The effects of endothelin-1 on the cardiorespiratory physiology of the freshwater trout (Oncorhynchus mykiss) and the marine dogfish (Squalus acanthias).

The aim of the present study was to evaluate the effects of endothelin-l-elicited cardiovascular events on respiratory gas transfer in the freshwater rainbow trout (Oncorhynchus mykiss) and the marine dogfish (Squalus acanthias). In both species, endothelin-1 (666 pmol kg(-1)) caused a rapid (within 4 min) reduction (ca. 30-50 mmHg) in arterial blood partial pressure of O2. The effects of endothelin-1 on arterial blood partial pressure of CO2 were not synchronised with the changes in O2 partial pressure and the responses were markedly different in trout and dogfish. In trout, arterial CO2 partial pressure was increased transiently by approximately 1.0 mmHg but the onset of the response was delayed and occurred 12 min after endothelin-1 injection. In contrast, CO2 partial pressure remained more-or-less constant in dogfish after injection of endothelin-1 and was increased only slightly (approximately 0.1 mmHg) after 60 min. Pre-treatment of trout with bovine carbonic anhydrase (5 mg ml(-1)) eliminated the increase in CO2 partial pressure that was normally observed after endothelin-1 injection. In both species, endothelin-1 injection caused a decrease in arterial blood pH that mirrored the changes in CO2 partial pressure. Endothelin-1 injection was associated with transient (trout) or persistent (dogfish) hyperventilation as indicated by pronounced increases in breathing frequency and amplitude. In trout, arterial blood pressure remained constant or was decreased slightly and was accompanied by a transient increase in systemic resistance, and a temporary reduction in cardiac output. The decrease in cardiac output was caused solely by a reduction in cardiac frequency; cardiac stroke volume was unaffected. In dogfish, arterial blood pressure was lowered by approximately 10 mmHg at 6-10 min after endothelin-1 injection but then was rapidly restored to pre-injection levels. The decrease in arterial blood pressure reflected an increase in branchial vascular resistance (as determined using in situ perfused gill preparations) that was accompanied by simultaneous decreases in systemic resistance and cardiac output. Cardiac frequency and stroke volume were reduced by endothelin-1 injection and thus both variables contributed to the changes in cardiac output. We conclude that the net consequences of endothelin-1 on arterial blood gases result from the opposing effects of reduced gill functional surface area (caused by vasoconstriction) and an increase in blood residence time within the gill (caused by decreased cardiac output.     

The effects of endothelin-1 on the cardiorespiratory physiology of the freshwater trout (Oncorhynchus mykiss) and the marine dogfish (Squalus acanthias)

The aim of the present study was to evaluate the effects of endothelin-1-elicited cardiovascular events on respiratory gas transfer in the freshwater rainbow trout (Oncorhynchus mykiss) and the marine dogfish (Squalus acanthias). In both species, endothelin-1 (666 pmol kg^-1) caused a rapid (within 4 min) reduction (ca. 30-50 mmHg) in arterial blood partial pressure of O₂. The effects of endothelin-1 on arterial blood partial pressure of CO₂ were not synchronised with the changes in O₂ partial pressure and the responses were markedly different in trout and dogfish. In trout, arterial CO₂ partial pressure was increased transiently by ~1.0 mmHg but the onset of the response was delayed and occurred 12 min after endothelin-1 injection. In contrast, CO₂ partial pressure remained more-or-less constant in dogfish after injection of endothelin-1 and was increased only slightly (~0.1 mmHg) after 60 min. Pre-treatment of trout with bovine carbonic anhydrase (5 mg ml^-1) eliminated the increase in CO₂ partial pressure that was normally observed after endothelin-1 injection. In both species, endothelin-1 injection caused a decrease in arterial blood pH that mirrored the changes in CO₂ partial pressure. Endothelin-1 injection was associated with transient (trout) or persistent (dogfish) hyperventilation as indicated by pronounced increases in breathing frequency and amplitude. In trout, arterial blood pressure remained constant or was decreased slightly and was accompanied by a transient increase in systemic resistance, and a temporary reduction in cardiac output. The decrease in cardiac output was caused solely by a reduction in cardiac frequency; cardiac stroke volume was unaffected. In dogfish, arterial blood pressure was lowered by ~10 mmHg at 6-10 min after endothelin-1 injection but then was rapidly restored to pre-injection levels. The decrease in arterial blood pressure reflected an increase in branchial vascular resistance (as determined using in situ perfused gill preparations) that was accompanied by simultaneous decreases in systemic resistance and cardiac output. Cardiac frequency and stroke volume were reduced by endothelin-1 injection and thus both variables contributed to the changes in cardiac output. We conclude that the net consequences of endothelin-1 on arterial blood gases result from the opposing effects of reduced gill functional surface area (caused by vasoconstriction) and an increase in blood residence time within the gill (caused by decreased cardiac output.     

