Effects of arfaptin 1 on guanine nucleotide-dependent activation of phospholipase D and cholera toxin by ADP-ribosylation factor

Arfaptin 1, a approximately 39-kDa protein based on the deduced amino acid sequence, had been initially identified in a yeast two-hybrid screen using dominant active ARF3 (Q71L) as bait with an HL-60 cDNA library. It was suggested that arfaptin 1 may be involved in Golgi functions, since the FLAG-tagged protein was associated with Golgi membranes when expressed in COS-7 cells and could be bound to Golgi in vitro in an ADP-ribosylation factor (ARF)- and GTPgammaS-dependent, brefeldin A-inhibited fashion. Arfaptin 2, found in the same two-hybrid screen as arfaptin 1, is 60% identical in amino acid sequence and may or may not have an analogous function. We now report some effects of arfaptin 1 on ARF activation of phospholipase D and cholera toxin ADP-ribosyltransferase. Arfaptin 1 inhibited activation of both enzymes in a concentration-dependent manner and was without effect in the absence of ARF. Two ARF1 mutants that activated the toxin, one lacking 13 N-terminal amino acids and the other, in which 73 residues at the N terminus were replaced with the analogous sequence from ARL1, were not inhibited by arfaptin, consistent with the conclusion that arfaptin interaction requires the N terminus of ARF. This region has also been implicated in phospholipase D activation, but whether the two proteins interact with the same structural elements in ARF remains to be determined. Arfaptin inhibition of the action of ARF5 and ARF6 was less than that of ARF1 and ARF3; its effects were less on nonmyristoylated than myristoylated ARFs. Arfaptin effects on guanine nucleotide binding by ARFs were minimal whether or not a purified ARF guanine nucleotide-exchange protein was present. These findings indicate that arfaptin acts as an inhibitor of ARF actions in vitro, raising the possibility that it has a similar role in vivo.

Inhibition of gastric emptying and intestinal transit by amphetamine through a mechanism involving an increased secretion of CCK in male rats

1. The effect of amphetamine on gastrointestinal (GI) transit and the plasma levels of cholecystokinin (CCK) were studied in male rats. 2. Gastric emptying was inhibited both acutely and chronically by the administration of amphetamine. GI transit was decreased by the acute administration of amphetamine but not affected by the chronic administration of amphetamine. 3. Plasma CCK levels were increased dose-dependently by amphetamine. 4. Proglumide, a CCK receptor antagonist, prevented amphetamine-induced inhibition of gastric emptying and the decrease in GI transit in male rats. 5. The selective CCK(A) receptor antagonist, lorglumide, dose-dependently attenuated the amphetamine-induced inhibition of gastric emptying in male rats. In contrast, the selective CCK(B) receptor antagonist, PD 135,158, did not reverse the effect of amphetamine on gastric emptying. 6. Both lorglumide and PD 135,158 reversed the inhibitory effect of amphetamine on GI transit in male rats. 7. These results suggest that amphetamine-induced inhibition of gastric emptying and intestinal transit is due in part to a mechanism associated with the hypersecretion of endogenous CCK.

Effects of aging on erythropoietin secretion in female rats

The secretion of erythropoietin (EPO) in old (22 25 months), middle (mid)-aged (15-17 months), adult (6-7 months), and young (3 months) female rats was studied. Rats of different ages were bled by cardiac puncture for measuring plasma EPO, estradiol, and progesterone levels. The metabolic clearance rate of EPO was determined by a single-injection method. The effects of ovariectomy and replacement of estradiol (E) and/or progesterone (P) on plasma EPO concentration were also investigated. Analysis of direct effects of E and/or P on EPO from kidney tissues was carried out in an in vitro study. Plasma EPO levels were higher in both mid-aged and old rats than in young rats (P < 0.01). The metabolic clearance rate of EPO was also greater in adult, mid-aged and old rats than in young rats (P < 0.01). Ovariectomy increased rat plasma EPO concentration which might be inhibited by E (P < 0.01), P (P < 0.01), or E and P (P < 0.05) replacement. Neither E (10(-10) or 10(-9) M) nor P (10(-8) or 10(-7) M) alone altered EPO release from kidney tissue in vitro. Combination of E (10(-10) M) and P (10(-8) x or 10(-7) M) stimulated the EPO release from kidney tissue (P < 0.01). These data suggest that the mechanism of the secretion of EPO by kidneys in female rats during aging is ovarian steroid hormones independent.

