bluuebunny/crossref_metadata_2025 huggingface dataset:
MECHANISMS OF IMPAIRMENT OF ENDOTHELIUM‐DEPENDENT RELAXATION TO ACETYLCHOLINE IN WATANABE HERITABLE HYPERLIPIDAEMIC RABBIT AORTAS
Authors: Kagota Satomi , Yamaguchi Yu , Shinozuka Kazumasa , Kunitomo Masaru
Published: June 2007

1. The mechanism of impairment of the endothelium‐dependent relaxation in response to acetylcholine (ACh) in aortas from Watanabe heritable hyperlipidaemic (WHHL) rabbits was investigated using a modified sandwich (layered) technique. Intact aortas from WHHL rabbits or Japanese white (JW) rabbits as the control were used as donor strips of endothelium‐derived relaxing factor (EDFU?) and endothelium‐denuded aortas from JW rabbits were used as detector strips. The EDRF released from a donor strip could be directly detected as the relaxation response in a detector strip.

2. The endothelium‐dependent relaxations in all rabbit arteries were almost abolished by treatment with NG‐nitro‐l‐arginine methyl ester (an inhibitor of nitric oxide synthase).

3. The ACh‐induced endothelium‐dependent relaxations in the donor strips were impaired in WHHL rabbits in comparison with relaxations in JW and heterozygous WHHL rabbits. Similarly, the relaxation in the detector strips induced by EDRF released from donor strips was reduced in WHHL rabbits. There was a good negative correlation between the aortic total cholesterol content in the donor strips and the degree of relaxation in the detector strips from WHHL rabbits.

4. The reduced relaxation in the detector strips when using donor strips with high cholesterol accumulation or atheromatous plaque was not affected by superoxide dismutase plus catalase (scavengers of superoxide anions), indomethacin (an inhibitor of cyclo‐oxygenase), ONO‐3708 (an antagonist of endoperoxide/ thromboxane receptor) and 97–139 (an antagonist of endothelin ETA receptor).

5. These results suggest that the mechanism of impaired endothelium‐dependent relaxations in atherosclerotic WHHL rabbit aortas may be due to the reduced amount of EDRF, probably nitric oxide, from the endothelium and not due to its inactivation by oxygen‐derived free radicals or masking by increased production of endothelium‐derived contracting factors.
A PRIMING DOSE OF PROPRANOLOL REDUCES THE AVAILABILITY OF A SUBSEQUENT DOSE IN THE ISOLATED PERFUSED RAT LIVER PREPARATION
Authors: Ghabrial Hany , Sewell Richard B. , Smallwood Richard A. , Morgan Denis J.
Published: June 2007

1. A 50 μL bolus dose containing (±)‐propranolol hydrochloride (200 μg) and [14C]‐sucrose, or antipyrine (2 mg) and [14C]‐sucrose, or [14C]‐taurocholate sodium was injected into the portal vein of the isolated perfused rat liver preparation and perfusate outflow samples were collected frequently for the next 30min. After a 20 min washout period this procedure was repeated.

2. [14C]‐Sucrose, antipyrine and [14C]‐taurocholate each eluted as a single peak at 18, 31 and 28 s, respectively, after each dose. In contrast, propranolol eluted with two peaks at approximately 18 and 128 s after dosing.

3. There was no significant difference in dose‐corrected area under the outflow curve (AUC) for [14C]‐sucrose, antipyrine or [14C]‐taurocholate between the first and second doses whereas the mean propranolol AUC for the second dose was only 0.577 ± 0.439 that for the first dose (P <0.05).

4. Unmetabolized propranolol accounted for more than 80% of the drug in hepatic tissue for the first and second doses at 18 s and greater than 50% at 128 s, and there was no significant difference in these values at each time between the first and second doses.

5. These findings suggest that for an avidly extracted drug, such as propranolol, systemic availability of orally administered drug will be highly dependent on factors that influence the hepatic tissue binding of the drug.
PHOSPHODIESTERASE IV INHIBITORS SYNERGISTICALLY POTENTIATE RELAXATION INDUCED BY FORSKOLIN IN GUINEA‐PIG TRACHEA
Authors: Tanizawa Makoto , Watanabe Takako , Kurne Hiroaki , Yarnaki Kenichi , Miyamoto Kenichi , Takagi Kenzo
Published: June 2007

1. β‐Adrenoceptor receptor agonists are the principal bronchodilator agents used in the treatment of bronchial asthma. However, the regular use of β‐adrenoceptor agonists in asthmatic patients is likely to increase asthma severity because of a defective β‐adrenoceptor function. Bronchodilators that bypass this defective function are therefore needed.

2. Our objectives in this study were: (i) to assess the effects of an agent that directly activates adenylate cyclase (forskolin) on guinea‐pig tracheal smooth muscle; (ii) to study the interactions between selective cyclic nucleotide phosphodiesterase (PDE) inhibitors and forskolin by measuring isometric tension; and (iii) to compare these results with the interaction between PDE inhibitors and terbutaline, a β‐adrenoceptor agonist.

3. The relaxant effects of forskolin alone, which is now under development as a new bronchodilator for bronchial asthma therapy, were slightly weaker than those of terbutaline on guinea‐pig tracheal smooth muscle.

4. Both denbufylline and Ro 20–1724, cyclic nudeotide PDEIV inhibitors, synergistically increased the relaxant effects of forskolin and terbutaline, while other PDE isozyme inhibitors (amrinone, vinpocetine and zaprinast) had only a minor influence.

5. In conclusion, a good synergistic interaction between forskolin and PDE IV inhibitors, especially denbufylline, may provide a means for bypassing β‐adrenoceptors. Thus, the combination of forskolin and PDE inhibitors would become useful in the treatment of bronchial asthma.
ROLE OF NITRIC OXIDE IN THE DEVELOPMENT OF CORTICOTROPIN‐INDUCED HYPERTENSION IN SHEEP
Authors: Tresham JJ , May CN
Published: June 2007

1. The possibility that altered synthesis of vascular nitric oxide (NO) plays a role in the development of corticotropin‐induced hypertension in sheep was examined by determining the effect of concomitant infusion of L‐arginine, a precursor of NO, on the development of the hypertension.

