Effects of progesterone blockade over cocaine-induced genital reflexes of paradoxical sleep-deprived male rats

Paradoxical sleep deprivation (PSD) enhances cocaine-induced genital reflexes (penile erection [PE] and ejaculation [EJ]) in male rats and induces a significant increase in progesterone concentration. As progesterone treatment facilitates PE in PSD castrated rats, we may speculate that progesterone appears to be a relevant hormonal factor eliciting genital reflexes in PSD males. In order to expand the latter finding, different doses of antiprogestin mifepristone (vehicle, 2.5, 5, 10, and 20 mg/kg, s.c.) were administered to PSD rats at the end of a 4-day period of PSD 1 h prior to cocaine administration (7 mg/kg, i.p.) and placed in observation cages for the evaluation of genital reflexes. Pretreatment with vehicle induced PE in all rats and this effect was significantly reduced by mifepristone at 5 to 20 mg/kg doses that lowered the proportion to 40% of the rats. The frequency of PE was also significantly reduced for all doses used. There were no significant differences between vehicle and mifepristone in EJ behavior. As for hormone concentrations, mifepristone reduced progesterone concentrations at the 5-20 mg/kg doses compared to vehicle group. At 20 mg/kg, it also elevated testosterone concentrations. In addition, mifepristone administration induced a significant decrease in the duration of PS episodes at all doses. These data suggest that progesterone exerts an essential role in erectile response induced by cocaine in PSD male rats.     

Progesterone reduces erectile dysfunction in sleep-deprived spontaneously hypertensive rats

Background  

Paradoxical sleep deprivation (PSD) associated with cocaine has been shown to enhance genital reflexes (penile erection-PE and ejaculation-EJ) in Wistar rats. Since hypertension predisposes males to erectile dysfunction, the aim of the present study was to investigate the effects of PSD on genital reflexes in the spontaneously hypertensive rat (SHR) compared to the Wistar strain. We also extended our study to examine how PSD affect steroid hormone concentrations involved in genital events in both experimental models.     

Interaction between nitric oxide and renal myogenic autoregulation in normotensive and hypertensive rats

Blood pressure fluctuates continuously throughout life and autoregulation is the primary mechanism that isolates the kidney from this fluctuation. Compared with Wistar rats, Brown Norway (B-N) rats display impaired renal myogenic autoregulation when blood pressure fluctuation is increased. They also are very susceptible to hypertension-induced renal injury. Because blockade of nitric oxide augments myogenic autoregulation in Wistar rats, we compared the response of the myogenic system in B-N rats to nitric oxide blockade with that of other strains [Wistar, Sprague-Dawley, Long-Evans, spontaneously hypertensive (SHR)]. Renal blood flow dynamics were assessed in isoflurane anesthetized rats before and after inhibition of nitric oxide synthase by Lomega-nitro-arginine methyl-ester (L-NAME, 10 mg/kg, iv). Under control conditions, myogenic autoregulation in the B-N rats was weaker than in the other strains. Myogenic autoregulation was not augmented after L-NAME administration in the SHR, but was augmented in all the normotensive rats. The enhancement was significantly greater in B-N rats so that after L-NAME the efficiency of autoregulation did not differ among the strains. The data suggest that nitric oxide is involved in the impaired myogenic autoregulation seen in B-N rats. Furthermore, the similarity of response in Wistar, Long-Evans, and Sprague-Dawley rats suggests that modulation by nitric oxide is a fundamental property of renal myogenic autoregulation.     

II. DIFFERENCES IN ADRENAL MEDULLA NUCLEAR DNA CONTENT AMONG RATS OF DIFFERENT STRAINS FOLLOWING INTERMITTENT EXPOSURE TO COLD

The amount of DNA per nucleus in the adrenal medulla cells of four different strains of rats (Wistar, Sprague-Dawley, Long-Evans, and Italico) is determined both under control conditions and after 300 hr of intermittent exposure to cold. The adrenal medulla nuclei of the four strains of rats contain the same amount of DNA; however, the loss of DNA observed after the same experimental treatment differs markedly in the different strains. The loss is small in Wistar and Sprague-Dawley rats (8–13%), larger in Long-Evans rats (20%) and still larger in Italico rats (45%). The DNA loss in Wistar rats increases if the animals are fed the same diet as the Italico rats, and the DNA loss in Italico rats is reduced if the animals are fed the same diet as the Wistar rats. The different behavior of the four strains is discussed in terms of turnover of DNA.     

