高血压大鼠不同血管平滑肌肌球蛋白磷酸化和脱磷酸化酶的变化

本文比较了正常和高血压大鼠不同动脉血管肌球蛋白轻链激酶（ＭＬＣＫ）和依赖Ｃａ＾２＋的钙调素磷酸酶（Ｃａ＾２＋／ＣａＭ－ＰＰ）活性的变化。结果表明：在自发性高血压大鼠（ＳＨＲ）不同血管ＭＬＣＫ的活性不同,依次为主动脉（Ａ）〉尾动脉（ＣＡ）〉肠系膜动脉（ＭＡ）;而在ＷＫＹ大鼠,该酶在不同血管的活性依次为Ａ〈〈ＣＡ〈〈ＡＭ。在ＷＫＹ大鼠,ＭＡ Ｃａ＾２＋／ＣａＭ－ＰＰ活性明显高于ＳＨＲ。在肾性高血压大鼠     

Determination of phase I metabolic enzyme activities in liver microsomes of Mrp2 deficient TR- and EHBR rats

The canalicular multispecific organic anion transporter/multidrug resistance protein 2 (cMOAT/Mrp2) plays a major role in the transport of anionic xenobiotics across the bile canalicular membrane. Transport deficient rats (TR-) and Eisai-hyperbilirubinemic rats (EHBR), defective in Mrp2, are mutants of Wistar and Sprague Dawley (SD) rats, respectively. In this study, Phase I metabolic enzyme activities in liver microsomes prepared from these mutant male and female rats were compared to their corresponding non-mutant rats. The total cytochrome P450 contents and NADPH-cytochrome P450 reductase activity in male and female TR- rats were significantly higher than in Wistar rats. In male TR- rats, ethoxyresorufin O-deethylation (EROD), pentoxyresorufin O-deethylation (PROD), testosterone 2alpha, 7alpha and 16 alpha-hydroxylase activities were higher, but testosterone 6beta-hydroxylase activity and the rate of androstenedione formation were lower than in Wistar rats. Female TR- rats had higher 7alpha-hydroxylase activity, but EROD activity was lower in female Wistar rats. Similar studies conducted in EHBR versus SD rats demonstrated increased total cytochrome P450 content in male and female EHBR rats; NADPH-cytochrome P450 reductase activity was not significantly affected. Decreased PROD activity and the rate of androstenedione formation were observed in male and female EHBR rats. Furthermore, testosterone 6beta-hydroxylase activity was lower in male EHBR rats than in male SD rats while testosterone 7alpha-hydroxylase activity was significantly higher in male and female EHBR rats. Thus, in addition to Mrp2 deficiency, differential expression of CYP isoforms and their potential impact on the metabolism and pharmacokinetics of compounds should be considered when interpreting data from these rat strains.     

Experimental stroke: ischaemic lesion volume and oedema formation differ among rat strains (a comparison between Wistar and Sprague-Dawley rats using MRI)

Investigating focal cerebral ischaemia requires animal models that are relevant to human stroke. This study was designed to evaluate the influence of early reperfusion and choice of rat strains on infarct volume and oedema formation. Thirty-six Wistar and Sprague-Dawley rats were subjected to temporary middle cerebral artery occlusion (MCAO) for 90 min (groups I and II) or to permanent MCAO (groups III and IV) using the suture technique. Ischaemic lesion volume and oedema formation were quantified 24 h after MCAO using 7T-magnetic resonance imaging (MRI). Impact of rat strains: Reperfusion led to significant larger ischaemic lesion volumes in Wistar rats as compared to Sprague-Dawley rats (P<0.0005). Oedema formation was similar in both rat strains. Permanent MCAO led to significantly larger ischaemic lesion volumes in Sprague-Dawley rats (P<0.05). Oedema formation, however, was significantly more accentuated in Wistar rats (P<0.005). Impact of reperfusion: Reperfusion did not cause any changes in ischaemic lesion volume in Wistar rats. Oedema formation, however, was significantly reduced (P<0.0005). In Sprague-Dawley rats, reperfusion caused a significant reduction of ischaemic lesion volume (P<0.00005), but did not modify oedema formation. These findings emphasize the critical importance of rat strain differences in experimental stroke research.     

