Responses of cardiac sympathetic nerve activity to changes in circulating volume differ in normal and heart failure sheep

Factors controlling cardiac sympathetic nerve activity (CSNA) in the normal state and those causing the large increase in activity in heart failure (HF) remain unclear. We hypothesized from previous clinical findings that activation of cardiac mechanoreceptors by the increased blood volume in HF may stimulate sympathetic nerve activity (SNA), particularly to the heart via cardiocardiac reflexes. To investigate the effect of volume expansion and depletion on CSNA we have made multiunit recordings of CSNA in conscious normal sheep and sheep paced into HF. In HF sheep (n = 9) compared with normal sheep (n = 9), resting levels of CSNA were significantly higher (34 +/- 5 vs. 93 +/- 2 bursts/100 heart beats, P < 0.05), mean arterial pressure was lower (76 +/- 3 vs. 87 +/- 2 mmHg; P < 0.05), and central venous pressure (CVP) was greater (3.0 +/- 1.0 vs. 0.0 +/- 1.0 mmHg; P < 0.05). In normal sheep (n = 6), hemorrhage (400 ml over 30 min) was associated with a significant increase in CSNA (179 +/- 16%) with a decrease in CVP (2.7 +/- 0.7 mmHg). Volume expansion (400 ml Gelofusine over 30 min) significantly decreased CSNA (35 +/- 12%) and increased CVP (4.7 +/- 1.0 mmHg). In HF sheep (n = 6) the responses of CSNA to both volume expansion and hemorrhage were severely blunted with no significant changes in CSNA or heart rate with either stimulus. In summary, these studies in a large conscious mammal demonstrate that in the normal state directly recorded CSNA increased with volume depletion and decreased with volume loading. In contrast, both of these responses were severely blunted in HF with no significant changes in CSNA during either hemorrhage or volume expansion.     

Effect of dry-matter concentration of milk substitute and method of feeding on intake and performance by lambs

Forty-eight lambs were artificially reared from 1 day old and offered milk substitute reconstituted to give diets containing 10, 16, 22 and 28% dry matter (DM). Three feeding methods were used for each diet: milk substitute available ad libitum (AL); restricted to a mean daily intake of 1300 g liquid milk substitute (RLQ); and restricted to a mean daily intake of 247 g milk substitute DM (RDM).Solid food intake and lamb growth rate were measured both before and after weaning at 28 days.For method AL, decreasing DM concentration in the milk substitute increased intake of the liquid but decreased that of DM. When DM intakes were held constant, neither method of feeding nor DM concentration had an effect on lamb growth, and level of reconstitution of the milk substitute had no effect on its digestibility. Differences in growth rate before weaning were due entirely to differences in intake of milk substitute DM.After weaning, lambs which had received the diet containing 10% DM tended to perform less well than those that had received the other diets.The lambs were slaughtered at 35 kg live weight. There were no effects of treatment on gains of water, fat and protein.     

Hypertonic sodium resuscitation after hemorrhage improves hemodynamic function by stimulating cardiac, but not renal, sympathetic nerve activity

Small volume hypertonic saline resuscitation can be beneficial for treating hemorrhagic shock, but the mechanism remains poorly defined. We investigated the effects of hemorrhagic resuscitation with hypertonic saline on cardiac (CSNA) and renal sympathetic nerve activity (RSNA) and the resulting cardiovascular consequences. Studies were performed on conscious sheep instrumented with cardiac (n=7) and renal (n=6) sympathetic nerve recording electrodes and a pulmonary artery flow probe. Hemorrhage (20 ml/kg over 20 min) caused hypotension and tachycardia followed by bradycardia, reduced cardiac output, and abolition of CSNA and RSNA. Resuscitation with intravenous hypertonic saline (1.2 mol/l at 2 ml/kg) caused rapid, dramatic increases in mean arterial pressure, heart rate, and CSNA, but had no effect on RSNA. In contrast, isotonic saline resuscitation (12 ml/kg) had a much delayed and smaller effect on CSNA, less effect on mean arterial pressure, no effect on heart rate, but stimulated RSNA, although the plasma volume expansion was similar. Intracarotid infusion of hypertonic saline (1 ml/min bilaterally, n=5) caused similar changes to intravenous administration, indicating a cerebral component to the effects of hypertonic saline. In further experiments, contractility (maximum change in pressure over time), heart rate, and cardiac output increased significantly more with intravenous hypertonic saline (2 ml/kg) than with Gelofusine (6 ml/kg) after hemorrhage; the effects of hypertonic saline were attenuated by the β-receptor antagonist propranolol (n=6). These results demonstrate a novel neural mechanism for the effects of hypertonic saline resuscitation, comprising cerebral stimulation of CSNA by sodium chloride to improve cardiac output by increasing cardiac contractility and rate and inhibition of RSNA.     

