Recognition of neuropeptides FMRFamide and LPLRFamide by chicken cerebellum avian pancreatic polypeptide binding sites

Binding isotherms were constructed for the binding of synthetic tetrapeptide and pentapeptide fragments to membranes prepared from chicken cerebellar tissue. Both the tetrapeptide (FMRFamide), which was originally isolated from ganglia of mollusks, and the pentapeptide (LPLRFamide) previously isolated from chicken brain are known to increase blood pressure and modulate brain neurons in rats. The C-terminal dipeptide sequences of the two peptides are identical and both show similarity to the dipeptide sequence established for the pancreatic polypeptide (PP) family. Specific high-affinity binding sites exist for the latter peptide, sites which are competed for (though with less affinity) by neuropeptide Y (NPY). Affinity for cerebellar membranes was virtually equivalent for the synthetic peptide LPLRFamide and FRMFamide; the binding affinities (IC50) of all fragments tested (C-terminal pentapeptides of avian PP and NPY, and FMRFamide and LPLRFamide) fell in the same approximate range. Since the N-terminal residues of FMRFamide and LPLRFamide are not homologous with equivalent residues of APP or NPY, our results indicate that only Arg-Tyr-NH2 or Arg-Phe-NH2 sequences are necessary for binding of the carboxy terminus peptides of the PP family. In this respect, these sequences are functionally equivalent.     

Cardiovascular effects of intraventricular injection of FMRFamide, Met-enkephalin and their common analogues in the rat

The molluscan neuropeptide, Phe-Met-Arg-Phe-NH2 (FMRFamide), the mammalian opioid peptide met-enkephalin, and their common analogues, met-enkephalin-Arg6-Phe7 (YGGFMRF) and Tyr-Gly-Gly-Phe-Met-Arg-Phe-amide (YGGFMRFamide), were injected into the lateral ventricle of the rat; the cardiovascular effects were studied. FMRFamide caused a rapid, transient elevation in blood pressure accompanied by a great increase in pulse pressure. These effects were followed by secondary increases in blood and pulse pressures. Met-enkephalin produced an initial reduction in blood pressure which was followed by a gradual increase at the higher of two test doses (300 nmole). Injection of YGGFMRF resulted in a gradual increase in blood pressure. This response resembled that to met-enkephalin. The initial response to YGGFMRFamide was similar to that to FMRFamide: increases in both blood and pulse pressures after injection. However, the secondary effect of YGGFMRFamide, a prolonged reduction in blood pressure, was not produced by FMRFamide. These results suggest that the initial excitatory cardiovascular responses may be due to the presence of the C-terminal amide. All of the cardiovascular effects of injecting these peptides into the lateral ventricle were abolished by pre-treatment with naloxone in a dose that, itself, produced no cardiovascular changes. In conclusion, these peptides seem to act via the naloxone sensitive opiate receptors in the rat brain.     

Stimulation of brain Na+ channels by FMRFamide in Dahl SS and SR rats

Stimulation of brain Na+ channels by Phe-Met-Arg-Phe-NH2 (FMRFamide) increases sympathetic nerve activity and blood pressure (BP) in Wistar rats. Blockade of brain ouabain-like compounds (OLC) by specific antibody Fab fragments prevents these responses to intracerebroventricular FMRFamide. In the present study, we evaluated the effects of high-salt intake on brain FMRFamide levels and the responses of BP and brain OLC to intracerebroventricular infusion of FMRFamide in Dahl salt-sensitive (SS) and salt-resistant (SR) rats. FMRFamide and OLC content was measured with the use of RIA and ELISA, respectively. A high-salt diet (1,370 micromol Na+/g) for 2 wk significantly increased BP in Dahl SS but not in SR rats. On a regular salt diet, Dahl SS and SR rats showed similar FMRFamide levels in the whole hypothalamus, pons and medulla, and spinal cord. A high-salt diet for 2 wk did not affect FMRFamide levels in these tissues in both Dahl SS and SR rats. In Dahl SS but not in SR rats, chronic intracerebroventricular infusion of FMRFamide (200 nmol. kg(-1).day(-1)) for 2 wk significantly increased BP (mean arterial pressure: 116 +/- 5 vs. 100 +/- 2 mmHg; P < 0.01). Chronic intracerebroventricular infusion of FMRFamide significantly increased hypothalamic and pituitary OLC in Dahl SS but not SR rats. These results indicate that Dahl SS rats exhibit enhanced central responses to FMRFamide. In Dahl SS but not in SR rats on a high-salt diet, enhanced Na+ entry through FMRFamide-activated brain Na+ channels may increase brain OLC release, thereby leading to hypertension.     