Influence of intrauterine growth restriction on renal function in the adult rat

Intrauterine growth restriction (IUGR) has been shown to influence renal development and lead to fewer nephrons. Data on long term renal function after IUGR are limited. We studied the effect on renal function of IUGR in aging rats. IUGR was induced using a model of bilateral uterine artery ligation in pregnant Wistar rats. Renal function was studied at the age of 18 months. In male IUGR rats, estimated glomerular filtration rate was significantly decreased compared to male control rats [1.1 (SD 0.3) 1.7 (SD 0.3) ml x min(-1), p<0.05]. Female IUGR rats showed an increased urinary protein excretion compared with female control rats [84 (SD 73) vs. 12 (SD 13) mg x 24h(-1), p<0.01]. All male rats showed heavy proteinuria (p<0.01 vs. female rats from same experimental group), with no significant differences between the groups. Tubular reabsorption of phosphorus was lower in females, but showed no differences between the experimental groups. In conclusion, IUGR impairs renal function in the rat. It is suggested that a low nephron endowment leads to proteinuria as a sign of glomerular damage, and ends with a decrease in glomerular filtration rate as a sign of glomerular loss.     

Comparison of Invasive Blood Pressure Measurements from the Caudal Ventral Artery and the Femoral Artery in Male Adult SD and Wistar Rats

Background and Purpose

Studies have suggested that the caudal ventral artery is a potential site for continuous arterial blood pressure monitoring in rats. However, the agreement of mean arterial pressure values between the femoral artery and the caudal ventral artery has not been investigated. This study was performed to identify whether the caudal ventral artery could be safely used for continuous blood pressure monitoring as an alternative site to the femoral artery.

Methods

Rats were randomized into four groups: Sprague Dawley rats under normothermia; Wistar rats under normothermia; Sprague Dawley rats under hypothermia; Wistar rats under hypothermia. Each rat underwent simultaneous monitoring of blood pressure using femoral artery and caudal ventral artery catheterization during a stable hemodynamic state and three periods of acute severe hemodynamic changes. The effects of rat strain, rectal temperature, experimental time course and hemodynamic factors on pressure gradients, the concordance of mean arterial pressure values between the femoral artery and the caudal ventral artery, and the rates of distal ischemia after surgery were determined.

Results

There was a significant difference in the rate of distal ischemia between femoral and caudal ventral arteries after catheterization (25% vs 5%, P<0.05). The overall mean gradient and the mean gradient under a steady hemodynamic state were 4.9±3.7 mm Hg and 5.5±2.5 mm Hg, respectively. The limits of agreement (bias±1.96 SD) were (−2.5 mm Hg, 12.3 mm Hg) and (-0.5 mm Hg, 10.5 mm Hg), respectively. Although the concordance decreased during the first 30 sec of each period of severe hemodynamic changes, the degree of agreement was acceptable regardless of the effects of rat strain and rectal temperature.

Conclusions

Based on the degree of agreement and the safety of catheterization, the caudal ventral artery may be a preferred site for continuous arterial blood pressure monitoring without acute severe hemodynamic changes.     

SEM observations of the elastic networks in canine femoral artery

Scanning electron microscopy was used to study the normal architectural arrangement of elastic tissue in a medium-sized muscular artery. Selective NaOH sonication digestion or formic acid digestion was used to expose and isolate the elastic networks in the femoral arteries of four healthy dogs. The digested segments were neutralized and freeze-dried before mounting for scanning electron microscopy (SEM) observation. The fenestrated internal elastic lamina (IEL) had a smooth surface with scattered regions of the fine elastic fibers that made up lacy networks protruding from the luminal surface. Prominent ellipsoid fenestrae, randomly scattered across the surface, were grouped into small and large sizes based on their mean diameter. The openings of most fenestrae were bridged by elastic fibers to give the fenestrae a sieve-like appearance. Large, transversely oriented, fusiform gaps were randomly scattered along the length of the IEL. These gaps, filled in by an elastic fiber network, sometimes spanned as much as a quarter of the vessel circumference. It is suggested that these gaps represent splits in the IEL that have been repaired. The tunica media contained a complex network of anastomosing elastic fibers and lamellae that were primarily circumferential in orientation. A well-defined external elastic lamina formed a solid sheet at the junction of the tunica media and the tunica adventitia. The tunica adventitia contained 8-10 incomplete lamellae of large, interconnecting, longitudinally oriented fibers. The architecture of the elastic network in canine femoral artery was compared with that previously described in medium-sized canine veins and in the rat femoral artery.     

