Nitric oxide inhibition abolishes sleep-wake differences in cerebral circulation

Nitric oxide (NO), being produced by active neurones and also being a cerebral vasodilator, may couple brain activity and blood flow in sleep, particularly during active sleep (AS), which is characterized by widespread neural activation and markedly elevated cerebral blood flow (CBF) compared with quiet wakefulness (QW) and quiet sleep (QS). This study examined CBF and cerebral vascular resistance (CVR) in lambs (n = 6) during spontaneous sleep-wake cycles before and after infusion of N(omega)-nitro-L-arginine (L-NNA), an inhibitor of NO synthase. L-NNA infusion produced increases in CVR and decreases in CBF during all sleep-wake stages, with the greatest changes occurring in AS (DeltaCVR, 88 +/- 19%; DeltaCBF -24 +/- 8%). The characteristic CVR and CBF differences among AS, QS, and QW disappeared within 1-3 h of L-NNA infusion, but had reappeared by 24 h despite persisting cerebral vasoconstriction. These experiments show that NO promotes cerebral vasodilatation during sleep as well as wakefulness, particularly during AS. Additionally, NO is the major, although not sole, determinant of the CBF differences that exist between sleep-wake states.     

Cyclooxygenase inhibition attenuates sympathetic responses to muscle stretch in humans

Passive muscle stretch performed during a period of post-exercise muscle ischemia (PEMI) increases muscle sympathetic nerve activity (MSNA), and this suggests that the muscle metabolites may sensitize mechanoreceptors in healthy humans. However, the responsible substance(s) has not been studied thoroughly in humans. Human and animal studies suggest that cyclooxygenase products sensitize muscle mechanoreceptors. Thus we hypothesized that local cyclooxygenase inhibition in exercising muscles could attenuate MSNA responses to passive muscle stretch during PEMI. Blood pressure (Finapres), heart rate, and MSNA (microneurography) responses to passive muscle stretch were assessed in 13 young healthy subjects during PEMI before and after cyclooxygenase inhibition, which was accomplished by a local infusion of 6 mg ketorolac tromethamine in saline via Bier block. In the second experiment, the same amount of saline was infused via the Bier block. Ketorolac Bier block decreased prostaglandin synthesis to approximately 34% of the baseline. Before ketorolac Bier block, passive muscle stretch evoked significant increases in MSNA (P < 0.005) and mean arterial blood pressure (P < 0.02). After ketorolac Bier block, passive muscle stretch did not evoke significant responses in MSNA (P = 0.11) or mean arterial blood pressure (P = 0.83). Saline Bier block had no effect on the MSNA or blood pressure response to ischemic stretch. These observations indicate that cyclooxygenase inhibition attenuates MSNA responses seen during PEMI and suggest that cyclooxygenase products sensitize the muscle mechanoreceptors.     

Cyclooxygenase 2 inhibition promotes IFN-gamma-dependent enhancement of antitumor responses

In previous studies, we demonstrated an immune suppressive network in non-small cell lung cancer that is due to overexpression of tumor cyclooxygenase 2 (COX-2). In this study, we assessed the vaccination response to tumor challenge following either pharmacological or genetic inhibition of COX-2 in a murine lung cancer model. Treatment of naive mice with the COX-2 inhibitor, SC-58236, skewed splenocytes toward a type 1 cytokine response, inducing IFN-gamma, IL-12, and IFN-gamma-inducible protein 10, whereas the type 2 cytokines IL-4, IL-5, and IL-10 remained unaltered. Fifty percent of mice receiving SC-58236 and an irradiated tumor cell vaccine completely rejected tumors upon challenge. Those mice that did form tumors following challenge demonstrated a reduced tumor growth. In contrast, all mice either vaccinated with irradiated tumor cells alone or receiving SC-58236 alone showed progressive tumor growth. Studies performed in CD4 and CD8 knockout mice revealed a requirement for the CD4 T lymphocyte subset for the complete rejection of tumors. To determine the role of host COX-2 expression on the vaccination responses, studies were performed in COX-2 gene knockout mice. Compared with control littermates, COX-2(-/-) mice showed a significant tumor growth reduction, whereas heterozygous COX-2(-/+) mice had an intermediate tumor growth reduction following vaccination. In vivo depletion of IFN-gamma abrogated the COX-2 inhibitor-mediated enhancement of the vaccination effect. These findings provide a strong rationale for additional evaluation of the capacity of COX-2 inhibitors to enhance vaccination responses against cancer.     

