J.A. Linares

Effects of a restricted diet on in vitro spontaneous activity and glucose metabolism in isolated rat uterus. Influence of castration

The effects of a restricted-diet (50% of the normal intake during 25 d) on the isometric developed tension (IDT), the metabolism of labelled glucose, and the levels of glycogen, of uteri isolated from ovariectomized (25 d) and non-ovariectomized rats were explored. The restriction of food intake produced a fall in the contractile activity of normal, non-ovariectomized, rats in permanent diestrous compared to normally fed rats in diestrous. On the contrary, in castrated rats, the IDT of isolated uterus from underfed rats, was significantly higher than its normal-fed controls. In normal rats the formation of 14CO2 from U 14C-glucose was significantly lower in uterine preparations from restricted-diet animals than the control one. On the other hand, in castrated rats, the formation of 14CO2 increased as a result of underfeeding. The post-incubation levels of glycogen in uteri from normal-fed animals diminished significantly in comparison to 0 time values. In uteri from rats subjected to a dietary restriction, the initial glycogen values were lower than in normal-fed controls, but they did not decline further after incubation in KRB medium. On the contrary, even when the levels of glycogen were significantly lower at 0 time than in diestrous animals, they diminished in ovariectomized rats after incubation, no matter the diet. The above results indicate that the effects of restricted-diet on contractile activity, levels of glycogen and glucose metabolism were not observed in ovariectomized rats. Further researches are needed to clarify that point.

Effects of Morphine and Naloxone on Glucose Metabolism in Uterine Strips from Ovariectomized and Non-Ovariectomized Restricted Diet Rats

The effect of underfeeding over glucose metabolism in uteri isolated from ovariectomized and non-ovariectomized rats subjected to a restricted diet for 25 days (50% of the normal food intake), was studied. Underfeeding decreases 14CO2 formation from U14 C-glucose in intact animal uteri. While in ovariectomized rats (25 days), the effect is the opposite. The addition of morphine 10−6 M to the medium does not affect rats fed ad libitum. However, 14CO2 levels increase significantly in intact animals receiving a restricted diet. In ovariectomized rats morphine does not show any activity, regardless of the type of diet rats were subjected to. None of the rat groups seems to be sensitive to naloxone 10−6 M. The s.c. injection of morphine (4 mg.kg−1) increases glucose metabolism only in intact rats provided with a restricted diet, while naloxone (2.5 mg.kg−1) produces a decrease of 14CO2 in ovariectomized underfed animals. To conclude, morphine either ‘in vivo’ or ‘in vitro’ is active only in uteri from intact rats subjected to underfeeding. Naloxone produces a decrease in 14CO2 production, particularly when it is s.c. injected to ovariectomized rats undergoing a dietary restriction. Since the uterus does not react to naloxone, the effect of the opiod blocker may be the result of endogenous opioids originated in other tissues.

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

The effects of fasting for 4 days on the isometric developed tension (IDT) and on the metabolism of labelled glucose and arachidonic acid in uteri from intact and spayed (25 days) rats, were explored. Starvation produces a fall in the contractile activity of intact rats, while in ovariectomized ones, no differences can be seen with respect to their controls. Fasting produces a fall in the glucose metabolism of both intact and ovariectomized rats, being more noticeable in the former group. Indomethacin (5 x 10(-6) M) increases the metabolism of labelled glucose in all experimental groups, significantly. The metabolism of exogenous arachidonic acid into different eicosanoids, PGE2, PGF2 alpha, 6-keto-F1 alpha and TXB2, shows that total food deprivation diminishes significantly the production of PGE2 in intact rats. In contrast, in ovariectomized starved rats, PGE2 increases markedly. The rest of the metabolites studied are not influenced by fasting. These results show that the effects of fasting on the contractile activity and on the release of some metabolites from arachidonic acid by the uteri isolated from intact rats are not seen in ovariectomized animals.

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.

Effects of 17 β estradiol on the metabolism of labelled arachidonic acid in uteri isolated from intact and ovariectomized rats. Influence of a restricted diet

The effects of restricted diet (50% of the normal intake during 25 days) on the metabolism of 14U arachidonic acid, were explored in uterine horn strips isolated from intact and ovariectomized rats, treated by 17 beta-estradiol or controls. The metabolism of arachidonic acid into different eicosanoids, PGE2, PGF2alpha, 6-keto PGF1alpha and TXB2, showed that the restricted diet diminished PGE2 and PGF2alpha, in intact rats, significantly. In contrast, this kind of feeding did not produce any change in castrated rats. Tissue preparations from previously estrogenized intact and castrated normal-fed rats showed that the production of different metabolites decreased. A similar result was obtained in intact rats subjected to a restricted diet. Nevertheless, in castrated underfed rats, estrogens did not produce any effect on the various eicosanoids analysed. These results showed that in isolated uteri, the effects of 17 beta-estradiol, on metabolite production from labelled arachidonic acid, are different from controls in ovariectomized diet-restricted rats.

Effect of interleukin 1α and interleukin 2 over glucose metabolism in isolated uterus of restricted diet rats. Influence of NO and COX-2

A 25-day dietary restriction (50% of the normal diet) produce a fall in the production of 14CO2 from 14C-glucose in rats isolated uteri. The addition of 10 or 20 ngml(-1) interleukin 1alpha (IL-1alpha) or interleukin 2(IL-2) to the Krebs-Ringer bicarbonate solution medium stimulates glucose metabolism in uteri from underfed rats. Such concentrations are not effective in control rats. The addition of Nomega-nitro-L arginine methyl ester--an inhibitor of both the constitutive and inducible forms of nitric oxide synthase (NOS)--and of aminoguadinine--a preferential inhibitor of the inducible form of NOS--block such stimulation. In other experiments, the addition to the medium of arginine-a substrate for the formation of nitric oxide-increases interleukin stimulation of glucose metabolism, which is blocked by NOS inhibitor. At the same time, NS-398--a selective inhibitor of inducible cyclooxygenase (COX)--eliminates the interleukin metabolism stimulation. We conclude that IL-1alpha and IL-2 produce an increase of glucose metabolism in uteri isolated from underfed rats. Nitric oxide produced by the inducible form of NOS mediates the interleukins-induced glucose metabolism stimulation with the participation of inducible COX.