Distribution of the vasoconstrictor and vasorelaxant effects of norbormide along the vascular tree of the rat

Norbormide is a vasoconstrictor of rat peripheral arteries and a relaxant in rat aorta. To characterise norbormide actions within the rat vascular tree we have investigated its effects on the contractile function of rings from several arteries and veins. A maximal norbormide concentration (50 microM) failed to contract thoracic aorta and carotid artery, whereas in pulmonary artery, abdominal aorta, iliac, caudal, and femoral arteries it induced a contractile effect that was respectively 4.8 +/- 0.6, 18.4 +/- 1.5, 39 +/- 5, 144 +/- 7, and 260 +/- 22% of that induced by 90 mM KCl. In pulmonary, carotid, and iliac arteries, and in thoracic and abdominal aorta, 50 microM norbormide inhibited KCl-induced responses. Norbormide (50 microM) contracted all veins investigated. The effect, expressed as % of KCl-induced contraction, was 121 +/- 25, 154 +/- 14.5, 154 +/- 18.2, 203 +/- 19, and 267 +/- 33 for pulmonary vein, thoracic and abdominal vena cava, iliac and jugular veins, respectively. In jugular vein, as previously shown in rat caudal artery, norbormide contraction was abolished in Ca2+-free medium, was unaffected by the Ca2+ channel blocker nifedipine, and was relaxed by SK&F 96365, a blocker of store-operated Ca2+ channels. In conclusion: i) rat veins represent the main target for contractile norbormide action; ii) in both artery and veins norbormide contractions are generally inversely related to the calibre of the vessel; iii) norbormide-induced contraction is mediated by the same mechanism/s in arteries and veins; iiii) in norbormide-contracted arteries the drug activates both contractile and relaxing mechanisms.     

Myogenic reactivity is reduced in small renal arteries isolated from relaxin-treated rats

Administration of the ovarian hormone relaxin to nonpregnant rats vasodilates the renal circulation comparable to pregnancy. This vasodilation is mediated by endothelin (ET), the ET(B) receptor, and nitric oxide. Furthermore, endogenous relaxin mediates the renal vasodilation and hyperfiltration that occur during gestation. The goal of this study was to investigate whether myogenic reactivity of small renal and mesenteric arteries is reduced in relaxin-treated rats comparable to the pregnant condition. Relaxin or vehicle was administered to virgin female Long-Evans rats for 5 days at 4 microg/h, thereby producing midgestational blood levels of the hormone. The myogenic responses of small renal arteries (200-300 microm in diameter) isolated from these animals were evaluated in an isobaric arteriograph system. Myogenic reactivity was significantly reduced in the small renal arteries from relaxin-treated compared with vehicle-treated rats. The reduced myogenic responses were mediated by the ET(B) receptor and nitric oxide since the selective ET(B) receptor antagonist RES-701-1 and the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester restored myogenic reactivity to virgin levels. The influence of relaxin was not limited to the renal circulation because myogenic reactivity was also reduced in small mesenteric arteries isolated from relaxin-treated rats. Thus relaxin administration to nonpregnant rats mimics pregnancy, insofar as myogenic reactivity of small renal and mesenteric arteries is reduced in both conditions.     

Protease-sensitive urinary pheromones induce region-specific Fos-expression in rat accessory olfactory bulb.

Vomeronasal organs of female Wistar rats were exposed with sprayed urine preparations of male Wistar rats prior to sacrifice. Exposure to crude urine and ultrafiltrated urine preparation (<5000 Da) induced significant Fos expression, which is correlated with cellular activity, in the mitral/tufted cell layer of the accessory olfactory bulb (AOB), while exposure to the remaining substances after ultrafiltration (>5000 Da) and control salt solution did not. Exposure to urine preparation treated with papain induced expression of Fos-immunoreactive cells in the rostral region of the AOB, but did not induce such expression in the caudal region. Exposure to urine preparation treated with pronase induced urine-specific Fos immunoreactivity neither in the rostral nor in the caudal region. These results suggest that at least two different peptides carrying pheromonal activities are contained in male Wistar rat urine.     

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.     

Matrix metalloproteinase-2 activity, protein, mRNA, and tissue inhibitors in small arteries from pregnant and relaxin-treated nonpregnant rats.