Arousal and cardiopulmonary responses to hyperoxic hypercapnia in lambs

Experiments were done to investigate the arousal and cardiopulmonary responses to hyperoxic hypercapnia in 8 lambs. Each lamb was anaesthetized and instrumented for recordings of electrocorticogram, electro-oculogram, nuchal and diaphragm electromyograms and measurements of arterial blood pressure and haemoglobin oxygen saturation. No sooner than 3 days after surgery, measurements were made in quiet sleep and active sleep during control periods when the animal was breathing 21% oxygen and during experimental periods of hyperoxic hypercapnia when the animal was breathing 10% carbon dioxide and 30% oxygen. Hyperoxic hypercapnia was terminated during each epoch by returning the inspired gas mixture to 21% oxygen once the animal aroused from sleep. Arousal occurred from both sleep states during hyperoxic hypercapnia but was delayed in active sleep compared to quiet sleep (active sleep 58 +/- 17 s; quiet sleep 21 +/- 10 s; mean +/- 1SD). There were no significant changes in heart rate or blood pressure during hyperoxic hypercapnia before arousal. However, respiratory rate and diaphragm electrical activity did increase during hyperoxic hypercapnia before arousal. Thus, our data provide evidence that hypercapnia can initiate arousal from sleep in young lambs. The mechanisms responsible for this response are yet to be determined.     

Cyclooxygenase inhibition and baroreflex sensitivity in humans

Animal studies suggest that prostanoids (i.e., such as prostacyclin) may sensitize or impair baroreceptor and/or baroreflex responsiveness depending on the site of administration and/or inhibition. We tested the hypothesis that acute inhibition of cyclooxygenase (COX), the rate-limiting enzyme in prostanoid synthesis, impairs baroreflex regulation of cardiac period (R-R interval) and muscle sympathetic nerve activity (MSNA) in humans and augments pressor reactivity. Baroreflex sensitivity (BRS) was determined at baseline (preinfusion) and 60 min after (postinfusion) intravenous infusion of a COX antagonist (ketorolac; 45 mg) (24 +/- 1 yr; n = 12) or saline (25 +/- 1 yr; n = 12). BRS was assessed by using the modified Oxford technique (bolus intravenous infusion of nitroprusside followed by phenylephrine). BRS was quantified as the slope of the linear portion of the 1) R-R interval-systolic blood pressure relation (cardiovagal BRS) and 2) MSNA-diastolic blood pressure relation (sympathetic BRS) during pharmacological changes in arterial blood pressure. Ketorolac did not alter cardiovagal (19.4 +/- 2.1 vs. 18.4 +/- 2.4 ms/mmHg preinfusion and postinfusion, respectively) or sympathetic BRS (-2.9 +/- 0.7 vs. -2.6 +/- 0.4 arbitrary units.beat(-1).mmHg(-1)) but significantly decreased a plasma biomarker of prostanoid generation (plasma thromboxane B2) by 53 +/- 11%. Cardiovagal BRS (21.3 +/- 3.8 vs. 21.2 +/- 3.0 ms/mmHg), sympathetic BRS (-3.4 +/- 0.3 vs. -3.2 +/- 0.2 arbitrary units.beat(-1).mmHg(-1)), and thromboxane B2 (change in -1 +/- 12%) were unchanged in the control (saline infusion) group. Pressor responses to steady-state incremental (0.5, 1.0, and 1.5 microg.kg(-1).min(-1)) infusion (5 min/dose) of phenylephrine were not altered by ketorolac (n = 8). Collectively, these data indicate that acute pharmacological antagonism of the COX enzyme does not impair BRS (cardiovagal or sympathetic) or augment pressor reactivity in healthy young adults.     