2. Corticotropin (5 μg/kg per h) infused over 2 days increased mean arterial pressure (MAP) from 83 ± 4 to 99 ± 4 mmHg in five conscious sheep. Concomitant infusion of L‐arginine (60 mg/kg per h) did not alter this response; infusion of L‐arginine alone had no effect on blood pressure.

3. The dose of L‐arginine (60 mg/kg per h) used blocked the rise in MAP (+16 mmHg) in response to a 5 h infusion of N‐nitro‐L‐arginine (1 mg/kg per h).

4. These findings suggest that disruption of NO synthesis does not play a role in the development of corticotropin hypertension in sheep.
ACUTE EFFECTS OF ORAL GLIBENCLAMIDE ON BLOOD PRESSURE AND FOREARM VASCULAR RESISTANCE IN DIABETICS
Authors: Sundaresan Purnima , Lykos Denise , Daher Ali , Morris Richard , Diamond Terence , Howes Laurence G.
Published: June 2007

1. To determine the effects of an acute oral dose of glibenclamide on blood pressure (BP), basal forearm vascular resistance (FVR) and FVR responses to the K+atp channel activating vasodilator diazoxide, a placebo‐controlled, double‐blind cross‐over study was performed in eight male volunteers with non‐insulin‐dependent diabetes mellitus.

2. Changes in vascular responses to progressively increasing concentrations of diazoxide (3.75–30 mg/kg per min) and nor‐adrenaline (25–100 ngkg per min) were measured by venous occlusion plethysmography.

3. Glibenclamide significantly lowered plasma glucose levels compared with placebo (P < 0.02) and attenuated the decrease in FVR (P < 0.05) and the decrease in systolic BP (P < 0.05) that followed a meal. However, vasodilator responses to diazoxide were potentiated by the administration of oral glibenclamide (P < 0.01).

4. Acute administration of oral glibenclamide attenuates the normal decrease in FVR and systolic BP that follows a meal and potentiates rather than inhibits forearm vasodilator responses to intra‐arterial diazoxide, probably via indirect humoral effects. These results suggest that glibenclamide has direct or indirect vasoconstrictor effects that antagonize the normal increase in forearm blood flow that follows a meal and that the inhibition of vascular K+ atp channels following acute oral glibenclamide administration is clinically insignificant compared with other indirect vascular effects of the drug.
VASORELAXATION OF RAT THORACIC AORTA CAUSED BY 14‐DEOXYANDROGRAPHOLIDE
Authors: Zhang CY , Tan BKH
Published: June 2007

1. The pharmacological effects of 14‐deoxyandrographolide on rat isolated thoracic aorta were examined.

2. 14‐Deoxyandrographolide (2.5‐120 μmiol/L) inhibited contractions induced by phenylephrine (PE; 0.1 μmol/L) and high K+ (80mmol/L) in a concentration‐dependent manner in endothelium‐intact aorta. The effect was attenuated in endo‐thelium‐denuded aorta without modifying the maximal response. Like verapamil, 14‐deoxyandrographolide produced a much greater vasorelaxant effect in aorta precontracted by KCI than by PE. 14‐Deoxyandrographolide (20‐60 μmol/L) also inhibited responses of the rat aorta to PE.

3. In Ca2+‐free medium (KCI 55mmol/L), 14‐deoxyandrographolide (20‐80 μmol/L) antagonized Ca2+‐induced vasocon‐traction in a concentration‐dependent manner and transient contractions induced by both caffeine (10mmol/L) and noradrenaline (1μmol/L) were suppressed or almost abolished by 14‐deoxyandrographolide.

4. The vasorelaxant effect of 14‐deoxyandrographolide was partially antagonized by NG‐nitro‐L ‐arginine methyl ester (25 μmol/L), a specific and competitive nitric oxide synthase (NOS) inhibitor, and methylene blue (10 μmol/L), a soluble guanylate cyclase inhibitor, but was not affected by indomethacin (20 μmol/L), a cyclo‐oxygenase inhibitor, or glibenclamide (10 μmol/L), an ATP‐sensitive K+‐channel blocker.

5. These results suggest that the vasorelaxant activity of 14‐deoxyandrographolide may be mediated via the activation of NOS and guanylate cyclase, as well as the blockade of Ca2+ influx through both voltage‐ and receptor‐operated Ca2+ channels.
TIME‐DEPENDENT CYCLOSPORINE A‐INDUCED NEPHROTOXICITY IN RATS
Authors: Yamauchi Hitoshi , Kobayashi Eiji , Sugimoto Koh‐ichi , Tsuruoka Shuichi , Yabana Machiko , Ishii Masao , Fujimura Akio
Published: June 2007

1. We investigated the toxicity of cyclosporine A (CsA) with reference to the timing of its administration in rats.

2. To elucidate the time‐dependent effects of CsA on renal function and survival rate, CsA (75 mg/kg per day) or vehicle was orally administered once daily at four different times (3,9, 15 and 21 h after lights on; HALO) over a period of 21 days to male Wistar rats (n= 56) kept in rooms with a 12 h light‐dark cycle.

3. On the 7th day after treatment, creatinine clearances (Ccr) of groups dosed at 3 and 9 HALO (inactive period) were not reduced in comparison with clearances of time‐matched control rats, whereas Ccr significantly decreased in rats dosed at 15 and 21 HALO (active period). Cyclosporine A markedly increased urinary N‐acetyl‐β‐D‐glucosaminidase (NAG) excretion in all dosed groups at the 7th day after treatment, except for rats dosed at 3 HALO. In rats dosed at 3 HALO, Ccr decreased progressively; however, it did not decrease progressively in rats dosed at 9 HALO. In surviving rats treated during the inactive period, urine NAG subsequently returned to control levels. Survival rates were greater in animals dosed during inactive periods than those in groups dosed during active periods.

