Effect of fasting on the contractile activity and metabolism of labelled glucose and arachidonic acid in uteri isolated from intact and ovariectomized rat

Restricted diet modifies carbohydrate metabolism in immature rats

The aim of the present work was to study the effect of a restricted diet on carbohydrate metabolism in submandibular glands of female prepuber rats and the influence of arachidonic acid derivatives. Rats of 21 days of age were divided into three groups. Group I: normally fed rats. Group II: restricted diet (50% of the normal food intake). Group III: normally restricted diet with re-feeding. The baseline concentration of tissue glycogen was significantly higher in Group II than in I or III and after 60 min of incubation in a glucose free medium all groups showed a glycogen drop. In addition, the glucose metabolism was increased in Group II. Cycloxigenase inhibitors failed to alter (14)CO(2) levels in Groups I and III. In Group II, indomethacin and acetylsalicylic acid inhibited glucose metabolism, which was reverted by PGE(2) addition. The exogenous arachidonic acid metabolism and different eicosanoids showed that restricted diet significantly increased the production of PGE(2) but diminished PGF(2)(alpha) production. Our results suggest that a restricted diet would lead to a new dynamic equilibrium of glucose homeostasis. Prostaglandins E(2) and F(2)(alpha) would participate by adapting the source of energy to tissue demands while maintaining the metabolic features that characterize puberty.

Influence of insulin on the metabolism of glucose in uteri isolated from ovariectomized and non ovariectomized underfed rats

The effects of insulin on the metabolism of U14C-glucose in uteri isolated from ovariectomized and non-ovariectomized rats receiving a restricted diet (50% of the normal food intake) for 25 days, were studied. As a result of food restriction, the production of 14CO2 diminishes in intact rats, while results are reversed in ovariectomized ones. Various concentrations of insulin were added to the medium, but only 0.50 IU. ml(-1)was effective in increasing glucose metabolism in intact rats receiving a restricted diet; neither underfed castrated animals nor control ones receiving a normal diet, reacted to this concentration. The increase of 14CO2 produced by insulin is not affected by acetyl salicylic acid. Insulin does not alter the effect of underfeeding over arachidonic acid metabolism. On the contrary, the increase in glucose metabolism was blocked by N(G)methyl-L-arginine or by hemoglobin, increased with the addition of L arginine and is not affected by acetyl salicylic acid. Hemoglobin and L-arginine show no effects without insulin. We can conclude that the stimulating effect of insulin on glucose metabolism in uteri isolated from intact rats subjected to dietary restriction, is nitric oxide dependent.

Effects of inhibitors of nitric oxide synthase on isolated uteri of fasting rats

The effects of inhibitors of nitric oxide synthase on the glucose metabolism of uteri isolated from 4-day underfed rats were studied. In control rats receiving normal feeding, the addition of indomethacin (5 x 10(-6) M); acetyl salicylic acid (10(-4) M); 400 microM of N(G)methyl-L-arginine, (L-NMMA) or 400 microM of sodium nitroprusside (SNP), does not modify the production of 14CO2 from U14C-glucose. On the contrary, in fasted rat uteri, indomethacin increases glucose oxidation significantly, while acetyl salicylic acid does not alter it. Also, the addition of L-NMMA has no effect. In another group of experiments, in the preparations containing indomethacin of uteri isolated from underfed rats, the addition of L-NMMA significantly changes the effect of indomethacin. Another inhibitor of nitric oxide synthase, N(omega)nitro-L-arginine methyl ester (L-NAME), or hemoglobin (2 microg ml(-1)) a nitric oxide scavenger have the same effects while N(omega)nitro arginine-D-methyl ester (D-NAME) does not. However (SNP), a nitric oxide donor, does not alter the production of 14CO2 in uteri isolated from fasted rats. These results show that in underfed rats, indomethacin increases glucose oxidation independently from its inhibiting effect on cyclooxygenase. Specific inhibitors of nitric oxide synthase can reverse this effect.