Localization of endothelin-1 (ET-1), ET-2, and ET-3, mouse VIC, and sarafotoxin S6b binding sites in mammalian heart and kidney

Quantitative in vitro receptor autoradiography was used to identify and compare binding sites for endothelin-1 (ET-1), ET-2, and ET-3, mouse vasoactive intestinal contractor (VIC), and sarafotoxin S6b in human, porcine, and rat cardiac and renal tissues. In the rat kidney, the highest densities of binding sites for all five labeled peptides were present in the glomeruli, with lower levels in the papilla, cortex, and inner band of the medulla. A similar pattern was found in porcine and human kidney except that no discrete glomerular binding could be detected. In the heart, higher densities were detected in the atria compared to the ventricle. Although the pattern of binding in cardiac and renal tissue was similar for all four labeled ET isoforms, nonspecific binding was consistently higher with ET-3, resulting in lower levels of specific binding. These results suggest that these peptides could be acting via the same population of binding sites, but multiple receptor subtypes may exist that differ in their rank order of affinity for the ET isoforms and sarafotoxin S6b, as proposed in other tissues.

Molecular aspects of atrial natriuretic factor physiology

Circulating atrial natriuretic factor (ANF) may interact with binding sites in many tissues to produce the characteristic pharmacological effects seen after intravenous administration. In addition to hormonal effects, ANF may have a local regulatory role. We have examined this hypothesis by using techniques designed to localise specific binding sites (defining target cells) and the messenger ribonucleic acid (mRNA) for ANF (defining cells with the capacity to synthesise ANF). We have demonstrated a topological relationship between the distribution of binding sites and mRNA transcripts in the heart and adrenal gland. This data supports functional evidence that ANF may have local effects, possibly including the regulation of both cardiac rhythmicity and contractility and its own secretion from the heart, and the maintenance of the cortical zones of adrenal steroid production.

Long term anesthesia using a continuous infusion of guaifenesin, ketamine and xylazine in cats

Cats (Felis catus) were anesthetized with a solution containing guaifenesin, ketamine and xylazine (GKX) in 0.9% saline. Anesthesia was induced by intravenous (IV) injection and was maintained for 6 hours by IV infusion. Heart rate, respiratory rate and PvO2 did not change significantly during the 6 hour monitoring period and remained consistently within the published normal ranges for cats. Although the PvCO2 did not change significantly, many values were abnormal. Venous pH decreased to slightly below normal values. Lead II ECG tracings showed no abnormalities. Loss of response to pedal pinch and jaw tone indicates maintenance of a surgical plane of anesthesia and adequate muscle relaxation throughout the 6 hour anesthetic period. Cats exhibited voluntary motor movement and were in sternal recumbency in just over 2 hours and were showing no residual clinical effects of the anesthesia 16 hours later. Although a transient mild acidosis was observed, we conclude that GKX provides a safe, effective and easily administered anesthetic regime for cats for periods up to 6 hours.

Induction of severe experimental autoimmune neuritis with a synthetic peptide corresponding to the 53-78 amino acid sequence of the myelin P2 protein

We generated a synthetic peptide (SP-26), corresponding to the amino acid residues 53-78 of bovine P2 protein, which induced severe clinical and pathological characteristics of experimental autoimmune neuritis (EAN) in Lewis rats. Lymph node cell populations from SP-26-immunized rats elicited a proliferative response to the peptide and to the P2 protein. After 16 cycles of antigen stimulation with the peptide, the SP-26 T cell line shows a decreased response to P2, but not to SP-26. Fluorescence-activated cell sorter (FACS) analysis of a SP-26 T cell line indicated the majority of cells to be of CD4+ CD8-. This report demonstrates that the synthetic peptide SP-26 can induce severe EAN in Lewis rats in a dose-dependent manner. Furthermore, specific T cell lines reactive to SP-26 can be generated from the lymph nodes of SP-26-immunized rats.

Atrial natriuretic factor mRNA and binding sites in the adrenal gland

The factor inhibiting aldosterone secretion produced by the adrenal medulla may be atrial natriuretic factor (ANF), since the latter abolishes aldosterone release in response to a number of secretagogues, including angiotensin II and K+. In this study we have shown that cells in the adrenal medulla contain ANF mRNA and therefore have the potential to synthesize this peptide. The presence of binding sites for ANF predominantly in the adrenal zona glomerulosa suggests that, if ANF is synthesized in the medulla and transferred to the cortex, it may affect mineralocorticoid status.

