Long-term administration of NG-nitro-L-arginine methyl ester (L-NAME) induces development of hypertension and hypertrophy of the left ventricle in rats. The aim of the present study was to demonstrate the effect of chronic L-NAME treatment on DNA and RNA concentration, and protein synthesis in the rat heart, aorta, brain and kidney and to determine the effect of angiotensin converting enzyme (ACE) inhibitor captopril on these potential alterations. Four groups of rats were investigated: control, L-NAME (40 mg kg-1 day-1), captopril (100 mg kg-1 day-1), and L-NAME (40 mg kg-1 day-1) + captopril (100 mg kg-1 day-1). NO synthase activity in the heart, aorta, brain and kidney was found to be decreased in the L-NAME group. In the group of rats treated with L-NAME + captopril, captopril did not affect NO synthase inhibition. Captopril, however, completely prevented development of hypertension and left ventricular hypertrophy in this group. In the L-NAME group, DNA and RNA concentrations, as well as [14C]leucine incorporation, were significantly increased in all the tissues investigated. In the L-NAME + captopril group, captopril completely prevented the enhancement of DNA and RNA concentrations and [14C]leucine incorporation in all tissues compared to the L-NAME group. Moreover, a significant decrease in RNA concentration and [14C]leucine incorporation below control values was found in the captopril group as well as the L-NAME + captopril group in all the tissues investigated. We conclude that captopril prevented the development of hypertension and increase in nucleic acid concentration and protein synthesis in the heart, aorta, brain and kidney in rats treated with L-NAME + captopril. However, this protective effect of captopril was not associated with increased NO synthase activity in this model of hypertension.

We have previously shown that extracellular fluid (ECF) is translocated by atrial contraction. Following on from this finding we have proposed a two-step sequential mechanism for the regulation of stretch-activated secretion of atrial natriuretic peptide (ANP): myocytic release of ANP into the surrounding paracellular space followed by the translocation of ECF with the released ANP into the bloodstream. This latter step is induced by atrial contraction, and is therefore controlled by atrial workload. However, the mechanism that regulates the changes in translocation of the ECF has not been defined. To define the relationship between the atrial workload, ECF translocation, size of the extracellular space (ECS) and ANP secretion, experiments have been performed in isolated perfused beating rabbit atria. Atrial workload, transendocardial translocation of the ECF and the secretion of ANP were quantified. Changes in the size of the atrium and the ECS were determined by a newly developed methodology in the beating atria. Atrial workload determined the translocation of the ECF and released ANP with waning of the translocation at higher myocardial workloads. Atrial workload inversely determined the size of the atrium and the ECS. The latter directly determined the translocation of the ECF in terms of atrial workload. From these data we suggest that the size of the ECS is an intimate modulator of the translocation of the ECF and released ANP, and that the phenomenon of waning of the transendocardial translocation that appeared at higher atrial workloads is closely related to the shrinkage of the ECS. Experimental Physiology (2002) 87.2, 185-194.

I guess everyone who is asked to give one of the Physiological Society's Prize Lectures feels honoured, but I feel particularly honoured to have been asked to give the Joan Mott Prize Lecture. I first met Joan Mott in 1980 at the Oxford meeting of the Physiological Society. I had just given a communication on baro- and chemoreceptor influences on the cardiovascular system and she came to introduce herself to me. I was a young lecturer at the time, and still felt a rather junior member of the Society. I had seen Joan Mott at many Physiological Society meetings. I had heard her give communications and had heard her entering into lively discussions after papers, and I knew she was a well respected scientist. I was therefore flattered that she should have come to talk to me about my work. After that we met at many Physiological Society meetings and she always made a point of asking how our research was going and we would talk of common interests. To me this is one of the most important aspects of Physiological Society meetings, that young and older members of the Society can rub shoulders with one a nother and discuss science openly with no barriers. Joan Mott had an influence on me that I have tried to remember as I have become a more senior member of the Society.

