The mode of action of forskolin is of clinical and scientific interest since forskolin has been shown to have potentially therapeutic bone anti-resorptive and anti-hypertensive properties. Forskolin is thought to inhibit the bone resorptive activity of osteoclasts by elevating cytosolic cAMP and to mimic as well as augment the anti-resorptive effect of calcitonin (CT). Other studies have found that forskolin has a dose-dependent dual effect in mouse calavaria, stimulating bone resorption at low doses and having an inhibitory effect at high doses. However, the acute effect of forskolin on osteoclast functional modality has never been studied. The present investigation examined the effect of low (1 mM) and high doses (10 mM) of forskolin on superoxide anion (O2Σ-) generation in isolated bone-resorbing rat osteoclasts. Forskolin was found to have a bimodal cAMP-independent effect on O2Σ- generation, being stimulatory at a low dose and having an inhibitory effect at a higher dose. These findings also suggest that CT-induced inhibition of O2Σ- generation in the osteoclasts is likely to be mediated by cAMP-independent pathways, perhaps involving [Ca2+]i modulation.

The aim of this investigation was to determine whether reflex cardiovascular responses were obtained to localised distension of the intrapulmonary arterial and venous circulations in a preparation in which the stimuli to other major reflexogenic areas were controlled and the lung was shown to possess reflex activity. Dogs were anaesthetised with α-chloralose, artificially ventilated, the chests widely opened and a cardiopulmonary bypass established. The intrapulmonary region of the left lung was isolated and perfused through the left pulmonary artery and drained through cannulae in the left pulmonary veins via a Starling resistance. Intrapulmonary arterial and venous pressures were controlled by the rate of inflow of blood and the pressure applied to the Starling resistance. Pressures to the carotid, aortic and coronary baroreceptors and heart chambers were controlled. Responses of vascular resistance were assessed from changes in perfusion pressures to a vascularly isolated hind limb and to the remainder of the subdiaphragmatic circulation (flows constant). The reactivity of the preparation was demonstrated by observing decreases in vascular resistance to large step changes in carotid sinus pressure (systemic vascular resistance decreased by -40 ± 5 %), chemical stimulation of lung receptors by injection into the pulmonary circulation of veratridine or capsaicin (resistance decreased by -32 ± 4 %) and, in the four dogs tested, increasing pulmonary stroke volume to 450 ml (resistance decreased by -24 ± 6 %). However, despite this evidence that the lung was innervated, increases in intrapulmonary arterial pressure from 14 ± 1 to 43 ± 3 mmHg or in intrapulmonary venous pressure from 5 ± 2 to 34 ± 2 mmHg or both did not result in any consistent changes in systemic or limb vascular resistances. In two animals tested, however, there were marked decreases in efferent phrenic nerve activity. These results indicate that increases in pressure confined to the intrapulmonary arterial and venous circulations do not cause consistent reflex vascular responses, even though the preparation was shown to be reflexly active and the lung was shown to be innervated.

We investigated the influence of ambient temperature on the thermoregulatory response to hypoxia in developing lambs before (at 4 and 14 days of age) and after (17 and 30 days of age) carotid body denervation (CBD). Lambs were studied during non-rapid eye movement sleep at thermoneutral (23-15°C) and cool (10-5°C) ambient temperatures, during normoxia and acute hypoxia (inspired oxygen content of 13 %). Measurements of oxygen consumption, arterial partial pressures of O2 and CO2, colonic temperature, incidence of shivering and plasma concentrations of thyroid hormones, cortisol, insulin and glucose were made under each condition. Oxygen consumption was higher at cool compared with thermoneutral ambient temperatures and decreased during hypoxia during cooling at all stages. At 4 days of age, only one lamb shivered during cooling in normoxia, but 4 out of 12 lambs shivered during hypoxia and colonic temperature fell, significantly, by 0·2°C. At 14 days, 8 out of 12 lambs shivered during cooling, of which 6 continued to shiver during hypoxia but colonic temperature did not change significantly. Plasma triiodothyronine concentrations increased on cooling at 4 and 14 days, an affect that was inhibited by hypoxia at 4, but not 14 days of age. At 17 days of age, i.e. post-CBD, plasma thyroid hormone concentrations and oxygen consumption were lower during cold exposure compared with intact lambs at 14 days of age. In CBD lambs, imposing further hypoxia resulted in colonic temperature falling 0·6°C during cooling, with only 2 out of 10 lambs shivering. Plasma glucose and insulin, but not cortisol, concentrations decreased during hypoxia, irrespective of age or CBD. It is concluded that hypoxia has an important influence on metabolism and thermoregulation, which is modulated by age and environmental conditions. Compromised carotid body function, in lambs older than 2 weeks of age, can result in severe hypoxia and thermoregulatory dysfunction even with modest environmental cooling.