Efficacy and tolerance of doxazosin: a review

The objective of therapy in the hypertensive patient is not the reduction of blood pressure (BP), but the prevention of coronary heart disease. Since assessment of the long-term efficacy of therapy takes many years, new antihypertensive agents are evaluated by four main criteria: predictable lowering of BP; achievement of target BP in a high proportion of patients; once daily administration; good tolerance. Comparative studies, mostly against other antihypertensive agents show that doxazosin meets all these criteria and in addition has no adverse effects on the serum lipids and may also act directly on the coronary vascular smooth muscle to inhibit the proliferative stage of atherogenesis.

Atrial natriuretic peptide in primary pulmonary hypertension

Plasma levels of atrial natriuretic peptide (ANP) were determined during cardiac catheterization in nine patients with primary pulmonary hypertension (PPH) and the effect of prostacyclin infusion via a right heart catheter studied. The role of hypoxia on the release of ANP was investigated in a control group of six normal subjects who underwent an acute hypoxic challenge. Patients showed the typical haemodynamic changes of primary pulmonary hypertension with elevation of mean (SD) pulmonary artery pressure, 71.3 (13.8) mmHg, and low cardiac index, 1.9 (0.5) l.min-1.m-2. Plasma ANP was also elevated; mean pulmonary artery plasma ANP was 96.3 (77.6) pmol.l-1 in PPH patients compared with mean venous plasma ANP of 8.9 (5.6) pmol.l-1 in normal subjects. Prostacyclin infusion in PPH patients and hypoxic challenge in normal subjects did not significantly alter plasma ANP levels. The elevated levels of ANP in PPH are due to the altered haemodynamics secondary to increased pulmonary vascular resistance and may be responsible for the lack of peripheral oedema seen in this condition.

Atrial natriuretic peptide in primary pulmonary hypertension

Plasma levels of atrial natriuretic peptide (ANP) were determined during cardiac catheterization in nine patients with primary pulmonary hypertension (PPH) and the effect of prostacyclin infusion via a right heart catheter studied. The role of hypoxia on the release of ANP was investigated in a control group of six normal subjects who underwent an acute hypoxic challenge. Patients showed the typical haemodynamic changes of primary pulmonary hypertension with elevation of mean (SD) pulmonary artery pressure, 71.3 (13.8) mmHg, and low cardiac index, 1.9 (0.5) l.min-1.m-2. Plasma ANP was also elevated; mean pulmonary artery plasma ANP was 96.3 (77.6) pmol.l-1 in PPH patients compared with mean venous plasma ANP of 8.9 (5.6) pmol.l-1 in normal subjects. Prostacyclin infusion in PPH patients and hypoxic challenge in normal subjects did not significantly alter plasma ANP levels. The elevated levels of ANP in PPH are due to the altered haemodynamics secondary to increased pulmonary vascular resistance and may be responsible for the lack of peripheral oedema seen in this condition.

A 5-hydroxytryptamine receptor in human atrium

1. The effects of 5-hydroxytryptamine (5-HT) were investigated on right atrial appendages obtained from patients treated with beta-adrenoceptor blocking agents who were undergoing open heart surgery. Atrial strips were paced under isometric conditions. 2. 5-HT increased contractile force to approximately one half of the force produced by a saturating concentration of (-)-isoprenaline. Both 5-HT and (-)-isoprenaline accelerated the onset of relaxation, as indicated by an abbreviation of time to peak force. 3. The effects of 5-HT were resistant to blockade by 0.4 microM (+/-)-propranolol, 1 microM (-)-pindolol, 0.4 microM methiothepin, 4 microM yohimbine, 0.4 microM ketanserin, 10 microM phenoxybenzamine, 1 microM methysergide, 2 microM MDL 72222 and 20 microM granisetron. 4. Cocaine 6 microM potentiated the effects of 5-HT, increasing the pEC50 from 6.6 to 7.4. The inotropic potency of 5-HT is five times greater than that of (-)-noradrenaline. 5. ICS 205930 antagonized competitively the effects of 5-HT with a pKB of 6.7. 6. In the presence of 0.4 microM (+/-)-propranolol, 10 microM 5-HT increased both adenosine 3':5' cyclic-monophosphate (cyclic AMP) levels and cyclic AMP-dependent protein kinase activity by approximately one half and two thirds respectively, of the corresponding effects of 200 microM (-)-isoprenaline. 7. Both the increase in cyclic AMP levels and the stimulation of protein kinase activity are consistent with the inotropic effects of 5-HT being mediated by cyclic AMP-dependent phosphorylation of Ca2+ channels and of proteins involved in contraction and relaxation. 8. The human atrial 5-HT receptor resembles the neuronal 'so called' 5-HT4 receptor of rodents both in increasing cyclic AMP levels and in its affinity for ICS 205930.