4. Significant differences in CsA‐induced toxicity were obvious as a result of the timing of its administration. A different time course between Ccr and urine NAG excretion was observed during repeated CsA administration. Degenerative changes in proximal tubules were demonstrated after chronic administration of CsA, suggesting that severe and persistent tubular damage cannot be assessed by urinary NAG excretion.
IDENTIFICATION OF CARDIOVASCULAR PATHWAYS IN THE SYMPATHETIC NERVOUS SYSTEM
Authors: Anderson CR
Published: June 2007

1. Sympathetic autonomic neurons show distinct patterns of expression of a range of neurochemicals that can be detected immunohistochemically. Often, functionally homologous neurons in the autonomic nervous system express identical combinations of substances that serve as a chemical code that allows them to be identified among other autonomic neurons.

2. In the rat stellate ganglion, where many neurons express either immunoreactivity (IR) to neuropeptide Y (NPY) or the calcium‐binding protein calbindin, a population of large postganglionic neurons found along the medial border of the stellate ganglion, around the origin of the cardiac nerves, expressed intense IR to both substances at all ages examined, from early postnatal to adult.

3. In the heart, in the first few postnatal weeks, many nerve terminals were IR for both NPY and calbindin, but, with increasing age, calbindin‐IR was progressively lost from NPY‐IR terminals. Nerve terminals IR for both calbindin and NPY were not seen around pulmonary blood vessels or in the trachea or the thymus.

4. Nerve terminals IR for calretinin, another calcium‐binding protein, were present in dense pericellular baskets around neurons in the stellate IR for both calbindin and NPY. The terminals also contained nitric oxide synthase (NOS)‐IR.

5. It is suggested that the calbindin‐ and NPY‐IR neurons in the stellate ganglion are the post‐ganglionic neurons that innervate the heart and that the nerve terminal containing calretinin and NOS‐IR that surround them are the cardiac preganglionic terminals. It thus appears possible, in the rat, to identify the sympathetic cardiac pathway arising in the spinal cord and controlling the heart purely on the basis of chemical coding.
NICOTINE EXCITES CARDIAC VAGAL NEURONS VIA THREE SITES OF ACTION
Authors: Mendelowitz David
Published: June 2007

1. Nicotine is involved in many cardio‐respiratory diseases, including hypertension and sudden infant death syndrome (SIDS), which is the most common cause of death in infants between 1 month and 1 year of age. While the aetiology of SIDS remains largely unknown, recent clinical studies suggest maternal cigarette smoking is a major risk factor in SIDS and an abnormality of cardio‐respiratory control, particularly a centrally mediated slowing of the heart that precedes or accompanies apnoea, is involved.

2. Because the sites, mechanisms of action and diverse receptor types of nicotine within the central nervous system are controversial and poorly understood, in the present study we examined the effects of nicotine on specific brainstem neurons that control heart rate. Cardiac vagal neurons were identified in anin vitroslice preparation using a retrograde fluorescent tracer and were studied using both whole‐cell and perforated patch‐clamp electrophysiological techniques.

3. We have found there are different pre‐ and post‐synaptic nicotinic receptors that have dramatic effects on glutamatergic neurotransmission as well as directly activating vagal cardio‐inhibitory neurons.
FUNCTIONAL SIGNIFICANCE OF THE 10 Hz RHYTHMIC DISCHARGES IN SYMPATHETIC NERVES
Authors: Kishi Erika , Ootsuka Youichirou , Rong Weifang , Terui Naohito
Published: June 2007

1. By measuring renal vascular conductance in anaesthetized and immobilized rabbits, the functional significance of the 10 Hz rhythmic discharges in the sympathetic nerves was assessed by electrical stimulation of the renal nerve. This stimulation mimicked the intermittently occurring 10 Hz rhythmic discharges.

2. Comparison of high‐frequency (10‐20 Hz) intermittent electrical stimulation with continuous low‐frequency (5 Hz) stimulation showed that the intermittent high‐frequency stimulation evoked faster (smaller time constant) and larger responses of the renal vascular conductance if the total number of stimulus pulses was the same.

3. Therefore, the intermittently occurring 10 Hz rhythmic discharges in the sympathetic nerve produces faster and larger effects on peripheral organs than effects produced by continuous discharges if the number of spikes is equal.
ROLE OF NITRIC OXIDE AND TPEN, A POTENT METAL CHELATOR, IN ISCHAEMIC AND REPERFUSED RAT ISOLATED HEARTS
Authors: Ferdinandy Peter , Appelbaum Yori , Csonka Csaba , Blasig Ingolf E. , Tosaki Arpad
Published: June 2007

1. The role of nitric oxide (NO) was studied in the control of ischaemic/reperfused cardiac function and the effect of N, N, N', N'‐tetrakis‐[2‐pyridylmethyl]‐ethylenediamine(TPEN), a potent metal chelator, on the regulation of cardiac NO formation.

2. Rat isolated working hearts were subjected to 30 min is‐chaemia and reperfusion. The incidence of reperfusion‐induced ventricular fibrillation (VF), ventricular tachycardia (VT) and the recovery of cardiac function were measured. Nitric oxide was detected by electron spin resonance (ESR) spectroscopy.

3. With 5.0, 7.5 and 10.0 μmol/L of TPEN administered prior to ischaemia, the drug produced a reduction in the incidence of VF from its control value of 100% to 25% (P<0.05), 17% (P<0.05) and 8% (P<0.05), respectively. The incidence of VT followed the same pattern.

4. When TPEN was given at the moment of reperfusion, a reduction in the incidence of VF and VT was still observed. Reduction in the incidence of VF and VT was reflected in the improvement of cardiac function both in the pre‐ and post‐ischaemic TPEN‐treated groups.

5. TPEN reduced basal cardiac NO content and prevented the accumulation of NO during ischaemia/reperfusion.

6. The results show that TPEN exerts beneficial effects on postischaemic cardiac function and dysrhythmias in relation to inhibition of the accumulation of NO in ischaemic/reperfused myocardium.
ACETYLCHOLINE‐INDUCED SYSTEMIC VASODILATION RESISTANT TO NG‐NITRO‐L‐ARGININE IN ANAESTHETIZED RATS
Authors: Kakizoe Eiichi , Wang Dan‐Qiao , Kobayashi Yuta , Shimoura Keiko , Okunishi Hideki
Published: June 2007

1. The effects of NG‐nitro‐L‐arginine (l‐NNA; 20mg/kg bodyweight (BW), i.v.) and metyrapone (300 mg/kg BW, s.c.) on acetylcholine (ACh)‐induced depressor responses were investigated in anaesthetized rats.