Feto-maternal vascular (PDF-M) and amniotic-maternal (PDA-M) potential differences were measured simultaneously on seven occasions in six conscious pigs of 100-106 days gestation. Resting values of PDF-M and PDA-M were not significantly different although the range was wide. Fetal intravascular injection of 20 µg adrenaline, but not of saline, was associated with a prompt reversible change, of equal magnitude, in both PDF-M and PDA-M. In some experiments polarity was reversed. Feto-amniotic potential difference did not change. There was no change in fetal plasma K+ and Na+ concentrations. Because of the simultaneous and equal alterations in PDF-M and PDA-M following adrenaline and the anatomical configuration of the pig conceptus, we conclude that the catecholamine modifiable component of PDF-M is generated by electrogenesis in the pig placenta, probably by its chorionic (trophoblastic) cell layer.

It has been suggested that the glucose transport system of human erythrocytes contains an arginine shield to prevent the leak of potassium through the transporter. To investigate this suggestion we treated human erythrocytes with the specific arginine reagent 1,2-cyclohexanedione. Under conditions which produce a covalent reaction between arginine and the reagent, a steady leak of potassium occurs. If glucose, maltose or the inhibitor phloretin are present during the reaction the extent of the leak is reduced. These findings support the view that arginines have a role in preventing potassium loss through the glucose transporter.

The present study was designed to investigate the renal responses to hypotensive haemorrhage early in life and the role of renal sympathetic nerves in modulating these renal responses. To this end, experiments were carried out in conscious, chronically instrumented lambs with either intact renal nerves (n = 7, Intact) or bilateral renal denervation performed at the time of surgery (n = 5, Denervated). Parameters of renal function were measured before and after 20 % haemorrhage (experiment 1) and 0 % haemorrhage (experiment 2), the latter serving as a time control. The two experiments were performed in random order at intervals of 24-48 h. Within 20 min of hypotensive haemorrhage in intact lambs, glomerular filtration rate decreased by ~60 %; this response was not altered by renal denervation. Since renal plasma flow remained constant after haemorrhage, the filtration fraction also decreased. After 20 % haemorrhage, urinary flow rate decreased in intact lambs; this response was also not altered by renal denervation. Excretion rates of Na+ and K+ as well as urinary osmolality and free water clearance were not altered by haemorrhage in either intact or denervated lambs. These data provide the first description of renal responses to haemorrhage early in life. In addition, the present findings provide new information that renal responses to haemorrhage early in life do not appear to be modulated by renal sympathetic nerves. Experimental Physiology (2002) 87.5, 557-562.

