Effects of vasopressin on female sexual behavior in male rats

Intracerebroventricular (i.c.v.) injection of an Arg-vasopressin (AVP) antagonist did not stimulate female sexual behavior in adult castrated male rats treated with ovarian hormone but stimulated this behavior in male rats which were castrated on the day of birth. It is suggested that neonatal androgen stimulation in the male rat offsets the influence of AVP on female sexual behavior in the adult.     

Centrally administered galanin inhibits osmotically stimulated arginine vasopressin release in conscious rats.

The effect of centrally administered galanin on arginine vasopressin (AVP) release was investigated in conscious rats. Intracerebroventricular injection of porcine galanin suppressed hypertonic saline-induced increase in plasma AVP in a dose-dependent manner (12.5-100 pmol/rat) at 10 min after the injection. Pretreatment with subcutaneous injection of naloxone (1 mg/100 g b.wt.) partially blocked the galanin-induced effect on plasma AVP. These results suggest that central galanin inhibits osmotically stimulated AVP release and endogenous opioids are, at least in part, involved in the mechanism.     

Acute alkalosis, but not acute hypocalcemia, increases panic behavior in an animal model

Non-pretrained, randomized adult rats were tested in a panic-inducing model of passive avoidance. Intravenous treatment with alkalinizing agents (sodium lactate 0.5 M, 0.5 ml/100 g b.wt., or NaHCO3, 0.5 mEq/100 g b.wt.), but not with a hypocalcemic dose of EDTA (75 mg/kg) 3 min before testing, significantly increased panic behavior. These data may support the hypothesis that panic attacks are due to alkalosis and not to lactate-induced hypocalcemia.     

Behavioral and cardiac responses to mild stress in young and aged rats: effects of amphetamine and vasopressin.

Young (3-month-old) male Wistar rats showed a relative decrease in heart rate to a sudden silence superimposed on low intensity background noise. This bradycardia was accompanied by immobility behavior. In 26-month-old rats the magnitude of the heart rate response was reduced while immobility behavior remained in the same order of magnitude as in young controls. In the aged rats a shift in autonomic regulation of heart rate in the direction of increased sympathetic influence was indicated by the results obtained by blocking the autonomic input with atropine methyl-nitrate (0.5 mg/kg) or atenolol (1 mg/kg) given subcutaneously (SC) 30 min prior to testing. Pretest (30 min) administration of amphetamine (0.5 mg/kg SC) reinstated the bradycardiac response in aged rats to a level seen in young ones. Arginine-vasopressin (AVP, 10 micrograms/kg SC), administered 60 min before the experiment, markedly facilitated the cardiac response in young animals but failed to restore cardiac responses in aged ones. The immobility behavior in the peptide-treated aged rats was also absent. The present findings suggest that a diminished central aminergic drive in aged rats is causing a reduction of the parasympathetic cardiac response to stress of sudden silence. The results also indicate an age-related vasopressinergic modulation of behavioral and cardiac responses to mild stress.     

Ascorbic acid metabolism in rats and guinea pigs after the administration of ethanol

Ascorbic acid metabolism was studied in guinea pigs and rats after the administration of ethanol and a high dose of ascorbic acid (AA). Male guinea pigs were maintained for 30 days as follows: (1) controls (1 mg AA/100 g body wt.); (2) ethanol (1 mg AA/100 g body wt. + 900 mg ethanol/100 g body wt); (3) ascorbic acid (25 mg AA/100 g body wt.); (4) ascorbic acid + ethanol (25 mg AA/100 g body wt. + 900 mg ethanol/100 g body wt.). Rats were also grouped into four groups as in the case of guinea pigs, but the dose of AA was 200 mg/100 g body weight. Rats adjusted to ethanol intoxication by enhancing the biosynthesis of ascorbate as evidenced by elevated activity of L-gulono lactone oxidase (GLO). Hence ascorbate levels were not lowered in rats after administration of alcohol. However, alcohol administration lowered tissue levels of ascorbate in guinea pigs. But the supplementation of ascorbate along with alcohol raised the tissue level of this vitamin. Guinea pigs responded to the ascorbate deficiency during alcohol administration by lowering the degradation of ascorbate, as seen by the lower activity of the degrading enzyme gulono lactone hydrolase. It is concluded that on the administration of alcohol, guinea pigs are dependent upon additional exogenous supplies of ascorbic acid, whereas rats are not.     

Influence of epidermal growth factor (EGF) on renal transport of PAH and amino acids in amino acid loaded rats.