Effects of ovarian steroid hormones and thyroxine on calcitonin secretion in pregnant rats

In the present study, the roles of ovarian steroid hormones and thyroxine (T4) in regulating the secretion of calcitonin (CT) in pregnant rats were examined. The levels of plasma progesterone, pre- and post-CaCl2 plasma CT, and recovery time of plasma CT and calcium after calcium challenge were greatest in midterm pregnant rats. The levels of basal plasma progesterone, CT, calcium, and recovery time of plasma CT after calcium challenge were less in late pregnant rats, but basal plasma estradiol was highest in late pregnancy. The concentrations of plasma T4 were gradually decreased in rats during pregnancy. Regardless of the presence of estradiol, administration of progesterone in ovariectomized (Ovx) rats resulted in an increase of plasma T4 as well as the basal and calcium-induced secretion of CT. Administration of estradiol alone did not alter the CaCl2-induced levels but decreased the post-CaCl2 levels of plasma calcium in Ovx rats. The basal levels of plasma CT were decreased in Ovx rats treated with T4. These results suggest that the hypercalcitoninemia in midterm pregnant rats is due to an increased secretion of progesterone. Hypocalcitoninemia in late pregnant rats, however, is due in part to lower plasma calcium.

Acute effects of thyroid hormones on the production of adrenal cAMP and corticosterone in male rats

The acute effects of thyroid hormones on glucocorticoid secretion were studied. Venous blood samples were collected from male rats after they received intravenous 3,5,3'-triiodothyronine (T3) or thyroxine (T4). Zona fasciculata-reticularis (ZFR) cells were treated with adrenocorticotropic hormone (ACTH), T3, T4, ACTH plus T3, or ACTH plus T4 at 37 degrees C for 2 h. Corticosterone concentrations in plasma and cell media, and also adenosine 3',5'-cyclic monophosphate (cAMP) production in ZFR cells in the presence of 3-isobutyl-1-methylxanthine, were determined. The effects of thyroid hormones on the activities of steroidogenic enzymes of ZFR cells were measured by the amounts of intermediate steroidal products separated by thin-layer chromatography. Administration of T3 and T4 suppressed the basal and the ACTH-stimulated levels of plasma corticosterone. In ZFR cells, both thyroid hormones inhibited ACTH-stimulated corticosterone secretion, but the basal corticosterone was inhibited only with T3 > 10(-10) M or T4 > 10(-8) M. Likewise, T3 or T4 at 10(-7) M inhibited the basal- and ACTH-stimulated levels of intracellular cAMP. Physiological doses of T3 and T4 decreased the activities of 3 beta-hydroxysteroid dehydrogenase, 21-hydroxylase, and 11 beta-hydroxylase. These results suggest that thyroid hormones counteract ACTH in adrenal steroidogenesis through their inhibition of cAMP production in ZFR cells.

Interaction between triiodothyronine and ovarian steroid hormones on the regulation of the release of thyrotropin and thyrotropin-releasing hormone in vitro

In vivo and in vitro experiments were designed to examine [1] the effect of triiodothyronine (T3) and/or ovarian steroids on the spontaneous and thyrotropin-releasing hormone (TRH)-stimulated release of thyrotropin (TSH) by the anterior pituitary gland (AP) in vitro; and [2] the in vivo effects of T3 and ovarian steroids on TRH-release in vitro. In the experiment 1, ovariectomized-thyroidectomized (Ovx-Tx) rats were injected with triiodothyronine (T3, 2 micrograms/kg), estradiol benzoate (EB, 25 micrograms/kg), progesterone (P, 10 mg/kg), T3 plus EB, T3 plus P, EB plus P, or T3 plus EB and P for 6 days before decapitation. The AP was incubated with Locke's medium, challenged with TRH (30 nM), recovered and then with T3 (10 nM) only or with T3+TRH, 30 min for each interval. Mediobasal hypothalami (MBHs) were challenged with high potassium (60 mM) for 30 min. In the experiment 2, the APs of Ovx-Tx rats were enzymatically dispersed and the AP cells were pretreated with or without EB (0-6 nM) for 72 h, and further with T3 (10 nM) for 24 h, followed by an incubation for 30 min with TRH (0-100 nM). The spontaneous and TRH-induced release of TSH in vitro from rat APs, and pituitary TSH content were increased by T3, or T3 plus P as compared with the animals injected with vehicle, or P alone. EB inhibits the effect of T3 on TSH release in vitro. Application of T3 in vitro prevented the release of TSH in response to TRH. EB dose-dependently relieved the inhibitory effect of T3 on TRH-induced TSH release in vitro. TRH release from MBH was increased by EB and inhibited by T3 or P. EB prevented the inhibitory effect of T3 on TRH release. P plus T3 potentiated the stimulatory effects of EB on TRH release. These results suggest that [1] the reduction of the concentration of plasma TSH by T3 is at least in part due to the inhibitory effects of T3 on TRH release from mediobasal hypothalamus, and TSH release in response to TRH, [2] the increased content and release of TSH from rat AP tissue by T3 via an in vivo effect may be involved in a short feedback loop of TSH on TRH release, and [3] ovarian steroid hormones play an inhibitory role in regulating T3 effects on the release of TSH and TRH.