2. Acetylcholine (0.05,0.5,5 μg/kg BW, i.v.) dose‐dependently evoked a sharp fall in mean blood pressure (BP) followed by a slow recovery under control conditions.

3. Basal BP level was elevated when rats were treated with l‐NNA, indicating endogenous nitric oxide (NO) participated in BP regulation. However, pretreatment with l‐NNA did not attenuate but rather augmented the ACh‐induced maximum vasodilation. In contrast, the time for recovery of mean BP to the pre‐ACh administration level was shortened by l‐NNA. These observations suggested that ACh‐induced vasodilation consisted of two phases: a sharp and transient fall (phase 1) that was resistant to l ‐NNA followed by a longer depressor response (phase 2) that was suppressed by l‐NNA.

4. To examine whether augmentation of phase 1 by l‐NNA resulted from the elevation of basal BP, an appropriate dose of phenylephrine was infused to obtain similar BP elevation. Phenylephrine infusion augmented the phase 1 in a similar manner to l‐NNA pretreatment but showed little effect on phase 2, supporting the selective inhibition of phase 2 by l‐NNA.

5. The s.c. pretreatment with metyrapone for 3 days failed to attenuate phase 1. Thus, the involvement of endothelium‐derived hyperpolarizing factor that could be formed by a metyrapone‐sensitive oxidase in phase 1 was unlikely.

6. These results suggest that some factor(s), which is not inhibitable by l‐NNA or metyrapone, may induce the phase 1 depressor response to ACh while NO is responsible for the phase 2 response. The mechanism inducing the phase 1 response remains to be identified.
PRECONDITIONING IMPROVES MYOCARDIAL FUNCTION AND REFLOW, BUT NOT VASODILATOR REACTIVITY, AFTER ISCHAEMIA AND REPERFUSION IN ANAESTHETIZED DOGS
Authors: Loke Kit E. , Woodman Owen L.
Published: June 2007

1. The present study examines whether three cycles of brief coronary artery occlusion and reperfusion (i.e. ischaemic preconditioning; PC) can prevent vasodilator dysfunction and the impairment of myocardial reflow caused by prolonged ischaemia. Coronary blood flow, left ventricular dP/dt, systemic arterial blood pressure and heart rate were measured in open‐chest anaesthetized dogs.

2. Sixty minute occlusion of the left circumflex coronary artery (LCx) and 60 min LCx reperfusion (ISC/REP; group 1) significantly reduced resting coronary blood flow (CBF, initial 29±3mL/min; ISC/REP 20±3mL/min, P<0.05 vx initial) and increased coronary vascular resistance (CVR, initial 4.1±0.6 mmHg/min per mL; ISC/REP 5.8±1.0 mmHg/min per mL, P<0.05 vs initial). By contrast CBF and CVR were not affected in dogs subjected to preconditioning before ischaemia (group 2: CBF, initial 24±4mL/min; PC+ISC/REP 23±4mL/min; CVR, initial 4.7±0.6 mmHg/min per mL; PC+ ISC/REP 5.3±1.0 mmHg/min per mL). These data suggest that ischaemic preconditioning prevents the ischaemia‐induced impairment of myocardial reflow.

3. Ischaemia and reperfusion impaired coronary dilator responses to the endothelium‐dependent dilator acetylcholine (ACBF, after ISC/REP: 50±6% of initial) and the endothelium‐independent dilator glyceryl trinitrate (ΔCBF, ISC/REP: 46±6% of initial). Despite the improvement in reperfusion in the preconditioned group, there was no significant improvement in responses to acetylcholine (PC+ISC/REP 52±6% of initial) or glyceryl trinitrate (PC+ISC/REP 59±6% of initial) after ischaemia and reperfusion.

4. The reduction in left ventricular dP/dt after ischaemia and reperfusion was significantly smaller in the preconditioned group indicating a lower level of impairment of cardiac contractility. In addition, we confirmed that preconditioning caused a significant reduction in infarct size and a reduction in the release of lactate dehydrogenase indicating less cardiac injury.

5. These results suggest that although ischaemic preconditioning was able to improve both myocardial reperfusion and contractility, it was not able to preserve vasodilator function. Such a reduction in vasodilator reserve could prevent adequate myocardial perfusion under conditions of elevated oxygen demand.
EFFECTS OF AMLODIPINE AND NIFEDIPINE RETARD ON AUTONOMIC NERVE ACTIVITY IN HYPERTENSIVE PATIENTS
Authors: Minami Junichi , Ishimitsu Toshihiko , Kawano Yuhei , Matsuoka Hiroaki
Published: June 2007

1. The effects of 1,4‐dihydropyridine calcium antagonists with different biological half‐lives, amlodipine and nifedipine retard on 24 h blood pressure (BP), heart rate (HR) and autonomic nerve activity in patients with essential hypertension were compared.

2. Twenty patients (six men and 14 women; mean (±SEM) age 63±2 years) with essential hypertension were enrolled in the present study. Their ambulatory BP and electrocardiograms were monitored for 24 h at intervals of 30 min with a portable recorder after a 4 week drug‐free period, after a 4 week treatment period with amlodipine (2.5 or 5 mg once daily) and after a 4 week treatment period with nifedipine retard (10 or 20 mg twice daily). The order of the three periods was randomized. Autonomic nerve activity was evaluated by power spectral analysis of HR variability, using the high frequency (HF) component as an index of parasympathetic activity and the ratio of the low frequency (LF) to the HF component as an index of sympathovagal balance.

