Gap junctions in the hypothalamic arcuate neurons of ovariectomized and estradiol-treated rats

Freeze-fracture methodology was used to study the organization of the neuronal plasma membrane in the rat arcuate nucleus, an estrogen sensitive area of the hypothalamus. Freeze-fracture replicas were prepared from 6 adult ovariectomized rats injected with a single dose of 17 beta-estradiol and from 6 ovariectomized littermates injected with vehicle. Rats were sacrificed 2 days after the injection. Occasional gap junctions were observed in freeze-fractured neuronal membranes from both groups of animals and their incidence was increased (P less than 0.01) in estradiol treated rats. This study demonstrates gap junctions in arcuate neurons and suggests that these structures may be affected by gonadal hormones.     

Dietary self-selection,activity and carcass composition of rats fed thiouracil

The interaction of dietary self-selection and spontaneous running wheel activity as fat regulating mechanisms was studied in rats treated with thiouracil. Both hypothyroid and euthyroid rats were given the opportunity to either select their diets, engage in running activity or both. Thiouracil treated rats reduced carbohydrate intake while maintaining protein intake levels equal to those of controls. Thiouracil treatment reduced running activity levels when the rats were given the opportunity to select their diets, but did not affect the running levels of rats fed a control diet. All groups given access to running wheels were at the same carcass fat level except the control diet fed, thiouracil treated rats which were at a lower fat level. It was suggested that, at least for hypothyroid rats, the combination of dietary self-selection and running activity is a more efficient mechanism for regulating carcass composition than is either behavior alone.     

Effects of Silastic progesterone implants on activity cycles and steroid levels in ovariectomized and intact female rats

We have previously shown that although Silastic implants of progesterone reduce the amount of running of animals living in activity wheels, progesterone-treated animals continue to show periodic fluctuations or peaks in activity. We hypothesized that although progesterone treatment inhibited estrous cycles, ovaries of animals treated with Silastic implants of progesterone continued to secrete estradiol in amounts adequate to stimulate moderate levels of running. In the present study we tested this hypothesis by removing ovaries from progesterone-treated animals and comparing their running behavior and steroid levels to progesterone-treated animals who received sham ovariectomies. Although progesterone treatment significantly inhibited running activity, removal of ovaries in progesterone-treated animals further suppressed running activity. In addition, both estradiol and progesterone levels were significantly reduced following removal of ovaries in progesterone-treated animals. We conclude that although Silastic progesterone implants inhibit normal ovarian and estrous activity cycles, ovaries produce sufficient estradiol to stimulate running behavior.     

Dietary self-selection in insulin-injected hamsters

Adult male golden hamsters were given access to a variety of nutrient sources and were observed following the administration of regular insulin. It was hypothesized that if insulin produced hyperphagia in hamsters by the activation of a glucoprivic feeding mechanism, a selective increase in carbohydrate consumption would be observed. All animals received subcutaneous injections of 10, 30, 50 and 100 units/kg of insulin as well as a control injection of saline. Food consumption was recorded at +3, +6 and +24 hours after injections. In Experiment 1 hamsters having continuous access to Purina lab chow, fat (Crisco) and sucrose (sugar cubes) increased their total caloric consumption in response to insulin, but did not do so by selectively increasing their carbohydrate intake. In Experiment 2 hamsters maintained on Purina chow and sugar cubes consistently increased their carbohydrate intake as well as their total caloric consumption in response to insulin, but again the increase in carbohydrate intake was not selective; increased consumption of both sugar cubes and Purina chow occurred, and neither the proportion of total calories derived from carbohydrate nor the proportion of total calories derived from sugar cubes was affected by insulin administration. The results support the conclusion that insulin-induced hyperphagia in hamsters results from the activation of a non-glucoprivic feeding mechanism.     

Vasopressin induces a luteinizing hormone surge in ovariectomized, estradiol-treated rats with lesions of the suprachiasmatic nucleus.