In anaesthetized adult female rats, the influence of epidermal growth factor (EGF) on renal transport of p-amino-hippurate (PAH), electrolytes, and amino acids was investigated. After loading with PAH (200 mg/100 g b.wt. iv.), PAH excretion in EGF treated rats (8 microg/100 g b.wt. subcutaneously for 8 days, twice daily 8 a.m. and 4 p.m.) was increased by about 20 %. Continuous infusions of glutamine, arginine (both 50 mg/100 g b.wt. per hour), or alanine (90 mg/ 100 g b.wt. per hour) were followed by an increase in the fractional excretion (FE) of the administered amino acids as well as of the other endogenous amino acids. Under load conditions (alanine, arginine or glutamine), EGF pretreatment was followed by a stimulation of renal amino acid reabsorption. These changes in amino acid transport were connected with a significant reduction of GFR after EGF pre-treatment (0.96+/-0.10 vs. 0.62+/-0.07 ml/min x 100 g b.wt.), with a distinct increase in sodium excretion (2.98+/-0.55 vs. 4.97+/-0.71 microval/100 g b.wt. x 20 min) and with a retarded normal kidney weight gain (874+/-18 vs. 775+/-32 mg/100 g b.wt.). A simultaneous PAH load reduced amino acid reabsorption as a sign of overloading of renal tubular transport capacity, but in EGF pretreated animals the amino acid excretion was only slightly increased under these conditions.     

Effect of low amphetamine doses on cardiac responses to emotional stress in aged rats.

In young Wistar rats conditioned emotional stress can be characterized by a learned bradycardiac response to an inescapable footshock. In aged rats this bradycardiac response is attenuated and accompanied by suppressed behavioral arousal in response to novelty. In the present study, cardiac responses to emotional stress and behavioral reactivity to a novel experience in an open field were tested in aged and young rats under the influence of a low dose of d-amphetamine (AMPH, 0.5 mg/kg IP). AMPH administration in 27-month-old rats reinstated the bradycardiac response to emotional stress, while it failed to influence the resting heart rate in the home cage. Age-associated differences in open-field ambulation, present in drug-free conditions, were antagonized by low doses of AMPH (0.25-1.0 mg/kg). It is concluded that enhanced arousal by aminergic stimulation with AMPH in the aged rat invoked cardiac and behavioral response patterns resembling those at younger ages.     

Vasopressin prolongs behavioral and cardiac responses to mild stress in young but not in aged rats.

In young male Wistar rats sudden silence superimposed on low intensity background noise evokes a relative decrease in heart rate. This bradycardia is accompanied by immobility behavior. In the present study, involving young (3 month), late-adult (14 month), aged (20 month), and senescent (25 month) rats the magnitude of the stress-induced bradycardia shows an age-related reduction while the behavioral immobility response remained unchanged during the process of aging. Arginine-8-vasopressin (AVP, 6 micrograms/kg SC) administered 60 min prior to the experiment led to a prolonged behavioral and cardiac stress response in young and late-adult rats, but not in aged and senescent animals. The peripheral and central mechanisms possibly involved in the failure of systemically applied AVP to improve bradycardiac stress responses in aged rats are discussed.     

Administration of pigment epithelium-derived factor inhibits left ventricular remodeling and improves cardiac function in rats with acute myocardial infarction

Oxidative stress and inflammation are involved in cardiac remodeling after acute myocardial infarction (AMI). We have found that pigment epithelium-derived factor (PEDF) inhibits vascular inflammation through its anti-oxidative properties. However, effects of PEDF on cardiac remodeling after AMI remain unknown. We investigated whether PEDF could inhibit left ventricular remodeling and improve cardiac function in rats with AMI. AMI was induced in 8-week-old Sprague-Dawley rats by ligation of the left ascending coronary artery. Rats were treated intravenously with vehicle or 10 μg PEDF/100 g b.wt. every day for up to 2 weeks after AMI. Each rat was followed until 16 weeks of age. PEDF levels in infarcted areas and serum were significantly decreased at 1 week after AMI and remained low during the observational periods. PEDF administration inhibited apoptotic cell death and oxidative stress generation around the infarcted areas at 2 and 8 weeks after AMI. Further, PEDF injection suppressed cardiac fibrosis by reducing transforming growth factor-β and type III collagen expression, improved left ventricular ejection fraction, ameliorated diastolic dysfunction, and inhibited the increase in left ventricular mass index at 8 weeks after AMI. The present study demonstrated that PEDF could inhibit tissue remodeling and improve cardiac function in AMI rats. Substitution of PEDF may be a novel therapeutic strategy for cardiac remodeling after AMI.     