Vascular gelatinase activity is essential for pregnancy- and relaxin (Rlx)-induced renal vasodilation and hyperfiltration in rats. The objective of this study was to further elucidate the mechanisms for the increase in vascular matrix metalloproteinase (MMP)-2 activity caused by pregnancy and Rlx. We first corroborated our earlier work by showing that pro- and active forms of MMP-2 were increased in small renal arteries from pregnant compared with virgin rats and Rlx-treated compared with vehicle-treated nonpregnant rats. We next investigated other artery types and showed that MMP-2 activity was upregulated in mesenteric arteries from pregnant rats (pro-MMP-2 by 50% and active MMP-2 by 40%, both P<0.05) and from Rlx-treated nonpregnant rats (pro-MMP-2 by 50% and active MMP-2 by 90%, both P<0.005) compared with their respective controls. To corroborate these results obtained by gelatin zymography, pro-MMP-2 protein was determined by Western analysis in the same small arteries. Pro-MMP-2 protein was increased in small renal arteries from pregnant compared with virgin rats and from Rlx- compared with vehicle-treated nonpregnant rats: pro-MMP-2-to-beta-actin ratio=0.29 vs. 0.21 (P<0.01) and 0.43 vs. 0.32 (P<0.005). Findings were similar for mesenteric arteries. MMP-2 mRNA as measured by real-time PCR was increased in small renal arteries from pregnant and Rlx-treated nonpregnant rats compared with their respective controls. There were no significant differences in tissue inhibitor of metalloproteinase (TIMP-1 or TIMP-2) activity by reverse zymography in small renal arteries. Thus increases in MMP-2 mRNA and protein expression are major factors contributing to increased MMP-2 activity in small arteries from pregnant and Rlx-treated nonpregnant rats.     

Influence of gender and estrous cycle on plasma and renal catecholamine levels in rats

Several studies have demonstrated that gonadal hormones show significant effects on the brain and signaling pathways of effector organs/cells that respond to neurotransmitters. Since little information is available concerning the impact of male and female gonadal hormones on the renal and peripheral sympathetic system, the objective of this study was to further assess whether and how the renal content and plasma concentration of catecholamines are influenced by gender and the estrous cycle in rats. To achieve this, males Wistar rats were divided into 4 groups: (i) sham (i.e., control), (ii) gonadectomized, (iii) gonadectomized and nandrolone decanoate replacement at physiological levels or (iv) gonadectomized and nandrolone decanoate replacement at high levels. Female Wistar rats were divided into 6 groups: (i) ovariectomized (OVX), (ii) estrogen replacement at physiological levels and (iii) estrogen replacement at at high levels, (iv) progesterone replacement at physiological levels and (v) progesterone replacement at at high levels, and (vi) sham. The sham group was subdivided into four subgroups: (i) proestrus, (ii) estrus, (iii) metaestrus, and (iv) diestrus. Ten days after surgery, the animals were sacrificed and their plasma and renal catecholamine levels measured for intergroup comparisons. Gonadectomy led to an increase in the plasma catecholamine concentration in females, as well as in the renal catecholamine content of both male and female rats. Gonadectomized males also showed a lower level of plasma catecholamine than the controls. The urinary flow, and the fractional excretion of sodium and chloride were significantly increased in gonadectomized males and in the OVX group when compared with their respective sham groups.     

Early liver alterations induced by the sex-dependent hepatocarcinogen beta-blocker ZAMI 1305

Liver alterations occurring after 1, 6 or 10 days of treatment with the hepatocarcinogen beta-blocker DL-1-(2-nitro-3-methyl-phenoxy)-3-tert-butyl-amino-propan-2-ol (ZAMI 1305) were studied in male and female Wistar rats. In agreement with its sex-dependent oncogenicity, ZAMI 1305 administration causes DNA damage in the liver of the female but not of the male rat, with the only exception of 2 out of 4 males treated for 6 days. In female rat, the amount of DNA damage increases from 1 to 6 days of treatment, being unchanged at 10 days; a small portion of DNA is however damaged. ZAMI 1305 administration to female rat induces also: (i) an increase of the relative liver weight, of the DNA and RNA synthesizing activity; (ii) a decrease of the number of hepatocytes in mitosis; (iii) a minimal oval cell hyperplasia. When the same parameters were studied in ZAMI 1305-treated male rats, they were unaffected or changed to a less extent in respect to female rats.     