The prion was defined by Stanley B. Prusiner as the infectious agent that causes transmissible spongiform encephalopathies. A pathological protein accumulating in the brain of scrapie-infected hamsters was isolated in 1982 and termed prion protein (PrPSc). Its cognate gene Prnp was identified more than a decade ago by Charles Weissmann, and shown to encode the host protein PrPC. Since the latter discovery, transgenic mice have contributed many important insights into the field of prion biology, including the understanding of the molecular basis of the species barrier for prions. By disrupting the Prnp gene, it was shown that an organism that lacks PrPC is resistant to infection by prions. Introduction of mutant PrP genes into PrP-deficient mice was used to investigate the structure-activity relationship of the PrP gene with regard to scrapie susceptibility. Ectopic expression of PrP in PrP knockout mice proved a useful tool for the identification of host cells competent for prion replication. Finally, the availability of PrP knockout mice and transgenic mice overexpressing PrP allows selective reconstitution experiments aimed at expressing PrP in neurografts or in specific populations of haemato- and lymphopoietic cells. The latter studies have allowed us to clarify some of the mechanisms of prion spread and disease pathogenesis.

The aim of this study was to investigate if the alertness connected with seeing water increased arterial blood pressure and heart rate to the same extent as the act of drinking, and if ingestion of warm water caused a different effect compared with ingestion of cool water on these cardiovascular variables. Seven goats of the Swedish domestic breed (Capra hircus) were used in a cross-over design. The animals were dehydrated for 24 h. They were allowed to watch water being prepared for 11-16 min, after which they were given access to warm (35°C) or cool (15°C) water. The goats drank 6.86 ± 0.36 l of the warm water and 4.54 ± 0.35 l of the cool water (P < 0.05) within the first hour. The arterial blood pressure, heart rate and activity of the animals were registered by an implanted telemetric device. Dehydration did not affect the cardiovascular variables, except before feeding in the morning, when the heart rate accelerated faster in dehydrated goats. Heart rate increased abruptly when dehydrated goats saw water being prepared, remained at the increased level during drinking and then slowly declined. It increased again during the afternoon feeding, to a level similar to that on control days, but between 18.00 and 06.00 h the heart rate was higher than during control nights. Blood pressure did not change when the goats saw water, but increased when they drank. On the morning following rehydration, the rise in heart rate in response to feeding was delayed compared with that during control and dehydration periods. It is concluded that seeing water caused arousal in the goats, resulting in an accelerated heart rate. The additional rise in blood pressure during the act of drinking appears to be a combination of excitement and sensory inputs from the pharyngeal region, causing a temporary activation of the sympathetic nervous system.

The role of nitric oxide (NO) in mediating pancreatic endocrine responses to moderate hypoglycaemia has been investigated in conscious unrestrained calves. The synthesis of endogenous NO was inhibited by the administration of N-nitro-L-arginine methyl ester (L-NAME; 100 mg kg-1 I.A.), while sodium nitroprusside was infused continuously (2-4 μg min-1 kg-1 I.V.) to mimic the tonic production of NO. This effectively abolished the rise in plasma pancreatic polypeptide (PP) concentration during moderate hypoglycaemia (0·7 nmol kg-1 insulin I.V.) and significantly reduced the response to more intense hypoglycaemia (2·0 nmol kg-1 insulin I.V.). In contrast, the glucagon response was not significantly affected in either group, although consistently higher plasma glucagon values were obtained in response to the higher dose of insulin following the administration of L-NAME. It is concluded that, in the absence of L-NAME, production of NO contributes to the PP response, but not the glucagon response to hypoglycaemia in this species under physiological conditions.

We examined whether protein kinase C(PKC) modulates the transport systems involved in lactate movements across the plasma membranes of rat jejunum. In vitro phosphorylated membrane vesicles were used to perform uptake studies, the results of which suggested that PKC activation exerts an inhibitory effect on basolateral H+–lactate symport, as well as on apical Na+–glucose cotransport. The specificity of the response to PKC was confirmed by using staurosporine, chelerythrine or 4-α-PMA. Experiments performed using the whole tissue incubated in vitro confirmed the reduction of lactate transport elicited by PKC and gave evidence for an associated inhibition of fluid transport. Na+,K+-ATPase activity seems to be unaffected by the kinase and inhibited by Ca2+. Taken together, our results suggest that the overall action of PKC results from the simultananeous modulation of multiple pathways, targeted to a reduction of both lactate and bicarbonate transports without altering cell pH homeostasis.