Effect of Endothelin on Vasomotor and Respiratory Neurons in the Rostral Ventrolateral Medulla in Rats

1. We have previously shown that intracisternal administration of endothelin-1 (ET-1) elicited cardiorespiratory responses acting on the ventral surface of the medulla oblongata (VSM) subjacent to the rostral ventrolateral medulla (RVLM). In this study, we examined whether vasomotor and respiratory neurons in RVLM participate in above-mentioned responses and whether those neurons respond to direct iontophoretic application of ET-1 and/or an ET-A receptor antagonist, FR139317.2. Unit activity of vasomotor, respiratory, or nociceptive neurons in RVLM was recorded together with arterial blood pressure (AP) and heart rate (HR) in urethane-anesthetized Sprague-Dawley rats.3. Intracisternal administration or topical application of ET-1 (0.1–1 pmol) to VSM caused excitation of the majority of vasomotor neurons (15/18) and respiratory neurons (10/11) but not in nociceptive neurons (0/7). Changes in neuronal activity were in similar time course with corresponding changes in AP and HR. Iontophoretic application of ET-1 to the vicinity of recording neuron caused excitation in 19 of 21 vasomotor neurons without affecting AP nor HR. Remaining two neurons were insensitive to ET-1. FR139317 did not affect basal activity of the vasomotor neurons but inhibited ET-1-evoked excitation. Twenty-four of 40 respiratory neurons were excited and 13 were inhibited by iontophoretic application of ET-1. Five of ET-1-excited respiratory neurons were inhibited by FR139317 alone while six of ET-1-inhibited neurons were not affected by FR139317 alone. In both cases, FR139317 inhibited the effect of simultaneously applied ET-1. Iontophoretic application of ET-1 excited only one out of 10 nociceptive neurons so far tested.4. These results support the view that intracisternally administered ET-1 alters activity of vasomotor and respiratory neurons in the RVLM, at least in part by acting directly on neurons themselves and hence causes systemic cardiorespiratory changes. Majority of vasomotor and respiratory neurons should express ET-A receptors and some respiratory neurons are under tonic excitatory control by ET-1.     

电刺激猫小脑顶核对动脉血压和肾交感神经放电的影响

在38只麻醉及人工呼吸的猫,观察到电刺激小脑顶核嘴侧部能引起动脉血压显著升高;肾交感神经放电于刺激期间显著增加。去缓冲神经对刺激顶核所引起的血压反应的幅度和肾交感神经放电均无明显影响,但可明显延长血压反应升高相以及血压恢复期的时间。静脉注射氯庄定引起血压降低、心率减慢及肾交感神经放电的抑制,并能减弱刺激顶核引起的血压反应,但增强了刺激顶核引起的肾神经放电的变化。电解损毁延髓腹外侧面引起血压降低及肾交感神经放电的抑制,然而无论单侧还是双侧损毁延髓腹外侧面都不能阻断刺激顶核所引起的血压和肾交感神经放电的反应。以上结果表明,电刺激顶核能引起明显的心血管反应,其反应的下行性通路可能不通过延髓腹外侧面。     

The effect of 4-week streptozotocin-induced diabetes on responses to endothelin-1 in rat isolated atria

The effect of endothelin-1 has been examined on isolated spontaneously beating right atria and electrically driven left atria from diabetic rats and age-matched controls. Diabetes was induced by a single i.v. injection of streptozotocin (65 mg/kg) 4–5 weeks before the experiments. Endothelin-1 (0.01–100 nM) caused concentration-dependent increases in atrial rate and force; the increases were not different between atria from diabetic and control rats. The ability of endothelin-1 to reduce chronotropic and inotropic responses to noradrenaline was also not different between the two groups. Endothelin-1 (10 nM) decreased the chronotropic response to sympathetic nerve stimulation (2 Hz, 10 s) in atria from control rats by 68 ± 5% (n = 8), but this decrease was slightly smaller (45 ± 6%, N = 8) in atria from diabetic rats.

