Effects of continuous infusion of vasopressin on circadian rhythms of food and water intake, urine output and electrolyte excretion in Brattleboro rats

Food intake (FI), water intake (WI), urine output (UO), Na+ and K+ excretions were investigated for 2 days at 4-h intervals during continuous infusion of saline or vasopressin (VP) 1.0 UI/day, in male Brattleboro vasopressin-deficient rats. Continuous VP infusion reduced significantly 24-h amounts of WI and UO, and increased Na+ excretion. A significant (3.5 h) phase advance of the circadian rhythm of WI was observed, while the group circadian rhythm of Na+ excretion was eliminated due to irregular phase shifts in the different rats. The results suggest that VP do not play a role in the generation of the circadian rhythms of water input and output, but it may participate in their internal synchronization.     

Androgen responsiveness of the liver of the developing rat

The activities of the hepatic microsomal 2alpha-, 2beta-, 7alpha- and 18-hydroxylase systems active on 5alpha-[4-(14)C]androstane-3alpha,17beta-diol were studied in male and female rats which had been castrated at birth and at the age of 7, 13, 21, 27, 34, 43 and 55 days, treated for 5 days with 2mg of testosterone propionate/kg body weight and killed 6 days after castration. The 7alpha-hydroxylase system was affected very little by androgen treatment at all stages during development. On the other hand it was found that the rat liver passed through three phases during development with respect to androgen responsiveness as judged by changes in the activities of the 2alpha, 2beta- and 18-hydroxylase systems: a first phase (from the neonatal period up to about 19 days of age) with a relative androgen unresponsiveness in both male and female rats, a second phase (from about 27 to about 33 days of age) when male and female rats responded equally well to androgens and a final phase (from about 40 days of age) with a successively decreasing androgen responsiveness in female rats but with a retained responsiveness in male rats. The hypothesis is presented that neonatal imprinting of the liver by testicular androgen(s) determines the development and degree of androgen responsiveness of liver tissue in the rat.     

Neonatal caffeine induces sex-specific developmental plasticity of the hypoxic respiratory chemoreflex in adult rats

Caffeine is widely used to treat apneas of prematurity during the neonatal period; however, the potential consequences of administering a neonatal caffeine treatment (NCT) during a critical period for respiratory control development are unknown. The present study therefore determined whether NCT in rats alters the hypoxic respiratory chemoreflex measured at adulthood. Newborn rats received either caffeine (15 mg/kg) or water (control) each day from postnatal day 3 to 12. The ventilatory response to a hypoxic challenge (inspired O(2) fraction = 0.12) was first evaluated in awake adult female and male rats using whole body plethysmography. Results showed that NCT increased the initial phase of the breathing frequency response to hypoxia in males only. This result was confirmed in anesthetized and artificially ventilated adult male rats where NCT also increased the phrenic burst frequency response to hypoxia. RT-PCR assessment of mRNA encoding for adenosine A(1A) and A(2A) receptors, dopamine D(2) receptors, and tyrosine hydroxylase in the rat carotid bodies showed that NCT enhanced mRNA expression levels of adenosine A(2A), dopamine D(2) receptors, and tyrosine hydroxylase of males but not females. Subsequent experiments on awake male rats showed that injection of the adenosine A(2A) receptor antagonist ZM2413855 (1 mg/kg ip) before ventilatory measurements abolished, in NCT rats, the enhanced respiratory frequency response observed during the early phase of hypoxia. We propose that NCT elicits a sex-specific increase in the hypoxic respiratory chemoreflex, which is related, at least partially, to an enhancement in adenosine A(2A) receptors in the rat carotid body.     