3. Amlodipine and nifedipine retard significantly lowered the 24 h BP to a similar extent (amlodipine: −12.7±2.6/−5.6±1.4mmHg, P<0.01/P<0.01; nifedipine retard: −15.1±2.1/−6.9+1.5 mmHg, P<0.01/<P0.01). Amlodipine did not change the 24 h average HR, while nifedipine retard significantly increased it (+3.3±1.2 b.p.m., P<0.05). Amlodipine also did not change the HF component or the ratio of the LF to the HF component. However, nifedipine retard significantly decreased the HF component (P<0.01) and increased the ratio of the LF to the HF component (P<0.05).

4. These results suggest that nifedipine retard caused a decrease in parasympathetic activity and an increase in sympathetic activity with reflex tachycardia in these patients with essential hypertension, while amlodipine did not produce such effects on the autonomic nervous system.
INHIBITORY EFFECT OF ALDOSTERONE ON THE NATRIURETIC RESPONSE TO ATRIAL NATRIURETIC PEPTIDE IN HYPOCAPNIC RATS
Authors: Kanauchi Hajime , Mimura Yoshikazu
Published: June 2007

1. Previous studies have shown that acute hypocapnia blunts the natriuretic effect of atrial natriuretic peptide (ANP) independently of the renal nerves and that the effect of ANP is restored by total adrenalectomy. We investigated the natriuretic response to ANP in potassium canrenoate (aldosterone receptor antagonist)‐treated rats to clarify whether aldosterone contributes to the attenuated natriuretic response to ANP during hypocapnia.

2. Wistar rats, challenged with either canrenoate or saline vehicle, were infused with 10 μg/kg per h ANP during acute hypocapnia achieved by mechanical ventilation.

3. In saline‐treated hypocapnic rats, ANP infusion failed to increase the fractional excretion of sodium (FENa) (from 3.49± 0.26 to 5.03±0.42%, respectively; n= 6) which was similar to values for time control rats (from 3.00±0.61 to 4.41±0.68%; n= 6). The hyporesponsiveness to ANP during hypocapnia was also evident when the FENa was compared with that of normocapnic rats (from 3.92±0.69 to 7.87±0.45%; P < 0.05; n= 6). In canrenoate‐treated rats, ANP infusion caused greater increases in sodium excretion (FENA from 3.05±0.71 to 7.21±0.45%; P < 0.05; n= 8) than saline infusion (FENa from 4.16± 1.11 to 5.47±0.66%; n= 6), despite the hypocapnia. The increase in FENa after ANP infusion during hypocapnia (4.16±0.86%) was similar to the increase seen during normocapnia (3.89±0.86%; n= 9).

4. In conclusion: (i) acute hypocapnia blunts the natriuretic effects of ANP; and (ii) this attenuation is restored by potassium canrenoate treatment. The data suggest that aldosterone plays an important role by limiting the renal actions of ANP during acute hypocapnia.
INHIBITION OF CARDIAC BAROREFLEX SENSITIVITY AFTER CENTRAL DOPAMINERGIC STIMULATION
Authors: van den Buuse Maarten , Wilks David P. , Cornish Jennifer L.
Published: June 2007

1. Stimulation of the mesolimbic dopamine system, by microinjection of the substance P analogue [pGlu5, MePhe8, Sar9]sub‐stance P (DiMe‐C7) into the ventral tegmental area induced a prolonged increase in blood pressure and circulating levels of vasopressin.

2. In the present study, this treatment produced a significant decrease of cardiac baroreflex sensitivity in conscious rats. After pretreatment with the dopamine receptor antagonist raclopride, central stimulation failed to produce any changes in baroreflex parameters.

3. The central dopamine‐mediated decrease in baroreflex sensitivity may be involved in functionally potentiating the circulatory actions of vasopressin.
A LINKAGE AND CROSS‐SECTIONAL STUDY OF HYPERTENSION AND OBESITY USING A POLY(A) Alu‐REPEAT POLYMORPHISM AT THE GLUCAGON RECEPTOR GENE LOCUS (17q25)
Authors: Rutherford S. , Boatwright SD , Samwell GA , Morris BJ , Griffiths LR
Published: June 2007

1. Previous glucagon receptor gene (GCGR) studies have shown a Gly40Ser mutation to be more prevalent in essential hypertension and to affect glucagon binding affinity to its receptor. An Alu‐repeat poly(A) polymorphism colocalized to GCGR was used in the present study to test for association and linkage in hypertension as well as association in obesity development.

2. Using a cross‐sectional approach, 85 hypertensives and 95 normotensives were genotyped using polymerase chain reaction primers flanking the Alu ‐repeat. Both hypertensive and normotensive populations were subdivided into lean and obese categories based on body mass index (BMI) to determine involvement of this variant in obesity. For the linkage study, 89 Australian Caucasian hypertension affected sibships (174 sib‐pairs) were genotyped and the results were analysed using genehunter, Mapmaker Sibs, erpa and splink (all freely available from http://linkage.rockefeller.eduVsoft/list.html).

3. Cross‐sectional results for both hypertension and obesity were analysed using Chi‐squared and Monte Carlo analyses. Results did not show an association of this variant with either hypertension (X2= 6.9, P= 0.14; Monte Carlo X2= 7.0, P= 0.11; n= 5000) or obesity (X2= 3.3, P= 0.35; Monte Carlo X2= 3.26, P= 0.34; n= 5000). In addition, results from the linkage study using hypertensive sib‐pairs did not indicate linkage of the poly(A) repeat with hypertension. Hence, results did not indicate a role for the Alu‐repeat in either hypertension or obesity. However, as the heterozygosity of this poly(A) repeat is low (35%), a larger number of hypertensive sib‐pairs may be required to draw definitive conclusions.
EFFECTS OF LONG‐TERM EXTRARENAL ANGIOTENSIN II INFUSION ON RENAL VASCULAR RESPONSIVENESS TO VASOACTIVE AGENTS
Authors: Fitzgerald Sharyn M. , Stevenson Kathleen M. , Evans Roger G. , Anderson Warwick P.
Published: June 2007

1. We tested whether chronic intrarenal angiotensin II (AngH) infusion altered renal vascular responsiveness to vasoactive agents, which would provide evidence of vascular structural changes.