The mdx mouse is the most commonly used animal model for Duchenne muscular dystrophy. We tested the null hypothesis that 20 weeks of clenbuterol treatment (∼2 mg kg-1 day-1) of mdx and control mice would have no effect on the absolute and specific force (Po, kN m-2) and absolute and normalised power output (W kg-1) of extensor digitorum longus (EDL) and soleus muscles. For mdx and control mice, clenbuterol treatment produced modest increases in the mass of the two muscles but did not increase absolute or specific force or normalised power output. For absolute power output, only the EDL muscles of mdx mice showed a difference following treatment, with the power output of treated mice being 118 % that of the untreated mice. The modest effects of clenbuterol treatment on the dynamic properties of skeletal muscle provide little support for any improvement in muscle function for the dystrophic condition. Experimental Physiology (2000) 85.3, 295-299.

We postulated that chronic placental insufficiency would be associated with reduced expression of renal renin and angiotensinogen genes in the fetal sheep. Placental development was restricted in ewes by removing the majority of caruncles prior to mating (placentally restricted (PR) group). The weights of PR fetuses were significantly reduced (P < 0.05, 2.98 ± 0.33 kg) compared to control fetuses (4.20 ± 0.30 kg). Kidney weights were also significantly reduced in the PR fetuses (P < 0.05, 8.4 ± 0.9 g) compared with control fetuses (12.2 ± 1.3 g). The ratios of renal renin β-actin mRNA levels were significantly reduced in PR fetuses (P < 0.001, 0.35 ± 0.02) when compared to control animals (0.98 ± 0.13). The renal angiotensinogen mRNA/18S rRNA ratio was significantly lower (P < 0.05, 0.28 ± 0.13) in PR fetuses compared with control fetuses (0.72 ± 0.10), while hepatic angiotensinogen was unaffected. There was a positive correlation between renal renin mRNA and renal angiotensinogen mRNA levels (r = 0.65, P < 0.05, n = 12). It is unlikely that these changes in renal angiotensinogen and renin mRNA were due to the small increment in plasma cortisol levels (< 5 nmol l-1). There was, however, a positive correlation between arterial PO2 and renal renin mRNA (r2 = 0.77, P < 0.01). Plasma renin levels were not different between the two groups. Thus, restriction of nutrient and oxygen supply throughout fetal life was associated with suppression of renal renin and renal angiotensinogen gene expression, with no effect on hepatic angiotensinogen mRNA levels. This specific suppression of fetal renal renin and angiotensinogen expression could alter the activity of the intrarenal RAS and so affect growth and development of the kidney.

Effects of prostaglandin E2 (PGE2) on exocytosis of mucin were studied in mucous cells isolated from guinea-pig antrum using video-microscopy. Stimulation with PGE2 elicited a sustained increase in the frequency of exocytotic events in a dose-dependent manner, which was under regulation by both Ca2+ and cAMP. Stimulation with a selective prostanoid EP4 receptor agonist (ONO-AEI-329, 10 µM), which activates cAMP signals, elicited a sustained increase in the frequency of exocytotic events (30 % of that evoked by 1 µM PGE2). Stimulation with an EP1 agonist (17-P-T-PGE2, 1 µM), which activates Ca2+ signals, increased the frequency of exocytotic events to a lesser extent (5 % of that evoked by 1 µM PGE2), while addition of an EP1 antagonist (ONO-8713, 10 µM) decreased the frequency of exocytotic events (approximately 40 % of that evoked by 1 µM PGE2). However, addition of the EP1 agonist potentiated the frequency of exocytotic events evoked by the EP4 agonist or forskolin (which elevates cAMP levels) and increased the sensitivity of the exocytotic events to forskolin. These results suggest that the Ca2+ signal activated via the EP1 receptor potentiates the cAMP-regulated exocytotic events activated via the EP4 receptor during PGE2 stimulation, by increasing the sensitivity of the exocytotic response to cAMP. In conclusion, exocytotic events in PGE2-stimulated antral mucous cells were regulated by interactions between EP1 and EP4 receptors. Experimental Physiology (2001) 86.4, 451-460.

Growing pigs were fed diets supplying 45 % (low), 70 % (intermediate) and 100 % (high) recommended dietary allowances of calcium (the Ca:P ratio was kept constant), but otherwise adequate in nutrients. The effects of varying calcium and phosphorus intakes on bone and plasma osteocalcin were monitored. Mineral content of the diet did not affect feed conversion and live weight gain. Plasma phosphorus concentrations decreased significantly in pigs fed a low mineral diet compared with those fed the high mineral diet, but there were no changes in plasma calcium and osteocalcin concentrations. Bones from the low mineral group had marked reductions in dry matter, calcium and phosphorus contents, as well as increased collagen, pyridinoline and deoxypyridinoline concentrations: osteocalcin concentrations in bone were unaffected by treatment. The results showed no direct link between osteocalcin and the degree of bone mineralization.