The anabolic effects of vitamin D-binding protein-macrophage activating factor (DBP-MAF) and a novel small peptide on bone

Vitamin D-binding protein-macrophage activating factor (DBP-MAF) has previously been shown to stimulate bone resorption and correct the skeletal defects associated with osteopetrosis in two nonallelic mutations in rats. This same protein and a small fragment of the protein have now been shown to demonstrate an anabolic effect on the skeleton of both newborn and young adult, intact rats. The novel peptide fragment was synthetically produced based on the human amino acid sequence at the site of glycosylation in the third domain of the native protein (DBP). The peptide tested is 14 amino acids in length and demonstrates no homologies other than to that region of DBP. Newborn rats were injected i.p. with saline, peptide (0.4 ng/g body wt.) or DBP-MAF (2 ng/g body wt.) every other day from birth to 14 days of age. On day 16 the rats were euthanized and the long bones collected for bone densitometry by pQCT. After 2 weeks of treatment with either the whole protein (DBP-MAF) or the small peptide, bone density was significantly increased in the treated animals compared to the saline controls. Young adult female rats (180 grams) were given s.c. injections of saline or peptide (0.4 ng/g body wt. or 5 ng/g body wt.) every other day for 2 weeks; 2 days after the final injections, the rats were euthanized and the femurs and tibias collected for bone densitometry. Both doses of the peptide resulted in significant increases in bone density as determined by pQCT. Young adult rats were injected locally with a single dose of the peptide (1 microg) or saline into the marrow cavity of the distal femur. One week after the single injection, the bones were collected for radiographic and histological evaluation. The saline controls showed no evidence of new bone formation, whereas the peptide-treated animals demonstrated osteoinduction in the marrow cavity and osteogenesis of surrounding cortical and metaphyseal bone. These data suggest that DBP-MAF and the synthetic peptide represent therapeutic opportunities for the treatment of a number of bone diseases and skeletal disorders. Systemic administration could be used to treat osteoporosis and a number of other osteopenias, and local administration could be effective in fractures, bony defect repairs, spinal surgery, and joint replacement.     

不同环境温度对精氨酸加压素引起的大鼠低温的影响及其与尾部散热变化的关系

 目的：探讨不同环境温度对精氨酸加压素（AVP）引起的大鼠低温及其与尾部散热变化的关系,以确定是否外周给予AVP能提高大鼠尾部散热反应。方法：实验用成年雄性SD大鼠,在3种不同环境温度（12 ℃、22 ℃和32 ℃）下,用无线遥测技术连续记录体核温度和尾部皮肤温度。上午10:00给大鼠腹腔注射AVP(10 μg/kg)或V1a受体阻断剂(30 μg/kg)。同时观察AVP或V1a受体阻断剂对大鼠背斜方肌微血管直径和理毛行为的影响。结果：(1)在3种不同环境温度中,AVP引起大鼠低温均伴有尾部皮肤温度降低反应。(2) V1a受体阻断剂能够阻断AVP引起低温和尾部皮肤温度降低效应。(3)AVP能明显引起背斜方肌微血管收缩反应。(4)AVP能提高大鼠的理毛行为(唾液理毛),而且这种作用也能被外周给予V1a受体阻断剂所阻断。(5)内源性AVP不参与正常大鼠尾部散热过程。结论：外周给予AVP引起大鼠低温,不是由于其降低了体温调定点,可能是由于其抑制了体温调节性产热和提高唾液理毛活动以增加体表蒸发散热所致。     

Periodic maternal deprivation induces gender-dependent alterations in behavioral and neuroendocrine responses to emotional stress in adult rats.

There is evidence that stressful events during the neonatal "stress hyporesponsive period" may influence both emotional behavior and the maturation of the hypothalamic-pituitary-adrenal (HPA) axis in rats. We tested whether periodic maternal deprivation (180 min daily on postnatal days 3-10, PMD) caused chronic changes in emotional behavior and HPA axis activity in either male or female adult rats, or both. In addition, HPA secretory responses to human/rat corticotropin-releasing factor (CRH, 50 ng/kg i.v.) were determined in the adult males. In the elevated plus-maze test, adult (4-5 months of age) PMD-treated animals of both sexes displayed increased anxiety-related behavior compared to control rats. This was indicated by a reduction in the number of entries (male: 70% reduction, p < 0.01; female: 31% reduction, p < 0.01) and amount of time spent on the open arms (male: 86% reduction, p < 0.01; female: 40% reduction, NS). Neuroendocrine parameters were also altered in PMD-treated rats in a gender-dependent manner. Whereas basal plasma adrenocorticotropin (ACTH) and corticosterone levels did not differ significantly between PMD and control groups of either sex, the ACTH response to elevated plus-maze exposure, a predominantly emotional stressor, was higher in male (p < 0.01), but not female, PMD animals than in the respective controls. In contrast, PMD had no effect on behavioral (duration of struggling) or HPA axis responses to forced swimming (90 s, 19 degrees C), a complex and predominantly physical stressor, in either male or female rats. In response to CRH stimulation, PMD-treated males did not show differences in the ACTH secretion compared to controls, indicating alterations in HPA axis regulation at a suprapituitary level. Thus, PMD caused long-term changes in the emotional behavior of adult rats of both sexes, although to a differing degree in males and females, whereas it appeared to cause predominantly alterations in the HPA axis response in males, depending on the characteristics of the stressor used.     