高寒草甸物种多样性对藏系牧羊放牧行为的影响

为探究草原植物物种多样性对家畜放牧行为的影响及其机制,在青藏高原高寒草甸开展藏系牧羊轮牧试验,调查植被物种多样性,观察藏系牧羊采食速率、觅食速率和采食时间,并计算藏系牧羊日采食量。结果表明：两年间,植物物种丰富度与藏系牧羊采食速率呈显著正相关关系（P<0.05）;觅食速率、采食时间和日采食量对放牧率响应敏感（P<0.05）,呈夏秋增冬春减的趋势。植物Shannon-Wiener指数与藏系牧羊的采食时间显著负相关（P<0.05）;在暖季或8羊/hm²放牧率下植物Shannon-Wiener指数与藏系牧羊日采食量呈显著正相关（P<0.05）。Pilelou均匀度指数与藏系牧羊采食速率和采食时间显著负相关（P<0.05）;在暖季或8羊/hm²放牧率下Pilelou均匀度指数与藏系牧羊日采食量呈显著负相关（P<0.05）。植物物种丰富度对藏系牧羊放牧行为贡献较大,且放牧藏系牧羊的采食速率和采食时间比觅食速率和日采食量对植物物种丰富度响应更敏感,以用植物物种丰富度为自变量可以更好预测藏系牧羊放牧行为。放牧管理通过影响植被物种多样性从而进一步影响了藏系牧羊放牧行为。放牧行为不仅是评价草地营养价值和家畜生产力的关键指标,也是草地健康管理的基础。因此,明确草原植物物种多样性-藏系牧羊放牧行为的互作机制有助于更好的提高藏系牧羊地生产力,维护草原生态健康。     

The role of the autonomic nervous system in the depression of parotid salivary secretion during hyperkalaemia in conscious sheep.

The rate of flow and electrolyte concentration of parotid saliva were measured before, during and after intravenous and contralateral intracarotid infusion of KCl (0.5 mol.1(-1)) and NaCl (0.5 mol.1(-1)) at 385-625 mumol. min(-1) for 40 min into 5 sheep. In intact conscious sheep contralateral intracarotid infusion of KCl caused marked depression of salivary secretion in all experiments whereas infusion of NaCl had no consistent effect on flow. Intravenous infusion of KCl into the intact conscious sheep caused a slight depression of salivary secretion but minimum flow was significantly higher than that during intracarotid infusion. When the sheep were anaesthetized salivary flow rates were low and contralateral intracarotid infusion of KCl either had no effect on flow or caused an increase in flow. After ipsilateral cervical sympathectomy contralateral intracarotid infusion of KCl into the conscious sheep caused a marked depression of salivary flow similar to that occurring when the sheep were intact. After section of the secretomotor nerve of the gland salivary flow rates were low and contralateral intracarotid infusion of KC1 had no effect on flow. The salivary flow responses of the sheep were consistent, regardless of whether the KCl infusions were given within 24 h or 1-2 weeks after cervical sympathectomy or secretomotor nerve section. Salivary sodium concentration was negatively correlated with salivary flow in all experiments. It was concluded that potassium acted at a site located in the head but by direct action on the salivary gland. The depression of salivary secretion by hyperkalaemia resulted from a decline in neural activity in the parasympathetic secretomotor innervation of the parotid gland.     