The results provide no evidence to suggest that the diabetic state markedly alters cardiac responses to endothelin-1.     

Effect of intrathecal administration of ET-1, ET-3 and ET(16–21) on blood pressure and micturition reflex in anesthetized rats

In urethane-anesthetized rats, intrathecal administration of endothelin-1 (ET-1), endothelin-3 (ET-3) (3–100 pmol/rat) or the C-terminal hexapeptide ET(16–21) (10–100 nmol/rat) dose-dependently increased mean blood pressure (MBP) and suppressed the supraspinal micturition reflex (SMR). ET(16–21), at 100 nmol, produced a pressor response comparable to that induced by ET-1 at 100 pmol.

Guanethidine and hexamethonium pretreatment significantly reduced the increase of MBP induced by ET-1 but was inactive in antagonizing inhibition of SMR. Neither naloxone nor adrenalectomy were effective in preventing the responses to ET-1.

The high degree of lethality (60–100%), observed with ET-1 (10–100 pmol), was not reduced by guanethidine, naloxone, adrenalectomy or by hexamethonium.

ET-3, at 100 pmol or 1 nmol, induced death in about 50% of cases. The symptoms before death were reduction of the respiratory rate followed by respiratory arrest.

These findings indicate that the pressor response to intrathecally-administered endothelins involves activation of sympathetic preganglionic elements; induction of secretion of catecholamines from adrenal glands was excluded.

Lethality and inhibition of SMR does not involve opioids, sympathetic activation or release of catecholamines from the adrenal glands.     

Increases in arterial blood pressure in the rat in response to a new vertebrate neuropeptide, LPLRFamide, and a related molluscan peptide, FMRFamide

Vasopressor responses in urethane-anaesthetized rats were evoked by a new peptide from chicken brain, LPLRFamide, and the immunochemically related molluscan neuropeptide, FMRFamide. In doses of 50 to 200 nmol X kg-1, i.v., both peptides produced a rapid increase in arterial pressure that returned to basal in 1-2 min. When given intracisternally in similar doses the two peptides again increased arterial pressure, but the time to peak response (1-2 min) and the duration of the responses (5-8 min) were prolonged. There was a marked, reversible, specific, tachyphylaxis following intracisternal but not intravenous injection of LPLRFamide, indicating separate sites of action after administration by these routes. Guanethidine and phentolamine blocked the responses to both intravenous and intracisternal administration, and hexamethonium significantly reduced the response to intracisternal administration. Both by intravenous and intracisternal routes it is therefore likely that responses are mediated by noradrenaline release from sympathetic endings. In addition, following adrenalectomy and propranolol the response to intravenous (but not intracisternal) LPLRFamide was increased, suggesting that adrenaline released from the adrenal medulla might act at beta-adrenoreceptors causing vasodilatation. The physiological significance of these observations remains to be established, but it is significant that peptides immunochemically related to FMRFamide and LPLRFamide occur in areas of rat brain concerned with autonomic control.     

Effects of intraplantar injections of nociceptin and its N-terminal fragments on nociceptive and desensitized responses induced by capsaicin in mice