Electric responses of the cerebral cortex to central excitation and inhibition

An attempt was made to evaluate critically the extent to which the background electrocorticogram, neuronal impulse activity, and evoked potentials reflect the state of cortical excitation and inhibition. It was shown that during electrocorticogram desynchronization, firing neurons predominated in the surface (mainly afferent) layers, while inhibited neurons were in the majority in the lower layers of the cortex. Consequently, desynchronization does not reflect diffuse excitation of the cortex and cannot be taken as an index of central excitation. Slow electrocortical waves cannot be used as indicators of an inhibitory state, even though they may be associated with processes leading to the development of inhibition. Under the effects of different stimuli, the number of neurons participating in impulse condition, and the number of neurons temporarily inhibiting impulse activity in the projection cortical area were stable (ratio 2:1). It was found that the correlation between impulse discharges of neuronal pairs increases during both central excitation and central inhibition. Nonetheless, differences between cortical excitation and inhibition were seen in the reorganization of neuronal columns. The use of evoked potentials to determine cortical excitation or inhibition is complicated by the fact that the amplitude of evoked-potential components reflects the divergent influences of many factors. It was shown that conditional excitation diminished the evoked potential to a light stimulus in the projection cortical area, but caused it to increase in the region of the motor analyzer. The elaboration of a conditional inhibition (extinction) is accompanied by the growth of an evoked potential to a stimulus in the primary cortical area, and by its repression in the region of the motor analyzer. In this case, a large delayed negative wave appears in the evoked potential.This report was presented at the All-Union Symposium on Electric Responses of the Cerebral Cortex to Afferent Stimuli, Kiev, October, 1969.Rostov-on-Don State University. Translated from Neirofiziologiya, Vol. 2, No. 2, pp. 140–154, March–April, 1970.     

Cardiorespiratory responses of white sturgeon to environmental hypercapnia

Cardioventilatory variables and blood-gas, acid-base status were measured in cannulated white sturgeon (Acipenser transmontanus) maintained at 19 degrees C during normocapnic and hypercapnic (Pw(CO(2)) approximately 20 Torr) water conditions and after the injection of adrenergic analogs. Hypercapnia produced significant increases in arterial PCO(2), ventilatory frequency, and plasma concentration of cortisol and epinephrine, and it produced significant decreases in arterial pH and plasma concentration of glucose but no change in arterial PO(2), hematocrit, and concentration of lactate or norepinephrine. Hypercapnia significantly increased cardiac output (Q) by 22%, mean arterial pressure (MAP) by 8%, and heart rate (HR) by 8%. However, gut blood flow (GBF) remained constant. In normocapnic fish, phenylephrine significantly constricted the splanchnic circulation, whereas isoproterenol significantly increased Q and produced a systemic vasodilation. During hypercapnia, propranolol significantly decreased Q, GBF, MAP, and HR, whereas phentolamine significantly decreased MAP and increased GBF. These changes suggest that cardiovascular function in the white sturgeon is sensitive to both alpha- and beta-adrenergic modulation. We found microspheres to be unreliable in predicting GBF on the basis of our comparisons with simultaneous direct measurements of GBF. Overall, our results demonstrate that environmental hypercapnia (e.g., as is experienced in high-intensity culture situations) elicits stress responses in white sturgeon that significantly elevate steady-state cardiovascular and ventilatory activity levels.     

Cyclooxygenase inhibition during allergic sensitization increases STAT6-independent primary and memory Th2 responses

Immune sensitization and memory generation are required for the development of allergic inflammation. Our previous studies demonstrate that the cyclooxygenase (COX) metabolic pathway is actively involved in allergic responses and COX inhibition increases allergic airway inflammation in a STAT6-independent fashion. To test the hypothesis that COX inhibition augments allergic inflammation by enhancing immune sensitization and memory, we sensitized STAT6 knockout mice with an i.p. injection of OVA with aluminum hydroxide as an adjuvant and treated the mice with the COX inhibitor indomethacin or vehicle for analyses of the primary and memory immune responses. We found that COX inhibition during immune sensitization, but not the allergic challenge phase, was necessary and sufficient to increase allergic inflammation. COX inhibition during sensitization increased the numbers of mature dendritic cells and activated CD4 T cells in the spleen and augmented OVA-specific IL-5 and IL-13 responses of the splenic CD4 T cells at day 5 after sensitization. COX inhibition during sensitization also augmented allergic Th2 response to OVA challenge 90 days after the sensitization. Therefore, COX inhibition during allergic sensitization augments allergic responses by enhancing Th2 cell activation and memory generation and the proallergic effect is STAT6-independent. These findings provide a mechanistic explanation for the increased allergic inflammation previously shown in the mice treated with COX inhibitors and in COX-deficient mice and suggest that use of COX-inhibiting drugs during initial allergen exposure may increase the risk of developing allergic responses.     