Inhibition of bufalin on pituitary and testicular function in rats

The effects of bufalin on the secretion of testosterone and luteinizing hormone (LH) and the accumulation of testicular adenosine 3':5'-cyclic monophosphate (cAMP) were studied. Male rats were injected with bufalin, human chorionic gonadotropin (hCG), gonadotropin releasing hormone (GnRH), hCG plus bufalin or GnRH plus bufalin via a jugular catheter. Blood samples were collected at several intervals subsequent to the challenge. In the in vitro study, rat testis blocks were incubated with bufalin, hCG or both for 1 h. The anterior pituitary gland was incubated with bufalin, GnRH or both for 30 min. The media were analyzed for testosterone or LH. For studying cAMP accumulation, testicular blocks were incubated for 1 h with the medium containing isobutyl-1-methylxanthine. After incubation, tissues were extracted by ethanol before measuring cAMP concentration. A single intravenous injection of bufalin decreased the basal and hCG-stimulated levels of plasma testosterone. Administration of bufalin in vitro resulted in an inhibition of both basal and hCG-stimulated release of testosterone. Bufalin diminished cAMP accumulation in rat testes. However, the basal levels of plasma and medium LH were not altered by bufalin administration. Likewise, the LH response to GnRH was diminished by bufalin administration, both in vivo and in vitro. These results suggest that the inhibition of testosterone production by bufalin is partly caused by a decrease of testicular cAMP accumulation and LH response to GnRH in rats.

The importance of a proper helical structure in the promoter-10 binding region to Bacillus subtilis sigma A structure and function

Two Bacillus subtilis sigA mutants with amino acid substitutions tending to disrupt the structure of the promoter -10 binding helix of B. subtilis sigma A factor were constructed. B. subtilis DB1001 which contained an A197P substitution was very sensitive to temperature elevation. B. subtilis DB1002 had a T199G substitution and was low in growth potential at the elevated temperature. Degradation of sigma A in B. subtilis DB1001 (t(1/2)=63.2 min) and DB1002 (t(1/2)=186.0 min) occurred readily even at 37 degrees C; however, sigma A in B. subtilis DB2 (wild-type) was fairly stable at the same temperature. The activities of both DB1001 and DB1002 sigma A factors on groE promoter (sigma A-type) were lower than those of the wild-type counterpart at both permissive and restrictive temperatures. The failure of a higher sigma A concentration to suppress the Ts phenotype of DB1001 indicated that the temperature sensitivity of B. subtilis DB1001 was due to altered function, rather than insufficient concentration, of sigma A in the cells. Taken together, our results suggest that the helicity of the promoter -10 binding helix is essential to the packing interaction in the hydrophobic core region of sigma A, which helps to maintain the stable and functional sigma A structure.