Early myelin lesions in experimental allergic neuritis

We examined the evolution of demyelination in spinal roots of Lewis rats immunized with whole nerve and complete Freund's adjuvant. Roots were morphologically normal until 11 days after immunization, when we found endoneurial edema and myelin vesiculation in the absence of mononuclear cell contacts. Macrophage-associated myelin stripping was not detected until day 12. Macrophage infiltrations were extensive by day 14, but lymphocytes were sparse. These observations indicate that in experimental allergic neuritis, myelin injury may occur before macrophage-mediated demyelination, and provide support for an early role of serum factors in the development of this disorder.

Effects of dilevalol on human atrial muscle

The beta 1- and beta 2-adrenoceptor agonist effects of dilevalol on human heart tissue were studied in vitro. The receptors were studied independently of one another through the use of selective antagonists. Human right atrial appendages were generally cut into four strips which were then set up in parallel in an organ bath system. All tissues were incubated either with 300 nM CGP 20712A to block beta 1-adrenoceptors, or with 50 nM ICI 118551, to block beta 2-adrenoceptors. Alpha-adrenoceptors and tissue uptake of catecholamines were blocked using 5 microM phenoxybenzamine. The atrial strips from one patient were then exposed either to vehicle or to cumulative additions of dilevalol, (+)- pindolol or salbutamol (10(-8) to 10(-5) M) and the resulting force of contraction was expressed as a percentage of the inotropic response obtained with a saturating dose of (-)-isoprenaline. The beta-antagonist effects of the three substances were also studied, by running a dose-response curve to noradrenaline or adrenaline as appropriate following the addition of the substance of interest. Neither dilevalol nor (+)-pindolol had any intrinsic sympathomimetic activity at the atrial beta 1- or beta 2-adrenoceptors. Both dilevalol and (+)-pindolol caused marked antagonism of the atrial beta-adrenoceptors. They caused similar blockade of the beta 2-adrenoceptors but not of the beta 1-adrenoceptors.

Selective beta 1-adrenoceptor blockade enhances positive inotropic responses to endogenous catecholamines mediated through beta 2-adrenoceptors in human atrial myocardium

We determined the relative contribution of beta 1- and beta 2-adrenoceptor stimulation to the positive inotropic responses of human atrial myocardium to catecholamines. (-)Norepinephrine produced stimulation predominantly through beta 1-receptors and (-)epinephrine through both beta 1- and beta 2-receptors. However, there were marked differences in the responses of tissues from patients treated with the beta 1-selective antagonist atenolol compared with non-beta-blocker-treated patients; surprisingly, beta 2-mediated responses were enhanced, and beta 1-mediated responses were unaltered. There was an enhanced responsiveness to (-)epinephrine (atenolol treated: -log M EC50, 7.57 +/- 0.07; non-beta-blocker treated: -log M EC50, 6.77 +/- 0.17; p less than 0.001), and the relative importance of beta 2-adrenoceptor stimulation was increased for both (-)norepinephrine and (-)epinephrine. In tissues from atenolol-treated patients, salbutamol, a beta 2-selective partial agonist, had an enhanced potency and a greater intrinsic activity (atenolol treated: -log M EC50, 7.13 +/- 0.09; intrinsic activity, 0.86 +/- 0.04; non-beta-blocker treated: -log M EC50, 5.76 +/- 0.44; intrinsic activity, 0.39 +/- 0.13). We investigated possible mechanisms underlying the enhanced responsiveness to beta 2 stimulation. Determination of beta 2-adrenoceptor affinity for salbutamol showed no change of affinity in atenolol-treated patients. Responses of the tissues to the cyclic AMP analogue dibutyryl cyclic AMP were not different between atenolol-treated and non-beta-blocker-treated patients. The results suggest that chronic blockade of beta 1-adrenoceptors causes enhanced coupling of beta 2-adrenoceptors to adenylate cyclase or to other mechanisms leading to increased contractile force.