2. The renal blood flow (RBF) responses to renal arterial administration of bolus doses of acetylcholine, glyceryl trinitrate, AngH and noradrenaline were measured before commencement of and 1 day after cessation of 28 days intrarenal Angll infusion (0.5 ng/kg per min) in chronically instrumented conscious dogs.

3. The RBF responses to these vasoactive agents were unaltered by chronic intrarenal Angll infusion in conscious dogs.

4. These functional studies provide no evidence for renal vascular hypertrophy in response to chronic intrarenal Angll infusion in conscious dogs.
SPECIAL ARTICLE: NON‐INVASIVE MEASUREMENT OF ENDOTHELIAL FUNCTION
Authors: Playford DA , Watts GF
Published: June 2007

1. Endothelial dysfunction, due to reductions in nitric oxide (NO) action, is an early feature of macrovascular disease.

2. Non‐invasive measurement of endothelial function may be assessed by postischaemic dilatation of forearm vessels, using plethysmography, or flow‐mediated dilatation of the brachial artery, using ultrasound.

3. Brachial flow‐mediated dilatation reflects NO release and/or action more than forearm hyperaemia.

4. These techniques have been used as surrogate measures of coronary endothelial function.

5. Methodological, physiological and clinical aspects of the techniques are discussed.
EFFECTS OF NITRIC OXIDE SYNTHASE INHIBITION AND ENDOTHELIN ETA RECEPTOR BLOCKADE ON HAEMODYNAMICS IN HYPERTENSIVE RATS
Authors: Granstam S‐O , Lind L. , Granstam E. , Fellström B.
Published: June 2007

1. The objectives of the present study were to study regional differences in haemodynamics between spontaneously hypertensive (SHR) and normotensive Wistar‐Kyoto (WKY) rats induced by the nitric oxide synthase (NOS) inhibitor NG‐monomethyl ‐l‐arginine (l‐NMMA) and the endothelin ETA receptor antagonist BQ123 in vivo in tissues known to be important for blood pressure (BP) regulation (heart, kidney and skeletal muscle). Furthermore, the effect of acetylcholine (ACh) infusion (2 μg/kg per min) was examined after l‐NMMA or BQ 123. The microsphere method was used for determinations of cardiac index (CI) and regional haemodynamics.

2. NG‐Monomethyl‐l‐arginine (20mg/kg) increased BP (26–48%; P < 0.01) and reduced CI in both rat strains. BQ 123 (1 mg/kg) reduced BP slightly (‐4 to 11 %; P < 0.05).

3. NG ‐Monomethyl‐l‐arginine significantly increased myocardial and skeletal muscle vascular resistance in SHR only; however, in the kidney, l‐NMMA reduced blood flow and increased vascular resistance in both rat strains.

4. BQ 123 induced minor changes in regional haemodynamics that were not significantly different between the two strains.

5. Acetylcholine following BQ123 induced an increase in myocardial blood flow in WKY rats, but decreased blood flow in SHR. Acetylcholine following l‐NMMA reduced myocardial blood flow in both strains.

6. Acetylcholine following BQ 123 induced renal vasodilation in WKY rats but, following l‐NMMA, ACh did not induce renal vasodilation in either rat strain. In contrast, l‐NMMA did not abolish the vasodilation of acetylcholine in skeletal muscle in WKY rats.

7. In conclusion, the contribution of nitric oxide to basal vessel tone was not impaired in the heart, skeletal muscle and kidney in SHR. Antagonism of ETA receptors caused similar haemodynamic responses in both rat strains in these organs. Furthermore, NOS inhibition, but not ETA blockade, blunted the expected ACh‐induced vasodilation in the heart and kidney in WKY rats, but not in skeletal muscle in both strains.
EMBRYONIC GLOBINS OF THE MARSUPIAL THE TAMMAR WALLABY (MACROPUS EUGENII): BIRD LIKE AND MAMMAL LIKE
Authors: Holland Robert AB , Gooley Andrew A. , Hope Rory M.
Published: June 2007

1. Tammar Wallaby embryonic blood has been shown to have three α‐like and two β‐like globin chains in its four haemoglobin components and partial sequences of several chains have been determined.

2. The major embryonic β‐like chain (ɛ) is similar to other mammalian embryonic p‐like chains on the basis of sequencing its first 60 amino acids.

3. There is another embryonic β‐like chain present in one haemoglobin component. It was designated to and, in its first 54 amino acids, it has features that are more like avian globins than mammalian globins.

4. The one α‐like embryonic globin sequenced has mammalian rather than avian characteristics.

5. A provisional phylogenetic tree of β‐like globins has been determined. The Tammar ω‐globin forms a monophyletic group with marsupial and other mammalian embryonic globins; the to‐globin forms a monophyletic group with bird adult and embryonic globins.
STUDIES OF EVOLUTIONARY TEMPERATURE ADAPTATION: MUSCLE FUNCTION AND LOCOMOTOR PERFORMANCE IN ANTARCTIC FISH
Authors: Franklin Craig E.
Published: June 2007

1. Studies of evolutionary temperature adaptation of muscle and locomotor performance in fish are reviewed with a focus on the Antarctic fauna living at subzero temperatures.

2. Only limited data are available to compare the sustained and burst swimming kinematics and performance of Antarctic, temperate and tropical species. Available data indicate that low temperatures limit maximum swimming performance and this is especially evident in fish larvae.

3. In a recent study, muscle performance in the Antarctic rock cod Notothenia coriiceps at 0°C was found to be sufficient to produce maximum velocities during burst swimming that were similar to those seen in the sculpin Myoxocephalus scorpius at 10°C, indicating temperature compensation of muscle and locomotor performance in the Antarctic fish. However, at 15°C, sculpin produce maximum swimming velocities greater than N. coriiceps at 0°C.