Arterially perfused, decerebrate preparations of the insectivore, Suncus murinus were made to determine whether the emetic reflex could be activated in such a preparation using a range of stimuli shown to be emetic in conscious or anaesthetised Suncus. Efferent phrenic and vagus nerve activities and electromyograms (EMGs) from the temporalis, abdominal oesophagus and trapezius muscles were recorded, as well as longitudinal shortening of the oesophagus and dorso-ventral movements of the thorax. The preparations swallowed spontaneously every 0.6 to 6.5 min. The duration of a swallow was 3.1 ± 0.3 s (recorded as the time taken for the oesophagus to shorten and recover to its resting position) and the oesophagus shortened by 3.5 ± 0.4 mm during a swallow. The emetic reflex was activated by electrical stimulation (30 Hz, 10-20 V, 0.2 ms pulse width, for 30 s) of abdominal vagal afferents (latency < 30 s) or by arterial perfusion with either 40 nM of the capsaicin analogue resiniferatoxin (latency 1.7 ± 0.6 min), 6 µM nicotine (latency 1.6 ± 0.1 min) or 1 µM of the phosphodiesterase IV inhibitor CP-80,633 (latency 8.9 ± 3.9 min). These emetic stimuli produced somatic and visceral movements in Suncus preparations indicative of activation of the emetic reflex. There were pronounced contractions of the thorax that occurred simultaneously with oesophageal shortening and mouth opening, separated by thorax expansion and a burst of phrenic nerve activity. During emetic-like episodes, oesophageal shortenings were only 0.84 ± 0.1 s in duration, faster than the duration of shortening observed during swallowing (cf. swallowing, 3.1 ± 0.3 s; P < 0.0001). The shortening of the oesophagus during emetic-like episodes was 6.2 ± 0.4 mm, which was greater than the shortening seen during swallowing (cf. swallowing, 3.5 ± 0.4 mm; P < 0.0001). We conclude that the emetic reflex can be activated in our Suncus preparations and that this non-sentient small adult animal model can now be used to study the neurophysiology and pharmacology of swallowing and emesis. Experimental Physiology (2002) 87.5, 563-574.

It has previously been postulated that rapid red cell capillary transit through the human lung plays a role in the mechanism of diffusion limitation in some endurance athletes. Methodological limitations currently prevent researchers from directly measuring pulmonary capillary transit times in humans during exercise; however, first pass radionuclide cardiography allows direct measurement of red blood cell (RBC) transit times through the whole lung at various exercise intensities. We examined the relationship between mean whole lung red cell pulmonary transit times (cardiopulmonary transit times or CPTT) and different levels of flow in 88 healthy humans (76 males, 12 females) from several studies (mean age 31 years). The pooled data suggest that the relationship between CPTT and cardiac index (CI), beginning at rest and progressing through to maximum exercise demonstrates that CPTT reaches its minimum value when CI is about 8.1 l m2 min-1 (2.5-3 times the CI value at rest), and does not significantly change with further increases in CI. Cardiopulmonary blood volume (CPBV) index also does not change significantly until CI reaches 2.5 to 3 times the CI value at rest and then increases roughly linearly after that point. Consequently, the systematic increase in CPBV index with increasing pulmonary blood flow between 8.1 and 20 l m2 min-1 displays an adaptive response of the cardiopulmonary system by augmenting CPBV (and perhaps pulmonary capillary blood volume through distension and recruitment) to offset the reduction in CPTT, as no significant difference in mean CPTT is observed between these levels of flow (P > 0.05). Therefore, these data demonstrate that CPBV does not reach maximum capacity during strenuous or maximum exercise. This does not support the principle of quarter-power allometric scaling for flow when explaining modifications during exercise. Therefore, we speculate that the observed relationships between CPTT, CBPV index and flow may prevent mean CPTT (and perhaps mean pulmonary capillary transit times) from decreasing below the threshold time required for oxygenation. Experimental Physiology (2003) 88.2, 191-200.