Cyclooxygenase inhibition by diclofenac formulated in bioadhesive carriers

Adverse effects and gastrointestinal toxicity limit the use of Diclofenac, a frequently-used NSAID for treatments of rheumatic disorders and other chronic inflammatory diseases. Diclofenac-carrier formulations may alleviate adverse effects, increase efficacy and allow local administration. We report here our first step, biophysical and biochemical investigations of Diclofenac formulated in our previously-developed bioadhesive liposomes carrying hyaluronan (HA-BAL) or collagen (COL-BAL) on their surface. Both liposome types encapsulated Diclofenac at high efficiency, encapsulated doses reaching 13 mg drug/ml, and performed as sustained-release Diclofenac depots, half-lives of drug release (under fastest conditions) ranging from 1 to 3 days. Therapeutic activity of liposomal Diclofenac was evaluated in CT-26 cells that possess the CD44 hyaluronan receptors and integrins, and are a bench-mark for intracellular COX enzymes. HA-BAL and COL-BAL showed high cellular-affinity that was 40 fold and 6 fold over that of regular liposomes. Free, and liposome-encapsulated, Diclofenac showed similar activities. For example: 2-3nM Diclofenac given to intact cells generated COX-inhibition levels in the range of 60-70% for free drug and for encapsulated drug in COL-BAL and in HA-BAL. We propose these novel Diclofenac formulations possess key physicochemical and biochemical attributes for task performance, meriting the next step into in vivo studies.     

Cyclooxygenase inhibition by diclofenac formulated in bioadhesive carriers

Adverse effects and gastrointestinal toxicity limit the use of Diclofenac, a frequently-used NSAID for treatments of rheumatic disorders and other chronic inflammatory diseases. Diclofenac-carrier formulations may alleviate adverse effects, increase efficacy and allow local administration. We report here our first step, biophysical and biochemical investigations of Diclofenac formulated in our previously-developed bioadhesive liposomes carrying hyaluronan (HA-BAL) or collagen (COL-BAL) on their surface. Both liposome types encapsulated Diclofenac at high efficiency, encapsulated doses reaching 13mg drug/ml, and performed as sustained-release Diclofenac depots, half-lives of drug release (under fastest conditions) ranging from 1 to 3days. Therapeutic activity of liposomal Diclofenac was evaluated in CT-26 cells that possess the CD44 hyaluronan receptors and integrins, and are a bench-mark for intracellular COX enzymes. HA-BAL and COL-BAL showed high cellular-affinity that was 40 fold and 6 fold over that of regular liposomes. Free, and liposome-encapsulated, Diclofenac showed similar activities. For example: 2-3nM Diclofenac given to intact cells generated COX-inhibition levels in the range of 60-70% for free drug and for encapsulated drug in COL-BAL and in HA-BAL. We propose these novel Diclofenac formulations possess key physicochemical and biochemical attributes for task performance, meriting the next step into in vivo studies.     

Respiratory responses to CO2 by controlled alveolar hypercapnia

A method is suggested for evaluating the respiratory response to the hypercapnic stimulus by means of increasing the alveolar pCO2 in accordance with the program assigned. The results obtained are not related to the metabolic level, respiratory resistance or other factors. In contra-distinction to the widely applied method of recurrent respiration, the method suggested allows a comparison of CO2 ventilatory sensitivity at rest, during muscular exercise, at altered respiratory resistance, etc. It can be used both clinically and experimentally.     