4. It is recommended that strict hypothesis‐driven investigations using ecologically relevant measures of performance are undertaken to study temperature adaptation in Antarctic fish. Recent detailed phylogenetic analyses of the Antarctic fish fauna and their temperate relatives will allow a stronger experimental approach by helping to separate what is due to adaptation to the cold and what is due to phytogeny alone.
MOLECULAR AND STRUCTURAL BIOLOGY OF THYROID HORMONE RECEPTORS
Authors: Apriletti James W. , Ribeiro Ralff CJ , Wagner Richard L. , Feng Weijun , Webb Paul , Kushner Peter J. , West Brian L. , Nilsson Stefan , Scanlan Thomas S. , Fletterick Robert J. , Baxter John D.
Published: June 2007

1. Thyroid hormone receptors (TR) are expressed from two separate genes (α and β) and belong to the nuclear receptor superfamily, which also contains receptors for steroids, vitamins and prostaglandins.

2. Unliganded TR are bound to DNA thyroid hormone response elements (TRE) predominantly as homodimers, or as heterodimers with retinoid X‐receptors (RXR), and are associated with a complex of proteins containing corepressor proteins. Ligand binding promotes corepressor dissociation and binding of a coactivator.

3. Recent studies from our group have focused on the acquisition and use of X‐ray crystallographic structures of ligand‐binding domains (LBD) of both the rat (r) TRα and the human (h) TRβ bound to several different ligands. We have also developed ligands that bind selectively to the TRβ, which may provide ways to explore the differential functions of TRα compared with TRβ isoforms.

4. The LBD is comprised mostly of α‐helices. The ligand is completely buried in the receptor and forms part of its hydrophobic core. Kinetic studies suggest that the limiting step in formation of high‐affinity ligand‐receptor complexes is the rate of folding of the receptor around the ligand. Ligands can be fitted tightly in the ligand‐binding pocket and small differences in this fitting may explain many structure‐activity relationships. Interestingly, analysis of the structures of antagonists suggests that they have chemical groups, ‘extensions', that could impair receptor folding around them and, thus, prevent the agonist‐induced conformation changes in the receptor.

5. The TR structures allowed us to see that the mutations that occur in the syndrome of generalized resistance to thyroid hormone are located in the vicinity of the ligand‐binding pocket.

6. X‐ray structure of the TR has also been used to guide construction of mutations in the TR surface that block binding of various proteins important for receptor function. Studies with these TR mutants reveal that the interfaces for homo‐ and heterodimerization map to similar residues in helix 10 and 11 and also allow the definition of the surface for binding of coactivators, which appears to be general for nuclear receptors. Formation of this surface, which involves packing of helix 12 of the TR into a scaffold formed by helices 3 and 5, appears to be the major change in the receptor structure induced by hormone occupancy.
DEVELOPMENTAL BIOLOGY AT THE HOWARD FLOREY INSTITUTE
Authors: Beck Felix
Published: June 2007

1. A brief account of the history of developmental biology at the Howard Florey Institute, as well as in a wider general context, is presented and some of the results of developmental studies performed at the Institute over the past 7 years are discussed.

2. In the foetal rat, parathyroid hormone rather than parathyroid hormone‐related protein is produced by the parathyroid anlage. This contrasts with results reported by others for the sheep.

3. The control of imprinting of H19 and insulin‐like growth factor‐II has been studied in the mouse using gene knockout of the coding region of the H19 gene. Bi‐allelic expression of H19 in some liver and gut cells was observed.

4. Gene knockout of the homeobox gene Cdx2 produced dramatic effects. Homozygous embryos did not implant in the uterus. Heterozygotes exhibited homeosis involving the gut and skeleton. Animals developed intestinal tumours within a few weeks of birth.
ALDOSTERONE ACTION: FACT, FAILURE AND THE FUTURE
Authors: Funder John W.
Published: June 2007

1. It is now 45 years since aldosterone was isolated and 25 years since its genomic action, via mineralocorticoid receptors (MR), was first described.

2. Although the classic physiological role of aldosterone is to promote unidirectional transepithelial sodium transport, our ignorance of the mechanisms involved remains profound.

3. Unanswered questions include: (i) the physiological significance of the equivalent, high affinity of MR for aldosterone, progesterone, corticosterone and Cortisol; (ii) the protein(s) induced as a direct transcriptional response to aldosterone; (iii) the physiological roles of MR in non‐epithelial tissues where aldosterone, in concert with salt loading, produces direct pathophysiological effects; (iv) how aldosterone occupies epithelial MR, despite the 100‐fold ‘advantage’ it enjoys over cortisol/corti‐costerone due to transcortin binding/11β‐hydroxysteroid dehydrogenase activity, as plasma glucocorticoid levels are approximately 2000‐fold higher; and (v) how epithelial MR, normally overwhelmingly occupied by glucocorticoids, are not transcriptionally active under normal circumstances in vivo, in contrast with transfection systems or the syndrome of apparent mineralocorticoid excess.

4. Possible avenues for consideration of the last two of these questions are briefly proposed.
CORTISOL AND HYPERTENSION
Authors: Kelly JJ , Mangos G. , Williamson PM , Whitworth JA
Published: June 2007

1. In humans, the hypertensive effects of adrenocorticotropic hormone (ACTH) infusion are reproduced by intravenous or oral Cortisol. Oral Cortisol increases blood pressure in a dose‐dependent fashion. At a dose of 80–200 mg/day, the peak increases in systolic pressure are of the order of 15mmHg. Increases in blood pressure are apparent within 24 h.

2. Cortisol‐induced hypertension is accompanied by a significant sodium retention and volume expansion. Co‐administration of the type I (mineralocorticoid) receptor antagonist spironolactone does not prevent the onset of cortisol‐induced hypertension. Thus, sodium retention is not the primary mechanism of cortisol‐induced hypertension.

3. Direct and indirect measures of sympathetic activity are unchanged or suppressed during Cortisol administration, suggesting that cortisol‐induced hypertension is not mediated by increased sympathetic tone.

4. Preliminary evidence in humans suggests that suppression of the nitric oxide system may play a role in cortisol‐induced hypertension.