The luteinizing hormone surge in the female rat is the result of the integration of multiple signals within the medial preoptic area. The medial preoptic area contains gonadotropin-releasing hormone neurons that are responsible for the release of luteinizing hormone, neurons containing estrogen receptors and terminals originating from the suprachiasmatic nucleus with, for example, vasopressin as neurotransmitter. Both the medial preoptic area and suprachiasmatic nucleus are crucial for the occurrence of luteinizing hormone surges, since lesioning of either nucleus prevents pre-ovulatory and steroid-induced luteinizing hormone surges. In this study, we investigated whether vasopressin in the medial preoptic area could be the daily neuronal signal from the suprachiasmatic nucleus responsible for the timing of the luteinizing hormone surge. Vasopressin (50 ng/microl) or Ringer solution was administered by reverse microdialysis from Zeitgeber times 7.5 to 12.5 into the medial preoptic area of ovariectomized, estradiol-treated rats. The suprachiasmatic nucleus was lesioned to remove all cyclic luteinizing hormone secretion. This was evaluated by monitoring behavioral activity; animals that were arrhythmic were included in the experiments. Hourly blood samples were taken to measure plasma luteinizing hormone levels. Preoptic vasopressin administration induced a surge-like luteinizing hormone pattern in suprachiasmatic nucleus-lesioned animals, whereas constant, basal luteinizing hormone levels were found in the control animals. These data show that vasopressin, by itself, is able to trigger the luteinizing hormone surge in suprachiasmatic nucleus-lesioned rats. We propose that vasopressin is a timing signal from the suprachiasmatic nucleus responsible for the activation of the hypothalamo-pituitary-gonadal axis in the female rat.     

Dietary self-selection in normal and diabetic rats after gastric loads of pure macronutrients

Rats which were experimentally diabetic (streptozotocin, 45 or 70 mg/kg, or pancreatectomized) and their nondiabetic controls were allowed to select ad lib from three pure macronutrient sources of carbohydrate (CHO), protein, and fat. After full adaptation, the intakes were examined 2, 4, 6, and 24 hr following an intragastric load given at the end of the daytime. Noncaloric (control) or isocaloric loads of CHO or protein or fat were studied. Fat loads suppressed subsequent fat intake reasonably selectively; CHO and protein loads suppressed the intake of the corresponding macronutrient, but less selectively. There were no major qualitative differences between diabetic and nondiabetic rats.     

Estradiol treatment and precopulatory behavior in ovariectomized female rats

Female rats of Wistar strain were injected SC, starting at Day 5 after ovariectomy, with estradiol dipropionate (ED) at weekly intervals. Forty-eight hours after each injection they were subjected to standardized mating tests. A 6 μg ED dose showed to be insufficient to maintain estrous behavior. Both precopulatory and lordosis behavior disappeared in the course of eight weeks. On the other hand, the behavioral effectiveness of 10 and 30 μg ED increased with the number of injected doses. Under these circumstances, estradiol proved to be sufficient to induce not only full copulatory readiness but also all the degree of precopulatory behavior of pattern (Presenting, Hopping ending in Presenting, and Darting ending in Presenting). Although there are large individual differences in behavioral effectiveness of ED, the estradiol thresholds for inducing Presenting, Hopping, and Darting were found to increase in the given order. However, prolonged (up to Week 12) treatment with 30 μg ED resulted in the disappearance all estrous behaviors. This decline of estradiol effectiveness was reversed by increasing the estradiol dose to 100 μg.     

Effects of interscapular brown adipose tissue denervation on body weight and energy metabolism in ovariectomized and estradiol-treated rats

Ovariectomy-induced increases and estradiol-induced decreased in body weight cannot be fully accounted for by changes in energy intake and appear to reflect alterations in thermogenesis. Because changes in energy expenditure have been linked to altered sympathetic nervous system (SNS) activity in brown adipose tissue (BAT), the role of estradiol in thermogenesis and body weight, as mediated by the SNS innervation of interscapular BAT (IBAT), was examined. The IBAT of ovariectomized rats was bilaterally or unilaterally surgically denervated. The chow-fed, bilaterally denervated group gained more weight than the unilaterally denervated or sham-operated group, an effect that was exaggerated by sucrose feeding. Food intake did not differ among the groups within each dietary condition. Estradiol benzoate (EB) injections decreased body weight in all groups. Bilateral, and to a lesser extent, unilateral IBAT denervation blocked the EB-induced increase in thermogenesis. Treatment with EB increased IBAT wet weight regardless of surgical treatment. Because IBAT denervation markedly decreased lipoprotein lipase activity and fatty acid synthesis/uptake, the estradiol-induced increase in denervated IBAT wet weight is most likely due to decreased lipolysis produced by the surgical sympathectomy. These results are discussed in terms of the role of the SNS and IBAT in the mediation of estradiol-induced changes in body weight and energy metabolism.     