FMRF-amide and L-Arg-L-Phe increase blood pressure and heart rate in the anaesthetised rat by central stimulation of the sympathetic nervous system

The neuropeptide FMRFamide (L-Phe-L-Met-L-Arg-L-Phe-NH2) increases mean arterial blood pressure (MABP) and heart rate (HR) in the anaesthetised rat at concentrations ranging from 10-1000 micrograms/kg. Here, we demonstrate that peptides containing L-arginyl-L-phenylalanine (L-Arg-L-Phe), the C-terminal sequence of FMRFamide, mimic its haemodynamic effects. L-Arg-L-Phe was approximately 4 fold more potent in increasing MABP and HR than FMRFamide. In 40 different peptides investigated, the following order of potency of the effective compounds was established: L-Arg-L-Phe-L-Ala = L-Arg-L-Phe greater than FMRFamide greater than L-Met-L-Arg-L-Phe = L-Arg-L-Trp greater than L-Arg-L-Tyr greater than D-Arg-L-Phe = L-Arg-L-Phe-OMe greater than L-Arg-L-Leu = L-Arg-L-Ile greater than L-Lys-L-Phe greater than L-Arg-L-Met. L-Arg-L-Phe or FMRFamide did not cause any pressor response in pithed rats, indicating a central mechanism of action. In anaesthetised rats, intravenous injections of FMRFamide or L-Arg-L-Phe (100 micrograms/kg) were associated with a 2-3 fold increase in plasma noradrenaline levels, whereas plasma adrenaline levels remained unchanged. Thus, L-Arg-L-Phe may represent the active principle of FMRFamide acting by a central mechanism involving the release of noradrenaline from sympathetic nerve terminals.     

Endothelin-1 modulates cardiorespiratory control by the central nervous system

In urethane-anesthetized, vagotomized and immobilized rats under artificial ventilation, an intracisternal injection of 0.1 pmol of endothelin-1 resulted in immediate increases, lasting for 3–15 min, in arterial pressure, heart rate and renal sympathetic nerve activity. Phrenic nerve activity and the rate of its burst activity (burst rate) also increased initially but subsequently decreased for 5–20 min. At doses of 1 or 10 pmol, the initial increases (phase I) were followed by a period of decreases in all variables, that lasted for 20–80 min, below the pre-injection level (phase II). Phrenic nerve activity often disappeared completely. All the variables usually returned to, or often exceeded, pre-injection levels (phase III). However, arterial pressure sometimes remained below control for at least 2 h. Topical application of endothelin-1 to the ventral surface of the medulla produced the same pattern of changes as with intracisternal injection. This particular response pattern was not generated by local administration to any other brain sites examined.

In conclusion, intracisternally administered endothelin-1 modulates cardiorespiratory control by the central nervous system. The effect on the central respiratory control was especially powerful. The ventral surface of the medulla appears to play a crucial role in this modulation.     