Pituitary hormones have an important role during exercise yet relatively little is known about the stimulus for their release. Body temperature progressively increases during prolonged steady-state exercise in the heat and we have investigated the role that this may play in the release of prolactin, growth hormone and cortisol (as an indicator of adrenocorticotropic hormone) into the circulation. Fit young male subjects exercised at 73 %O2,max until volitional fatigue at 20 °C and at 35 °C (30 % relative humidity at both temperatures). Rectal temperature and mean skin temperature were monitored and blood samples analysed for lactate, glucose, cortisol, growth hormone and prolactin concentrations. During the first 20 min, core temperature rose continuously and to a similar extent at both temperatures, while mean skin temperature was approximately 4 °C lower during exercise in the cool. Blood glucose concentration was essentially constant throughout the period of exercise while lactate concentration increased in the first 10 min and then remained constant with very similar changes in the two exercise conditions. Prolactin and growth hormone concentrations both increased during the exercise period while the concentration of cortisol declined slightly before rising slightly over the 40 min period. Prolactin release was significantly greater when exercise was carried out in the heat while there was no difference in the release of growth hormone or cortisol in the two conditions. When plotted as a function of rectal temperature, growth hormone concentration showed a linear relationship which was the same at ambient temperatures of 35 °C and 20 °C. Prolactin concentration had a curvilinear relationship with rectal temperature and this differed markedly at the two ambient temperatures. Cortisol concentration showed no dependence on any measure of body temperature. Our results are consistent with some aspect of body temperature being a stimulus for growth hormone and prolactin secretion; however, the precise mechanism clearly differs between the two hormones and we suggest that skin temperature modulates prolactin release, but does not affect the release of growth hormone. Experimental Physiology (2003) 88.5, 627-635.

Bronchoconstriction of small bronchioles plays a major role in the increase in airway resistance following agonist challenge. There is evidence that the airway smooth muscle (ASM) of small bronchioles differs functionally from that in larger airways. Little is known however about the electrophysiology of small bronchioles. Ion currents were therefore studied in airway smooth muscle cells freshly dissociated from human intralobular bronchioles, with a diameter between 0·3 and 1·0 mm. As previously reported for human large airways, the major outward current in these cells was due to activity of large conductance K+ (BK) channels, with a relatively minor component due to a voltage-gated delayed rectifier current (IDR), which was only observed in [sim]30 % of cells. Three distinct types of iberiotoxin- and TEA-sensitive large conductance K+ channel contributed to large conductance K+ current (IBK). These included a highly voltage- and Ca2+-sensitive 200 pS channel previously reported in human large airways, and two smaller channels of 150 and 100 pS previously seen only in human fetal or cultured ASM. In contrast to large airways, ASM cells from bronchioles also demonstrated a voltage-gated inward rectifier current (IIR). IIR was activated by hyperpolarisation below the K+ equilibrium potential and could be blocked by submillimolar concentrations of Cs+ or Ba2+, and partially by physiological concentrations of Na+. Corresponding single channels with a conductance of [sim]>17 pS could also be recorded in the cell-attached configuration. A small voltage-independent current was also observed which was resistant to classic K+ and Cl- channel blockers but which could be abolished by replacement of Na+ with the impermeant cation N-methyl-D-glucamine (NMDG+). Corresponding non-selective single channels of [sim]20 pS could be seen in inside-out mode. These results demonstrate that ASM from small bronchioles differs in terms of ion currents and channels from ASM derived from large airways, with possible implications for function.

We used implanted miniature data loggers to measure brain and arterial blood temperatures in three free-ranging zebras (Equus burchelli) in their natural habitat, every 5 min for 9 days. The animals experienced globe temperatures exceeding 40°C, and radiant heat load of about 1000 W m-2. Arterial blood exhibited a moderate amplitude (1.7°C) nychthemeral rhythm, with an acrophase at 19.00 h and a nadir late in the morning, at 10.00 h. Brain temperature consistently exceeded blood temperature, on average by 0.2-0.4°C, and changes in brain temperature closely tracked changes in blood temperature. There was no evidence of selective brain cooling, even during the hyperthermia which followed surgery or that associated with intense, short-duration exercise. The relationship between brain and arterial blood temperatures in free-ranging zebras was unlike that reported for horses in the laboratory. Our results do not support the view that mammals lacking a carotid rete can achieve selective brain cooling.