Transpulmonary prostaglandin F2 alpha metabolism in sheep: an in vivo model

We investigated transpulmonary enzymatic conversion of prostaglandin F2 alpha (PGF) to the 13,14-dihydro-15-keto metabolite (PGFM) in normal and acutely lung injured sheep. PGF was infused directly into the right ventricle. Sequential, simultaneous blood samples were drawn from the pulmonary artery (PA) and aorta (A). PGF and PGFM plasma concentrations were quantitated by double antibody radioimmunoassay (RIA). The pulmonary conversion rate of PGF in normal lung was established over a wide range of concentrations in intubated, normoxic, and hemodynamically stable sheep. Both zero and first order kinetics were present. PGF had no physiological effects on either pulmonary or systemic hemodynamics at any infusion rate studied. Acute lung injury was produced by intravenous injections of oleic acid into the PA until the resting mean pulmonary artery pressure doubled. Infusions were then repeated and fractional metabolism of PGF across the lung was assessed. PGF, at infusion rates of 2 micrograms/kg/min and 8 micrograms/kg/min, was metabolized greater than 70% respectively. Thus, there was no difference between control or experimental groups in PGF conversion. We conclude that the in vivo sheep lung has an extensive substrate-dependent capacity to metabolize PGF and this mechanism is resistant to severe acute oleic acid lung injury.     

Long-term effects of short-term provision of protein-enriched diets on resistance to nematode infection, and live-weight gain and wool growth in sheep.

Weaner sheep that had been hand-fed on diets containing increasing concentrations of protein for a 9-week period (when uninfected, or infected with Haemonchus contortus) were studied during the next 69 weeks when put on to pasture as a single, unsupplemented flock. During the 9-week period, groups of 12 sheep (six infected, six uninfected) were offered one of five iso-energetic (9.0 MJ kg(-1)) diets containing 10, 13, 16, 19 or 22% crude protein. All sheep were treated with anthelmintic at the end of the 9 weeks and then put out to pasture for 69 weeks, where they were all subject to the same environmental variables including nematode larval challenge. During the grazing period, animals that had previously received the higher protein diets consistently had higher live-weight gain and wool production, higher antibody responses to both H. contortus and Trichostrongylus colubriformis antigenic challenge in vitro, and lower faecal nematode egg counts than did the lambs previously offered the lower protein diets. Faecal egg counts of the grazing sheep that had been artificially infected with H. contortus while being hand-fed were similar to those of the uninfected sheep and there was no interaction between previous infection and dietary protein concentration. We conclude that short periods of enhanced post-weaning nutrition can have long-term and perhaps life-long effects on production.     

Separation of late bronchial responses from airway hyperresponsiveness in allergic sheep

Allergic sheep with antigen-induced early and late responses were used to determine whether airway hyperresponsiveness (AHR) to carbachol is present during the late response and whether blocking the late response with the leukotriene D4 (LTD4) antagonist MK-571 also blocks this AHR. To do this, we first showed that MK-571 blocked the antigen-induced late response, and then, in a separate study, we determined the effect of MK-571 treatment on airway responsiveness 6 h after antigen challenge (at the start of the late response). MK-571 (5 mg, by metered dose inhaler) given 30 min before and 4 h after Ascaris suum challenge had no effect on the acute response to antigen but blocked (P less than 0.05) the late response compared with placebo (n = 7). In the second study (n = 6), the antigen-induced acute increases in mean specific lung resistance (sRL) were also similar in the placebo (249%) and drug trials (247%). By 6 h postchallenge, however, mean sRL in the placebo trial began to increase (54%, P less than 0.05), whereas in the drug trial mean sRL was baseline. Nevertheless, AHR was apparent in both trials as indicated by a mean twofold leftward shift in the dose-response curves to inhaled carbachol (P less than 0.05 vs. prechallenge). Bronchoalveolar lavage at 6 h showed that MK-571 did not prevent the inflammatory cell influx into the lung. These observations suggest that although LTD4 may be a mediator of the late response in sheep, it is not a primary mediator affecting cholinergic AHR during this period.     