Endothelin-1 mRNA is widely expressed in porcine and human tissues

Endothelin-1 (ET-1) is a potent vasoconstrictor peptide isolated from porcine endothelial cells. We have previously demonstrated widespread binding sites for ET-1 in blood vessels, heart, kidney, adrenal, lung, and brain in a distribution that paralleled that of endothelial cells. To determine whether these cells are capable of synthesizing ET-1 in close proximity to its binding sites, amplification of cDNA using the polymerase chain reaction and in situ hybridization were used to study the distribution of ET-1 mRNA. We have found widespread transcription of ET-1 mRNA in human and porcine tissues. The identity of the transcripts was confirmed by prediction of restriction fragment lengths or sequencing. In situ hybridization in the kidney showed that the regional expression of these transcripts is localized, probably to small blood vessels, but the failure to visualize ET-1 mRNA in the capillaries may reflect absence of expression or insufficient sensitivity of the technique. These results should permit investigation of the role of ET-1 as a local factor in vascular pathophysiology.

A sensitive radioimmunoassay measuring endothelin-like immunoreactivity in human plasma: comparison of levels in patients with essential hypertension and normotensive control subjects

1. A radioimmunoassay has been developed for measuring endothelin-like immunoreactivity in human plasma using an antibody raised against endothelin-1 which also cross-reacts with big endothelin-1 and endothelin-2 but not endothelin-3. 2. The sensitivity of the assay was 1 fmol/tube with inter- and intra-assay coefficients of variation of 13% and 9%, respectively. Cross-reactivity with endothelin-3 and non-endothelin peptides was less than 1%. 3. Endothelin-like immunoreactivity was present in the plasma of hypertensive patients (n = 25) at a concentration of 5.7 +/- 0.5 pmol/l (mean +/- SEM), which was not significantly different from that of age-matched control subjects (5.1 +/- 0.5 pmol/l). At these levels, endothelin-1 is unlikely to function as a circulating hormone. 4. Within the normotensive group, the concentration of endothelin-like immunoreactivity in plasma was positively correlated with mean arterial blood pressure, but in hypertensive patients it showed a significant negative correlation.

Effects of circulating endogenous catecholamines on plasma glucose, potassium and magnesium

1. To examine the metabolic effects of increases in circulating endogenous plasma catecholamines, we measured plasma glucose, potassium and magnesium in 14 patients undergoing elective coronary artery bypass grafting. The patients were randomized into two groups and received either sodium nitroprusside (a direct-acting vasodilator) or trimetaphan camsylate (a ganglion-blocking agent) for routine control of blood pressure during the operation. 2. There were significant differences between the two groups in the levels of all three metabolic variables studied. Plasma glucose levels rose in both groups, but were significantly higher in the sodium nitroprusside group [peak levels 9.14 (SEM 0.72)mmol/l compared with 6.71 (0.88) mmol/l, P less than 0.001, analysis of variance]. The cardioplegia solution caused a large increase in plasma magnesium in both groups but in the sodium nitroprusside group the level rose higher [to 1.59 (0.12)mmol/l compared with 1.34 (0.06)mmol/l] and fell faster (P less than 0.05, analysis of variance). In the group receiving sodium nitroprusside, plasma potassium fell, by a mean of 0.34mmol/l, as plasma catecholamine levels rose; no such fall was seen in the group receiving trimetaphan camsylate (P less than 0.05, analysis of variance). 3. It is concluded that the sympathoadrenal system is important in causing metabolic changes during cardiopulmonary bypass and may be relevant in other conditions such as acute myocardial infarction.

125I-neuropeptide Y binding activity of pig spleen cell membranes: effect of solubilisation

Crude preparations of pig spleen cell membranes were obtained by differential centrifugation. 125I-NPY bound specifically to these membranes with a KD of 56 +/- 13 pM and Bmax of 44 +/- 4.0 fmols/mg protein. After treatment with 1% CHAPS* and 10 mM 2-mercaptoethanol in the presence of 2 microM leupeptin, 2 microM pepstatin A, 10 microM phosphoramidon, 200 microM PMSF and 0.1% bacitracin, followed by centrifugation at 100,000 g a soluble preparation was obtained that contained a single population of specific 125I-NPY binding sites. The KD of the soluble receptor was significantly higher at 1.38 +/- 0.2 nM (P less than 0.01) but the Bmax of 59.6 +/- 6.6 fmols/mg protein was similar (N.S.). This is the first description of a method for obtaining NPY receptors in soluble form and should enable their purification and characterisation, though the low affinity of the soluble receptor may reflect disruption of the ligand binding site upon removal of the receptor from the membrane.

Effect of experimental allergic neuritis serum on normal rat peripheral nerve

To study the possible in vivo activity of experimental allergic neuritis (EAN) serum, we injected serum from rats immunized with whole nerve, P2 protein or adjuvant alone into the sciatic nerve of normal Lewis rats. Serum from whole nerve and P2-immunized animals produced demyelination 24 h after injection. Only high-titer anti-P2 serum was active and no control serum had this effect. Anti-P2 antibodies or other serum factors may contribute to the pathogenesis of whole nerve and P2-induced EAN.