Inhalational administration of cocaine in sheep

A pipe for administration of inhaled cocaine and its pyrolytic products in laboratory animals was developed and tested. In-vitro trials showed 30.0 +/- 5.2% (mean +/- SE) recovery of cocaine in solvent. Five non-pregnant ewes were instrumented with tracheal T-tubes and vascular catheters. After surgical recovery, ewes received three doses of cocaine (free base) in a randomized fashion; 2 mg/kg and 4 mg/kg both by inhalation, and 2 mg/kg intravenously. Arterial blood samples were collected and assayed for cocaine and its major metabolites by high performance liquid chromatography. Blood pressure and heart rate were continuously recorded. Cocaine administered by inhalation was eliminated with a half-life of 1.6 +/- 0.5 min (mean +/- SE) compared to 3.4 +/- 0.9 following intravenous administration (p less than 0.03). Likewise, clearance values were greater following inhalation, 5532 +/- 1756 ml/min/kg, than following intravenous administration, 163 +/- 20.6 ml/min/kg (p less than 0.04). Both routes of administration led to significant elevations in blood pressure, 7.5% increase after smoking vs 20% increase after intravenous administration. No correlation was found between inhalational dose of cocaine and peak plasma cocaine concentration.     

Systemic NO synthase inhibition blunts the chronotropic, but not the inotropic response to isoprenaline in man.

There is evidence that nitric oxide (NO) is involved in the chronotropic, the inotropic, and the vasodilator response to beta-adrenoceptor agonists. In the present study we hypothesized that inhibition of NO synthase may modulate the systemic vascular and cardiac effects of isoprenaline, a beta-adrenoceptor agonist, in healthy subjects. Subjects received stepwise increasing doses of isoprenaline (0.1-0.8 microg/min) in the absence or presence of systemic NO-synthase inhibition using two intravenous doses of N-monomethyl-L-arginine (L-NMMA; dosage 1, 3.0 mg/kg over 5 min, followed by 30 microg/kg/min over 75 min; dosage 2, 6.0 mg/kg over 5 min, followed by 60 microg/kg/min over 75 min) or peripheral vasoconstriction using exogenous endothelin-1 (ET-1; 5.0 ng/kg/min for 80 min). The chronotropic (RR interval) and the inotropic (QS2c) responses were assessed by noninvasive measurement of systolic time intervals. L-NMMA alone did not influence QS2c, but did increase the RR interval (P < 0.001) and the mean arterial blood pressure (P = 0.003). L-NMMA did not attenuate the blood pressure and the QS2c responses to isoprenaline, but significantly and dose-dependently blunted the heart rate response to beta-adrenoceptor stimulation (P = 0.029). ET-1 decreased the RR interval (P < 0.001) and increased the mean arterial blood pressure (P = 0.028). Our results indicate that beta-adrenoceptor mediated effects on the heart rate are much more susceptible to NOS inhibition than inotropic responses. This indicates that NO has an important role in heart rate control during beta-adrenoceptor stimulation.     

Respiratory depressant effects of GABA alpha- and beta-receptor agonists in the cat

The aim of this study was to evaluate the cardiorespiratory effects of intravenously administered gamma-aminobutyric acid (GABA) alpha-(4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol, THIP) and beta-(baclofen) receptor agonists and to locate the site of action of these drugs in the brain. THIP and baclofen were administered to alpha-chloralose-anesthetized cats while minute ventilation (VE), arterial blood pressure (AP), and heart rate were monitored. THIP, in doses of 0.5 to 2 mg/kg decreased VE, tidal volume (VT), and AP. No changes in respiratory rate (f) or inspiratory (TI) or expiratory (TE) duration were observed. Baclofen, in doses of 0.5 to 4 mg/kg, decreased VE, f, and AP. VT and TI increased and an "apneustic" breathing pattern was seen. THIP (9.5 micrograms), applied bilaterally to the glycine-sensitive area of the ventral medulla, reproduced the effects seen with intravenous administration. Application of 10 micrograms of bicuculline bilaterally to this area reversed the effects of intravenous THIP but not those of baclofen. Baclofen (5.6-56 micrograms), administered by the intracisternal route, produced the same respiratory effects seen with intravenous administration. We conclude that activation of GABA alpha- and beta-receptors produces cardiorespiratory depression. However, this is accomplished by different mechanisms and by actions exerted at different central nervous system sites.     