Steroid antagonism of the ‘hypertensinogenic’ activity of 9α-fluoroprednisolone

We have previously reported that adrenocortical steroids raise blood pressure by a ‘hypertensinogenic’ mechanism of action which is not simply related to their classical ‘mineralocorticoid’ or ‘glucocorticoid’ actions. This study presents evidence for specific antagonism of this ‘hypertensinogenic’ activity. The effects of separate IV infusions of prednisolone (P) 100 mg/d and 9α-fluoro-prednisolone (9αF-P) 0.6 mg/d on mean arterial pressure (MAP), plasma [K], plasma [glucose] and urinary NA excretion (UNaV) after 2 days were studied in sheep. In the same group of sheep which received P alone for 2 days, 9αF-P was given for a further 2 days while continuing the P infusion (P + 9αF-P). P alone had no effect on MAP or plasma [K] or U_NaV but increased plasma [glucose], effects which are characteristic of ‘glucocorticoid’ activity. 9αF-P alone increased MAP by 14 mmHg (P<0.001) and reduced plasma [K] and U_NaV but had no effect on plasma [glucose]. Thus 9αF-P exhibited both ‘hypertensinogenic’ and ‘mineralocorticoid’ activity. In the sheep which received the combined P + 9αF-P infusion, the increase in MAP normally produced by 9αF-P was blocked. Although pretreatment with P blocked the pressor effect of 9αF-P, it did not alter the ‘mineralocorticoid’ effects, namely hypokalaemia and urinary Na retention, produced when 9αF-P was infused alone. These results provide further evidence for our concept of a ‘hypertensinogenic’ class of steroid activity and are the first demonstration of specific antagonism of steroid induced hypertension.     

Catestatin, a chromogranin A-derived peptide, is sympathoinhibitory and attenuates sympathetic barosensitivity and the chemoreflex in rat CVLM

Hypertension is a major cause of morbidity. The neuropeptide catestatin [human chromogranin A-(352-372)] is a peptide product of the vesicular protein chromogranin A. Studies in the periphery and in vitro studies show that catestatin blocks nicotine-stimulated catecholamine release and interacts with β-adrenoceptors and histamine receptors. Catestatin immunoreactivity is present in the rostral ventrolateral medulla (RVLM), a key site for blood pressure control in the brain stem. Recently, we reported that microinjection of catestatin into the RVLM is sympathoexcitatory and increases barosensitivity. Here, we report the effects of microinjection of catestatin (1 mM, 50 nl) into the caudal ventrolateral medulla (CVLM) in urethane-anesthetized, bilaterally vagotomized, artificially ventilated Sprague-Dawley rats (n = 8). We recorded resting arterial pressure, splanchnic sympathetic nerve activity, phrenic nerve activity, heart rate, and measured cardiovascular homeostatic reflexes. Homeostatic reflexes were evaluated by measuring cardiovascular responses to carotid baroreceptor and peripheral chemoreceptor activation. Catestatin decreased basal levels of arterial pressure (-23 ± 4 mmHg), sympathetic nerve activity (-26.6 ± 5.7%), heart rate (-19 ± 5 bpm), and phrenic nerve amplitude (-16.8 ± 3.3%). Catestatin caused a 15% decrease in phrenic inspiratory period (T(i)) and a 16% increase in phrenic expiratory period (T(e)) but had no net effect on the phrenic interburst interval (T(tot)). Catestatin decreased sympathetic barosensitivity by 63.6% and attenuated the peripheral chemoreflex (sympathetic nerve response to brief hypoxia; range decreased 39.9%; slope decreased 30.1%). The results suggest that catestatin plays an important role in central cardiorespiratory control.     