Detection of bone marrow-derived cells in neointimal thickening in the rat carotid artery by nested polymerase chain reaction

The bone marrow origin of cells involved in neointimal formation after injury of the luminal surface of the vessel was confirmed by highly sensitive nested polymerase chain reaction on isolated vascular wall cells. The model of intimal hyperplasia after balloon angioplasty of the carotid artery in radiation bone marrow chimeras between male and female Wistar rats was used. The Y chromosomes of rat male donors of the bone marrow for irradiated females were used as a marker of bone marrow-derived cells. This approach demonstrated a bone marrow origin of a large fraction of α-actin-positive (smooth muscle) neointimal cells.     

Infections of forest rat filaria, Breinlia booliati, in neonate and juvenile laboratory white rats

The kinetics of Breinlia booliati infection in 3 inbred rat strains (Lewis, Wistar and Sprague Dawley) were investigated. One group of rats was infected as neonates (less than 24 hours of age) with third-stage larvae of B. booliati and the other group was infected as juveniles (4 weeks of age). The results showed that infection in the neonates were significantly different from the infection in the juveniles. The 60 rats infected as neonates, when necropsied between 8 to 10 months postinfection, yielded adult worms. The 2 neonatal infection groups of Lewis and Wistar strains showed highest susceptibility to the infections. The mean prepatent period was 85 days. Ninety to 95% of the infected rats were patent with microfilaraemia and a large percentage (33 to 47%) of them had high microfilaraemia counts exceeding 3000 mff/20 mm3 of blood and larger sizes (mean 157.11 mm for female adult worms and 61.88 mm for male adult worms. The adult worms were distributed equally in both the pleural (57%) and peritoneal cavity (43%). In most aspects, the neonatal infection group of the Sprague-Dawley strain was intermediate in susceptibility between the 2 neonatal infection groups of the Lewis and Wistar strains and the 3 juvenile infection groups. In contrast to neonatal infection groups, the 3 juvenile infection groups exhibited low infection rates (37%, 58% and 47% for the Lewis, Wistar and Sprague Dawley strains respectively), longer prepatent periods (mean 101 days), lower recovery rates (2 to 4%), lower adult worm loads (mean 0.4 to 0.8 female worms, and 0.2 to 0.8 male worms per rat), and smaller sizes (mean 141.24 mm for female adult worms and 53.75 mm for male adult worms). Forty-four to 57% of these infected rats harboured either single male or single female adult worms in the body cavity. Most (92%) of the adult worms recovered from the juvenile infection groups resided in the pleural cavity and the remaining 8% were recovered from the peritoneal cavity. Microfilaraemia could be detected in only 3/20 Lewis rats, 5/20 Wistar rats and 5/20 Sprague Dawley rats. The mean peak microfilaraemia of the 3 pooled juvenile infection groups was 632 mff/20 mm3 of blood, ranging from 7 mff/20 mm3 to 1856 mmf/20 mm3. Our results indicate that the susceptibility to B. booliati infection in white rats is both genetic and age-associated. The responses of the 2 distinct infection groups to B. booliati infections are discussed.     

Decreased epoxygenase and increased epoxide hydrolase expression in the mesenteric artery of obese Zucker rats

Previous studies suggest that epoxyeicosatrienoic acids (EETs) are vasodilators of the mesenteric artery; however, the production and regulation of EETs in the mesenteric artery remain unclear. The present study was designed 1) to determine which epoxygenase isoform may contribute to formation of EETs in mesenteric arteries and 2) to determine the regulation of mesenteric artery cytochrome P-450 (CYP) enzymes in obese Zucker rats. Microvessels were incubated with arachidonic acid, and CYP enzyme activity was determined. Mesenteric arteries demonstrate detectable epoxygenase and hydroxylase activities. Next, protein and mRNA expressions were determined in microvessels. Although renal microvessels express CYP2C23 mRNA and protein, mesenteric arteries lacked CYP2C23 expression. CYP2C11 and CYP2J mRNA and protein were expressed in mesenteric arteries and renal microvessels. In addition, mesenteric artery protein expression was evaluated in lean and obese Zucker rats. Compared with lean Zucker rats, mesenteric arterial CYP2C11 and CYP2J proteins were decreased by 38 and 43%, respectively, in obese Zucker rats. In contrast, soluble epoxide hydrolase mRNA and protein expressions were significantly increased in obese Zucker rat mesenteric arteries. In addition, nitric oxide-independent dilation evoked by acetylcholine was significantly attenuated in mesenteric arteries of obese Zucker rats. These data suggest that the main epoxygenase isoforms expressed in mesenteric arteries are different from those expressed in renal microvessels and that decreased epoxygenases and increased soluble epoxide hydrolase are associated with impaired mesenteric artery dilator function in obese Zucker rats.     