Responses to endothelin-1, human proendothelin (1–38) and porcine proendothelin (1–39) in the rat on intravenous administration and in the blood perfused mesentery

Human proendothelin (1–38) and porcine proendothelin (1–39) were respectively 4.3 and 19.2 times less potent than endothelin-1 as systemic pressor agents on i.v. administration but the maximum response to the porcine precursor was significantly greater than that to endothelin-1. The time courses of response were very similar for the 3 peptides. All 3 peptides caused dose-dependent depressor responses which preceded the pressor response and the rank order of potency was similar for both these systemic responses. High doses of endothelin-1 and human proendothelin (1–38) were toxic and death was preceded by disturbance of the ECG and, often, by bradycardia. Mesenteric perfusion pressure in situ was increased dose-dependently by all 3 peptides on close arterial administration without being accompanied by systemic pressor responses. The time courses of the responses were again similar. The human and porcine precursors appeared to be equipotent and approx. 10 times less potent than endothelin-1 itself. The highest doses given by this route commonly caused death which was accompanied only by falls in systemic blood pressure even though changes in ECG occurred which were similar to those seen after i.v. administration. Discolouration of the gut occurred which suggested extravasation of erythrocytes had occurred. The results lend some support to the hypothesis that there is more than one type of receptor for the endothelin family of peptides and suggest that both human and porcine proendothelin have a direct action at these receptors. However, it is possible that some of their actions in vivo are mediated by rapid conversion to endothelin-1.     

Effect of alpha-phenyl-N-tert-butylnitrone on brain cell membrane function and energy metabolism in experimental Escherichia coli meningitis in the newborn piglet

We evaluated the efficacy of alpha-phenyl-N-tertbutylnitrone as an adjunctive therapy in experimental bacterial meningitis in the newborn piglet. Meningitis was induced by intracisternal injection of 10(8) colony-forming units of Escherichia coli in 100 microl of saline. Alpha-Phenyl-N-tert-butylnitrone 100 mg/kg was given as a bolus intravenous injection 30 min before induction of meningitis. Although it completely abolished the elevated CSF tumor necrosis factor-a level observed in the meningitis group, alpha-phenyl-N-tert-butylnitrone did not down-modulate parameters of inflammatory responses such as increased intracranial pressure, hypoglycorrhachia, elevated CSF lactate level, and CSF leukocytosis observed in this group. However, alpha-phenyl-N-tert-butylnitrone treatment mitigated alterations in brain cell membrane structure and function during meningitis, evidenced by amelioration of increased brain cell membrane lipid peroxidation products (conjugated dienes) and decreased Na+, K+-ATPase activity. Reduced mean arterial blood pressure, cerebral perfusion pressure, brain glucose concentration, and cerebral energy stores and marginally increased brain lactate level observed in the meningitis group were also ameliorated. These results suggest that although it failed to attenuate the inflammatory responses, alpha-phenyl-N-tert-butylnitrone was effective in ameliorating brain injury in neonatal bacterial meningitis.     

Increased nitric oxide concentrations in posterior hypothalamus and central sympathetic function on nitrate tolerance following subcutaneous nitroglycerin.