Increased cardiac sympathetic nerve activity in heart failure is not due to desensitization of the arterial baroreflex

Increased sympathetic drive to the heart worsens prognosis in heart failure, but the level of cardiac sympathetic nerve activity (CSNA) has been assessed only by indirect methods, which do not permit testing of whether its control by arterial baroreceptors is defective. To do this, CSNA was measured directly in 16 female sheep, 8 of which had been ventricularly paced at 200-220 beats/min for 4-6 wk, until their ejection fraction fell to between 35 and 40%. Recording electrodes were surgically implanted in the cardiac sympathetic nerves, and after 3 days' recovery the responses to intravenous phenylephrine and nitroprusside infusions were measured in conscious sheep. Electrophysiological recordings showed that resting CSNA (bursts/100 heartbeats) was significantly elevated in heart-failure sheep (89 +/- 3) compared with normal animals (46 +/- 6; P < 0.001). This increased CSNA was not accompanied by any increase in the low-frequency power of heart-rate variability. The baroreceptor-heart rate reflex was significantly depressed in heart failure (maximum gain -3.29 +/- 0.56 vs. -5.34 +/- 0.66 beats.min(-1).mmHg(-1) in normal animals), confirming published findings. In contrast, the baroreflex control of CSNA was undiminished (maximum gain in heart failure -6.33 +/- 1.06 vs. -6.03 +/- 0.95%max/mmHg in normal sheep). Direct recordings in a sheep model of heart failure thus show that resting CSNA is strikingly increased, but this is not due to defective control by arterial baroreceptors.     

The effects of intracerebroventricular infusion of atrial natriuretic factor in conscious sheep

The effects of 24-hour intracerebroventricular infusion of human atrial natriuretic factor (ANF) and two related fragments were studied in conscious sheep. ANF (1-28) had no effect on either mean arterial pressure (MAP) or heart rate (HR) when infused at 3 or 10 micrograms/hr, however a small diuresis and an increase in urinary sodium (Na) excretion was observed. The smaller fragment, ANF (5-27) infused at 10 micrograms/hr, increased MAP, HR and body temperature, although the same rate of infusion of ANF (5-28) was without effect. All peptides increased plasma sodium concentration and plasma osmolality. None of the peptides affected plasma ACTH, glucose or renin concentration. ANF (1-28) had no effect on either Na intake or water intake in Na-depleted sheep. These studies suggest that members of the ANF family can influence a number of physiological functions following central administration.     

Reproduction in Indonesian sheep and goats at two levels of nutrition

Oestrus and ovulation were recorded for eight oestrous cycles after sheep and goats were put onto maintenance or supramaintenance levels of nutrition. Oestrous cycles were longer and more variable in goats than in sheep (20.3 ± 0.3 and 17.4 ± 0.2 days respectively), but in neither species was the incidence of oestrus affected by level of nutrition. There were no significant differences between sheep and goats in average body weight or mean ovulation rate. Animals fed at a maintenance level showed no significant changes in average body weight (19.0 ± 0.3 kg) or mean ovulation rate (1.69 ± 0.01). At the supramaintenance level, on the other hand, mean body weight increased progressively to a maximum of 24.8 ± 0.5 kg, and mean ovulation rate increased to a maximum of 2.65 at the sixth oestrus after the beginning of supramaintenance feeding. The effect of supramaintenance feeding on ovulation rate was reflected in subsequent lamb and kid production.     

Development of post-pump syndrome in a sheep after mitral valve stenting

A one-year-old healthy sheep received an implant stenting the mural ('posterior') leaflet of the mitral valve. The experiment was authorized by the Cantonal Ethical Committee. The surgery was performed on the open, beating heart during cardiopulmonary bypass (CPB). Management of anaesthesia was based on isoflurane with mechanical intermittent positive pressure ventilation (IPPV) of the lungs, combined with intercostal nerve blocks and intravenous fentanyl and lidocaine. Marked cardiovascular depression occurred towards the end of CPB time and required high doses of dopamine, dobutamine, lidocaine and ephedrine to allow for weaning off the CPB pump. Moreover, severe pulmonary dysfunction developed when IPPV was re-initiated after CPB. Hypoxaemia persisted throughout the recovery from general anaesthesia. Multiple organ failure developed gradually during the three postoperative days, leading to euthanasia of the animal. As described in this case, marked lung injury associated with some degree of failure of other vital organs may occur in sheep after CPB. Intraoperative cardiorespiratory complications when weaning-off may indicate the development of 'post-pump syndrome'.     