Correlation between gender and spontaneous C-cell tumors in the thyroid gland of the Wistar rat

In many rat strains, C-cell hyperplasia occurs in an age-dependent manner and is often associated with multifocal C-cell carcinoma. The purpose of this study was to investigate the spectrum of spontaneous, proliferative C-cell disorders by gender in Wistar rats throughout their lifespan. The incidence of C-cell hyperplasia shows a significant increase with age (P<0.001) and is much higher in female rats than in male rats (P<0.05). From 3 to 24 months of life, 27.5% of female rats showed a normal C-cell pattern, 55.0% showed C-cell hyperplasia, and 17.5% showed C-cell tumors; while 57.5% of male rats showed a normal C-cell pattern, 32.5% showed C-cell hyperplasia, and 10% showed C-cell tumors. Although the overall frequency of C-cell neoplasms in females was nearly double that in males, these data are not statistically significant. However, the number of C-cell tumors showed a significant increase with age (P<0.05). Therefore, we can conclude that there were significant differences in the incidence of the total spectrum of C-cell proliferative abnormalities in the thyroid gland of Wistar rats that were both age-dependent and gender-dependent.     

Two cases of spontaneous malignant fibrous histiocytoma in Wistar rats

Spontaneous malignant fibrous histiocytoma (MFH) of subcutaneous tissues was found in 2 Wistar rats of a 18-month-old male and a 21-month-old female. These tumors consisted of spindle, oval, myxoid and giant cells. In the female rat, a similar histological pattern was found in the metastatic tumor nodules in the lung and liver. In the electron microscopy, four differentiated cells of fibroblast-like, histiocyte-like, giant and undifferentiated cells were identified in these tumors. Spontaneous MFH of Wistar rats in the present study was quite similar to those reported in rats of other strains.     

In vitro synthesis of 16 alpha-hydroxyestrone by female rat liver microsomes: its possible role in the etiology of breast cancer

Liver homogenates from female rat strains (Sprague-Dawley, Wistar and Fisher) were incubated in a NADPH regenerating medium in the presence of labelled and unlabelled estrone. Liver microsomes isolated from male rats and female mice were used as positive controls. Using HPLC and paper chromatography, under the experimental conditions used it was found that liver homogenates from female rats were able to convert estrone to various metabolites such as 16 alpha-hydroxyestrone. In a mutagenicity assay (Ames test), with 16 alpha-hydroxyesterone as test substance, two strains (TA98 and TA1538) of the five strains tested showed a 2-3-fold increase in the number of his+ revertants relative to the control values. Estrone did not cause any mutagens in the test used. It is concluded that female rats are able to synthesize 16 alpha-hydroxyestron in vitro. Whether this compound is risk factor for breast cancer remains unclear.     

Differences in the immunoreactivity to phenylethanolamine-N-methyltransferase in the central adrenergic neurons of four strains of rats

Summary Immunocytochemistry was used to compare the immunoreactivity of adrenergic neurons to a well characterized specific immunoserum to phenylethanolamine-N-methyltransferase (PNMT) in different strains of rats commonly used in research studies. In adult animals, marked differences were found in the PNMT-immunoreactivity of neurons between Wistar rats and other strains, resulting in a lower PNMT-immunostaining intensity (i) within neuronal perikarya of the medulla oblongata, and (ii) more strikingly, within nerve fibers and terminals located in various brain regions. This low PNMT-immunoreactivity of nerve fibers was detected both in 14- and 35-day-old Wistar rats. On the other hand, the HPLC measurement of catecholamines, in particular of adrenaline in the hypothalamus and the medulla oblongata, did not show any difference between adult Wistar and Sprague-Dawley rats. These data suggest that the low PNMT-immunoreactivity observed in central adrenergic neurons of the Wistar rats is related to the poor recognition of the antigen by the PNMT-antibody used. Possibly, these nerve cells mainly display an isoform of the enzyme that is immunologically different from the PNMT contained within the adrenergic neurons of other rat strains.