NaCl detection thresholds: comparison of Fischer 344 and Wistar rats

Adult Fischer 344 (F344) rats fail to display any preference for NaCl solutions at concentrations typically preferred by other rat strains. To determine whether this behavior is due to a strain difference in NaCl detection threshold, a conditioned taste aversion (CTA) was first established to a suprathreshold concentration of NaCl (0.1 M). Then, a series of dilute NaCl solutions, ranging from 0.0 to 0.011 M NaCl, were presented to F344 (n = 16) and Wistar (n = 16) rats. The lowest concentration at which there was a reliable difference in the preference scores of conditioned and control rats was defined as the detection threshold. Results indicate that the detection threshold for NaCl lies between 0.001 and 0.002 M NaCl for both F344 and Wistar rats. The addition of the sodium channel blocker amiloride to the NaCl solutions raised the detection threshold 10-fold to 0.03-0.04 M NaCl for both strains of rats. These results suggest that the NaCl detection thresholds of F344 and Wistar rats are similar and that these strains do not differ in the degree to which amiloride raises this threshold.     

Comparison of characteristics between F344 and Slc:Wistar rats--Slc:Wistar rats cannot be distinguished from the F344 strain

With respect to F344/DuCrj and Slc: Wistar rats, both widely used in Japan, it was found that there is a close similarity in the changes of body weights and survival rates, and in the organ distribution and incidence of spontaneous tumors. To examine the degree of homozygosity between F344 and Slc: Wistar strains, tumor transplantation and skin grafting were performed. The bladder carcinomas that originated from F344/DuCrj rats grew subcutaneously in the other F344 strains and Slc: Wistar rats, but did not grow in the other Wistar-derived strains. The skin grafts between F344/DuCrj or F344/NSlc and Slc: Wistar rats were accepted, but those between F344/DuCrj or Slc: Wistar and the other Wistar-derived strains were rejected. These results suggest that Slc: Wistar rats cannot be distinguished genetically from the F344 strain of rats.     

Orchiectomized Fischer 344 male rat models body composition in hypogonadal state

The hypogonadal state in men is accompanied by substantial decreases in muscle and bone mass and by an increase in adiposity. Most of the strains of orchiectomized (ORX) rat that have been used to model this state display substantial losses in bone, but only subtle changes in adiposity and muscle mass. In order to identify a rat model displaying a robust catabolic response to ORX, we studied three strains: Fischer 344 (F344), Brown Norway and Wistar. ORX caused a significant and sustained decrease in weight gained by F344, but only a trend toward reduced weight gain in Brown Norway rats and a modest reduction weight gain in Wistar rats that was significant only after 56days. ORX suppressed food intake in F344 rats, and to a lesser degree in Brown Norway and Wistar rats. ORX reduced muscle mass significantly in F344 rats, but not in Brown Norway or Wistar rats. ORX increased adiposity moderately in F344 rats and substantially in Wistar rats. ORX caused a marked reduction in prostate mass and increase in bone resorption in all three strains. Thus, F344 was the only strain in which ORX produced substantial decreases in food intake, body weight and muscle mass with increased adiposity and increased bone resorption. We conclude that the F344 rat displays a broad range of catabolic effects following ORX and is the best rat model for studying the androgenic pathway and strategies for reversing catabolic changes induced by hypogonadism.     