Peripheral chemoreceptor contributions to sympathetic and cardiovascular responses during hypercapnia

We tested the hypothesis that integrated sympathetic and cardiovascular reflexes are modulated by systemic CO2 differently in hypoxia than in hyperoxia (n = 7). Subjects performed a CO2 rebreathe protocol that equilibrates CO2 partial pressures between arterial and venous blood and that elevates end tidal CO2 (PET(CO2)) from approximately 40 to approximately 58 mmHg. This test was repeated under conditions where end tidal oxygen levels were clamped at 50 (hypoxia) or 200 (hyperoxia) mmHg. Heart rate (HR; EKG), stroke volume (SV; Doppler ultrasound), blood pressure (MAP; finger plethysmograph), and muscle sympathetic nerve activity (MSNA) were measured continuously during the two protocols. MAP at 40 mmHg PET(CO2) (i.e., the first minute of the rebreathe) was greater during hypoxia versus hyperoxia (P < 0.05). However, the increase in MAP during the rebreathe (P < 0.05) was similar in hypoxia (16 +/- 3 mmHg) and hyperoxia (17 +/- 2 mmHg PET(CO2)). The increase in cardiac output (Q) at 55 mmHg PET(CO2) was greater in hypoxia (2.61 +/- 0.7 L/min) versus hyperoxia (1.09 +/- 0.44 L/min) (P < 0.05). In both conditions the increase in Q was due to elevations in both HR and SV (P < 0.05). Systemic vascular conductance (SVC) increased to similar absolute levels in both conditions but rose earlier during hypoxia (> 50 mmHg PET(CO2)) than hyperoxia (> 55 mmHg). MSNA increased earlier during hypoxic hypercapnia (> 45 mmHg) compared with hyperoxic hypercapnia (> 55 mmHg). Thus, in these conscious humans, the dose-response effect of PET(CO2) on the integrated cardiovascular responses was shifted to the left during hypoxic hypercapnia. The combined data indicate that peripheral chemoreceptors exert important influence over cardiovascular reflex responses to hypercapnia.     

Naloxone does not affect ventillatory responses to hypoxia and hypercapnia in rats

Ventilatory responses (tidal volume, respiratory frequency, and minute ventilation) to steady-state hypoxia and steady-state hypercapnia were measured plethysmographically in awake unrestrained adult rats, before and after subcutaneous injection of placebo (saline) or naloxone in doses up to 5.0 mg/kg. Naloxone did not alter the ventilatory responses to hypoxia or hypercapnia.     

Cerebral and myocardial blood flow responses to hypercapnia and hypoxia in humans

In humans, cerebrovascular responses to alterations in arterial Pco(2) and Po(2) are well documented. However, few studies have investigated human coronary vascular responses to alterations in blood gases. This study investigated the extent to which the cerebral and coronary vasculatures differ in their responses to euoxic hypercapnia and isocapnic hypoxia in healthy volunteers. Participants (n = 15) were tested at rest on two occasions. On the first visit, middle cerebral artery blood velocity (V(P)) was assessed using transcranial Doppler ultrasound. On the second visit, coronary sinus blood flow (CSBF) was measured using cardiac MRI. For comparison with V(P), CSBF was normalized to the rate pressure product [an index of myocardial oxygen consumption; normalized (n)CSBF]. Both testing sessions began with 5 min of euoxic [end-tidal Po(2) (Pet(O(2))) = 88 Torr] isocapnia [end-tidal Pco(2) (Pet(CO(2))) = +1 Torr above resting values]. Pet(O(2)) was next held at 88 Torr, and Pet(CO(2)) was increased to 40 and 45 Torr in 5-min increments. Participants were then returned to euoxic isocapnia for 5 min, after which Pet(O(2)) was decreased from 88 to 60, 52 and 45 Torr in 5-min decrements. Changes in V(P) and nCSBF were normalized to isocapnic euoxic conditions and indexed against Pet(CO(2)) and arterial oxyhemoglobin saturation. The V(P) gain for euoxic hypercapnia (%/Torr) was significantly higher than nCSBF (P = 0.030). Conversely, the V(P) gain for isocapnic hypoxia (%/%desaturation) was not different from nCSBF (P = 0.518). These findings demonstrate, compared with coronary circulation, that the cerebral circulation is more sensitive to hypercapnia but similarly sensitive to hypoxia.     