The role of cyclic AMP production, calcium channel activation and enzyme activities in the inhibition of testosterone secretion by amphetamine

1. The aim of this study was to investigate the mechanism by which amphetamine exerts its inhibitory effect on testicular interstitial cells of male rats. 2. Administration of amphetamine (10(-12)-10(-6) M) in vitro resulted in a dose-dependent inhibition of both basal and human chorionic gonadotropin (hCG, 0.05 iu ml(-1))-stimulated release of testosterone. 3. Amphetamine (10(-9) M) enhanced the basal and hCG-increased levels of adenosine 3':5'-cyclic monophosphate (cyclic AMP) accumulation in vitro (P<0.05) in rat testicular interstitial cells. 4. Administration of SQ22536, an adenylyl cyclase inhibitor, decreased the basal release (P<0.05) of testosterone in vitro and abolished the inhibitory effect of amphetamine. 5. Nifedipine (10(-6) M) alone decreased the secretion of testosterone (P<0.01) but it failed to modify the inhibitory action of amphetamine (10(-10)-10(-6) M). 6. Amphetamine (10(-10)-10(-6) M) significantly (P<0.05 or P<0.01) decreased the activities of 3beta-hydroxysteroid dehydrogenase (3beta-HSD), P450c17, and 17-ketosteroid reductase (17-KSR) as indicated by thin-layer chromatography. (t.l.c.). 7. These results suggest that increased cyclic AMP production, decreased Ca2+ channel activity and decreased activities of 3beta-HSD, P450c17, and 17-KSR are involved in the inhibition of testosterone production induced by the administration of amphetamine.

Interleukin-1 receptor antagonist modulates the progression of a spontaneously occurring IgA nephropathy in mice

Cytokines, such as interleukin-1 (IL-1), may play a key role in the pathogenesis of IgA nephropathy (IgAN). This study was conducted to evaluate the effects of IL-1 receptor antagonist (IL-1ra) in the treatment of a spontaneously occurring experimental IgAN in established phase. ddY mice (12/group) were injected twice daily with 3 mg/kg of IL-1ra, intraperitoneally, for 8 consecutive weeks. The placebo mice were injected with saline only. As normal controls, ddY mice, which were not treated with IL-1ra or saline, were killed at 6 weeks of age. Results showed a significant reduction of proteinuria in the IL-1ra-treated mice, compared with saline-treated mice (urinary albumin/creatinine, 0.24 +/- 0.04 v 0.39 +/- 0.03, P < 0.001). A significant improvement of renal 51Cr-EDTA (ethylenediaminetetra-acetic acid) clearance was observed in the IL-1ra-treated mice (t1/2, 12 +/- 2.7 minutes, compared with saline-treated mice 25 +/- 2.0 minutes, P < 0.001). Similarly, serum levels of creatinine (1.0 +/- 0.4 v 2.4 +/- 0.3 mg/dL, P < 0.001) and urea nitrogen (46 +/- 6 v 58 +/- 2 mg/dL, P < 0.01) were significantly lower in IL-1ra-treated mice than in saline-treated mice. In renal tissue studies, the IL-1ra-treated mice exhibited significantly decreased mesangial cell proliferation, compared with saline-treated mice (P < 0.001), as shown by light and electron microscopy. In addition, the IL-1ra-treated mice showed significantly lower glomerular expression of collagen type IV, fibronectin, laminin, and IL-6 (P < 0.001) than saline-treated mice, although they still showed higher glomerular expression of collagen type IV (P < 0.01), fibronectin (P < 0.01), laminin (P < 0.001), IL-1 (P < 0.001), and IL-6 (P < 0.01) than did normal control mice. Meanwhile, glomerular C3 deposition was significantly lower in IL-1ra-treated mice than in saline-treated mice (P < 0.001). These findings indicate that IL-1ra partially prevented the progression of spontaneously occurring IgAN in this experimental model. Data from these experiments also confirm the pathogenic effects of IL-1 in the established phase of IgAN in ddY mice.

Lactate and the effects of exercise on testosterone secretion: evidence for the involvement of a cAMP-mediated mechanism

The effects of swimming and lactate on the release of testosterone were examined in male rats. During in vivo experiments, male rats were catheterized via the right jugular vein and blood was collected at 0, 10, 15, 30, and 60 min following the exercise, or they were catheterized via the right jugular vein and the left femoral vein and blood was collected at 0, 2, 5, 10, 15, 30, 60, and 120 min after a 10-min infusion at lactate (13 mg.kg-1.min-1). Trunk blood and blood from the testicular vein were also collected after 10 min of swimming or water immersion. In an in vitro experiment, testicular fragments were challenged with lactate (0.01-10 mM) and/or human chorionic gonadotropin (hCG; 0.5 IU.mL-1), and the mediobasal hypothalamus (MBH) was challenged with lactate (8 mM). The post-exercise levels of plasma lactate and testosterone at 10, 15, and 30 min were higher than resting levels. Plasma luteinizing hormone (LH) was increased following 30 min of swimming. Administration of lactate or hCG increased in a dose dependent manner testicular cyclic adenosine 3':5' monophosphate (cAMP) and testosterone release. Plasma testosterone increased after swimming and lactate infusion. Incubation of MBH with lactate increased the gonadotropin-releasing hormone (GnRH) level in the medium. These results suggest that the increased plasma testosterone levels in male rats during exercise is at least partially a result of a direct and LH-independent stimulatory effect of lactate on the secretion of testosterone by increasing testicular cAMP production. Swim-elevated plasma LH may be a result of a rise of GnRH caused by lactate.