Influence of rat strain on P-glycoprotein expression in cultured hepatocytes

The amount and activity of the multi-drug transport P-glycoprotein (Pgp) have been measured in cultured hepatocytes derived from different rat strains. A marked increase in Pgp, as revealed by Western blotting, occurred 48 h after seeding in hepatocytes from Sprague-Dawley, Wistar and Fischer 344 rats, the last showing the highest value. The addition of dexamethasone (DEX) to culture medium delayed Pgp overexpression in all the strains, proportionally to the protein amount in the absence of hormone. The R-123 functional test for Pgp showed that Fischer 344 hepatocytes had the lowest ability to extrude the fluorescent dye as compared with Sprague-Dawley or Wistar rats. These results suggest that the Fischer 344 rat is more prone than other strains to culture stressing conditions, leading to an overexpression of Pgp that is not necessarily functional.Abbreviations DEX dexamethasone - FCS fetal calf serum - HRP horseradish peroxide - Pgp P-glycoprotein     

Influence of sex,strain, and species on trace metal status of insulin-deficient diabetic rodents

Previous studies have demonstrated marked alterations in trace metal metabolism in male Sprague-Dawley rats following chemical induction of the diabetic state. To determine whether such changes represented a general response to the insulin-deficient condition the levels of zinc, copper, and maganese in liver, kidney, and intestine of normal and streptozotocin (STZ)-diabetic male rats of the Sprague-Dawley, Wistar, and Long-Evans strains, female Sprague-Dawley rats, and male mice were measured. Significantly increased concentrations of zinc, copper, and maganese in liver, and zinc and copper in kidney were found in STZ-diabetic rats, regardless of sex and strain. In contrast, the zinc and copper contents in liver and kidney of control and STZ-diabetic mice were similar, but hepatic manganese levels were significantly elevated in both organs of the diabetic mouse. The concentrations of all three metals were similar in the intestine of control and diabetic rodents. Higher amounts of zinc and copper were bound to metallothionein in the liver and kidney of the diabetic rats. Nicotinamide injection prior to STZ administration protected rats against the development of diabetes and alterations in trace metal status. These data indicate that specific alterations in the metabolism of zinc, copper and manganese during episodes of pancreatic hormonal imbalance represent a general phenomenon in the rat. A possible explanation for the differential response of the STZ-diabetic mouse is discussed.     

Sexual dimorphism of vascular smooth muscle responsiveness is dependent on anions and estrogen.

Alteration of the extracellular anion environment by replacement of chloride ions (Cl-) with thiocyanate ions (SCN-) in normal Krebs-Ringer bicarbonate solution (NKRB) induced sustained development of basal tension in isolated aortas from male adult Sprague-Dawley and Long-Evans rats, but not from females of these strains. However, aortic smooth muscle isolated from sexually immature male and female Wistar rats underwent more marked tension development under such treatment, exhibiting no gender differences. Such SCN(-)-induced contractile responses are not tachyphylactic, completely dependent on extracellular calcium ([Ca2+]0), and could be aborted (relaxed to basal tone) by readmission of Cl-. Castration and replacement of male sex hormones with estradiol inhibited SCN(-)-induced contractions in isolated aortas from adult Wistar male rats, while castration and testosterone supplementation failed to induce contraction in aortic muscle of adult female Wistar rats exposed to SCN-. We believe these data are compatible with the notion that gender differences in vascular activity may be modulated by actions of estradiol on the metabolism of Cl- and other anions in vascular smooth muscle, which may be linked to transport of Ca2+ across the vascular muscle cell membrane.     

Slc:Wistar outbred rats show close genetic similarity with F344 inbred rats

Although Slc:Wistar rats are used widely in biomedical research as outbred rats, close similarities in growth curves, survival rates, and immunological and biochemical phenotypes have been reported between Slc:Wistar and F344 inbred rats. We reported previously that nine genetic variations that were fixed in Slc:Wistar rats had identical genotypes in F344 rats. Here, we examined the genetic characteristics of Slc:Wistar rats using 27 simple-sequence length polymorphism (SSLP) markers and compared them with other Wistar stocks available in Japan and with some F344 strains. Among 27 SSLP loci, 23 (85%) were fixed in the Slc:Wistar rats, which was the highest among the other Wistar stocks. The 23 fixed loci shared identical genotypes with corresponding loci in F344 rats. Further, the predominant allele types in the unfixed loci had allele frequencies as high as 80%, and these alleles were identical in the F344 rats. When the nine genetic variations reported previously are added, a total of 32 (89%) out of the 36 loci examined were fixed and identical in the Slc:Wistar and F344 rat genomes. These findings indicate the low genetic variation in Slc:Wistar rats and the high genetic similarity between the Slc:Wistar and F344 inbred rats. This study demonstrates the importance of characterizing outbred rats and the need to pay ample attention to the genetic characteristics the Slc:Wistar rats for their proper use.     