Capture methods in five subspecies of free-ranging bighorn sheep: an evaluation of drop-net, drive-net, chemical immobilization and the net-gun

Six hundred thirty-four bighorn sheep (Ovis canadensis) were captured in the western United States between 1980 and 1986, using four different methods: drop-net (n = 158), drive-net (n = 249), chemical immobilization (n = 90) and net-gun (n = 137). The net-gun was found to have considerable advantages over the use of ground nets and chemical immobilization methods for capturing bighorn sheep. Evaluation of specific outcome categories for individual sheep, including normal, compromised (stress-induced), mortality from capture myopathy (CM), and accidental mortality, revealed significant differences in these rates between capture groups (P less than 0.05). The use of the net-gun resulted in the lowest proportion of compromised sheep at 11% (15/137), had no CM mortality, and resulted in a 2% (2/137) accidental mortality. The use of drop-nets resulted in 15% compromised sheep (24/158), a CM mortality rate of 2% (3/158), and an accidental mortality rate of 1% (2/158). A similar proportion of sheep were compromised with the drive-nets (16%, 39/249). This method also had the highest CM mortality rate at 3% (7/249), and an accidental mortality rate of less than 1% (2/249). Chemical immobilization resulted in the most compromised sheep at 19% (17/90), had a CM mortality rate of 2% (2/90), and caused the most accidental deaths at 6% (5/90). Drop-nets and drive-nets were comparable when combining total mortality with rates for compromised bighorn sheep, 18% and 19%, respectively (29/158 and 48/249). Chemical immobilization had the highest combined measure of risk at 27% (24/90) and net-gun lowest at 12% (17/137).(ABSTRACT TRUNCATED AT 250 WORDS)     

Increased cleavage and blastocyst rate in ewes treated with bovine somatotropin 5 days before the end of progestin-based estrous synchronization

Treatment with bovine somatotropin (bST) during estrous synchronization increased fertility and prolificacy in sheep. In the present study, a single dose of bST 5 days before the end of progestin treatment improved cleavage and embryo development. Stage of estrous cycle was synchronized in ewes (n=32) with progestin and superovulation was induced by use of FSH. Five days before the end of progestin treatment, ewes were randomly assigned to two groups: bST group (n=16) received a depot injection of 125 mg of bST sc (Lactotropina, Elanco, México) and the control group (n=16) received saline solution. Estrous was detected with rams fitted with an apron every 2 h and estrous sheep were mated every 8 h whilst in estrous. Embryos were recovered on Day 7 post mating, assessed microscopically and fixed in 4% paraformaldehyde. Cell number in blastocysts was counted after Hoechst 33342 staining. Plasma concentrations of IGF-I, insulin and progesterone were determined in eight sheep per group from the day of bST treatment to the day of embryo recovery. Cleavage rate, percentage of transferable embryos (transferable embryos/cleaved) and percentage of embryos reaching the blastocyst stage (blastocyst/cleaved) were compared between groups by logistic regression. IGF-I, insulin and progesterone plasma concentrations were analyzed by ANOVA for repeated measurements and cell number by ANOVA. Cleavage rate was greater (P<0.01) in bST treatment group (86%) than in the control group (62%). Similarly, the proportion of embryos reaching the blastocyst stage (bST=68.7 vs control=42.5) and the number of cells per blastocyst (bST group 91.8±5.5 compared to control group 75±6) were greater (P<0.01) in the bST-treated sheep. Plasma concentrations of IGF-I and insulin were greater (P<0.01) in the bST-treated group. No changes were observed in progesterone concentrations (P=0.5). It is concluded that bST injection 5 days before progestin removal increases cleavage rate and the proportion of embryos that reach the blastocyst stage. These effects are associated with an increase in IGF-I and insulin concentrations.     

