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

Abstract

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.

Effect of starvation and refeeding on polyamine concentrations and ornithine decarboxylase antizyme in mammary gland of lactating rats

“…Thus there is a clear dissociation between the content of polyamines and of RNA in this situation. The activity of ornithine decarboxylase is also decreased (Brosnan et al, 1982, and the present study), and thus it is unlikely that these polyamines are synthesized from ornithine de novo. Although the polyamine content of blood of fed lactating rats is low, and the largest part of this is contained in the blood cells (Lundgren & Oka, 1978), the possibility of redistribution of polyamines from liver or other tissues during starvation must be considered.…”

“…The polyamine concentration in liver of lactating rats is shown in Table 3. In the fed rats, spermidine Discussion Putrescine content and ornithine decarboxylase antizyme Despite a marked decrease in ornithine decarboxylase activity by 6h of food deprivation (Brosnan et al, 1982), the putrescine content of mammary gland increased dramatically over 24h starvation. In mice starved for 24h, hepatic putrescine concentrations were increased, as a result of increased activity of spermidine Nl-acetyltransferase and subsequent oxidation of the Nl-acetylspermidine to putrescine by polyamine oxidase (Seiler et al, 1981b).…”

“…In each of these fluids, free putrescine and spermine are below the limits of detection (5 nmol/ml) of our method, and the free spermidine concentration is low in fed rats (blood, 43 + 13 nmol/ml, n = 4; milk 33+ 13 nmol/ml, n = 5), although the concentrations in blood from starved or refed rats are not known. Little milk is being released to the pups at this stage (Brosnan et al, 1982), and thus it is not likely that the secretion of free spermidine into milk is a significant source of its removal. Spermine could be acetylated, followed by oxidation to spermidine, and spermidine to putrescine, as proposed by Seiler et al (198 la).…”

“…The metabolism of rat mammary gland is very sensitive to alterations in the dietary state of the animals (Williamson, 1980). During short-term starvation, for example, the synthesis of lactose (Carrick & Kuhn, 1978) and lipid (Robinson et al, 1978), and the release of milk to the pups (Brosnan et al, 1982), are depressed. We have previously shown that the activity of ornithine decarboxylase (EC 4.1.1.17) in the mammary gland of starved rats is barely detectable, and the activity of S-adenosylmethionine decarboxylase (EC 4.1.1.50) is depressed (Brosnan et al, 1982).…”

“…During short-term starvation, for example, the synthesis of lactose (Carrick & Kuhn, 1978) and lipid (Robinson et al, 1978), and the release of milk to the pups (Brosnan et al, 1982), are depressed. We have previously shown that the activity of ornithine decarboxylase (EC 4.1.1.17) in the mammary gland of starved rats is barely detectable, and the activity of S-adenosylmethionine decarboxylase (EC 4.1.1.50) is depressed (Brosnan et al, 1982). These changes in enzyme activity would markedly depress the synthesis of spermidine from ornithine in mammary gland during starvation.…”