A comparison of plasma prolactin levels in young female Long-Evans and Holtzman rats as measured by Nb2 lymphoma bioassay and radioimmunoassay

This study was conducted to determine the plasma levels of prolactin in prepubertal and young, postpubertal, proestrus rats of mammary tumor-susceptible (Sprague-Dawley) and tumor-resistant (Long-Evans) strains using a sensitive bioassay-Nb2 lymphoma cell replication. Prepubertal Long-Evans rats had significantly higher levels of prolactin than did Holtzman Sprague-Dawley rats of the same age. Likewise, Long-Evans rats secreted significantly more prolactin into the blood on the afternoon and evening of proestrus than did Holtzman rats. Finally, ovariectomized Long-Evans rats released more prolactin into the blood at 1 day, but not at 8 or 15 days, of treatment with diethylstilbestrol. Prolactin levels determined by conventional radioimmunoassay and by bioassay were similar except on the afternoon of proestrus, when, in both strains of rats, the bioassay to radioimmunoassay ratio increased significantly above 1.0 during the late evening. In addition, the ratio was significantly less than 1.0 in the early and late afternoon in the Holtzman rats, but not Long-Evans rats. These data indicate that a strain of rats that is resistant to experimentally induced mammary cancer has higher prolactin levels in the blood than does a strain that is susceptible to mammary cancer at a time when mammary gland growth is rapid. Furthermore, there are times during the proestrus prolactin surge when the bioassay yielded higher and lower values of prolactin than radioimmunoassay of the same samples, suggesting functional heterogeneity of prolactin that may impact on mammary gland or other target tissue function.     

Improvement of high fat-diet-induced insulin resistance in dipeptidyl peptidase IV-deficient Fischer rats

F344/DuCrj rats are genetically deficient in dipeptidyl peptidase IV (DPPIV). This enzyme degrades glucagon-like peptide-1 (GLP-1), which induces glucose-dependent insulin secretion. Glucose tolerance of F344/DuCrj rats is improved as a result of enhanced insulin release induced by high levels of plasma GLP-1. In this study, we fed F344/DuCrj rats and DPPIV-positive F344/Jcl rats, aged five weeks, on a high-fat (HF) diet to examine the effect of DPPIV deficiency on food intake and insulin resistance. F344/Jcl rats gained significantly more body weight and consumed significantly more food than F344/DuCrj rats from Week 4 on either control or HF diet. Glucose excursion in the oral glucose tolerance test (OGTT) was improved in F344/DuCrj rats fed on the control or HF diet at all times examined, compared with F344/Jcl rats. Homeostasis model assessment (HOMA) insulin resistance values of F344/DuCrj and F344/Jcl rats fed on HF diet were higher than those of animals fed on control diet up to Week 6. However, HOMA insulin resistance values of F344/DuCrj rats fed on HF diet became significantly lower than those of F344/Jcl rats on HF diet during Weeks 8-10. The area under the insulin curve in the OGTT at Week 10 showed that the insulin resistance of HF-diet-fed F344/DuCrj rats was greatly ameliorated. Plasma active GLP-1 concentrations of F344/DuCrj rats in the fed state were significantly higher than those of F344/Jcl rats. These observations suggest that DPPIV deficiency results in improved glucose tolerance and ameliorated insulin resistance owing to enhanced insulin release and inhibition of food intake as a result of high active GLP-1 levels.     