Dietary self-selection in chronically insulin-treated golden hamsters

Adult male golden hamsters were maintained on either Purina Rat Chow (chow group) or a self-selection diet consisting of high-protein chow, pure carbohydrate, and pure fat (choice group). Animals were injected for 12 consecutive days with either long-acting insulin (20 U/kg for 4 days, 60 U/kg for 4 days, and 100 U/kg for 4 days) or physiological saline. Insulin-injected hamsters under both dietary conditions increased their total caloric consumption by up to 33% and gained significantly more weight than saline-injected controls. Choice hamsters increased their fat intake in response to the 60 and 100 U/kg doses of insulin, but carbohydrate and protein consumption increased only in response to the 100 U/kg dose. Choice hamsters derived approximately 65% of the excess calories ingested during insulin administration from fat, but only 20% from carbohydrate and 15% from protein. Results are related to those previously observed in other species.     

Dietary soy supplements produce opposite effects on anxiety in intact male and female rats in the elevated plus-maze

The effects of 2 popular, commercially available soy phytoestrogen supplements on anxiety in male, diestrus female, and proestrus female rats were examined with an elevated plus-maze. Both of the soy supplements were anxiolytic in proestrus females but anxiogenic in males as determined by time spent in the open arms. No effect of diet was seen in the diestrus females. The observed changes in anxiety were not because of altered levels of gonadal hormones, as serum estrogen and progesterone levels were unaffected by diet in the females. The results suggest that the soy supplements have sex- and cycle-specific effects on anxiety.     

Drospirenone increases central and peripheral beta-endorphin in ovariectomized female rats

OBJECTIVE: Drospirenone is the unique progestin derived from 17-spironolactone used for contraception and hormone therapy. Few data are available concerning the effects of drospirenone on the central nervous system and neuroendocrine milieu. The opioid beta-endorphin and the neurosteroid allopregnanolone are considered markers of neuroendocrine functions, and their synthesis and activity are regulated by gonadal steroids. The aim of the present study was to evaluate the effect of a 2-week oral treatment with drospirenone, estradiol valerate, and combined therapy of drospirenone + estradiol valerate on central and peripheral beta-endorphin and allopregnanolone levels in ovariectomized female rats. DESIGN: Seven groups of Wistar ovariectomized rats received oral drospirenone (0.1, 0.5, and 1.0 mg/kg per day), estradiol valerate (0.05 mg/kg per day), or drospirenone (0.1, 0.5, and 1.0 mg/kg per day) + estradiol valerate (0.05 mg/kg per day). One group of fertile and one group of ovariectomized rats were used as controls. beta-endorphin levels were measured in frontal and parietal lobes, hippocampus, hypothalamus, anterior and neurointermediate pituitary, and plasma, and allopregnanolone content was assessed in frontal and parietal lobes, hippocampus, hypothalamus, anterior pituitary, adrenal glands, and serum. RESULTS: Ovariectomy induced a significant decrease in beta-endorphin and allopregnanolone content in all brain areas analyzed and in circulating levels, whereas it increased allopregnanolone content in the adrenal gland. Estradiol valerate replacement increased beta-endorphin and allopregnanolone levels in all brain areas analyzed and in plasma/serum. Drospirenone treatment significantly increased beta-endorphin levels in all brain areas analyzed (with the only exception being the parietal lobe), whereas it produced no effect on allopregnanolone levels. The addition of drospirenone to estradiol valerate did not modify the effects of estradiol valerate on beta-endorphin or allopregnanolone levels. Drospirenone showed an additive and synergistic effect with estradiol in the neurointermediate lobe on beta-endorphin synthesis. CONCLUSIONS: Drospirenone significantly increases central and circulating beta-endorphin levels and does not seem to interfere with allopregnanolone production.     

