The mechanism of yohimbine-induced renin release in the conscious rat

Summary These studies were designed to determine the role of the central nervous system, the sympathetic nervous system, the adrenal glands and the renal sympathetic nerves in yohimbine-induced renin release in conscious rats. Yohimbine (0.3–10 mg/kg, s.c.) caused time- and dose-related increases in plasma renin activity (PRA) and concentration (PRC) which were accompanied by time- and dose-related elevations of plasma norepinephrine (NE) and epinephrine (Epi) concentrations. Significant positive correlations were found between the increases in PRA and the increases in plasma NE and Epi concentrations caused by yohimbine, and propranolol (1.5 mg/kg, s.c.) blocked 90% of yohimbine (3 mg/kg, s.c.)-induced renin release. Over the entire spectrum of doses of yohimbine, the increases in PRA and plasma NE and Epi concentrations were positively correlated with the decreases in mean arterial pressure (MAP), but the -intercept was positive in every case and the 1 mg/ kg dose of yohimbine consistently increased PRA independent of any change in MAP. Complete renal denervation, as evidenced by a greater than 90% reduction in renal NE content, did not alter the increase in PRA caused by yohimbine (3 mg/kg, s.c.). An increase in circulating plasma catecholamine concentrations appeared to mediate yohimbine-induced renin release since propranolol prevented the rise in PRA caused by yohimbine in renal denervated rats. Prior adrenalectomy (Adx) also failed to prevent the rise in PRA produced by yohimbine (3 mg/kg, s.c.), but a combination of Adx and renal denervation caused a significant impairment of yohimbine-induced renin release. However, neither Adx alone nor the combination of Adx and renal denervation affected the increase in plasma NE concentration caused by yohimbine. Complete transection of the spinal cord at C₈ caused a drastic reduction in plasma catecholamine concentrations but did not change basal PRC. Yohimbine (3 mg/kg, s.c.) did not increase PRC or plasma catecholamine concentrations after spinal transection. Based on these results, we conclude that 1) the stimulation of renin release by yohimbine is a secondary neurohormonal consequence of the generalized increase in sympathetic activity caused by yohimbine, 2) the sympathoadrenal activation produced by yohimbine results from an action in the brain which is amplified by the simultaneous blockade of prejunctional ₂-adrenoceptors and 3) vasodepressor effects of the larger doses yohimbine cause a baroreflexly-mediated increase in sympathetic activity which interacts in a positive fashion with the central and peripheral sympathoexcitatory effects of yohimbine. Send offprint requests to T. K. Keeton     

Formation of cyclic 1,N2-propanodeoxyguanosine and thymidine adducts in the reaction of the mutagen 2-bromoacrolein with calf thymus DNA

The interaction of the mutagen 2-bromoacrolein (2BA) with DNA and thymidine was studied in vitro by reaction of [3-3H]2BA with thymidine, RNA, single-stranded DNA, and double-stranded DNA in phosphate buffer (pH 7.4). After purification of the nucleic acids, they were incubated at alkaline pH to convert any (hydroxybromo)propano(deoxy)-guanosine adducts to their dihydroxy analogues. After acid or enzymatic hydrolysis, the hydrolysates were analyzed by reversed-phase high-performance liquid chromatography. At a concentration of 1.6 mM, the fraction of 2BA that became covalently bound to DNA was 2.3% of the amount added. Only 3% of the radioactivity bound to DNA after extensive purification could be accounted for as cyclic 1,N2-(6,7-dihydroxy)-propanoguanine adducts. More 2BA became covalently bound to single-stranded DNA and RNA as compared with double-stranded DNA. However, high-performance liquid chromatographic analyses showed that formation of cyclic 1,N2-(6,7-dihydroxy)propanoguanine adducts was also a minor reaction with these macromolecules. Because these data showed that other type(s) of reaction(s) are more important in the reaction of 2BA with nucleic acids, we have investigated the reaction of 2BA with other nucleosides. It was found that 2BA reacted well with thymidine in vitro, and the major product was identified by 500 MHz 1H and 75.43 MHz 13C nuclear magnetic resonance and thermospray mass spectrometry as 3-(2"-bromo-3"-oxopropyl)thymidine. This adduct was unstable and decomposed upon storage. After enzymatic hydrolysis of [3H]2BA-modified double-stranded DNA and subsequent analysis of the hydrolysate by high-performance liquid chromatography, 22% of the covalently bound radioactivity to DNA coeluted with decomposition products of the 3-(bromooxypropyl)thymidine adduct. This indicates that reaction of 2BA with this nucleotide in DNA is a major reaction.     

'Breaking' position-invariant object recognition

While it is often assumed that objects can be recognized irrespective of where they fall on the retina, little is known about the mechanisms underlying this ability. By exposing human subjects to an altered world where some objects systematically changed identity during the transient blindness that accompanies eye movements, we induced predictable object confusions across retinal positions, effectively 'breaking' position invariance. Thus, position invariance is not a rigid property of vision but is constantly adapting to the statistics of the environment.     