Central infusion of leptin does not increase AMPK signaling in skeletal muscle of sheep

In sheep, central leptin infusion reduces food intake and increases energy expenditure in adipose tissue and skeletal muscle. The mechanisms for these peripheral effects of central leptin in sheep are not known but, on the basis of rodent studies, may involve AMPK. In mice, central leptin acutely increases both skeletal muscle AMPK activation and glucose uptake. Thus, to investigate whether these effects exist in higher-order mammals, ovariectomized Corriedale ewes (n = 4 per group) received a continuous lateral ventricular infusion (60 μl/h) of either leptin (50 μg/h) or artificial cerebrospinal fluid (aCSF; CON) for 8 days. Tritiated glucose (3-(3)H-glucose) was infused intravenously for calculation of whole body glucose turnover during both acute (6 h) and chronic (7-8 days) leptin/aCSF infusion. Muscle biopsies were also obtained. Leptin infusion reduced (P < 0.05) food intake and body weight, and it also increased plasma epinephrine concentration at 6 h and 7 days, suggesting increased sympathetic nerve activity. Despite this, and in contrast to rodent studies, central leptin infusion did not increase skeletal muscle AMPKα Thr(172) phosphorylation or ACCβ Ser(221) phosphorylation. Surprisingly, the glucose rate of appearance (glucose Ra) and rate of disappearance (glucose Rd) were reduced by both acute and chronic leptin infusion. Direct infusion of the AMPK activator 5-aminoimidazole-4-carboxyamide-ribonucleoside (AICAR) into the femoral artery increased skeletal muscle AMPK phosphorylation. In conclusion, although central leptin infusion in sheep caused the predicted reduction in food intake and increases plasma epinephrine concentration, it had no effect on AMPK activation in skeletal muscle and actually reduced glucose disposal. This suggests that there are species differences in the peripheral responses to central leptin infusion.     

Glucocorticoid modulation of cardiovascular and autonomic function in preterm lambs: role of ANG II

The mechanisms by which antenatal glucocorticoids facilitate postnatal circulatory function in preterm infants are uncertain but may be related to augmented angiotensinergic functions. To test the hypothesis that the effects of glucocorticoids on postnatal cardiovascular and sympathetic activity are mediated via the renin-angiotensin system, we studied the effects of AT(1) receptor blockade on postnatal changes in heart rate (HR), mean arterial blood pressure (MABP), renal sympathetic nerve activity (RSNA), and baroreflex control of HR in prematurely delivered lambs. After maternal administration of betamethasone (12 mg im 48 and 24 h before delivery), chronically instrumented preterm lambs (118- to 123-day gestation, term 145 days) were studied before and after delivery by cesarean section; fetuses received either the AT(1) receptor antagonist losartan (10 mg iv, n = 6) or saline (n = 6) 1 h before delivery. A third group of animals (n = 6) received losartan without prior exposure to betamethasone. Compared with fetal values, betamethasone-treated animals demonstrated significant increases (P < 0.05) in MABP (47 +/- 2 to 58 +/- 2 mmHg) and RSNA (181 +/- 80% of fetal value) 1 h after delivery. Betamethasone + losartan-treated lambs also displayed increases in MABP (48 +/- 1 to 55 +/- 3 mmHg) and RSNA (198 +/- 96% of fetal value) 60 min after birth, similar to betamethasone alone lambs. Losartan alone treated animals had no postnatal increase in either MABP or RSNA, responses similar to those seen in nontreated sheep delivered at the same gestational age. The sensitivity of baroreflex-mediated changes in HR in response to increases in MABP was less in both groups of betamethasone-treated animals; no effect was seen with losartan. These results suggest the postnatal increases in MABP and RSNA seen with antenatal glucocorticoid treatment are not mediated by stimulation of peripherally accessible AT(1) receptors. We speculate that augmented cardiovascular function in glucocorticoid-treated premature lambs is dependent, in part, on a generalized sympathoexcitatory response and that this effect of glucocorticoids is mediated by central mechanisms.     