Exposure to a temperature of 14¡C was used to induce a progressive hypothermia in fourteen conscious newborn piglets. Heat production, body (rectal) and skin (between the shoulders) temperatures and shivering intensity assessed as the electromyographic activity (EMG) of longissimus thoracis muscle were measured until body temperature reached 30¡C and during a recovery period of 2 h at an ambient temperature of 24¡C (n = 7) or 34¡C (n = 7). During body cooling, heat production increased up to 9·67 ± 1·28 W (kg BW)-1, but started to decrease below a body temperature threshold of 34·4 ± 0·7¡C. EMG activity increased (P < 0·023) curvilinearly during body cooling; the main increase occurred between body temperatures of 38 and 33¡C (+142 %, P < 0·001), and changes in EMG activity between 33 and 30¡C were not significant (+18 %, P > 0·1). A marked increase in circulating levels of glucose (+312 %, P < 0·001), glucagon (+76 %, P < 0·05), adrenaline (+172 %, P < 0·05) and noradrenaline (+113 %, P < 0·05) occurred during body cooling. Insulin levels were not detectable at 2 h of life and increased during body cooling. During 2 h of rewarming at 24¡C, heat production and EMG activity remained elevated, changes in carbohydrate metabolism were not completely reversed and the final body temperature was only 35·6 ± 0·9¡C. Rewarming of the piglets was faster at 34¡C. There was a net influx of heat into the animals and heat production and shivering activity decreased when body temperature reached 33·9 ± 0·5¡C; the final body temperature was 37·5 ± 0·2¡C. Circulating levels of lactate, glucagon and catecholamines returned to control levels. These results show that in conscious piglets exposed to a constant cold temperature there is an inverse relationship between EMG activity and body temperature during moderate hypothermia and that the thermoregulatory response and carbohydrate metabolism of the piglet are seriously impaired below a body temperature of 34¡C.

Preterm delivery is the largest cause of perinatal mortality and morbidity, yet the treatment of preterm labour has not been demonstrated to improve outcome. The reasons are numerous and complex, but they include a failure to understand the mechanism(s) of preterm labour, the multitude of different causes, the difficulty in diagnosis and the problems of outcome measurement in clinical trials. Recently, an oxytocin antagonist (atosiban) has been introduced into clinical practice in Europe. Although it may be an effective tocolytic, a beneficial effect on perinatal outcome has not been demonstrated. Atosiban has an effect at both oxytocin and vasopressin (V1a) receptors, which (assuming efficacy) raises the question as to whether oxytocin or vasopressin V1a antagonism is required for tocolysis. This review examines the rationale for tocolysis in preterm labour, the evidence for administration of atosiban and the role for oxytocin, vasopressin and their receptors in the onset of labour. Experimental Physiology (2001) 86.2, 297-302.

The urinary bladder is a smooth muscle organ the function of which is to collect and store urine at low intravesical pressures, and then periodically to expel urine via a highly co-ordinated sustained contraction (Levin et al. 1990a; Anderson, 1993; Steers, 1994; Zderic et al. 1996a). The urethra functions to maintain continence during bladder filling, and then to provide a low-resistance pathway during micturition. The control of lower urinary tract function is through the autonomic nervous system. During bladder filling, the sympathetic nervous system is active and this produces an increase in tension of the bladder base and urethra via activation of a-adrenergic receptors, and relaxation of the bladder body via activation of ß-adrenergic receptors. In addition, sympathetic activity inhibits parasympathetic ganglionic transmission via postsynaptic sympathetic fibres which act upon a2-type receptors located in the ganglia. Micturition is mediated via the co-ordinated parasympathetic activation of cholinergic muscarinic receptors of the bladder body with the simultaneous inhibition of [alpha]-adrenergic tone of the bladder neck and urethra (Steers, 1994; Zderic et al. 1996a). Active urethral relaxation mediated by nitric oxide may also play a role during micturition (Anderson, 1993; Steers, 1994; Zderic et al. 1996a).