The present study was to examine the distributions of nitric oxide (NO) in the brain regions and peripheral vessels following subcutaneously administered nitroglycerin (NTG) and determine the noradrenergic activity and the role of central sympathetic function in acute nitrate tolerance. Tolerance to NTG was produced by subcutaneous (sc) administration of 4.0 mg NTG as four separate hourly pulse injections of 1.0 mg each in male (5-8 months) Sprague-Dawley rats. Rats in sham-treated group received sc injections of saline. Rats were killed by sodium pentobarbital (150 mg/kg, ip) at 10 min after last sc injection. The brain, gracilis muscle, aorta, superior mesenteric artery, coronary artery, and pulmonary vessels were quickly removed. Concentrations of nitrite (NO2-), nitrate (NO3-), and total NO2- plus NO3- (NOx-) were quantified in the micropunches of the anterior hypothalamus, the posterior hypothalamus (PH), the nucleus tractus solitarius, the lateral reticular nucleus, and the vessels in a blinded fashion. The central actions of acute tolerance to NTG were also determined using blockades of sympathetic functions in conscious rats. Four separate hourly pulse sc injections of 1.0 mg NTG produced a marked shift of the dose-response curve for arterial pressure depression induced by intravenous injection of the challenge doses of NTG. The same doses of sc NTG caused increases in NOx- [92+/-16% (mean +/- SE)] and NO3- productions (77+/-15%) in the PH, but did not significantly change in other brain regions (n = 6). NOx- and NO3- productions were significantly enhanced in the superior mesenteric artery, aorta, coronary artery, and pulmonary vessels following sc NTG, but were not altered in gracilis muscle by the treatment. The tolerance responses to arterial pressure depression were attenuated by intravenous administration of either prazosin (300 microg/kg), an alpha1-adrenoceptor antagonist, or chlorisondamine (10 mg/kg), a sympathetic ganglion blockading agent (n = 5-6). The results suggest that acute NTG tolerance predominately increases NO production in the PH. NO production was also markedly enhanced in the large and middle vessels but not in small vessels during acute NTG tolerance. The arterial pressure tolerance to NTG was reversed by blockade of central sympathetic function. We conclude that NO formation is increased in the PH following systemically administered NTG and NO in the PH may facilitate central sympathetic functions which contribute to nitrate tolerance.     

Intracisternal injection of TRH precursor, TRH-glycine, stimulates gastric acid secretion in rats

Intracisternal injection of thyrotropin-releasing hormone (TRH)-Gly (pGlu-His-Pro-Gly) produced a dose-dependent (1-100 micrograms) stimulation of gastric acid secretion in urethane-anesthetized rats implanted acutely with a gastric fistula. The peak response occurred 20-30 min after intracisternal injection and lasted for more than 2 h. Intravenous injection of TRH-Gly (100 micrograms) did not modify gastric acid secretion. Following intracisternal injection of TRH-Gly, a peak elevation of both TRH-Gly and TRH levels is observed in the cerebrospinal fluid (CSF) within 15 min. Thereafter, TRH values are returned to basal levels at 75 min after the injection, whereas TRH-Gly concentrations remain significantly elevated throughout the 2-h period of measurement. Compartmental analysis revealed that CSF conversion of TRH-Gly to TRH was only 0.0072%/min. Medullary coronal sections containing the dorsal vagal complex and the raphé nucleus revealed increased content of TRH-Gly, but not TRH, 40 min after administration of TRH-Gly at an intracisternal dose effective in stimulating gastric acid secretion (100 micrograms). In addition, TRH but not TRH-Gly (10(-7)-10(-5) M) displaced [3H]MeTRH binding from rat medullary blocks containing the dorsal vagal complex. These data suggest that the intracisternal TRH-Gly-induced stimulation of gastric acid secretion is not related to its conversion to TRH in the CSF, or direct activation of TRH receptors in the medulla. The acid secretory response of TRH-Gly may be due to the formation of TRH at the active brain sites, or alternatively to activation of its own specific receptors.     