Maturational differences in chlorpyrifos-oxonase activity may contribute to age-related sensitivity to chlorpyrifos

Chlorpyrifos (CPF), a commonly used cholinesterase-inhibiting insecticide, is lethal at much lower doses to young animals than adults. To explain this higher sensitivity in younger animals, we hypothesized that young rats have less chlorpyrifos-oxonase (CPFOase) activity than adults. To test this hypothesis, CPFOase activity was measured in the brain, plasma, and liver of male, postnatal day 4 (PND4) and adult (PND90) Long-Evans rats. CPFOase is biochemically defined as a Ca²⁺-dependent A-esterase that hydrolyzes chlorpyrifos-oxon (CPFO), the active metabolite of CPF. No brain CPFOase activity was detected at either age. Plasma and liver CPFOase activities were markedly lower at PND4 compared to adult: PND4 plasma and liver CPFOase activities were 1/11 and 1/2 the adult plasma and liver activities, respectively. Because the K_m of CPFOase activity was high (i.e., 210–380 μM), it was important to determine if this CPFOase activity could hydrolyze physiologically relevant concentrations (i.e., nM to low μM) of CPFO. This was accomplished by comparing the shifts in the tissue acetylcholinesterase (AChE) IC₅₀ for CPFO in the presence or absence of CPFOase activity. One would expect an increase in the “apparent” IC₅₀ if CPFOase hydrolyzes substantial amounts of CPFO during the 30 minutes the tissue is preincubated with the CPFO. In the adult, both plasma and liver AChE apparent IC₅₀ values were higher in the presence of CPFOase activity, suggesting that the CPFOase in those tissues was capable of hydrolyzing physiologically relevant concentrations of CPFO within 30 minutes. In young animals, however, there was less of a shift in the IC₅₀ curves compared to the adult, confirming that the young animal has less capacity than the adult to detoxify physiologically relevant concentrations of CPFO via CPFOase. © 1997 John Wiley & Sons, Inc. J Biochem Toxicol 11: 279–287, 1997.     

Strain differences in amiloride inhibition of NaCl responses in mice,Mus musculus

Summary The effects of lingual treatment with amiloride, an inhibitor of salt taste responses in several mammalian species, on NaCl responses of the chorda tympani nerve were compared between four inbred strains of mouse (BALB/cCrSlc, DBA/2CrSlc, C57BL/6CrSlc and C3H/HeSlc). In C57BL and C3H mice amiloride significantly suppressed responses of the chorda tympani nerve to NaCl at a concentration 0.1 M or more whereas in BALB and DBA mice the drug did not significantly affect the responses to NaCl at any concentration, suggesting a lack of the amiloride-sensitive receptor component for NaCl in the latter two strains.A two-bottle preference test demonstrated that all strains of mouse usually showed no preference for NaCl at any concentration and avoided NaCl at 0.3 M or more, although some differences were observed in that C57BL and C3H mice showed aversive responses to 0.1 and 0.15 M NaCl, whereas BALB and DBA mice were indifferent to these solutions.The results suggest that there exist prominent differences between mouse strains in the amiloride-sensitive component of their salt receptor systems. However, in mice the taste information derived from the amiloride-sensitive receptor component probably has no remarkable effect on behavioral responses to NaCl except for a possible contribution to decreasing aversion thresholds for NaCl by increasing overall taste information about NaCl.     

Differential sensitivities of cerebral and brachial blood flow to hypercapnia in humans.