Sexual hormones terminate in the rat: the significantly enhanced catecholaminergic/serotoninergic tone in the brain characteristic to the post-weaning period

The amount of dopamine released from the striatum, substantia nigra and tuberculum olfactorium, noradrenaline from locus coeruleus and serotonin from the raphe, was significantly higher in four and five weeks old rats than in three month old ones, proving that the catecholaminergic/serotoninergic activity enhancer (CAE/SAE) regulation works unrestrained during developmental longevity and is restricted thereafter. As the dampening of the CAE/SAE regulation (end to the second month of age) coincided temporally with the appearance of sexual hormones, we castrated three weeks old male and female rats and measured at the end of the third month of their life the release of catecholamines and serotonin from selected discrete brain regions. The amount of catecholamines and serotonin released from the neurons was significantly higher in castrated than in untreated or sham operated rats, signalting that sexual hormones inhibit the CAE/SAE regulation in the brain. We therefore treated male and female rats s.c. with oil (0.1 ml/rat), testosterone, (0.1 mg/rat), estrone (0.01 mg/rat) and progesterone (0.5 mg/rat), respectively, and measured their effect on the CAE/SAE regulation. Twenty-four hours after a single injection with the hormones, the release of noradrenaline, dopamine and serotonin was significantly inhibited in the testosterone or estrone treated rats, but remained unchanged after progesteron treatment. In rats treated with a single hormone injection, testosterone in the male and estrone in the female was the significantly more effective inhibitor. Remarkably, the reverse order of potency was found in rats treated with daily hormone injections for 7 or 14 days. After two-week treatment with the hormones estrone was in the male and testosterone in the female the significantly more potent inhibitor of the CAE/SAE regulation. The data indicate that sexual hormones terminate the hyperactive phase of adolescence by dampening the impulse propagation mediated release of catecholamines and serotonin in the brain.     

The antidepressant role of dietary long-chain polyunsaturated n-3 fatty acids in two phases in the developing brain

In this work we investigated the effect from fish oil (FO) supplementation, rich in n-3 fatty acids, on an antidepressant effect on adult rats in Phase A (supplementation during pregnancy and lactation) and phase B (supplementation during post-weaning until adulthood). During Phase A, female rats, used as matrix to obtain male rats, were divided in three groups: FO (daily supplemented), CF (coconut fat daily supplemented) and control (not supplemented). Our results showed that adult rats whose mothers were supplemented with FO during Phase A and rats supplemented during phase B demonstrated a significantly decreased immobility time when compared to control and CF groups. There was no difference in neither motor activity nor anxiety behavior in the three groups excluding false positive results. Our results suggest that n-3 fatty acids supplementation during Phases A and B had a beneficial effect on preventing the development of depression-like behavior in adult rats.     

The effect of prolonged immobilization on diuresis and water intake in rats

Diuresis and water intake was determined in 20 male albino rats during 8 weeks of immobilization and in 10 rats in post-immobilization recovery phase. Increase of diuresis and water intake during the immobilization period have been observed. Neither changes in sodium and potassium excretion nor in Na/K ratio were found. As the immobilization of the rats did not cause any changes of their natural body position in relation to the direction of gravity forces, the effect of immobilization on diuresis and water intake could not be related to an ortostatic shift of blood or inhibition of the hypothalamo-hypophyseal antidiuretic system.     

Exposure to Low Level of Arsenic and Lead in Drinking Water from Antofagasta City Induces Gender Differences in Glucose Homeostasis in Rats

Populations chronically exposed to arsenic in drinking water often have increased prevalence of diabetes mellitus. The purpose of this study was to compare the glucose homeostasis of male and female rats exposed to low levels of heavy metals in drinking water. Treated groups were Sprague-Dawley male and female rats exposed to drinking water from Antofagasta city, with total arsenic of 30 ppb and lead of 53 ppb for 3 months; control groups were exposed to purified water by reverse osmosis. The two treated groups in both males and females showed arsenic and lead in the hair of rats. The δ-aminolevulinic acid dehydratase was used as a sensitive biomarker of arsenic toxicity and lead. The activity of δ-aminolevulinic acid dehydratase was reduced only in treated male rats, compared to the control group. Treated males showed a significantly sustained increase in blood glucose and plasma insulin levels during oral glucose tolerance test compared to control group. The oral glucose tolerance test and the homeostasis model assessment of insulin resistance demonstrated that male rats were insulin resistant, and females remained sensitive to insulin after treatment. The total cholesterol and LDL cholesterol increased in treated male rats vs. the control, and triglyceride increased in treated female rats vs. the control. The activity of intestinal Na+/glucose cotransporter in male rats increased compared to female rats, suggesting a significant increase in intestinal glucose absorption. The findings indicate that exposure to low levels of arsenic and lead in drinking water could cause gender differences in insulin resistance.     