Renal nerve inhibition by central NaCl and ANG II is abolished by lesions of the lamina terminalis

The lamina terminalis is situated in the anterior wall of the third ventricle and plays a major role in fluid and electrolyte homeostasis and cardiovascular regulation. The present study examined whether the effects of intracerebroventricular infusion of hypertonic saline and ANG II on renal sympathetic nerve activity (RSNA) were mediated by the lamina terminalis. In control, conscious sheep (n = 5), intracerebroventricular infusions of 0.6 M NaCl (1 ml/h for 20 min) and ANG II (10 nmol/h for 30 min) increased mean arterial pressure (MAP) by 6 +/- 1 (P < 0.001) and 14 +/- 3 mmHg (P < 0.001) and inhibited RSNA by 80 +/- 6 (P < 0.001) and 89 +/- 7% (P < 0.001), respectively. Both treatments reduced plasma renin concentration (PRC). Intracerebroventricular infusion of artificial cerebrospinal fluid (1 ml/h for 30 min) had no effect. In conscious sheep with lesions of the lamina terminalis (n = 6), all of the responses to intracerebroventricular hypertonic saline and ANG II were abolished. In conclusion, the effects of intracerebroventricular hypertonic saline and ANG II on RSNA, PRC, and MAP depend on the integrity of the lamina terminalis, indicating that this site plays an essential role in coordinating the homeostatic responses to changes in brain Na(+) concentration.     

In vivo USPIO magnetic resonance imaging shows that minocycline mitigates macrophage recruitment to a peripheral nerve injury

ABSTRACT: BACKGROUND: Minocycline has proven anti-nociceptive effects, and delays the development of allodynia/hyperalgesia after peripheral nerve injury. However, the mechanism by which this occurs remains unclear. Inflammatory cells, in particular macrophages, are critical components of the response to nerve injury. Using ultrasmall superparamagnetic iron oxide-magnetic resonance imaging (USPIO-MRI) to monitor macrophage trafficking, the purpose of this project is to determine whether minocycline modulates macrophage trafficking to the site of nerve injury in vivo and, in turn, results in altered pain thresholds. RESULTS: Animal experiments were approved by Stanford IACUC. A model of neuropathic pain was created using the Spared Nerve Injury (SNI) model that involves ligation of the left sciatic nerve in the left thigh of adult Sprague-Dawley rats. Animals with SNI and uninjured animals (control) were then injected with/without USPIOs (300umol/kg IV) and with/without minocycline (50mg/kg IP). Bilateral sciatic nerves were scanned with a volume coil in a 7T magnet 7 days after USPIO administration. Fluid-sensitive MR images were obtained, and ROIs were placed on bilateral sciatic nerves to quantify signal intensity. Pain behavior modulation by minocycline was measured using the Von Frey filament test. Sciatic nerves were ultimately harvested at day 7, fixed in 10% buffered formalin and stained for the presence of iron oxide-laden macrophages. Behavioral measurements confirmed the presence of allodynia in the neuropathic pain model while the uninjured and minocycline-treated injured group had significantly higher paw withdrawal thresholds (p<0.011). Decreased MR signal is observed in the SNI group that received USPIOs (3.3+/-0.5%) compared to the minocycline-treated SNI group that received USPIOs (15.2+/-4.5%) and minocycline-treated group (no USPIOs; 41.2+/-2.3%) (p<0.04). Histology of harvested sciatic nerve specimens confirmed the presence USPIOs at the nerve injury site in the SNI group without minocycline treatment. CONCLUSION: Animals with neuropathic pain in the left hindpaw show increased trafficking of USPIO-laden macrophages to the site of sciatic nerve injury. Minocycline appears to retard the migration of macrophages to the nerve injury site, which may partly explain its anti-nociceptive effects. USPIO-MRI is an effective in vivo imaging tool to study the role of macrophages in the development of neuropathic pain.