Although it is known that the vasculatures of the brain and the forearm are sensitive to changes in arterial Pco(2), previous investigations have not made direct comparisons of the sensitivities of cerebral blood flow (CBF) (middle cerebral artery blood velocity associated with maximum frequency of Doppler shift; Vp) and brachial blood flow (BBF) to hypercapnia. We compared the sensitivities of Vp and BBF to hypercapnia in humans. On the basis of the critical importance of the brain for the survival of the organism, we hypothesized that Vp would be more sensitive than BBF to hypercapnia. Nine healthy males (30.1 +/- 5.2 yr, mean +/- SD) participated. Euoxic hypercapnia (end-tidal Po(2) = 88 Torr, end-tidal Pco(2) = 9 Torr above resting) was achieved by using the technique of dynamic end-tidal forcing. Vp was measured by transcranial Doppler ultrasound as an index of CBF, whereas BBF was measured in the brachial artery by echo Doppler. Vp and BBF were measured during two 60-min trials of hypercapnia, each trial separated by 60 min. Since no differences in the responses were found between trials, data from both trials were averaged to make comparisons between Vp and BBF. During hypercapnia, Vp and BBF increased by 34 +/- 8 and 14 +/- 8%, respectively. Vp remained elevated throughout the hypercapnic period, but BBF returned to baseline levels by 60 min. The Vp CO(2) sensitivity was greater than BBF (4 +/- 1 vs. 2 +/- 1%/Torr; P < 0.05). Our findings confirm that Vp has a greater sensitivity than BBF in response to hypercapnia and show an adaptive response of BBF that is not evident in Vp.     

Stimulation and inhibition of lipolysis in isolated rat adipocytes: evidence for age-related changes in responses to forskolin and PGE1

The ability of a number of hormones to activate cellular responses in a variety of cells declines with age. The mechanisms responsible for these alterations are complex and incompletely understood. Rat adipocytes have served as an important model to study blunted responses to stimulatory hormones which function by activating cAMP accumulation. We have previously found that the blunted lipolytic response of adipocytes from older rats to the beta adrenergic receptor agonist isoproterenol appeared to be due to a lessened ability of isoproterenol to activate cAMP accumulation. Further, the blunted response to isoproterenol was apparently caused by an accentuated inhibition of lipolysis, mediated by adenosine receptors activated by endogenously released adenosine. The present studies were designed to test and extend those conclusions. We have utilized forskolin to augment the cAMP accumulation that occurs in the presence of isoproterenol. Isoproterenol-activated lipolysis was greater in adipocytes from 2 month old rats compared with those from 12 month old rats (603 +/- 32 vs 450 +/- 29 nmol/10(5) cells/hr, P less than 0.01). However, in the presence of forskolin (10(-6) M), there was no significant difference in the response to isoproterenol between the two groups (646 +/- 23 vs 615 +/- 29 nmoles/10(5) cells/hr). As we had seen previously, the adenosine receptor agonist phenylisopropyladenosine more effectively inhibited lipolysis in the adipocytes from older rats. We now also find that PGE1 more efficaciously inhibits lipolysis in the cells from older rats. These data confirm that diminished cAMP accumulation in adipocytes from older rats appears to be a rate-limiting alteration in the regulation of lipolysis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Potent vasodilator responses to human urotensin-II in human pulmonary and abdominal resistance arteries

The peptide human urotensin-II (hUT-II) and its receptor have recently been cloned. The vascular function of this peptide in humans, however, has yet to be determined. Vasoconstrictor and vasodilator responses to hUT-II were investigated in human small muscular pulmonary arteries [approximately 70 microm internal diameter (ID)] and human abdominal resistance arteries (approximately 200 microm ID). Vasodilator responses were investigated in endothelin-1 (3 nM) precontracted vessels and, in the small pulmonary vessels, compared with the known vasodilators adrenomedullin, sodium nitroprusside, and acetylcholine. In human small pulmonary arteries, hUT-II did not induce vasoconstriction but was a potent vasodilator [-log M concentration causing 50% of the maximum vasodilator effect (pIC(50)) 10.4 +/- 0.5; percentage of reduction in tone (E(max)) 81 +/- 8% (vs. 23 +/- 11% in time controls), n = 5]. The order of potency for vasodilation was human urotensin-II = adrenomedullin (pIC(50) 10.1 +/- 0.4, n = 6) > sodium nitroprusside (pIC(50) 7.4 +/- 0.2, n = 6) = acetylcholine (pIC(50) 6.8 +/- 0.3, n = 6). In human abdominal arteries, hUT-II did not induce vasoconstriction but was a potent vasodilator [pIC(50) 10.3 +/- 0.7; E(max) 96 +/- 8% (vs. 43 +/- 16% in time controls), n = 4]. This is the first report that hUT-II is a potent vasodilator but not a vasoconstrictor of human small pulmonary arteries and systemic resistance arteries.