H3-phenylalanine incorporation into protein in the pituitary, hypothalamus and cerebral cortex of male rats during postnatal development.

Incorporation of H3-phenylalanine and concentration of protein in the anterior pituitary gland (APG), hypothalamus and cerebral cortex of male rats have been studied during postnatal development from day 21 to 120. APG and hypothalamus showed significantly higher rate of amino acid uptake and protein synthesis during the prepubertal phase, decrease at puberty and an age dependent variation thereafter. Protein concentrations and amino acid incorporation in the APG and hypothalamus are possibly influenced by the higher circulating levels of androgens during sexual maturation in marked contrast to their lack of effect on the cerebral cortex.     

Effects of genistein in the maternal diet on reproductive development and spatial learning in male rats

Endocrine disruptors, chemicals that disturb the actions of endogenous hormones, have been implicated in birth defects associated with hormone-dependent development. Phytoestrogens are a class of endocrine disruptors found in plants. In the current study we examined the effects of exposure at various perinatal time periods to genistein, a soy phytoestrogen, on reproductive development and learning in male rats. Dams were fed genistein-containing (5 mg/kg feed) food during both gestation and lactation, during gestation only, during lactation only, or during neither period. Measures of reproductive development and body mass were taken in the male offspring during postnatal development, and learning and memory performance was assessed in adulthood. Genistein exposure via the maternal diet decreased body mass in the male offspring of dams fed genistein during both gestation and lactation, during lactation only, but not during gestation only. Genistein decreased anogenital distance when exposure was during both gestation and lactation, but there was no effect when exposure was limited to one of these time periods. Similarly, spatial learning in the Morris water maze was impaired in male rats exposed to genistein during both gestation and lactation, but not in rats exposed during only one of these time periods. There was no effect of genistein on cued or contextual fear conditioning. In summary, the data indicate that exposure to genistein through the maternal diet significantly impacts growth in male offspring if exposure is during lactation. The effects of genistein on reproductive development and spatial learning required exposure throughout the pre- and postnatal periods.     

Effects of neonatal clomiphene citrate on fertility and sexual behavior in male rats

In order to investigate the participation of estrogen during the period of brain sexual differentiation, male rats were treated with clomiphene citrate in the neonatal phase. Fertility and sexual behavior were assessed during adult life. Sexual maturation, body weight, and wet weight of the testes were unchanged. Although the adult male rats treated with clomiphene in the neonatal phase presented a significant reduction in the frequency of mounts, 90% of these rats were able to mate with normal females, which became pregnant. However, these females exhibited a significantly increased number of pre- and post-implantation losses. When these adult male rats were castrated and received estrogen, 60% presented female sexual behavior (receptive behavior and acceptance of mount). Thus, treatment of pups with clomiphene immediately after birth has a long-term effect on the reproductive physiology and sexual behavior of male rats.     

Effect of exercise during pregnancy, graded as a percentage of aerobic capacity: maternal and fetal responses of the rat.

1. A number of variables were studied in pregnant rats that underwent strenuous exercise during pregnancy. They were: total weight gain, daily weight gain, length of pregnancy, number of offspring. Also the weight, the heart weight and fibre/capillary ratio of the newborn male rats and their VO2 max at 90 days were measured. 2. The exercise was graded in accordance to previous aerobic capacity as determined by VO2 max with relative loads of 60% (E60), 70% (E70), 80% (E80) and 90% (E90) of VO2 max being applied to the various groups (N = 6 per group). 3. The total weight gain and daily weight gain was significantly less in the E70, E80 and E90 groups. Weight gain in the anabolic phase (0-14d) was not different, but during the first week the weight gain in the E90 group was significantly less than control group. In the catabolic phase the observations were similar the first week of the anabolic phase. 4. Length of pregnancy, heart weight offspring and VO2 max of 90-day-old male rats were not significantly different. The number of offspring of the E90 group was significantly smaller than the control, E60 and E70 groups. 5. The offspring body weight was less in the E70, E80 and E90 groups than control group and was significantly less in the E90 group compared to the E60 and E70 groups. 6. The fibre/capillary ratio of the offspring was different in the E90 group compared to the control group. 7. These results suggest that the effect of exercise depends on the relative work load applied to the mother and these effects are particularly marked at high work loads.     