Injection of capsaicin into the hindpaw has been employed as a model of chemogenic nociception in mice. Intraplantar injection of nociceptin (30–240 pmol) produced a significant and dose-dependent antinociceptive activity in the capsaicin test. The nociceptin N-terminal fragments, (1–11) and (1–13), were also active with a potency higher than nociceptin and comparable to nociceptin, respectively. Intraplantar injection of the nociceptin (1–7) fragment had no effect on capsaicin-induced nociception. Antinociception induced by nociceptin or nociceptin (1–13) was reversed significantly by intraplantar co-injection of [Nphe¹]nociceptin (1–13)NH₂, an orphan opioid receptor-like 1 (ORL1) receptor antagonist, whereas local injection of the antagonist did not interfere with the action of nociceptin (1–11). Nociceptin (1–11) was approximately 2.0-fold more potent than naturally occurring peptide nociceptin, and 10-fold more active than intraplantar morphine. Nociceptive licking/biting response to intraplantar injection of capsaicin was desensitized by repeated injections of capsaicin at the interval of 15 min. Desensitization induced by capsaicin was attenuated significantly by co-injection of nociceptin at much lower doses than antinociceptive ED₅₀ for nociceptin. Capsaicin desensitization was also decreased by co-injection of nociceptin (1–11) and (1–13) to a similar extent. The present results indicate that not only nociceptin but also the N-terminal fragment (1–13) possesses a local peripheral antinociceptive action, which may be mediated by peripheral ORL1 receptors. In addition, the difference of the effective doses suggests that the antinociceptive action and inhibition of capsaicin-induced desenitization by nociceptin, nociceptin (1–11) and (1–13), may involve distinct mechanisms at the level of the peripheral nerve terminal.     

Electrical activity of phrenic nerve and diaphragm in utero.

Phrenic nerve activity, diaphragmatic EMG, and tracheal or pleural pressure changes were recorded in a chronic fetal sheep preparation. Three patterns of fetal phrenic nerve activity were observed: 1) a single burst; 2) irregular nonrhythmic bursts; and 3) prolonged rhythmic activity, seen only prior to fetal death. The total recording time was 54.53 h and the total duration of phrenic nerve activity was 65.34 min (2.16%). When an inactive period was defined as the absence of phrenic nerve activity for 60 s or more, active periods occupied 44.7% of the total time. Phrenic nerve activity was present in all fetuses and 97.5% of the time was coupled with diaphragmatic EMG. Both diaphragmatic EMG and intrapulmonary pressure changes occurred in the absence of phrenic nerve activity. In three fetal animals both phrenic nerves were transected. Tracheal pressure changes were seen which were not coupled with corresponding intrauterine pressure changes. Thus, changes in fetal tracheal pressure or diaphragmatic EMG do not necessarily represent the output of the fetal respiratory center. This study suggests that the fetal respiratory center is active in utero, but this activity is minimal and has a different pattern that that present after birth.     

Role of endothelin-1 in the central neural cardiovascular control

In acute experiments on cats, endothelin-1 (ET-1) was injected into the sympathoexcitatory neuronal structures of the ventrolateral medulla (VLM) and the effects of injections on the peripheral mechanisms of circulation control were studied. Effects of ET-1 appeared to be dose-dependent. Injections of 200 pmol ET-1 into the structures of the tested brain zone resulted in considerable regular hypertensive responses due to an increase in the common peripheral vascular resistance (PVR), which corresponds to vasospasm. ET-1 in a smaller dose (100 pmol) could cause either hypertensive or, in some cases, hypotensive responses. Hemodynamic responses induced by injections of 100 pmol ET-1 into the sites of localization of vasomotor neurons in the VLM were based on less expressed shifts in the peripheral vascular resistance, as compared with the effects of ET-1 in the dose of 200 pmol. The effects were related to either facilitation or suppression (in the cases of hypertensive or hypotensive responses, respectively) of descending sympathoexcitatory influences from the VLM on different vascular pools. The threshold for excitation of vasomotor neurons in the tested brain area is likely to be considerably lower as compared with that for medullary “cardiac” neurons, because injections of 200 pmol ET-1 in the site of localization of cardiac neurons were followed by either enhancement, or suppression of the contractile myocardiac activity, while the heart rate usually decreased. The effects of ET-1 were facilitated after blocking of GABAa receptors with bicuculline and attenuated after preliminary application of GABA to the ventral surface of the medulla. The results indicate the possibility of interaction ET-1 and GABA on the neurons in the VLM. Such interaction is likely to be directed toward providing an optimum mode of regulation of the blood circulation.     