Normal data for lumbar spine bone mineral content in healthy Chinese men

The aim of this study was to evaluate the influence of age on bone mineral density (BMD) of teh lumbar spine for health Chinese men. In 430 healthy Chinese men (ages 20-92 years) living on Taiwan, BMD at the level of the 2nd to 4th lumbar vertebraes (L2-L4) was determined with a commercial dual-energy X-ray absorptiometer (DXA). Our study found that the peak BMD value of lumbar spines of healthy Chinese men was 1.056 +/- 0.127 g/cm2 which occurs from age 20 to 29. The results show that a linear correlation between the age and BMD of lumbar vertebraes for healthy Chinese is notable. Only slight decreases of BMD values in the different age groups are found. In comparison with the normal data of white men and Asian men from Japan and Korea, the mean BMD values of lumbar spines of Chinese men seem to be lower than those of the white, Japanese, and Korean men of the same ages. Our findings indicate that the influence of age and ethnicity may exist in the BMD values for healthy Chinese males.

Role of radioisotope penile plethysmography in the evaluation of penile hemodynamics in impotent patients

Nineteen impotent patients were included in the study. Radioisotope penile plethysmography using technetium-99m-labelled RBC was performed on each patient before and after intracavernosal injection of prostaglandin E1 (PGE1) for quantitating the penile hemodynamic change. The peak penile blood flow (PPF) and penile blood volume change (dPV) were evaluated. The results revealed that (a) the PPF values (mean 2.24 +/- 1.38 ml/min) of all patients were lower than that of the patients with no arterial changes previously reported, and (b) there was good correlation between PPF and dPV (r = 0.75). We conclude that quantitative radioisotope penile plethysmography coupled with intracavernosal injection of PGE1 is a valuable method for the objective evaluation of the penile erectile response of impotent patients, and that the PPF values of the impotent patients with arterial insufficiency might be a reliable parameter of penile volume change.

Cytohesin-1, a cytosolic guanine nucleotide-exchange protein for ADP-ribosylation factor

Cytohesin-1, a protein abundant in cells of the immune system, has been proposed to be a human homolog of the Saccharomyces cerevisiae Sec7 gene product, which is crucial in protein transport. More recently, the same protein has been reported to be a regulatory factor for the alphaLbeta2 integrin in lymphocytes. Overexpression of human or yeast ADP-ribosylation factor (ARF) genes rescues yeast with Sec7 defects, restoring secretory pathway function. ARFs, 20-kDa guanine nucleotide-binding proteins initially identified by their ability to stimulate cholera toxin ADP-ribosyltransferase activity and now recognized as critical components in intracellular vesicular transport, exist in an inactive cytosolic form with GDP bound (ARF-GDP). Interaction with a guanine nucleotide-exchange protein (GEP) accelerates exchange of GDP for GTP, producing the active ARF-GTP. Both soluble and particulate GEPs have been described. To define better the interaction between ARF and Sec7-related proteins, effects of cytohesin-1, synthesized in Escherichia coli, on ARF activity were evaluated. Cytohesin-1 enhanced binding of 35S-labeled guanosine 5'-[gamma-thio]triphosphate [35S]GTP[gammaS] or [3H]GDP to ARF purified from bovine brain (i.e., it appeared to function as an ARF-GEP). Addition of cytohesin-1 to ARF3 with [35S]GTP[gammaS] bound, accelerated [35S]GTP[gammaS] release to a similar degree in the presence of unlabeled GDP or GTP[gammaS] and to a lesser degree with GDP[betaS]; release was negligible without added nucleotide. Cytohesin-1 also increased ARF1 binding to a Golgi fraction, but its effect was not inhibited by brefeldin A (BFA), a drug that reversibly inhibits Golgi function. In this regard, it differs from a recently reported BFA-sensitive ARF-GEP that contains a Sec7 domain.