Delay in the age of balano-preputial skinfold cleavage and alterations in serum profiles of testosterone, 5 alpha-androstane-3 alpha,17 beta-diol, and gonadotropins in adult rats treated during puberty with luteinizing hormone releasing hormone

Previous work has shown that chronic treatment of intact, immature male rats with luteinizing hormone releasing hormone (LHRH) decreases sex accessory gland weights and results in retardation of the normal developmental increase in the ratio of serum testosterone (T)/5 alpha-androstane-3 alpha,17 beta-diol (3 alpha-Diol) via an apparent enhancement of testicular 5 alpha-reductase or 3 alpha-hydroxysteroid oxidoreductase activities. In the present work, androgen dependent balano-preputial skinfold cleavage was significantly delayed by approximately one week in intact, immature male rats which were treated daily for two weeks with either 1.0 micrograms, 2.5 micrograms or 5.0 micrograms of LHRH during a discrete phase of pubertal development (28-41 days of age). In intact, adult (62 day old) animals which received LHRH treatments during pubertal development, serum T concentrations and sex accessory gland weights were reduced compared to control animal values. Serum 3 alpha-Diol content in the adult rats was either unaltered or increased significantly depending on the LHRH dosage employed during sexual development. Serum luteinizing hormone concentrations were not different between control and LHRH-pretreated adult rats whereas the highest dosage of LHRH employed (5.0 micrograms) during puberty resulted in a significant elevation of adult serum follicle stimulating hormone levels. It is suggested that chronic LHRH treatment of the male rat during puberty results in a perturbation in testicular androgen biosynthetic activities and an impairment of pituitary-testicular hormone feedback mechanisms which persist at least through early adulthood.     

Influence of the oestrous cycle on L-glutamate and L-aspartate transport in rat brain synaptosomes.

Oestrous cycle and sex differences in sodium-dependent transport of L-[3H]glutamate and L-[3H]aspartate were investigated employing well washed synaptosomes prepared from rat brain cortex. Transport was best analysed on the basis of two components, a high and low affinity transport site. Oestrous cycle and sex differences were observed for both substrates. The high affinity transporter displayed highest affinity for glutamate transport in synaptosomes from female rats during proestrous and oestrous. This differed significantly from glutamate transport during dioestrous and in male rats. High affinity aspartate transport displayed highest affinity during oestrous and differed significantly from transport during dioestrous. Maximal velocity of high affinity glutamate transport was higher in synaptosomes from females during dioestrous compared with oestrous and lower in synaptosomes from male rats when compared with female rats in dioestrous and metoestrous. The low affinity sodium-dependent glutamate transporter displayed a 10-fold higher affinity for glutamate during proestrous than during the other three phases of oestrous and in male rats. Exogenously applied oestradiol and progesterone to synaptosomes from male rats showed no effect on glutamate or aspartate transport. No acute effect of oestradiol or progesterone on glutamate currents in oocytes expressing EAAT1 or EAAT2 subtype of glutamate transporter was observed. These results suggest hormonal regulation of high and low affinity sodium-dependent excitatory amino acid transporters over the four day oestrous cycle in synaptosomes from rat cortex. This regulation is unlikely to be due to a direct effect of oestradiol or progesterone on glutamate transporters.     