Oxidants have been suggested to enhance contractile function in unfatigued muscle. In this study we aimed to determine the effect of oxidants on 'chemically skinned' diaphragm muscle fibre bundles. The sarcoplasmic reticulum and contractile proteins were exposed to superoxide anions (O2-) and hydrogen peroxide (H2O2) under controlled conditions. Application of O2- initially increased maximum Ca2+-activated force but subsequently reduced maximum Ca2+-activated force without altering myofilament Ca2+ sensitivity. Unlike myocardium, caffeine-induced Ca2+ release from the sarcoplasmic reticulum was also inhibited by O2- exposure in diaphragm fibre bundles. Application of H2O2 also increased maximum Ca2+-activated force but had additional effects on resting tension (which increased to 25 % of the control maximum Ca2+-activated force). H2O2 was without effect on myofilament Ca2+ sensitivity or caffeine-induced Ca2+ release from the sarcoplasmic reticulum. These data demonstrate that oxidants can potentiate contractile force in the diaphragm through a direct action on the contractile proteins. The potentiation of force is not sustained, however, and under these conditions the detrimental effects of O2- on Ca2+ release from the sarcoplasmic reticulum combined with the effects of oxidants on the contractile proteins will ultimately compromise excitation-contraction coupling in the diaphragm. Experimental Physiology (2001) 86.2, 161-168.

Incrementally applied static stretch over 3 weeks resulted in a 72 % increase in the weight of the in situ latissimus dorsi muscle in rabbits. True growth rather than tissue oedema was confirmed by increases in the protein content (130 %), the cross-sectional area of the type I fibres (30 %) and the muscle length (i.e. number of sarcomeres in series increased 25 %). Despite an increase in the proportion of fibres staining positive for the enzyme succinate dehydrogenase (SDH), the myosin ATPase stain showed no appreciable fibre type transformation. While total power output in the stretched muscle was unchanged, its maximum mass specific power output, as determined by oscillatory work loops, was decreased by 50 %. The cross-sectional area that was occupied by connective tissue increased from 15 to 19 % in the stretched muscles, with a concomitant increase in passive energy dissipation. Some incrementally stretched muscles were then allowed an additional 3 weeks of maintained stretch to determine whether the adaptive changes would be preserved or reversed. Previous gains in muscle weight, length and area of type I fibres all remained. In contrast, the connective tissue content and the passive properties returned to control values during this period.

Aside from its role as a hypothalamic stress hormone, corticotrophin releasing hormone (CRH) is also a placental hormone, at least in primates. Although the function of placentally derived CRH remains to be fully elucidated, elevated CRH levels have been associated with premature labour, suggesting that the hormone may be involved in regulating the duration of pregnancy. Indeed, pregnant human myometrium expresses functional CRH receptors (CRH R1 and CRH R2 subtypes) thought to signal predominantly via the second messenger cAMP. Thus, like other cAMP-producing hormones in the myometrium such as β2 agonists, CRH may play a part in maintaining uterine quiescence. However, several of the CRH receptor isoforms identified to date have a reduced ability to activate adenylate cyclase, raising the question as to whether they are linked to other signal transduction pathways. Here, we discuss critically the evidence for the peptide's role in regulating contractility, both directly at the myometrium and indirectly via the fetal membranes and decidua. The possibility of a role in myometrial growth modulation is also described. Experimental Physiology (2001) 86.2, 273-281.

A number of mitochondrial carrier systems function both in homologous and in heterologous exchange mode, which, in the case of the phosphate carrier is a homologous Pi--Pi- and a heterologous Pi--OH- exchange. In addition, we showed that mitochondrial carriers, e.g. the aspartate/glutamate and the phosphate carrier, can undergo a functional shift from coupled antiport to uncoupled uniport after modification of cysteine residues. In this transport mode a mixture of carrier- and channel-type properties is observed. To address this question on the molecular level, the phosphate carrier from yeast (S. cerevisiae) mitochondria was expressed in E. coli, solubilized, purified and functionally reconstituted. From three cysteine residues present in the yeast phosphate carrier at positions 28, 134 and 300, only one single cysteine residue (C28) was found responsible for the functional switch from antiport to uniport. Upon replacement by a serine residue, this interconversion was blocked. After incorporation of the carrier into giant liposomes, electrophysiological methods (patch clamp) were applied. Under these conditions, a fourth transport mode of the phosphate carrier was observed, namely an action as anion-selective channel, which could be reversibly blocked by phosphate.