Reflex increases in heart-rate induced by perfusing the hind leg of the rat with solutions containing lactic acid

The hypothesis that metabolic receptors in skeletal muscle influence heart-rate during exercise was tested by means of a perfused preparation of the rat's hind legs. The isolated leg was connected to the body only by nerve and bone and was perfused with tyrode solution. The humoral changes of exercise were simulated by perfusing with modified tyrode solutions in which concentration of K⁺, osmolality, concentrations of lactic acid, and inorganic phosphate were changed to reflect to those occurring during heavy exercise. Only perfusion with a solution enriched with lactic acid elicited a significant increase in heart-rate. The response disappeared when the nerve supply to the leg was cooled or sectioned. 20–60 s after the start of perfusion with solution of high [lactic acid] heart-rate began to increase reaching a maximum ( ± SE = 20.2 ± 8.2,n = 7) after about 2 min. The effect on heart-rate increased when the venous concentration of lactic acid was increased the range from 3 to 10 mmol/l. In further experiments, we tried to separate the effects of pH and lactate. Heart-rate responses were induced only at low pH and at low pH the extent to which heart-rate changed increased with increases in lactate concentration.     

Diuretic treatment and serum lipoproteins: Effects of tienilic acid and indapamide

Summary Treatment with the commonly used diuretic, chlorthalidone, has previously been found to increase the serum low-density-lipoprotein cholesterol (LDL-C) fraction. Therefore, the effects of two new agents, tienilic acid (a combined diuretic-uricosuric) and indapamide on serum lipid and lipoprotein levels were assessed. Six weeks of treatment with tienilic acid, 250 mg/day, markedly decreased serum uric acid and significantly increased LDL-C and triglycerides in 16 men. In contrast, indapamide 2.5 mg/day, had no apparent influence on serum lipids or lipoproteins in 18 men.Supported in part by the Swiss National Science Foundation     

2Mouse PAI-1 promotes placentation by increasing foetal and maternal angiogenesis

Introduction: Murine placentation is associated with trophoblast cells invasion of the maternal endometrium and extensive maternal and foetal angiogenesis. Both processes involve proteases‐dependent extracellular matrix remodelling. Among the protease inhibitors, plasminogen activator inhibitor‐1 (PAI‐1) is transiently produced by spongiotrophoblasts and trophoblast giant cells at days 10.5‐11.5 day post‐coitum (dpc). Although accumulating evidence demonstrates the key role of PA‐1 in pathological angiogenesis, its function during placental vascularisation remains to be elucidated. PAI‐1 knockout mice are fertile and the litter sizes are normal. We have therefore analysed the consequence of PAI‐1 deficiency on murine placentation. Material and Methods: We have studied the possible role of PAI‐1 by quantitating the placental vessel density, the relative thickness of the labyrinth, decidua and spongiotrophoblast at day 10.5, 12.5 and 14.5 dpc in mice deficient for PAI‐1 or in control mice. An original method of computer‐assisted image analysis allowed us to quantify alterations of several placental compartments identified with specific monoclonal antibodies (keratin, desmin, fibrinogen and MECA‐32). To investigate the differentially expressed genes, we performed laser capture microdissection (LCM), followed by genome‐wide expression profiling using high‐density oligonucleotides microarray analysis (GeneChip Mouse Genome 430 2.0 Array, Affymetrix). Data were analysed using Ingenuity Pathways Analysis (Ingenuity Systems^®, http://www.ingenuity.com ). Results: At 10.5 and 12.5 dpc, an abnormal placental morphology was observed in both labyrinth and spongiotrophoblast layers in PAI‐1‐/‐ mice. Lack of PAI‐1 resulted in a transient decreased maternal and fetal vascularisation of the placenta that caused (1) an enhancement in the decidua/labyrinth and labyrinth/spongiotrophoblast thickness ratios, (2) a significant increase of trophoblast density. Normalization of placental morphology occurred by day 14.5 dpc in PAI‐1 deficient mice. Statistical analysis of microarrays revealed 706 genes differentially expressed between PAI‐1 deficient and normal mice in the labyrinth zone at 10.5 dpc. At 14.5 dpc, only 205 genes are differentially expressed. Using Ingenuity Pathways Analysis, most of those genes were found to be associated to lipid metabolism, cellular growth and proliferation. Conclusion: Despite a transient PAI‐1 requirement for optimal placental angiogenesis, this gene does not appear to be essential for trophoblast invasion and placentation.     

Reliability and validity of the Biodex system 3 pro isokinetic dynamometer velocity,torque and position measurements

This study quantitatively assessed the mechanical reliability and validity of position, torque and velocity measurements of the Biodex System 3 isokinetic dynamometer. Trial-to-trial and day-to-day reliability were assessed during three trials on two separate days. To assess instrument validity, measurement of each variable using the Biodex System 3 dynamometer was compared to a criterion measure of position, torque and velocity. Position was assessed at 5° increments across the available range of motion of the dynamometer. Torque measures were assessed isometrically by hanging six different calibrated weights from the lever arm. Velocity was assessed (30°/s to 500°/s) across a 70° arc of motion by manually accelerating the weighted lever arm. With the exception of a systematic decrease in velocity at speeds of 300°/s and higher, the Biodex System 3 performed with acceptable mechanical reliability and validity on all variables tested.DisclosureThe Biodex dynamometer used for this investigation was donated to the laboratory by Biodex Medical Systems. The authors have no commercial or proprietary interest in this device.