Complete recovery of growth deficits after reversal of PTU-induced postnatal hypothyroidism in the female rat: a model for catch-up growth

Newborn rats of both sexes were treated from birth with the anti-thyroid goitrogen, n-propylthiouracil (PTU) given in the drinking water of the litter (0.1% w/v). One group received the treatment for 25 days, another for 50 days, and a third group for 120 days. The experimental rats showed growth retardation as well as all other classical signs of developmental arrest or delays induced by postnatal hypothyroidism. In order to assess the ability of the hypothyroid animals to recover spontaneously from the retarded state, at days 25, 50 and 120 postnatal the PTU water was replaced with tap water. In each case, within 5-7 days after PTU withdrawal the animals began to show marked compensatory growth accompanied by many signs of behavioral and physiological recovery. In general, the male rats showed higher compensatory growth rates as compared to the females, enabling them to attain significantly higher body weights. However, when growth recovery was followed for up to 6 months it was found that the male rats were unable to attain complete catch-up growth, regardless of the age at which recovery began, while the females of all age groups were able to achieve this goal. In view of the severity of PTU-induced growth retardation, these results suggest significant plasticity of growth processes in the rat, especially in the female. It is suggested that male and female rats recovering from prolonged PTU-induced growth retardation offer a good model system for the study of biochemical, anatomical and physiological aspects of growth recovery and catch-up growth at both the cellular and organismic levels, particularly in relation to the effects of thyroid, growth hormone, and other growth-promoting factors.     

Effects of dexamethasone on the development of radiation nephropathy in the rat.

Low-dose, chronic administration of the synthetic glucocorticoid, dexamethasone, to male CD-I rats in the drinking water or by osmotic minipumps implanted subcutaneously after supralethal irradiation of the kidneys (20 Gy) was studied. The effectiveness of treatment with dexamethasone in the drinking water at concentrations of 23 micrograms/l to 188 micrograms/l and treatment times varying from 33 to 166 days was evaluated. At monthly intervals kidney function was assayed by measuring the clearance of 51Cr-ethylenediaminetetraacetic acid. All dexamethasone treatment regimens increased survival times significantly and delayed the development of kidney dysfunction. The most effective combination of concentration of dexamethasone in drinking water and treatment interval after irradiation with respect to survival was 94 micrograms/l and 88 days. However, a slightly longer survival and a better functional result was obtained if an equivalent amount of dexamethasone was administered by minipumps. Shielding the adrenal glands during kidney irradiation did not prolong survival. This shows that the beneficial effect of dexamethasone is not due to compensation for reduced adrenal glucocorticoid production resulting from concomitant exposures of these glands during kidney irradiation.     

The influence of angiotensin II on sex-dependent proliferation of aortic VSMC isolated from SHR.

The growth response to angiotensin II (Ang II) was studied using cultured vascular smooth muscle cells (VSMC) isolated from the aortae of male and female spontaneously hypertensive rats (SHR). Systolic and mean arterial blood pressure of 10-week-old males was significantly higher when compared to age-matched females. The specific growth rate of male VSMC was significantly higher on the third and sixth day after synchronisation. Angiotensin II in concentration 10(-7) M stimulated the specific growth rate only in male VSMC during the exponential phase of growth. Moreover, doubling time was 3 hours shorter in male VSMC in comparison with the females. Our results suggest that both the increased specific growth rate and augmented growth-response of male VSMC to Ang II may explain the higher sensitivity of males to hypertensive stimuli.     

Low dose of bisphenol A impairs the reproductive axis of prepuberal male rats

The objective of the present work was to study the effect of a low dose of bisphenol A (BPA), on the reproductive axis of prepuberal male rats exposed to the endocrine disruptor (ED) during gestation and lactation period. Wistar-mated rats were treated with either 0.1 % ethanol or BPA in their drinking water until their offspring were weaned at the age of 21 days. The estimated average dose of exposure to dams was approximately 3 μg/kg/day of BPA. The pups were sacrificed on the 35th day of life. Body weight was measured during the development and at the moment of the sacrifice; testicular and seminal vesicles weight and their respective relative weights were also measured. LH, FSH and testosterone were determined and histological studies of testicular tissue were also performed. Body weight at the moment of the sacrifice was significantly higher in the group exposed to BPA; testicular weight decreased significantly; seminal vesicles weight and relative weights of testes and seminal vesicles were not modified by treatment. LH and FSH serum levels increased significantly after treatment, meanwhile testosterone showed no significant changes. Histological studies showed the lumen of seminal tubes reduced by the presence of immature cells of the spermatic lineage. Our results suggest that pre- and early postnatal exposure to a low dose of BPA disrupts the normal function of the reproductive axis in prepuberal male rats. The effects of the ED may be exerted at different levels of the axis and may be dependent on the dose, manner of administration, and the moment of exposure to the disruptor.     

