulin in the presence of two lactogenic hormones, hydrocortisone and prolactin, in milk protein synthesis. Insulin was shown to stimulate milk protein gene expression, casein synthesis and (14)C-lysine uptake in mammary explants from late pregnant cows. A global assessment of changes in gene expression in mammary explants in response to insulin was undertaken using Affymetrix microarray. The resulting data provided insight into the molecular mechanisms stimulated by insulin and showed that the hormone stimulated the expression of 28 genes directly involved in protein synthesis. These genes included the milk protein transcription factor, ELF5, translation factors, the folate metabolism genes, FOLR1 and MTHFR, as well as several genes encoding enzymes involved in catabolism of essential amino acids and biosynthesis of non-essential amino acids. These data show that insulin is not only essential for milk protein gene expression, but stimulates milk protein synthesis at multiple levels within bovine mammary epithelial cells.

Effects of cyclic nucleotides on ornithine decarboxylase activity in mammary gland explants from mid-pregnant mice

Dibutyryl cAMP and prolactin stimulated ornithine decarboxylase activity in mouse mammary gland explants which had been preincubated with insulin and cortisol for 1 day; maximally stimulatory concentrations of dibutyryl cAMP and prolactin produced a response which was greater than the sum of the responses of prolactin and dibutyryl cAMP when tested alone. 8-Bromo-cGMP inhibited ornithine decarboxylase activity whereas other derivatives of cyclic nucleotides were without effect. Cortisol concentrations were found to be important for optimizing the dibutyryl cAMP and prolactin responses. Optimal prolactin responses were obtained with cortisol concentrations greater than 10(-7) M, whereas optimal dibutyryl cAMP responses were observed with cortisol concentrations less than 10(-7) M. Despite the differing optimal cortisol concentrations for the prolactin and dibutyryl cAMP responses, it is concluded that prolactin and dibutyryl cAMP probably stimulate ornithine decarboxylase activity in the mammary gland via the same mechanism.

Regulation of the activity of ornithine decarboxylase and S-adenosylmethionine decarboxylase in mammary gland and liver of lactating rats. Effects of starvation, prolactin and insulin deficiency

1. Starvation caused a marked decrease in the activity of ornithine decarboxylase in mammary gland, together with a lesser decrease in the activity of S-adenosylmethionine decarboxylase and a marked fall in milk production. Liver ornithine decarboxylase and S-adenosylmethionine decarboxylase activities were unaffected. 2. Refeeding for 2.5 h was without effect on ornithine decarboxylase in mammary gland, but it returned the S-adenosylmethionine decarboxylase activity in mammary gland to control values and elevated both ornithine decarboxylase and S-adenosylmethionine decarboxylase in liver. 3. Refeeding for 5 h returned the activity of ornithine decarboxylase in mammary gland to fed-state values and resulted in further increases in S-adenosylmethionine decarboxylase in mammary gland and liver and in ornithine decarboxylase in liver. 4. Prolactin deficiency in fed rats resulted in decreased milk production and decreased activity of ornithine decarboxylase in mammary gland. The increase in ornithine decarboxylase activity normally seen after refeeding starved rats for 5 h was completely blocked by prolactin deficiency. 5. In fed rats, injection of streptozotocin 2.5 h before death caused a decrease in the activities of ornithine decarboxylase and S-adenosylmethionine decarboxylase in mammary gland, which could be reversed by simultaneous injection of insulin. Insulin deficiency also prevented the increase in S-adenosylmethionine decarboxylase in liver and mammary gland normally observed after refeeding starved rats for 2.5 h.

Activity and modulation of ornithine decarboxylase and concentrations of polyamines in various tissues of rats as a function of age

The activities of ornithine decarboxylase (ODC) on the soluble and nuclear fractions of the cerebral cortex, heart and lungs of 4- (young), 38- (adult) and 85-week (old) male rats were studied. Also, the effects of aminophylline, histamine and estradiol on the activity of soluble ODC have been determined in vitro using slices of these tissues. The activity of ODC is significantly higher in the soluble fraction of all the tissues in comparison to that of nuclear fraction. Its activity in both the fractions is highest in the immature and decreases with increasing age in all the tissues except in the nuclear fraction of the lungs in which it increases with age. The ODC of the heart, lungs and cerebral cortex appear to be different as seen from the differences in their sensitivities to aminophylline, histamine and estradiol. In general, there is a decrease in its sensitivity to the three effectors with increasing age. This may be due to a decrease in the receptors and a concomitant decrease in ODC activity. A direct relationship between ODC activity and polyamine levels of the brain exists at various ages of the rat.