Increases in heart rate and blood pressure produced by microinjections of atrial natriuretic factor into the AV3V region of rat brain

Recent studies have provided evidence for the dense localization of atrial natriuretic factor (ANF) in the anteroventral third ventricle (AV3V) region of the rat brain. This area is currently thought to be involved in the regulation of blood pressure and fluid and electrolyte balance. To investigate whether ANF may play a role in central cardiovascular regulation, the effects of microinjection of ANF into the preoptic suprachiasmatic nucleus (POSC), which is located in the AV3V region of the brain, were examined in the present study. Low doses of ANF (2–4 pmol) produced modest elevations in systolic and diastolic pressures, approximately 10–14%, and a small rise in HR of roughly 7%. Higher doses of ANF (20–40 pmol) produced significant increases in systolic (15–19%), mean arterial (12–14%) and pulse (25–36%) pressures. In addition, much larger increases in HR, approximately 20%, were produced by these higher doses of ANF. The onset of effects produced by ANF on BP and HR was seen 15–45 min after injection. Peak effects were usually observed approximately 60–150 min after onset, and the duration of the effect was 2–4 hours, after which time values usually returned to baseline. These studies indicate that ANF produces significant increases in BP and HR when injected at pmol doses into the POSC, and lends support to the idea that this peptide may play an important role in central cardiovascular regulatory mechanisms.     

Influence of cold stress on neuropeptide Y and sympathetic neurotransmission

Chronic cold stress of rats (4 °C; 1–3 weeks) induced a marked increase in gene expression (adrenal medulla; superior cervical ganglia), tissue content (mesenteric arterial bed) and nerve stimulation-induced overflow of NPY-immunoreactivity (NPYir) from the perfused mesenteric arterial bed. In contrast increased NPY neurotransmission was offset by an apparent decrease in the evoked overflow of norepinephrine (NE) due to a presumed deactivation of NE by nitric oxide (NO), despite increased sympathetic nerve activity. The net effect of these offsetting system was no change in basal or the evoked increase in perfusion pressure (sympathetic tone). It is concluded that differences in NPY and NE transmission act as an important compensatory mechanism preventing dramatic changes in arterial pressure when sympathetic nerve activity is high during cold stress.     

Influence of rostral ventrolateral medulla on renal sympathetic baroreflex in conscious rabbits

Previous studies with anesthetized animals have shown that the pressor region of the rostral ventrolateral medulla (RVLM) is a critical site in vasomotor control. The aim of this study was to develop, in conscious rabbits, a technique for microinjecting into the RVLM and to determine the influence of this area on renal sympathetic nerve activity (RSNA) and arterial pressure (AP) using local injections of glutamate, rilmenidine, ANG II and sarile. Rabbits were implanted with guide cannulas for bilateral microinjections into the RVLM (n = 7) or into the intermediate ventrolateral medulla (IVLM, n = 6) and an electrode for measuring RSNA. After 7 days of recovery, injections of glutamate (10 and 20 nmol) into the RVLM increased RSNA by 81 and 88% and AP by 17 and 25 mmHg, respectively. Infusion of glutamate (2 nmol/min) into the RVLM increased AP by 15 mmHg and the RSNA baroreflex range by 38%. By contrast, injection of the imidazoline receptor agonist rilmenidine (4 nmol) into the RVLM decreased AP by 8 mmHg and the RSNA baroreflex range by 37%. Injections of rilmenidine into the IVLM did not alter AP or RSNA. Surprisingly, treatments with ANG II (4 pmol/min) or the ANG II receptor antagonist sarile (500 pmol) into the RVLM did not affect the resting or baroreflex parameters. Infusion of ANG II (4 pmol/min) into the fourth ventricle increased AP and facilitated the RSNA baroreflex. Our results show that agents administered via a novel microinjecting system for conscious rabbits can selectively modulate neuronal activity in circumscribed regions of the ventrolateral medulla. We conclude that the RVLM plays a key role in circulatory control in conscious rabbits. However, we find no evidence for the role of ANG II receptors in the RVLM in the moment-to-moment regulation of AP and RSNA.     

