A. Goldraij

Effect of chronic underfeeding on uterine glycogen of rats. Influence of indomethacin and nordihydroguaiaretic acid

Glycogen values in uterine strips isolated from normal-fed estrous or diestrous rats, or from rats fed a restricted diet (50% of normal food intake for 25 days) were measured. Determinations were made immediately after killing (0 time or post-isolation) as well as after incubation in glucose-free medium (60 min time or post-incubation). The post-incubation levels of glycogen in the uteri from normal-fed animals diminished significantly in comparison to post-isolation values, and this decrement was not modified by the addition of indomethacin, nordihydroguaiaretic acid or exogenous prostaglandins E1, E2 or F2 alpha. In rats fed a restricted-diet, the initial glycogen values (0 time) were significantly lower than in normal-fed controls, but did not decline further after incubation in glucose-free medium (60 min time). The addition of indomethacin, acetylsalicylic acid or of nordihydroguaiaretic acid led to a significant fall in the glycogen levels, and exogenous PGE1, PGE2 or PGF2 alpha failed to alter the effects of the inhibitors. The values of PGE and PGF prostaglandins release to the medium by the uterus from restricted-diet rats did not differ from those obtained in the experiments with normal-fed animals. Administration of 17-beta estradiol to restricted-diet rats led to suppression of the effects of this diet on the glycogen concentration. The above results indicate that in rats subjected to a prolonged period of dietary restriction, the uterine glycogen becomes responsive to the effects of cyclooxygenase and lipoxygenase inhibitors, suggesting the operation of some regulatory mechanism during critical periods of nutrition.

Influence of underfeeding on the spontaneous contraction and on metabolism of labelled arachidonic acid in uteri isolated from intact and ovariectomized rats

The effects of restricted diet (50% of the normal intake during 25 days) on the isometric developed tension (IDT), and on the metabolism of labelled arachidonic acid in uteri from intact and spayed (25 days) rats, were studied. Underfeeding produced a fall in the contractile activity of intact rats, while in ovariectomized rats contractile activity increased. Indomethacin reduced uterine contractile activity in all the cases under study. The metabolism of arachidonic acid into different eicosanoids, PGE2, PGF2 alpha, 6-keto-F1 alpha, and TXB2, showed that the restricted diet diminished PGE2 and PGF2 alpha levels in intact rats significantly. The reduction in uterine contractile activity and reduced levels of the arachidonic acid metabolites, PGE2 and PGF2 alpha, were not seen in ovariectomized animals.

Influence of gonadic hormones on the rat submaxillary gland

The area of the granular tubules of the submaxillary gland was evaluated in male and female rats at 60 days of age. In males, this area was significantly greater than in females, corroborating the presence of sex dimorphism in this structure. Dimorphism disappeared after castration. Testosterone increased tubular area. Estrogen and progesterone as well as pregnancy reduced it. The tubular surface was significantly greater at term than at mid pregnancy.

Prostaglandin E2 and prostaglandin F2α regulation of triglyceride levels in uterine smooth muscle from restricted-diet estrous and diestrous rats☆

Triglyceride concentrations in uterine strips isolated from estrous and diestrous normal-fed or restricted-diet (50% food intake for 15 days) rats, were measured. Determinations were made immediately following killing (0 min, or postisolation) as well as after a period in glucose-free medium, (60 min or post-incubation) with or without additions. The postisolation levels of triglycerides (0 min) in the uterus from normal-fed estrous animals were lower than in diestrus but in each group did not differ in comparison with postincubation values (60 min), either without additions or in the presence of indomethacin (10-6M). Initial (0 min) tissue triglycerides of estrous and diestrous partially-starved rats were significantly higher than in their respective fed controls and exhibited different modifications depending on the stage of the sex cycle. In estrus, levels remained unaltered at the end of an incubating period without additions and declined in the presence of indomethacin. This influence of indomethacin was not modified by added PGF2 (10(-9)M) but was effectively abolished by PGE2 (10(-9)M). On the contrary, in diestrus, initial triglyceride levels diminished spontaneously following 60 min without additions, this being antagonized by indomethacin or propranolol (10(-6)M). Furthermore, exogenous PGE2 failed to alter the effect of indomethacin whereas PGF2 evoked its abolition. Propranolol, which effectively blocked the spontaneous decrement of triglycerides as did indomethacin, prevented also the influence of PGF2 on the action of indomethacin. The foregoing results are compatible with the notion that the regulation of triglycerides in rat uteri suspended in the absence of exogenous substrate, is affected differently by prostaglandin E2 and F2 alpha depending on the state of the sex cycle. They also suggest that the phenomenon may involve the activation of the beta adrenoreceptors.