Gastric emptying and gastrointestinal transit during lactation in rats

Female sex hormones can influence gastrointestinal function. To understand whether postpartum changes in female sex hormones may affect such function, gastric emptying and gastrointestinal transit were measured in rats on days 1-2, 10, 15, and 21 of lactation, on day 7 postweaning, and at the nonpregnant diestrous stage. Gastric emptying and gastrointestinal transit were assessed in conscious rats 15 min after intragastric instillation of a test meal containing charcoal and (51)Cr. The results showed that gastric emptying was increased throughout the first 2 wk of lactation, with a gradual decrease as lactation proceeded toward weaning, and returned to the level of the virgin rats by 1 wk postweaning. Gastrointestinal transit was greater in the early stage of lactation and was related to gastric emptying (P < 0.001). Increases in gastric emptying and intestinal length were correlated with lactation (P < 0.001) and plasma prolactin levels (P < 0.05) but not with plasma progesterone or estradiol levels. We concluded that the sex steroid hormones associated with lactation do not mediate a change in gastric emptying and gastrointestinal transit during lactation.

Epidural dexamethasone reduces the incidence of backache after lumbar epidural anesthesia

We performed a prospective, randomized, double-blind study to compare the effect of epidural dexamethasone on the incidence of postepidural backache after nonobstetric surgery. One thousand unpremedicated ASA physical status I or II patients scheduled for hemorrhoidectomy were randomly assigned to two groups: Group I patients received 25 mL 2% lidocaine with epinephrine 1:200,000 and 1 mL dexamethasone (5 mg) epidurally. Patients were interviewed at 24,48, and 72 h postoperatively using a standard visual analog scale (VAS) for evaluation of postepidural backache. A patient was considered to have postepidural backache when the postoperative VAS score was higher than the preoperative score. The incidence of postepidural backache in Group I patients for the 3 days were 22.8%, 17.4%, and 9.2%, all of which were significantly more frequent than observed in Group II patients (7.4%,5.6%, and 2.8%, P < 0.01). The severity and duration of postepidural backache were also significantly decreased in Group II patients. In our study, there was a significant association between postepidural backache and multiple attempts at epidural needle insertion. In summary, epidural dexamethasone reduced the incidence and severity of postepidural backache.

Inhibition of corticosterone secretion by thyroxine in male rats

The effects of thyroxine (T4) on the secretion of corticosterone both in vivo and in vitro in male rats were studied. Rats were thyroidectomized (Tx) or sham Tx. The Tx rats were subcutaneously with T4 (20 micrograms/kg) or saline once daily for two weeks. In an in vitro experiment, adrenal glands were incubated with ACTH, T4, or ACTH plus T4 in the presence or absence of 0.5 mM 3-isobutyl-1-methylxanthine (IBMX) at 37 degrees C for 60 min. Medium and ether-extracted plasma samples were analyzed for corticosterone by radioimmunoassay (RIA). The accumulation of cyclic adenosine monophosphate (cAMP) in adrenal tissues after incubation with IBMX was measured by RIA. The levels of plasma corticosterone in Tx rats were significantly increased as compared with euthyroid rats. T4 replacement in Tx rats restored plasma corticosterone to euthyroid level. Administration of T4 in vitro resulted in an inhibition of both basal and ACTH-stimulated release of corticosterone. Both basal and ACTH-stimulated generations of cAMP in adrenal tissues were decreased by T4. These results suggest that T4 inhibits the spontaneous and ACTH-stimulated secretion of corticosterone by acting directly at adrenal glands via a decrease in cAMP production.

Mouse RAD50 has limited epitopic homology to p53 and is expressed in the adult myocardium

Previous studies have identified a 180-kDa mouse cardiomyocyte phosphoprotein with limited epitopic homology to p53. In this study, the protein was purified and partially sequenced. Oligonucleotide probes based on the available amino acid sequence data were used to isolate cDNA clones. Sequence analyses revealed that the clones encoded a protein with regional homology to the yeast RAD50 gene product. Expression of the mouse cDNA rescued the methyl methanesulfonate-sensitive phenotype in rad50 mutant yeast, indicating that the cardiomyocyte phosphoprotein is the mammalian homologue of the yeast RAD50 gene product. Fluorescence in situ hybridization analyses localized the mouse RAD50 gene to the A5-B1 region of chromosome 11. Northern blot analyses demonstrated a complex pattern of RAD50 expression during mouse development which was further complicated by the presence of several alternatively spliced transcripts. High levels of RAD50 expression was evident in the adult myocardium, a somewhat surprising observation given the absence of DNA synthesis in adult cardiomyocytes.