5. These potential mechanisms of Cortisol action may be relevant in a number of clinical contexts, including Cushing's syndrome, apparent mineralocorticoid excess, the hypertension of liquorice abuse and chronic renal failure. There is also preliminary evidence suggesting a role for Cortisol in essential hypertension.
INTERACTION OF CIRCULATING HORMONES WITH THE BRAIN: THE ROLES OF THE SUBFORNICAL ORGAN AND THE ORGANUM VASCULOSUM OF THE LAMINA TERMINALIS
Authors: McKinley MJ , Allen AM , Burns P. , Colvill LM , Oldfield BJ
Published: June 2007

1. Most circulating peptide hormones are excluded from much of the brain by the blood‐brain barrier. However, they do have access to the circumventricular organs (CVO), which lack the blood‐brain barrier. Three of the CVO, the subfornical organ (SFO), organum vasculosum of the lamina terminalis (OVLT) and area postrema, contain neurons responsive to peptides such as angiotensin II (Angll), atrial natriuretic peptide and relaxin.

2. We have studied the patterns of neuronal activation, as shown by Fos expression, in the SFO and OVLT in response to systemically infused AngII, relaxin or hypertonic saline and have found subgroups of neurons activated by the different stimuli.

3. Systemic infusion of relaxin or hypertonic saline activated neurons almost exclusively in the outer regions of the SFO and in the dorsal cap of the OVLT. Many of these neurons send axonal projections to regions of the brain subserving vasopressin secretion and thirst, such as the median preoptic, supraoptic and hypothalamic paraventricular nuclei.

4. At moderate blood concentrations, AngII only stimulates neurons in the inner core of the SFO and lateral regions of the OVLT. Higher levels of AngII in the bloodstream activate additional neurons in the outer parts of the SFO that connect to the supraoptic, paraventricular and median preoptic nuclei and these probably mediate water drinking and vasopressin secretion induced by blood‐borne AngII. The efferent connections and the functions mediated by angiotensin‐sensitive neurons in the inner core of the SFO and lateral part of the OVLT are unknown.
REGULATION OF ALDOSTERONE BIOSYNTHESIS: THE END OF THE ROAD?
Authors: Müller Jürg
Published: June 2007

1. Because aldosterone is the minority hormone of the adrenal cortex, its proper function depends on protective physiological mechanisms. These include a particular site of aldosterone biosynthesis in the zona glomerulosa of the adrenal cortex as well as a complex multifactorial control system, which adapts aldosterone production to acute and chronic changes in body sodium and potassium content, irrespective of pituitary adrenocorticotropic hormone (ACTH) secretion.

2. Over the past decade, an important element of these mechanisms has been identified in the form of the enzyme involved in the final steps of aldosterone biosynthesis. In species such as the human, rat and mouse, the conversion of deoxycorticosterone to aldosterone is catalysed by an isozyme (CYP11B2) of cytochrome P450up (CYP11B1). The gene encoding this enzyme is expressed only in the zona glomerulosa. Its transcription is enhanced by sodium deficiency and potassium intake, but is suppressed by long‐term administration of high doses of ACTH.

3. In contrast, the gene encoding CYP11B1 (i.e. the major (non‐aldosterone‐producing) type of the enzyme) is expressed mainly in the zona fasciculata and its expression depends on physiological concentrations of ACTH.

4. In other animal species (cattle, pig, sheep), the major forms of cytochrome P45011β have an inherent aldosterone‐synthesizing activity, which is, however, selectively suppressed in mitochondria of zona fasciculata cells.

5. The elucidation of the mechanisms involved in this suppression or of those mediating alterations in CYP11B2 expression in response to physiological stimuli may be important areas of future research on the regulation of aldosterone biosynthesis.
ORIGINS OF ZONATION: THE ADRENOCORTICAL MODEL OF TISSUE DEVELOPMENT AND DIFFERENTIATION
Authors: Vinson Gavin P. , Ho Mei Mei
Published: June 2007

1. Although much work has addressed the functional significance of mammalian adrenocortical zonation, less attention has been paid to its developmental origins and the factors that maintain it. Recent concepts of tissue differentiation hold that cells respond to local morphogenic stimuli that are generated in a paracrine manner.

2. In fact, the adrenal cortex represents an ideal mammalian in vivo model for such studies: few others exist. While several components may contribute to the establishment of a developmental polarity in the gland, including products of capsular and neural elements, compelling evidence now suggests that the tissue renin‐angiotensin system (HAS) has a critical role.

3. We have examined the roles of these and other paracrine morphogens and growth factors and of specific transcription factors in adrenocortical cellular proliferation and development. From data obtained by using in situ hybridization to determine their cellular location, we propose a hierarchy of potential tissue modelling agents. These include morphogens, such as angiotensin II derived from the intra‐adrenal RAS, growth factors (e.g. basic fibroblast growth factor), which can be considered to be the paracrine amplifiers of the morphogenic signal, and, finally, transcription factors, such as C‐fos, that directly stimulate mitosis and other events of differentiation.
THE RENIN‐ANGIOTENSIN SYSTEM AND THE DEVELOPMENT OF THE KIDNEY AND ADRENAL IN SHEEP
Authors: Wintour E Marelyn , Alcorn Daine , Albiston Anthony , Boon Wah Chin , Butkus Aldona , Earnest Linda , Moritz Karen , Shandley Lynne
Published: June 2007

1. The earliest form of the kidney, the pronephros, does not really occur in the ovine embryo; instead, a giant glomerulus forms at the anterior end of the mesonephros.

2. In the sheep, the mesonephros is present from 11‐38% of total gestation (150 days) and produces a dilute urine, as well as expressing the genes for erythropoietin, renin, angioten‐sinogen, angiotensin‐converting enzyme and the angiotensin II (AngII) receptors AT1 and AT2.

3. The ovine metanephros begins to develop at 18% of gestation and nephrogenesis is complete several weeks before birth. AH components of the renin‐angiotensin system (RAS) are expressed from at least 27% of gestation.

4. Both AT1 and AT2 receptors are expressed by the adrenocortical cells early in gestation but, at mid‐gestation, exogenous AngII does not stimulate aldosterone secretion in vivo.

5. Preliminary results suggest that Angll has important roles in renal development in the ovine foetus but the role(s), if any, in adrenal development, remains to be investigated.