Presence and distribution of immunoreactive and bioactive FMRFamide-like peptides in the nervous system of the horseshoe crab, Limulus polyphemus

FMRFamide immunoreactivity was detected in all regions of the Limulus nervous system, including the brain (6.5 +/- 0.6 pg FMRFamide/mg), cardiac ganglion (2.06 +/- 0.67 pg FMRFamide/mg), and ventral nerve cord (5.8 +/- 0.7 pg FMRFamide/mg). The distribution of immunoreactive FMRFamide (irFMRFamide) was mapped by immunofluorescence and the distribution corresponded to regional RIA data. A good proportion of the CNS and cardiac ganglion neuropile contained irFMRFamide, and fluorescent cell bodies were observed in several areas. High performance liquid chromatography (HPLC) was employed to separate and characterize the FMRFamide-like peptides from extracts of Limulus brains. HPLC fractions were analyzed using coincidental radioimmunoassay and bioassay (the radula protractor muscle of Busycon contrarium). There appear to be at least three FMRFamide-like peptides in the Limulus brain, including one similar to clam FMRFamide. FMRFamide acts on Limulus heart in a biphasic manner at relatively high concentrations (10(-5)M), but has no effect on the activity of the isolated ventral nerve cord. These data suggest that in Limulus FMRFamide-like peptides are acting as neurotransmitters, or neuromodulators.     

Activation of angiotensin II receptors in brain potentiates the stimulating effect of endogenous opioid neurons on central sympathetic outflow

Endogenous opioid peptides appear to have neurotransmitter or neuromodulator functions in brain mediating a wide variety of effects. We have reported that intracisternal administration of synthetic human beta-endorphin increases plasma concentration of catecholamines, apparently by acting at unknown brain sites to increase sympathetic outflow to the adrenal medulla and sympathetic nerves. In the present study we examined the possibility that angiotensin II, acting in brain, modulates endorphin-induced catecholamine secretion. Simultaneous intracisternal administration of angiotensin II 1.0 nmol together with synthetic human beta-endorphin 1.45 nmol potentiated the plasma epinephrine, norepinephrine and dopamine responses to intracisternal beta-endorphin. In contrast, simultaneous intracisternal administration of the angiotensin II antagonist, [Sar1, Val5, Ala8]-angiotensin II (saralasin), 1.1 nmol together with beta-endorphin, blunted the plasma epinephrine, norepinephrine and dopamine responses to beta-endorphin. These data are consistent with the hypothesis that activation of angiotensin II receptors in brain potentiates the endorphin-induced stimulation of central sympathetic outflow. It remains to be demonstrated whether angiotensin II acting in brain to modulate activity of opioid neurons is synthesized in brain or is derived peripherally.     

Effects of intravenously administered Leu- or Met-enkephalin on arterial blood pressure

The purpose of these studies was to determine if two endogenous opioids, leucine (Leu) and methionine (Met) -enkephalin, alter blood pressure and, if so, by what mechanisms. Studies from our laboratory show that intravenous administration of Leu-enkephalin in doses of 0.032–320 μg/kg induced a biphasic response in pentobarbital-anesthetized cats. A transient rise in mean arterial pressure was followed by a more prolonged decline. Administration of Met-enkephalin caused only a decline in mean arterial pressure. Neither agent significantly altered heart rate, venous pressure or the EKG. Having determined that both enkephalins altered blood pressure and observed that the responses were qualitatively different, selected pharmacological antagonists were employed to see if the alterations in blood pressure could be blocked. Naloxone blocked the hypertensive responses and antagonized the hypotensive effects seen with the administration of Leu-enkephalin. Naloxone also shifted the dose-effect curve of Met-enkephalin to the right. Diphenhydramine attenuated both the hypertensive and hypotensive responses of Leu-enkephalin. However, diphenhydramine pretreatment did not alter the decline in blood pressure seen with the higher doses of Met-enkephalin. Propranolol exerted some antagonistic activity in association with the rise in blood pressure seen with Leu-enkephalin, but propranolol did not alter the drop in pressure observed with the administration of either enkephalin. These results show that intravenous administration of the enkephalins can alter blood pressure and these effects are not alike for each enkephalin. Additionally, the enkephalins are not blocked in the same fashion by antagonists, giving support to the hypothesis that the two enkephalins interact with different receptors.     