Isolation of a brefeldin A-inhibited guanine nucleotide-exchange protein for ADP ribosylation factor (ARF) 1 and ARF3 that contains a Sec7-like domain

Brefeldin A (BFA) inhibited the exchange of ADP ribosylation factor (ARF)-bound GDP for GTP by a Golgi-associated guanine nucleotide-exchange protein (GEP) [Helms, J.B. & Rothman, J.E. (1992) Nature (London) 360, 352-354; Donaldson, J.G., Finazzi, D. & Klausner, R.D. (1992) Nature (London) 360, 350-352]. Cytosolic ARF GEP was also inhibited by BFA, but after purification from bovine brain and rat spleen, it was no longer BFA-sensitive [Tsai, S.-C., Adamik, R., Moss, J. & Vaughan, M. (1996) Proc. Natl. Acad. Sci. USA 93, 305-309]. We describe here purification from bovine brain cytosol of a BFA-inhibited GEP. After chromatography on DEAE-Sephacel, hydroxylapatite, and Mono Q and precipitation at pH 5.8, GEP was eluted from Superose 6 as a large molecular weight complex at the position of thyroglobulin (approximately 670 kDa). After SDS/PAGE of samples from column fractions, silver-stained protein bands of approximately 190 and 200 kDa correlated with activity. BFA-inhibited GEP activity of the 200-kDa protein was demonstrated following electroelution from the gel and renaturation by dialysis. Four tryptic peptides from the 200-kDa protein had amino acid sequences that were 47% identical to sequences in Sec7 from Saccharomyces cerevisiae (total of 51 amino acids), consistent with the view that the BFA-sensitive 200-kDa protein may be a mammalian counterpart of Sec7 that plays a similar role in cellular vesicular transport and Sec7 may be a GEP for one or more yeast ARFs.

Effect of aging on erythropoietin secretion in male rats

The secretion of erythropoietin (EPO) and testosterone in response to hypoxia in old (22-25 months), middle (mid)-aged (15-17 months), adult (6-7 months), and young (3 months) male rats was studied. Rats of different ages were bled by cardiac puncture before and subsequent to 8 h exposure to 12% O2. The metabolic clearance rate of EPO was determined by a single-injection method. The effects of orchidectomy and replacement of testosterone propionate on plasma EPO concentrations were also investigated. Analysis of the direct effects of testosterone on EPO release from kidney tissue was carried out in an in vitro study. Both basal and hypoxia-induced EPO levels were lower in old rats than in mid-aged, adult, and young rats (p < .01). Plasma testosterone levels decreased in response to hypoxia in all rats (p < .01 for young, adult, and mid-aged rats, and p < .05 for old rats). The old rats also had lower plasma testosterone levels following hypoxia when compared with other rats (p < .05). The metabolic clearance rate of EPO was not affected by age. Orchidectomy decreased rat plasma EPO concentration (p < .05). This decrease could be restored to intact levels after testosterone propionate replacement. Both 10(-10) M (p < .05) and 10(-9) M (p < .01) testosterone stimulate EPO release from kidney tissue in vitro. Our findings indicate that the basal levels of plasma EPO and testosterone are decreased, and the hypoxia-induced EPO is also diminished with aging in male rats. These data suggest that the mechanism of tolerance to hypoxia and the endocrine function of the kidneys in male rats during the aging process are testosterone-dependent.

Lactate stimulates progesterone secretion via an increase in cAMP production in exercised female rats