Effects of insulin on cultured rat brain cells: stimulation of ornithine decarboxylase activity

Growth-promoting peptide hormones, including growth hormone and insulin, stimulate rat brain ornithine decarboxylase (ODC; EC 4.1.1.17) activity in vivo (Roger et al., 1974; Roger and Fellows, 1980). To determine if this is a result of a direct action on brain, we have investigated the effect of peptide hormones in primary cell cultures of brain from fetal rats of 20 days gestational age. Significant stimulation of ODC activity was observed 4 h after administration of porcine insulin and bovine growth hormone. On a molar basis, growth hormone was less potent than insulin. By contrast, glucagon, enkephalin, and angiotensin II did not stimulate ODC in this system. At 25 ng/ml, insulin stimulated ODC activity approximately threefold, with maximum stimulation of five- to sevenfold reached at 1 microgram/ml. After a 1-h lag, insulin-stimulated ODC activity increased to a maximum between 5 h and 8 h and returned to basal levels by 24 h. The apparent Km of ODC, 5.66 +/- 1.16 microM, was not significantly altered by insulin treatment, nor was any enzyme activator found in mediating insulin actions. Additional evidence suggests that insulin stimulation of ODC activity involves both de novo synthesis of the enzyme and a prolongation of ODC half-life by 50%. These findings, implicating insulin as a regulator of ODC activity in brain cells, suggest the possible involvement of insulin or an insulin-like peptide in the control of growth and development of the CNS.

Ornithine decarboxylase activity in insulin-deficient states

The activity of ornithine decarboxylase, the rate-controlling enzyme in polyamine biosynthesis, was determined in tissues of normal control rats and rats made diabetic with streptozotocin. In untreated diabetic rats fed ad libitum, ornithine decarboxylase activity was markedly diminished in liver, skeletal muscle, heart and thymus. Ornithine decarboxylase was not diminished in a comparable group of diabetic rats maintained on insulin. Starvation for 48h decreased ornithine decarboxylase activity to very low values in tissues of both normal and diabetic rats. In the normal group, refeeding caused a biphasic increase in liver ornithine decarboxylase; there was a 20-fold increase in activity at 3h followed by a decrease in activity, and a second peak between 9 and 24h. Increases in ornithine decarboxylase in skeletal muscle, heart and thymus were not evident until after 24-48h of refeeding, and only a single increase occurred. The increase in liver ornithine decarboxylase in diabetic rats was greater than in normal rats after 3h of refeeding, but there was no second peak. In peripheral tissues, the increase in ornithine decarboxylase with refeeding was diminished. Skeletal-muscle ornithine decarboxylase is induced more rapidly when meal-fed rats are refed after a period without food. Refeeding these rats after a 48h period without food caused a 5-fold increase in ornithine decarboxylase in skeletal muscle at 3h in control rats but failed to increase activity in diabetic rats. When insulin was administered alone or together with food to the diabetic rats, muscle ornithine decarboxylase increased to activities even higher than in the refed controls. In conclusion, these findings indicate that the regulation of ornithine decarboxylase in many tissues is grossly impaired in diabetes and starvation. They also suggest that polyamine formation in vivo is an integral component of the growth-promoting effect of insulin or some factor dependent on insulin.

Physical and kinetic distinction of two ornithine decarboxylase forms in Physarum

Two forms of ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) can be isolated from crude plasmodial homogenates of Physarum polycephalum. Both forms catalyze the stoichiometric production of putrescine and CO2 from ornithine, yet they are distinguished by (a) a large difference in their affinity for coenzyme (apparent Km values of 0.13 and 33 muM); (b) a differential stability to extended dialysis of crude homogenates at 4 degrees C; and (c) the tendency of the low affinity form to polymerize when suspended in low ionic strength borate and phosphate buffers. These forms appear to be alternate states of a basic catalytic subunit in that (a) they both demonstrate monomer and dimer molecular forms of 80 000 and 160 000 daltons, respectively, depending on the buffer content; (b) they coelute from DEAE-Cellulose ion-exchange columns; and (c) they vary in activity in approximately equivalent yet opposite directions in response to factors which alter this organism's growth or metabolism. These data suggest that ornithine decarboxylase activity may be modulated by the control of the transition of this enzyme between the active and the relatively less active form.

Action of prolactin on ornithine decarboxylase activity in mammary gland explants of mice

Prolactin stimulated ornithine decarboxylase activity in mammary gland explants from midpregnant mice. The enhanced enzyme activity occurred in explants which were preincubated for 1 day in medium containing insulin, hydrocortisone, insulin plus hydrocortisone, or in medium containing no hormones. The largest prolactin effect was observed in tissues which were pretreated with insulin plus hydrocortisone; a greater than ten-fold increase in ornithine decarboxylase activity was observed when these tissues were incubated with prolactin for 2 hours. An effect of prolactin on ornithine decarboxylase activity was also observed in explants prepared from lactating mouse mammary glands.

Ornithine decarboxylase activity in relation to DNA synthesis in mouse interfollicular epidermis and hair follicles

The relationship between ornithine decarboxylase (L-ornithine carboxylyase, EC 4.1.1.17) activity and DNA synthetic activity was studied in mouse epidermis. Interfollicular epidermis and hair follicles were investigated separately. It was found that, in hair follicles, the variations of DNA replicative activity, which are reflected in the cyclic growth of hair, are paralleled by corresponding changes in ornithine decarboxylase activity. In both interfollicular epidermis and hair follicles, stimulation of DNA synthetic activity by plucking of hair induced a rapid and marked increase in ornithine decarboxylase activity. The relationship of steady-state and induced ornithine decarboxylase activity to DNA synthetic activity was compared in hair follicles and interfollicular epidermis. A correlation between the activity of this enzyme and DNA replication was found thereby in each of these tissues.