Reflex responses to capsaicin: intravenous, aerosol, and intratracheal administration

Intravenous capsaicin elicits the "pulmonary chemoreflex" (apnea, bradycardia, and hypotension) presumably through the stimulation of "pulmonary C-fibers." The present study was designed to ascertain whether tracheobronchial C-fibers play a role in the above reflex response. We compared the effects of capsaicin injected intravenously, administered as an aerosol, and administered topically into the intrathoracic trachea in anesthetized dogs (n = 17) and rats (n = 17). We measured esophageal, subglottic, and arterial pressures together with abdominal muscle electromyogram. Changes in expiratory duration [(TE), measured as the ratio TEtest to TEcontrol, mean +/- SD] due to capsaicin were similar with all three routes of administration in both dogs (intravenous, 7.9 +/- 4.6; aerosol, 5.5 +/- 3.1; topically into intrathoracic trachea, 7.1 +/- 4.8) and rats (intravenous, 22.6 +/- 10.3; aerosol, 11.1 +/- 8.2; topically into intrathoracic trachea, 21.6 +/- 4.6). An increase in laryngeal resistance was a constant finding in the rat, but it was less frequent in the dog. Cardiovascular responses consisting of bradycardia and hypotension occurred with all three routes of administration but had longer delays than the respiratory responses. Capsaicin instillation into the extrathoracic trachea in dogs (n = 7) also induced qualitatively similar cardiorespiratory responses. We conclude that 1) capsaicin-sensitive receptors are accessible from both the pulmonary circulation and the airway lumen and 2) afferents, even in the extrapulmonary portion of the tracheobronchial tree, can play a role in the reflex responses to intraluminal capsaicin.     

Intravenous morphine infusion (IMF) to drug-naive, conscious rats evokes bradycardic, hypotensive effects, but pressor actions are elicited after IMF to rats previously given morphine

Hemodynamic (blood pressure and heart rate) responses of conscious drug-naive rats were studied following intravenous (i.v.) infusion of sterile saline, morphine sulphate, and then naloxone hydrochloride, as well as of other groups previously injected with morphine sulphate. Those groups chronically given morphine sulphate received twice daily injections of morphine sulphate (5 mg/kg, s.c. per injection) for 3 or 6 days before testing with the i.v. infusion of morphine sulphate. Drugs were infused (135 microL/min) through an indwelling femoral venous catheter via a Harvard infusion pump, and blood pressure was recorded from the abdominal aorta via a femoral arterial catheter. Other pretreatment studies were done to determine the receptor mechanisms mediating the blood pressure responses of drug-naive and chronic morphine-treated rats, whereby equimolar doses (0.32 mumol) of specific receptor antagonists were given as a bolus i.v. injection 5 min after saline but before subsequent infusion with morphine sulphate. Intravenous infusion of morphine sulphate (7.5 mg/kg total over 15 min) to drug-native rats caused a transient but precipitous fall in mean arterial pressure and mean heart rate with an associated rise in mean pulse pressure; these effects were blocked in other groups pretreated with atropine. Interestingly, however, rats chronically injected with morphine sulphate for 3 days previously evoked a transient pressor response when subsequently infused i.v. with morphine sulphate, actions that were blocked in other groups when pretreated i.v. with 0.32 mumol of phentolamine, yohimbine, prazosin, or guanethidine. A greater and persistent pressor response occurred following morphine infusion to groups of rats previously injected over 6 days with morphine sulphate, which was associated with tachycardia during the later stages of the 15-min morphine sulphate infusion period. The prolonged pressor and tachycardic responses of this 6-day chronically injected group were completely blocked in another group pretreated i.v. with both phentolamine and propranolol (0.32 mumol). The results suggest that morphine sulphate infusion to conscious, drug-naive rats evokes classical hypotensive effects due to decreases in mean heart rate caused by activation of parasympathetic vagal activity. With 3 or 6 days of chronic morphine sulphate administration beforehand, subsequent i.v. infusion of morphine sulphate evoked pressor actions felt to be caused by a progressive activation of the sympathetic nervous system.(ABSTRACT TRUNCATED AT 400 WORDS)     