Estradiol plus progesterone treatment and precopulatory behavior in ovariectomized female rats

The effects of progesterone in ovariectomized female Wistar rats, chronically injected with estradiol plus progesterone, were determined utilizing a scale of sexual responsiveness (SR) based on the hierarchical organization of copulatory (lordosis posture) and precopulatory (presenting posture, hopping, darting) behaviors. Standardized mating tests were performed 48 hours after estradiol dipropionate application (E) and 4 hours after progesterone (P) application. Experiment 1: Starting with the 5th day following ovariectomy animals in two groups were injected SC with 15 μg E in regular weekly intervals (for 8 weeks), the animals in one of the groups obtaining further SC injections of 1.0 mg P 44 hours later. The SR intensity induced by E and P application gradually increased and was eventually higher than in the E application. Experiment 2: Animals primed with 6 μg E were divided into four groups that received different P doses: 0.0, 0.4, 1.0 or 2.2 mg. This treatment lasted 11 weeks. Increased SR occurred only with the 1.0 and 2.2 mg P doses. However, these doses were equally effective. Experiment 3: Animals in five groups obtained 3, 5, 10, 15 or 30 μg E for 7 weeks. Every female was also given weekly injections of P that ranged from 0.0 to 2.4 mg. With 3, 5 and 10 μg E there were only small differences in the SR induced by small and large doses of P. On the other hand, animals receiving 15 μg E were differentially affected by P injections. Higher injected doses of P increased the SR induced by 15 μg E. The 30μg E dose combined with injections of P around 0.6 mg induced higher SR than when combined with injections of P over 1.0 mg. Experiment 4: Animals utilized in Experiment 3 which had received 30 μg E were subjected to further experimentation. The deletion of P caused a rapid decrease in SR. A predicted increase in SR was observed after reintroducing the 0.6 mg P administration. Finally, after the E and P administrations were stopped, precopulatory behavior disappeared but the females still exhibited the lordosis posture two weeks later. Based on these results the general conclusion is made that the dose-response relationship between progesterone and proceptive (precopulatory) behavior is dependent on the quantity of estradiol which is jointly administered. By certain combinations of dosage levels of estradiol and progesterone, the highest level of sexual responsiveness can be induced in ovariectomized rats.     

Dietary self-selection vs. complete diet: body weight gain and meal pattern in rats.

Food intake and body weight gain of male adult Wistar rats were examined in two groups of animals. One group (n = 14) was allowed to select its diet from separate sources of protein (casein, 3.1 kcal/g), fat (lard and sunflower oil, 7.9 kcal/g) and carbohydrate (CHO, starch and sucrose, 3.3 kcal/g). Another group (n = 10) received a nutritionally complete diet (3.3 kcal/g). After 2 weeks of adaptation to the diets, body weights and meal patterns were recorded for at least 4 days. The total caloric intake was nearly identical for the two groups of rats. Rats given dietary choice gained less weight over 4 days than rats fed chow and showed reduced feed efficiency. During the 24-h period, self-selecting rats consumed 20.8% of calories as proteins, 21% as fats and 58.2% as CHO. Self-selecting rats ate significantly less calories during the day than did rats given chow. The chow diet consisting of 17.3% calories as protein, 7.6% as fat and 75.1% as CHO. When comparing the self-selecting group nutrient intakes to those of chow-fed group it was observed that 24-h protein calorie intakes were identical in both groups. Fat intake was significantly higher and CHO reduced as compared to chow-fed rats. During the day, CHO intake was higher in self-selecting rats, and fat intake was not significantly reduced. During the night, protein and fat intakes were significantly higher in self-selecting rats, while CHO intake was significantly decreased, particularly in the last periods of the night.(ABSTRACT TRUNCATED AT 250 WORDS)     

Synthetic progestins and sweetness preference in intact female Sprague-Dawley rats

Intact Sprague-Dawley female rats were treated with 0.25 μg or 1.25 μg ethinyl-estradiol (EE) in combination with one of 3 synthetic progestins: (5 μg) norethindrone, norethynodrel, or norgestrel. In Experiment 1 both dosages of EE in combination with the synthetic progestins suppressed sweetness preference, with a somewhat greater effect for the 1.25 μg EE dosage. Norgestrel in combination with EE produced the longest suppression of sweetness preference. In Experiment 2 progestins administered in the absence of EE showed no significant effect on sweetness preference. When 1.25 μg EE was administered singularly, a significant decline in sweetness preference occurred, but not as great a decline as in combination with a progestin.     