Influence of intravenously administered leptin on nitric oxide production, renal hemodynamics and renal function in the rat

We investigated the effect of leptin on systemic nitric oxide (NO) production, arterial pressure, renal hemodynamics and renal excretory function in the rat. Leptin (1 mg/kg) was injected intravenously and mean arterial pressure (MAP), heart rate (HR), renal blood flow (RBF) and renal cortical blood flow (RCBF), were measured for 210 min after injection. Urine was collected for seven consecutive 30-min periods and blood samples were withdrawn at 15, 45, 75, 105, 135, 165 and 195 min after leptin administration. Leptin had no effect on MAP, HR, RBF, RCBF and creatinine clearance, but increased urine output by 37.8% (0–30 min), 32.4% (31–60 min) and 27.0% (61–90 min), as well as urinary sodium excretion by 175.8% (0–30 min), 136.4% (31–60 min) and 124.2% (61–90 min). In contrast, leptin had no effect on potassium and phosphate excretion. Plasma concentration of NO metabolites, nitrites+nitrates (NO_x), increased following leptin injection at 15, 45, 75 and 105 min by 27.7%, 178.1%, 156.4% and 58.7%, respectively. Leptin increased urinary NO_x excretion by 241.6% (0–30 min), 552.6% (31–60 min), 430.7% (61–90 min) and 88.9% (91–120 min). This was accompanied by increase in plasma and urinary cyclic GMP. These data indicate that leptin stimulates systemic NO production but has no effect on arterial pressure and renal hemodynamics.     

Critical developmental period for hyperoxia-induced blunting of hypoxic phrenic responses in rats.

Hypoxic ventilatory and phrenic responses are reduced in adult rats reared in hyperoxia (60% O(2)) for the first month of life but not after hyperoxia as adults. In this study, we identified the developmental window for susceptibility to hyperoxia. Phrenic nerve responses to hypoxia were recorded in anesthetized, vagotomized, paralyzed, and ventilated Sprague-Dawley rats (aged 3-4 mo) exposed to 60% O(2) for the first, second, third, or fourth postnatal week. Responses were compared with control rats and with rats exposed to 60% O(2) for the first month of life. Phrenic minute activity (burst amplitude x frequency) increased less during isocapnic hypoxia (arterial PO(2) = 60, 50, and 40 Torr) in rats exposed to hyperoxia for the first or second week, or the first month, of life (P < 0.01 vs. control). Functional impairment caused by 1 wk of hyperoxia diminished with increasing age of exposure (P = 0.005). Adult hypoxic phrenic responses are impaired by 1 wk of hyperoxia during the first and second postnatal weeks in rats, indicating a developmental window coincident with carotid chemoreceptor maturation.     

Opposite effects of cholecystokinin octapeptide (CCK-8) and tetrapeptide (CCK-4) after injection into the caudal part of the nucleus accumbens or into its rostral part and the cerebral ventricles

Neurons with colocalized cholecystokinin and dopamine are present predominantly in the ventral tegmental area and project mainly to the caudal part of the medial nucleus accumbens. The activity of this dopamine system can be evaluated by means of the intracranial self-stimulation behavior on male Wistar rats having chronic electrodes implanted into the medial forebrain bundle in the postero-lateral area of the hypothalamus. The direct injection of 150 pmol CCK-8 into the medio-caudal accumbens induced an increase of intracranial self stimulation while a similar administration into its rostral portion produced a slight decrease of intracranial self-stimulation. The administration of 300 pmol CCK-4 into the same medio-caudal part of the accumbens produced an inhibitory action on intracranial self stimulation lasting for 25 min. The injection of 70 to 1300 pmol CCK-4 into the cerebral ventricles produced no change on intracranial self-stimulation. The intracerebroventricular injection of 70 pmol CCK-8 induced a large decrease of intracranial self-stimulation lasting for 20 min. Sodium chloride 0.15 M or unsulphated CCK-8 injection were without effect in either case. These results support the ideas that intracerebroventricular CCK-8 injection inhibits accumbens dopaminergic activity but that CCK-8 injection into the medio-caudal part of the accumbens, where nerve terminals with colocalized CCK and DA are present, facilitates this dopaminergic activity. In addition at the level of medio-caudal accumbens, CCK-8 and CCK-4 have opposite effects.     