Effects of Impairments to Glucocorticoid Receptor Mechanisms in Early Ontogeny on the Activity of the Hypophyseal-Adrenocortical System and Behavior in Male Rats

The effects of treatment of rats with hydrocortisone (1 mg/100 g) or the glucocorticoid receptor blocker RU38486 (1 mg/100 g) from day 1 to day 5 of life on changes in the dynamics of the stress response of the hypophyseal-adrenocortical system (HAS), orientational-investigative activity, and anxiety in immature and adult male rats were studied. Excess glucocorticoid hormones during the early neonatal period was found to increase orientational-investigative activity and the level of anxiety in immature males without altering the functional activity of the HAS or behavior in adult rats. Conversely, impairment of glucocorticoid receptor mechanisms in brain structures in neonatal rats led to decreased feedback efficiency in the regulation of the HAS, decreases in motor activity, and increases in anxiety levels in conditions of contextual novelty, which was most clearly apparent at adult age. It is suggested that rearrangement of glucocorticoid reception during the neonatal period of development is among the causes of the various hormonal and behavioral impairments in adult individuals.     

Effect of DN-1417, a synthetic thyrotropin-releasing hormone analogue, on [3H]GABA binding in the cerebellum of ataxic rats

The neonatal administration of cytocine arabinoside (40 mg/kg, s.c.) induced marked ataxia and hypoplastic cerebellum in male Sprague-Dawley rats. Specific [3H]GABA binding in the cerebellum was significantly reduced by cytosine arabinoside, whereas [3H]GABA binding in the cerebral cortex was not changed. The administration of DN-1417 (1 mg/100 g body wt., i.p.), a synthetic derivative of thyrotropin-releasing hormone (TRH), significantly increased [3H]GABA binding in the cerebellum of cytosine arabinoside-induced ataxic rats. These results suggest that TRH may play a role in regulating GABA receptors involved in the function of the rat cerebellum.     

Thyroid hormone control of Na+-K+-ATPase and K+-dependent phosphatase in rat heart.

To assess the possible role of the Na+ pump in mediating physiological responses to thyroid hormone in the rat myocardium, we examined the effects of L-3,5,3'-triiodothyronine (T3) on the activities of the closely associated enzymes, Na+-K+-dependent adenosine triphosphatase (Na-K-ATPase) and K+-dependent p-nitrophenyl phosphatase (K-dep-pNPPase). In hypothyroid rats, administration of T3 (50 microng/100 g body wt) resulted in significant increases (greater than 50%) in Na-K-ATPase and K-dep-pNPPase activities in both crude homogenates and microsomal fractions of the rat ventricle. Significant effects on Na-K-ATPase activity were also attained with low doses (1 microng/100 g body wt) of T3. A method was developed for assaying K-dep-pNPPase activity in cardiac slices. With this technique, enhancement in K-dep-pNPPase activity of 89.2% was found in ventricle slices after treatment of hypothyroid rats with T3 (50 microng/100 g body wt), implying that augmentation of the capacity of the Na+ pump is achieved in vivo. The potent analogue, L-3,5-diiodo-3' isopropyl thyronine (isopropyl T2) had the same effects on cardiac growth and Na-K-ATPase as T3, in hypothyroid rats. In contrast, the relatively inactive isomer, L-3,3',5'-triiodothyronine (reverse T3) had no significant effect on the heart weight-to-body weight ratio or on ventricular Na-K-ATPase activity.     

Increase of food intake induced by glucagon in the rat

The effect of intraperitoneal administration of saline, glucose (25 mg/100 g b.w.), insulin (0.025 U/100 g b.w.) and glucagon (50 micrograms/kg b.w.) on glycemia, liver glycogen concentration and food intake was studied on 104 male adult Wistar rats. When saline was injected the amount of food ingested was similar to that expected at the metabolic moment selected for the tests. Glucose administration did not reduce food intake but both insulin and glucagon provoked a threefold increase during the 60 minutes ensuing the injection. The overall ingestion of food during the 24 hours after the injection of the hormones was significantly higher (about 10%) than the control values during the preceding or the succeeding 24 hours. A hyperphagic, rather than a hypophagic effect of glucagon administration is possibly related to the small dose used in the experiments. The mechanisms involved in the increase of food intake due to glucagon are discussed in terms of acceleration of the metabolic reactions that normally prevent large drops of glycemia as glucose utilization proceeds during the inter-meal periods and that in physiological conditions build up until the need for food arises.     