The effect of exercise on the production of ovarian progesterone was examined in female rats. During in vivo experiments, diestrous rats were catheterized via the right jugular vein (RJV), and blood samples were collected before and after 10, 15, 30, and 60 min of swimming. In addition, blood samples were collected from the RJV before and 2, 5, 10, 15, 30, 60, and 120 min after 10 min of infusion of lactate (13 mg.kg-1.min-1) through the left femoral vein. To explore if lactate modulates progesterone secretion by acting directly on rat ovary or on anterior pituitary gland (AP), an in vitro experiment that mimicked the in vivo condition was performed. The ovarian tissue was challenged with lactate (0.01-10 mM) or porcine follicle-stimulating hormone (1 microgram/ml) and 3-isobutyl-1-methylxanthine (1 mM) for 60 min, and the AP was challenged with lactate ranging from 0.1 to 10 mM or 10 nM gonadotropin-releasing hormone for 30 min. The postexercise levels of plasma glucose, lactate, and progesterone at 10, 15, and 30 min were significantly higher than the corresponding basal levels. Plasma luteinizing hormone (LH) did not change after exercise. An elevation of plasma lactate and progesterone was found at 15 and 30 min subsequent to 10 min of infusion of lactate. Lactate ranging from 0.01 to 10 mM significantly increased ovarian adenosine 3',5'-cyclic monophosphate (cAMP) and progesterone production in a dose-dependent manner. LH concentration in plasma was not changed subsequent to lactate infusion. LH level in media samples was not altered after incubation of AP with lactate. These results suggest that the increase of plasma progesterone level in rats during exercise is independent of LH secretion and at least in part is due directly to a stimulatory effect of lactate on the production of ovarian cAMP.

Comparison of bone mineral density between athletic and non-athletic Chinese male adolescents

For the evaluation of the effect of exercise on bone mineral density of adolescent athletes, twenty-nine Chinese male adolescent athletes, each of whom had regular training in his major sport which included baseball, swimming, judo and middle/long-distance running for one to six years and eight age-matched non-athletic controls were included in this study. Bone mineral density (BMD) was measured in all study subjects using dual photo absorptiometry at the second to fourth lumbar spines (L2-4) and the right femoral neck (FN). The results revealed the following: (1) the combined group of athletes had significantly greater BMD of L2-4 (1.08 +/- 0.09 g/cm2) than the control group (0.99 +/- 0.08 g/cm2) and a tendency for greater BMD of FN (1.15 +/- 0.13 g/cm2) than the control group (1.09 +/- 0.13 g/cm2); (2) judo majors had significantly greater BMD of L2-4 than baseball majors (P < 0.05), swimming majors (P < 0.01), track majors (P < 0.05) and controls (P < 0.005); (3) baseball majors had significantly greater BMD of L2-4 than controls (P < 0.05) and greater BMD of FN than swimming majors (P < 0.05), judo majors (P < 0.05), track majors (P < 0.005) and controls (P < 0.005); (4) body weight and body mass index (BMI) had good correlation with BMD of L2-4 and FN in control group, (5) in the combined group of athletes, weight and BMI were only strongly linked to BMD of FN, and not to BMD of L2-4. There was no good correlation between BMI and BMD of L2-4 and FN in any group of athletes. We concluded that (1) physical activity during adolescence may contribute significantly towards increasing BMD of athletes and (2) the training type may provide a specific stimulus for increasing BMD at specific localized sites experienced in training.

Abnormal gastric emptying and Helicobacter pylori infection in patients with cirrhosis of the liver

Thirty-seven patients aged 36-75 years with cirrhosis of the liver secondary to chronic hepatitis were included in the study. They were divided into three groups according to the modified Child's classification for cirrhotic severity, where A = good, B = fair and C = poor. In addition, the patients were divided according to the presence or absence of each of the following: ascites, splenomegaly and oesophageal varices. Radionuclide-labelled solid meals were used to evaluate gastric emptying and the 14C-urea breath test was used to detect Helicobacter pylori infection. Gastric emptying was represented by the gastric retention ratio of the solid meal at 90 min (RR90) and calculated using the following formula: the residual radioactivity within the region of interest (ROI) covering the whole stomach at 90 min divided by the initial radioactivity within the ROI at 0 min. We found that 75.7% (28/37) of the patients had abnormal gastric emptying and 45.9% (17/37) had H. pylori infection. No significant correlation was found between abnormal gastric emptying and H. pylori infection. There were no significant differences among the three groups regarding gastric emptying or H. pylori infection according to the modified Child's classification. However, the highest rates of abnormal gastric emptying and H. pylori infection were in patients in Child's class C. The differences in RR90 among patients with and without ascites, and patients with and without splenomegaly, were not significant (P > 0.05). However, there was a significant difference between the patients with and without oesophageal varices (P < 0.05). In addition, poor correlations (R2 < 0.01) were found between RR90 and serum levels of bilirubin and albumin.