The effect of ascorbic acid supplementation on sperm quality, lipid peroxidation and testosterone levels of male Wistar rats

This study was conducted to investigate the effects of ascorbic acid supplementation in drinking water on semen quality, lipid peroxidation and plasma testosterone level of male rats. In this investigation, 24 male Wistar rats were used. The animals were divided into three group, and 500, 250 and 0 (control) mg/kg/day ascorbic acid were supplemented with drinking water of rats in Groups A, B and C during 8 weeks, respectively. Ascorbic acid supplementation did not increase in the body weight and weights of the testis, epididymis, seminal vesicles and ventral prostate. Exogenous supplementation with ascorbic acid significantly increased (P<0.05) the concentration of ascorbic acid in the testes and blood plasma, and the level of lipid peroxidation significantly decreased (P<0.05) in these locations. There was no significant difference in spermatozoon motility among the three groups. However, epididymal sperm concentration and plasma testosterone level significantly increased (P<0.05) in the ascorbic acid treated animals when compared to the control animals. The results suggest that ascorbic acid supplementation improves reproductive traits of male rats that are associated with high fertility.     

Effects of wire-bottom caging on heart rate, activity and body temperature in telemetry-implanted rats

Some experimental procedures are associated with placement of animals in wire-bottom cages. The goal of this study was to evaluate stress-related physiological parameters (heart rate [HR], body temperature [BT], locomotor activity [LA], body weight [BW] and food consumption) in rats under two housing conditions, namely in wire-bottom cages and in bedding-bottom cages. Telemetry devices were surgically implanted in male Sprague-Dawley rats. HR, BT and LA were recorded at 5 min intervals. Analysis under each housing condition was performed from 16:00 to 08:00 h of the following day (4 h light, 12 h dark). During almost all of the light phase, the HR of rats housed in wire-bottom cages remained high (371 ± 35 bpm; mean ± SD; n = 6) and was significantly different from that of rats housed in bedding-bottom cages (340 ± 29 bpm; n = 6; P < 0.001; Student's t-test). In general, BT was similar under the two housing conditions. However, when rats were in wire-bottom cages, BT tended to fluctuate more widely during the dark phase. LA decreased when animals were housed in wire-bottom cages, in particular during the dark phase. Moreover, there was a significant difference with respect to the gain in BW: BW of rats housed in bedding-bottom cages increased 12 ± 2 g, whereas that of rats in wire-bottom cages decreased by 2 ± 3 g (P < 0.001). Our results demonstrate that housing rats in wire-bottom cages overnight leads to immediate alterations of HR, BW and LA, which might be related to a stress response.     

Immunohistochemical evidence of the presence of aromatase P450 in the rat hypophysis

In order to analyze whether aromatase is present in the hypophysis of adult rats, we have performed an immunohistochemical study in young adult male and female rats. Our study has revealed that the hypophysis of adult rats contains aromatase, although marked differences are found between the sexes. The hypophyses of male rats have cells immunoreactive for the enzyme, 34.40% of these hypophyseal cells showing reaction. By contrast, cells from female rats show very little reaction, only 0.84% of them being reactive. No significant differences in the percentage of immunoreactive cells between one phase and another are observed during the estrous cycle. Our results point to the immunohistochemical expression of aromatase in the hypophysis of adult rats and at the same time suggest that its expression is sex-dependent. The enzyme may therefore be involved in the regulation of adenohypophyseal cytology by androgens.