Close arterial infusion of calcitonin gene-related peptide into the rat stomach inhibits aspirin- and ethanol-induced hemorrhagic damage

Afferent neuron-mediated gastric mucosal protection has been suggested to result from the local release of vasodilator peptides such as calcitonin gene-related peptide (CGRP) from afferent nerve endings within the stomach. The present study, therefore, examined whether rat alpha-CGRP, administered via different routes, is able to protect against mucosal injury induced by gastric perfusion with 25% ethanol or acidified aspirin (25 mM, pH 1.5) in urethane-anesthetized rats. Close arterial infusion of CGRP (15 pmol/min) to the stomach, via a catheter placed in the abdominal aorta proximal to the celiac artery, significantly reduced gross mucosal damage caused by ethanol and aspirin whereas mean arterial blood pressure (BP) was not altered. Intravenous infusion of CGRP (50 pmol/min) did not affect aspirin-induced mucosal injury but significantly enhanced ethanol-induced lesion formation. Intravenous CGRP (50 pmol/min) also lowered BP and increased the gastric clearance of [14C]aminopyrine, an indirect measure of gastric mucosal blood flow while basal gastric output of acid and bicarbonate was not altered. Intragastric administration of CGRP (260 nM) significantly inhibited aspirin-induced mucosal damage but did not influence damage in response to ethanol. BP, gastric clearance of [14C]aminopyrine, and gastric output of acid and bicarbonate remained unaltered by intragastric CGRP. These data indicate that only close arterial administration of CGRP to the rat stomach, at doses devoid of a systemic hypotensive effect, is able to protect against both ethanol- and aspirin-induced mucosal damage. As this route of administration closely resembles local release of the peptide in the stomach, CGRP may be considered as a candidate mediator of afferent nerve-induced gastric mucosal protection.     

Rho kinase and Ca2+ entry mediate increased pulmonary and systemic vascular resistance in L-NAME-treated rats

The small GTP-binding protein and its downstream effector Rho kinase play an important role in the regulation of vasoconstrictor tone. Rho kinase activation maintains increased pulmonary vascular tone and mediates the vasoconstrictor response to nitric oxide (NO) synthesis inhibition in chronically hypoxic rats and in the ovine fetal lung. However, the role of Rho kinase in mediating pulmonary vasoconstriction after NO synthesis inhibition has not been examined in the intact rat. To address this question, cardiovascular responses to the Rho kinase inhibitor fasudil were studied at baseline and after administration of an NO synthesis inhibitor. In the intact rat, intravenous injections of fasudil cause dose-dependent decreases in systemic arterial pressure, small decreases in pulmonary arterial pressure, and increases in cardiac output. L-NAME caused a significant increase in pulmonary and systemic arterial pressures and a decrease in cardiac output. The intravenous injections of fasudil after L-NAME caused dose-dependent decreases in pulmonary and systemic arterial pressure and increases in cardiac output, and the percent decreases in pulmonary arterial pressure in response to the lower doses of fasudil were greater than decreases in systemic arterial pressure. The Ca(++) entry blocker isradipine also decreased pulmonary and systemic arterial pressure in L-NAME-treated rats. Infusion of sodium nitroprusside restored pulmonary arterial pressure to baseline values after administration of L-NAME. These data provide evidence in support of the hypothesis that increases in pulmonary and systemic vascular resistance following L-NAME treatment are mediated by Rho kinase and Ca(++) entry through L-type channels, and that responses to L-NAME can be reversed by an NO donor.