Cryopreservation of spermatozoa from closed colonies, and inbred, spontaneous mutant, and transgenic strains of rats

We attempted to cryopreserve spermatozoa from closed colonies (Jcl:SD and Jcl:Wistar), and inbred (BN/Crj, F3441 DuCrj, LEW/Crj, Long-Evans and WKY/NCrj), mutant (Zitter [WTC.ZI-zi] and Tremor [TRM]), transgenic (human A-transferase [A], and green fluorescent protein [GFP]) strains of rats. Rat epididymal spermatozoa suspended in cryopreservation solution (23% egg yolk, 8% lactose monohydrate, and 0.7% Equex Stm, pH 7.4, adjusted with 10% Tris [hydroxymethy] aminomethane) were frozen and stored at -196 degrees C. After thawing at 37 degrees C, the spermatozoa were instilled into the tip of each uterine horn of the recipients. A total of five recipient females for each strain were inseminated with cryopreserved spermatozoa, and normal live offspring of all strains (Jcl:SD: 11, Jcl:Wistar: 13, BN/Crj: 9, F344/DuCrj: 28, LEW/Crj: 4, Long-Evans: 6, WKY/NCrj: 8, TRM: 24, WTC.ZI-zi: 27, A: 30 and GFP: 20) were obtained.     

Strain differences in kidney copper concentrations of male rats

The copper concentrations of the kidneys of male rats of six inbred (BN, F344, LEW, SHR, WAG/Cpb, and WAG/Rij) and one random-bred Wistar strain were determined. In inbred rats the mean concentration varied between strains and ranged from 7.10 μg/g for F 344 to 23.48 μg/g for WAG/Cpb. The calculated coefficient of genetic determination (g²) was 0.88. A remarkable discrepancy was found between the two WAG inbred strains; the WAG/Cpb had a 2.5 times higher kidney Cu concentration than the WAG/Rij. Kidney Cu concentrations of random-bred rats varied considerably; the coefficient of variation of the means was 28 and 34% in two samples taken with a 1-yr interval, respectively, indicating inhomogeneity within the population. The results indicate that the individual differences in kidney Cu concentration have a genetic basis.     

Characteristics of the aortic elastic network and related phenotypes in seven inbred rat strains

Extracellular matrix (ECM) molecules such as elastin and collagen provide mechanical support to the vessel wall and are essential for vascular function. Evidence that genetic factors influence aortic ECM composition and organization was concluded from our previous studies showing that the inbred Brown Norway (BN) rat differs significantly from the outbred Long-Evans (LE) and the inbred LOU rat with respect to both thoracic aortic elastin content and internal elastic lamina (IEL) rupture in the abdominal aorta and iliac arteries. Here, we measured aortic elastin and collagen contents as well as factors that may modulate these parameters [insulin growth factor (IGF)-I, transforming growth factor (TGF)-beta(1), and matrix metalloproteinase (MMP)-2] in seven inbred rat strains, including BN and LOU. We also investigated whether IEL ruptures occur in strains other than BN. We showed that LOU, LE, BN, and Fischer 344 (F344) rats were significantly different for aortic elastin content and elastin-to-collagen ratio, whereas LE, Lewis, WAG, and Wistar-Furth (WF) were similar for these parameters. BN and F344 had the lowest values. BN was the only strain to present numerous IEL ruptures, whereas F344, LE, and WF presented a few and the other strains presented none. In addition, IGF-I and TGF-beta(1) levels in the plasma and aorta differed significantly between strains, suggesting genetic control of their production. Because inbred rat strains provide interesting models for quantitative trait locus analysis, our results concerning elastin, collagen, IEL ruptures, and cytokines may provide a basis for the search for candidate genes involved in the control of these phenotypes.     