A testosterone metabolite is rewarding to ovariectomized female rats

Anabolic androgenic steroids have become a major class of drugs of abuse among a growing population of male and female adolescents. Although the rewarding and reinforcing properties of androgens have been demonstrated in male rodents, it is unknown whether these properties are apparent in female rats. In this study, conditioned place preference and self-administration paradigms showed that the endogenous androgen metabolite 3alphaDIOL is rewarding and reinforcing in ovariectomized female rats. Because 3alphaDIOL can be synthesized de novo in the brain, it is hypothesized that this neurosteroid provides a permissive neurochemical environment that modulates reward processes.     

Estrogen influences stimulated water intake by ovariectomized female rats

To further elucidate the influence of estrogen on water consumption, we examined water intake by adult female rats stimulated by water deprivation, injection of hypertonic saline or injection of isoproterenol (ISOP), a beta-adrenergic agonist that activates the renin-angiotensin system (RAS). Rats were ovariectomized (OVX) then injected with estradiol benzoate (EB; 10 microg/0.1 ml oil) or the oil vehicle (OIL; 0.1 ml) for 2 consecutive days. Twenty-four hours after the second injection, rats were deprived of food and water. On the following day, rats were given water and intake was measured after 2 h. EB significantly decreased water intake compared with that by OIL-treated rats following water deprivation. Two additional groups of adult female rats were OVX and treated with EB or OIL. Forty-eight hours after EB or OIL treatment, rats were injected with hypertonic saline (1 ml of 2 M NaCl) or ISOP (30 microg/kg in 0.15 M saline) and water intake was measured after 2 h. EB significantly attenuated water intake following ISOP but not after hypertonic saline. Finally, we examined plasma sodium concentration (pNa) after hypertonic saline and plasma renin activity (PRA) after ISOP in EB- and OIL-treated rats and found no differences in pNa or PRA. These results suggest that the stimuli for water intake after hypertonic saline and ISOP were comparable in EB- and OIL-treated rats. Taken together, these results raise the possibility that EB attenuation of stimulated water intake is specific to water intake elicited by activation of the RAS.     

加减一阴煎改善去势大鼠内皮功能紊乱

目的:探讨加减一阴煎对去势大鼠内皮功能紊乱的影响。方法:采用血管张力仪测定SD大鼠内皮依赖性舒张功能,扫描电镜观察胸主动脉内皮细胞形态,Western blotting技术检测内皮脂肪酶的表达,HE染色观察大鼠子宫内膜的形态。结果:加减一阴煎逆转了去势大鼠内皮依赖性舒张功能的降低;加减一阴煎减少了去势大鼠内皮细胞脂质的堆积,降低了去势大鼠内皮脂肪酶的表达水平;加减一阴煎对去势大鼠子宫湿重的影响不大。结论:加减一阴煎可改善去势大鼠血管内皮依赖性舒张功能,维持内皮细胞形态的完整。     

Effects of paced coital stimulation on estrus duration in intact cycling rats and ovariectomized and ovariectomized-adrenalectomized hormone-primed rats

Feminine sexual behavior was examined in intact cycling rats and ovariectomized and ovariectomized-adrenalectomized hormone-primed rats with the use of a partitioned test cage in which the female controlled the timing of sexual contacts with males. Females received 9 or 10 intromissions in the partitioned test cage (paced) or with the partition removed (nonpaced) or received solitary exposure to the test cage or to mounts without intromission with the use of vaginal masks. Intact cycling (Experiment 1) and gonadectomized hormone-primed (Experiment 2) rats displayed similar patterns of contact with males: Exists from and latencies to return to the male compartment increased as the intensity of the antecedent coital stimulation increased (ejaculations greater than intromissions greater than mounts). Cycling females given experience with paced or nonpaced mating on the evening of proestrus did not exhibit differences in pacing behavior on a second test 17-24 days later. Those receiving paced coital stimulation showed a shorter duration of estrus than did those receiving nonpaced stimulation. Ovariectomized and ovariectomized-adrenalectomized paced rats given three successive doses of estradiol benzoate in combination with progesterone did not show shorter periods of estrus than nonpaced or mounts-only rats. These results suggest that ovarian output in response to paced cervical-vaginal stimulation may contribute to the termination of estrus in the rat.