Intracerebral connections after administration of kainate into the caudal part of ventral sections of the medulla oblongata]

It was found that 1 day after unilateral destruction with kainate of neurons in the caudal ventral medulla unanesthetized animals showed disorders of arterial pressure control with a prevalence of hypertensive response. In 7 days after operation there was a decrease in the rate of neuronal uptake of serotonin and an increase in choline-, dopamine-, noradrenaline-, and glycinergic mediation in the basal hypothalamus and rostral ventral medulla, which characterize the functional state of synaptic formations in the brain stem structures connected to neurons in the caudal ventral medulla and involved in cardiovascular regulation.     

Role of small conductance calcium-activated potassium channels expressed in PVN in regulating sympathetic nerve activity and arterial blood pressure in rats

Small conductance Ca(2+)-activated K(+) (SK) channels regulate membrane properties of rostral ventrolateral medulla (RVLM) projecting hypothalamic paraventricular nucleus (PVN) neurons and inhibition of SK channels increases in vitro excitability. Here, we determined in vivo the role of PVN SK channels in regulating sympathetic nerve activity (SNA) and mean arterial pressure (MAP). In anesthetized rats, bilateral PVN microinjection of SK channel blocker with peptide apamin (0, 0.125, 1.25, 3.75, 12.5, and 25 pmol) increased splanchnic SNA (SSNA), renal SNA (RSNA), MAP, and heart rate (HR) in a dose-dependent manner. Maximum increases in SSNA, RSNA, MAP, and HR elicited by apamin (12.5 pmol, n = 7) were 330 ± 40% (P < 0.01), 271 ± 40% (P < 0.01), 29 ± 4 mmHg (P < 0.01), and 34 ± 9 beats/min (P < 0.01), respectively. PVN injection of the nonpeptide SK channel blocker UCL1684 (250 pmol, n = 7) significantly increased SSNA (P < 0.05), RSNA (P < 0.05), MAP (P < 0.05), and HR (P < 0.05). Neither apamin injected outside the PVN (12.5 pmol, n = 6) nor peripheral administration of the same dose of apamin (12.5 pmol, n = 5) evoked any significant changes in the recorded variables. PVN-injected SK channel enhancer 5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazol-2-one (DCEBIO, 5 nmol, n = 4) or N-cyclohexyl-N-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-4-pyrimidin]amine (CyPPA, 5 nmol, n = 6) did not significantly alter the SSNA, RSNA, MAP, and HR. Western blot and RT-PCR analysis of punched PVN tissue showed abundant expression of SK1-3 channels. We conclude that SK channels expressed in the PVN play an important role in the regulation of sympathetic outflow and cardiovascular function.     

Long-lasting vasoconstriction and efficient regional extraction of endothelin-1 in human splanchnic and renal tissues

Six healthy subjects were given endothelin-1, intravenously in a dose of 4 pmol.kg-1.min-1 for 20 min. Blood samples were drawn from arterial, hepatic and renal vein catheters for determinations of splanchnic and renal blood flows and the extraction of endothelin-1 in these vascular beds. Intravenous infusion of endothelin-1 increased the mean arterial blood pressure by 6.8 +/- 2.0 mm Hg (p less than 0.05) and reduced splanchnic and renal blood flows by 34% (p less than 0.005) and 26% (p less than 0.001) respectively. Return to basal flow values occurred after about 1 hr for the splanchnic and 3 hrs for the renal blood flow. The fractional extractions of endothelin-1-like immunoreactivity corresponded to 75 +/- 2% and 60 +/- 2% in the splanchnic and renal vascular beds, respectively. The disappearance curve in plasma and two half-lives of 1.4 +/- 0.1 min and 35 +/- 2.8 min respectively.     

-MSH exhibits opioid antagonist-like effects in the brainstem of rats

Unilateral microinjections of -MSH (0.3, 1.2 and 12 pmol) into the nucleus tractus solitarius (NTS) of urethane-anaesthetized rats did not modify blood pressure or heart rate (HR). Using a dual microinjection technique, it has been shown that prior injection of -MSH (0.3 pmol) attenuated the pressor effect of a similar injection of dynorphin 1–9 (18 pmol) but did not modify the cardiovascular effects of [Met]enkephalin (14 pmol). Since -MSH has been localized in the NTS, the results indicate that this peptide may play a role in central cardiovascular control, possibly acting in an antagonistic manner to the endogenous opioid peptides.