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.

Dietary restriction alters the “in vitro” spontaneous or oxytocin-induced contractions of uterine smooth muscle from estrous rats. Possible participation of prostaglandins

Rats subjected to a restricted-diet (50% of the normal intake for 15 days) presented a progressive reduction of body weight. The isometric developed tension (IDT) of uterine horns obtained from these animals during estrus exhibited greater initial (postisolation) values and a better constancy with time than preparations from normal-fed controls. The enhanced contractions were diminished after a refeeding period of 6 days as well as following the addition into the suspending medium of inhibitors of cyclo-oxygenase (indomethacin or acetylsalicylic acid). Cumulative dose-response curves to oxytocin documented a greater sensitivity in uterine horns from restricted-diet rats than in those from controls or refed animals. The output of prostaglandin (PG) E2 but not that of PGF2 alpha into the external solution was significantly higher (P less than 0.001) in the case of uterine tissue from restricted-diet rats than in normal fed controls. The findings suggest that changes in IDT evoked by partial starvation are associated with the enhanced generation of some PGs by the uterus.

Effect of partial starvation on in vitro spontaneous activity and glycogen levels of uterine smooth muscle from pregnant and non pregnant rats

Effects of a restricted-diet (50% of the normal feeding) given during 14 days, on the isometric developed tension (IDT) of uterine horns isolated from pregnant and non pregnant (diestrous) rats, incubated in a KRB-medium without glucose, were explored. In 14 days-pregnant rats, dietary restriction did not alter the contractile activity with respect to normal-fed controls. Besides, levels of uterine glycogen, immediately after killing the animals or after 60 min incubation, remained unaltered. In advanced pregnancy partial starvation led to decay of spontaneous contractile activity after 60 min incubation. However, the considerable increment in the levels of tissue glycogen at 0 time was not modified, nor its decrease at the end of the in vivo experimental period. In non-pregnant rats, a reduced feeding did not alter the development of contractile tension, but exerted a pronounced effect on the glycogen levels: these were significantly lower than controls at 0 time but suffered no changes after 60 min on in vitro activity. Indomethacin appeared to have no effect on the spontaneous contractile activity of 14 days-pregnant rats. It significantly depressed contractility in 21 days-pregnant rats. Indomethacin did not modify the levels of glycogen in any of the experimental groups.

In vitro contractile responses of the uterus from ‘restricted diet’ rats to adrenoceptor agonists. Influence of cyclo-oxygenase inhibitors

The experiments concerned the effects of 15 days of restricted diet (50% of the normal food intake) on the magnitude of phasic contractions (Isometric Developed Tension, IDT) of uterine horns isolated from estrous rats. During 60 min following isolation, the IDT of normally fed controls diminished significantly whereas preparations from animals on the restricted diet had a better contractile constancy. This improved motility was prevented by blockers of prostaglandin (PG) synthesis as well as by return to a normal diet. Cumulative dose-response curves for isoproterenol, norepinephrine and methoxamine were made for the different groups. Isoproterenol and norepinephrine evoked a dose-dependent inhibition of IDT. This response was significantly shifted to the right with uteri from restricted diet animals. Following incubation with propranolol, norepinephrine stimulated the magnitude of contractions significantly more in uterine horns from restricted diet rats than in those from controls. The dose-response curve showing the enhancement of motility induced by methoxamine was displaced to the left in preparations from animals on a restricted diet. This shift was abolished by restoring the normal diet as well as by the presence in vitro of indomethacin or acetylsalicylic acid. The results suggest that tissue PGS, the prevalence of alpha-adrenoceptor mechanisms and the reduction of beta-ones, are involved in the contractile behavior of the uterus isolated from restricted diet rats.

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 a restricted diet on the metabolism of glucose in uteri isolated from immature rats: influence of indomethacin and nordihydroguaiaretic acid.

In immature female rats (21 days), a restricted diet (50% of the daily normal intake for 25 days) interrupts sexual development, leaving animals in a state of sexual immaturity. Food restriction does not affect the use of glycogen in uteri isolated and increases 14CO2 production from U14C-glucose in relation to animals receiving normal feeding that reach sexual maturity. Indomethacin and acetylsalicylic acid stop the increase of glucose metabolism produced by underfeeding, without affecting the uteri of rats receiving normal feeding. The addition of PGE2 and PGF2alpha changes the inhibitory effect of indomethacin. Nordihydroguaiaretic acid produces the opposite effect, increasing glucose metabolism only in uteri isolated from immature animals. These results show that immature animals have a higher glucose metabolism if compared to mature rats. The restricted diet, which slows down sexual maturity, keeps this parameter high due to the influence of some eicosanoids.