Acute noise stress, ACTH administration, and blood pressure alteration.

Two groups of male Wistar rats were submitted to a single noise exposure (2640 Hz, 30 W, 102 dB, 15 min) (St group) or to a single dose of ACTH (1.5 IU/100 g b.wt.) (Ac group), respectively. A control group of nontreated rats (Co group) was used. Blood pressure (BP) was measured using an indirect tail cuff method and corticosterone (B) levels were measured by specific RIA. Haematocrit (Hc) and blood pH values were also evaluated. Acute treatments of both noise exposure and ACTH administration produced corticosterone hypersecretion and blood pressure elevation, with lower haematocrit and higher blood pH values than those found in the Co group. No differences were found between St and Ac treatments.     

Effect of Neonatal Handling in Rats with Hereditary Stress-Induced Arterial Hypertension (NISAG Rats)

NISAG rats were subjected to handling on days 1-21 after birth. Blood pressure and plasma corticosterone concentration were measured in 6-month-old handled and control NISAG rats at rest and under stress conditions. Animal behavior was studied in the open-field test. Handling had no effect on body weight and relative weights of the heart and adrenal glands. In rats subjected to handling, changes in blood pressure and adrenal cortex produced by acute emotional stress (30-min restriction) were less pronounced than in control animals. Handled rats demonstrated less fear in a new environment and exhibited high exploratory activity in the open-field test. Our findings suggest that neonatal handling reduces stress reactivity and decreases the severity of hypertension in adult NISAG rats.     

Use of gene chip technology for the characterisation of the regulation of renal transport processes and of nephrotoxicity in rats

Gene expression profiling using microarrays (rat-specific array RG-U34A, Affymetrix, U.S.A.) was employed for the investigation of: (1) hormonal regulation of renal function and (2) nephrotoxicity. For this purpose about 8,800 genes were analysed in kidney and, additionally, in liver tissue.

Ad 1.) Kidney functions develop during postnatal life. Thus, in vivo transport and accumulation of p-aminohippurate (PAH) was investigated on renal cortical slices (RCS) from 10- and 55-day-old rats. The animals were treated with dexamethasone (DEXA; 60 μg/100 g b.wt./day) for 3 days, which caused a significant reduction in the accumulation of PAH in 10-day-old rats (42 ± 5% whereas it was only slightly reduced in 55-day-old rats (70 ± 8%). To further clarify the regulation of renal function by DEXA, results were compared with those obtained previously after in vitro stimulation with DEXA. RCS were incubated for 24 hours in DEXA-containing medium (10⁻⁹ M). Under these conditions DEXA significantly increased the PAH uptake capacity in RCS obtained from 10- and 55-day-old rats up to 126 and 136%, respectively. Thus a stimulation of tubular transport capacity is possible in vitro. The effect of DEXA treatment on the gene expression of the kidney (in vivo) was moderate. Focussing especially on transporters, ion channels, ATPases, glucuronyltransferases, glutathione-S-transferase and cytochrome P450, the expression of only few genes were significantly changed (3 to 50-fold up- or down-regulation). Moreover, distinct age differences were found after in vivo administration of DEXA. The investigation of in vitro effects of DEXA is currently been performed.

Ad 2.) The kidney is threatened by nephrotoxins because of its ability to accumulate them. We used a single administration of uranyl nitrate (UN; 0.5 mg/100 g b.wt.) as a model for chronic renal failure (CRF). Clearance experiments were performed 10 weeks after UN administration (maximal symptoms of CRF) in adult female rats. As expected, UN induced interstitial cicatrices with reduced GFR and diminished PAH transport capacity. Despite the impressive morphological and functional changes in the kidney after exposure to UN, the gene expression profiles in the kidneys were only minimally affected: we found significantly changed expression levels for only 20 genes (5 genes were up-regulated [e.g. transgelin], 15 down-regulated [among these the Na-K-Cl-symporter, insulin-like growth factor, kallikrein, and ornithine decarboxylase). The lack of agreement between gene expression data and the nephrotoxic effects of UN can probably be explained by the long time interval between dosing and the assessment of the effect. The results confirm that primary genomic responses are likely to be strongest transiently after exposure and then decrease in intensity.