Opposing effects of prostaglandin E(2)and F(2 alpha) on rat liver-associated natural killer cell activity in vitro

Strain differences in cancer incidence are proposed to be due partly to differences in immune function. As potential cancer-associated immunological regulators, the concentrations of hepatic prostaglandins E(2)(PGE(2 alpha)and F(2 alpha)(PGF(2 alpha)) were compared in 9-week-old male and female F344/N and Sprague-Dawley (SD) rats. There were no strain or gender differences in the concentrations of hepatic PGE(2). No strain difference was found in the concentration of hepatic PGF(2 alpha), but the hepatic PGF(2 alpha)concentration in female rats was two-fold that of the male rat (130 vs 60 ng/g). PGE(2)significantly inhibited hepatic natural-killer cell (NK) activity in vitro compared with untreated cells from both genders and strains (P<0.05), 25 ng PGE(2)/ml inhibited NK activity significantly more than did 10 ng PGE(2)/ml (P<0.05). In contrast, 50 ng PGF(2 alpha)/ml and 100 ng PGF(2 alpha)/ml significantly stimulated hepatic NK activity compared with untreated hepatic cells from both F344/N and SD rats. This study suggests that prostaglandins may have a negligible net effect on NK activity associated with rat liver, and may be unlikely to mediate cancer-related immune function.     

Lack of optimal activation of natural killer levels by interleukin-2 in rat spleen cells: evidence for suppression

The effect of human recombinant IL-2 on the levels of natural killer (NK) activity in spleen cells derived from BALB/c mice and different strains of rats was studied. Enhancement of murine NK activity in response to IL-2 was readily demonstrable. Levels of NK activity in control as well as IL-2-treated spleen cells from Wistar, Sprague-Dawley, Fischer, and Long-Evans rats increased initially and peaked on Day 1 or 2 of culture. No significant differences between the control and the IL-2-treated cultures was found in this duration. The subsequent fall in NK activity was slower in IL-2-treated cultures of Fischer and Long-Evans rat spleen cells resulting in a significant difference between the NK levels in control and IL-2-treated cells on Day 5 and Day 7 of the culture. In the case of Wistar and Sprague-Dawley rats, the boosting effect of IL-2 on NK levels was either poor or nonexistent. Even though NK activation was poor, spleen cells of all strains of rats did proliferate in response to IL-2, indicating that the IL-2 preparation used was biologically active on rat spleen cells. Rat spleen cells cultured alone or with IL-2 released a factor(s) in the culture supernatant which could suppress the IL-2-induced NK activation in mouse spleen cells. Indomethacin could block the release of suppressor factor by cultured rat spleen cells. Moreover the NK levels in rat spleen cells could be augmented by IL-2 in the presence of indomethacin. These results indicate that the subdued IL-2-induced NK activation in bulk cultures of rat spleen cells could be due to spontaneous release of prostaglandins by the cultured cells.     

Strain differences in in vitro rat hepatocyte unscheduled DNA synthesis (UDS): effect of UV is independent of strain while increased sensitivity is apparent using Fischer-344 instead of Sprague-Dawley rats

The unscheduled DNA synthesis (UDS) assay measures DNA repair following in vitro treatment of rat primary hepatocytes. This report compares the UDS response of primary hepatocytes from 2 widely used rat strains, the Fischer-344 (F344) and Sprague-Dawley (SD) strains. Ultraviolet (UV) light and 5 known genotoxic chemicals were evaluated in each strain in parallel experiments. The chemicals tested were 2-acetylaminofluorene (2-AAF), 4-aminobiphenyl (4-AB), benzidine, dimethylnitrosamine (DMN) and N-propyl-N'-nitro-N-nitrosoguanidine (PNNG). Four of these compounds (2-AAF, 4-AB, benzidine and DMN) require metabolic activation. Benzidine and PNNG were both negative using SD rat hepatocytes, but were weakly positive using F344 rat hepatocytes. In the first of 2 experiments, 4-AB was inconclusive in SD hepatocytes, but strongly positive in F344 cells. In the second experiment, 4-AB was positive in hepatocytes from both strains. 2-AAF was more strongly positive in F344 cells than in SD cells. DMN and UV light induced positive dose responses with little or no differences between strains. It is concluded that hepatocytes from F344 rats may be more sensitive, qualitatively and quantitatively, than hepatocytes from SD rats as indicators of UDS. This difference is not due to intrinsic differences in DNA repair mechanisms but is probably due to differences in drug-metabolizing enzymes between these strains. Thus, for routine screening, F344 rats are preferable for measurement of the in vitro UDS-inducing potential of compounds.