Selective suprasensitivity to calcitonin-gene-related peptide in the hands in Raynaud's phenomenon

The effects of intravenous infusion of three vasodilators on skin blood flow were studied in eight patients with Raynaud's phenomenon and eight controls, matched for age and sex, by means of the non-invasive technique of laser doppler flowmetry (LDF). The responses to calcitonin-gene-related peptide (CGRP) were compared with those to the endothelium-dependent vasodilator adenosine triphosphate (ATP) and the endothelium-independent vasodilator prostacyclin (epoprostenol; PGI2). In the patients with Raynaud's phenomenon, CGRP induced flushing of the face and hands accompanied by a rise in skin blood flow, whereas in the controls CGRP caused flushing and increased blood flow only in the face. PGI2 caused similar rises in skin blood flow in the hands and face in both groups. ATP did not cause any significant changes in skin blood flow in the face or hands in the patients, but in the controls it increased skin blood flow in the face. Since the suprasensitivity to CGRP of skin blood flow in the hands of patients with Raynaud's phenomenon is not common to other vasodilators, it may reflect a deficiency of endogenous CGRP release in this disorder.

A quantitative 'in-situ' hybridization method using computer-assisted image analysis. Validation and measurement of atrial-natriuretic-factor mRNA in the rat heart

We have validated a quantitative 'in-situ' hybridization method and computer-assisted image analysis of autoradiographs as a technique for measuring atrial-natriuretic-factor (ANF) mRNA in tissue sections of rat heart by: (i) producing radioactive standards to calibrate the autoradiograms and (ii) assessing: (a) specificity (through RNAase A background subtraction, comparison of ANF mRNA and non-ANF mRNA probe binding to sections, Northern analysis and section-thickness titration curves); (b) sensitivity (by calculating the limit of detection for ventricular levels of ANF mRNA); (c) precision [inter-assay CV (coefficient of variation) less than 10%; intra-assay CV 6-7%]; and (d) accuracy. We have found with this technique that deoxycortone and saline treatment of rats elevates ANF mRNA to a larger extent in the ventricles than in the atria and that, in neonatal-rat hearts, ANF mRNA is elevated in all cardiac chambers relative to adult levels.

Investigation of alpha 2-adrenoceptors in humans

Partial alpha 2-agonists are thought to lower blood pressure principally by stimulation of postsynaptic central nervous system alpha 2-adrenoceptors. It is possible for some to have also a peripheral action, either by acting on the inhibitory presynaptic or as an antagonist at the postsynaptic alpha 2-adrenoceptor. In order to assess these other actions, indices are required for these receptors. Plasma growth hormone is used for the central nervous system and skin blood flow for peripheral postsynaptic alpha 2-adrenoceptors. Plasma insulin is also an index for the latter, but a double-site assay is required to detect decreases within the fasting range. Plasma noradrenaline reflects both central nervous system and peripheral modulation of sympathetic nerve activity, so that "dynamic" tests (described next) are required to dissect these two control mechanisms. Selective peripheral alpha 2-adrenoceptor stimulation or blockade may be attractive for various therapeutic applications such as hypertension, diabetes, and Raynaud's phenomenon. The balance of opposing pre- and postsynaptic alpha 2-adrenoceptor effects will be important and this may require more dynamic tests than already mentioned, such as comparing the effect of alpha-methylnoradrenaline on plasma noradrenaline (presynaptic effect) and skin blood flow (postsynaptic effect) in the presence and absence of the partial alpha 2-agonist or antagonist under investigation. Since alpha-methylnoradrenaline does not penetrate the central nervous system, any blockade of its action by a drug must be peripherally mediated. Examples of all these indices, investigations, and drugs are presented.

The transport and culture conditions for optimum transformation responses of wildfowl lymphocytes to mycobacterial antigens

A method has been developed for increasing the survival of wildfowl lymphocytes during transport over considerable distances. Blood in an equal volume of heparinised RPMI was maintained at close to avian body temperature, i.e., approximately 40 degrees C. Using this system lymphocyte transformation in the presence of antigen (mycobacterial) has been successfully performed with wildfowl mononuclear cells for the first time. Duck cells were cultured in 10% autologous sera with 8 x 10(5) cells/well for 4 days. Cells from Hawaiian geese (Branta sandvicensis) required similar culture conditions but were incubated for 3 days.

Intracoronary injections of salbutamol demonstrate the presence of functional beta 2-adrenoceptors in the human heart

To demonstrate the presence of functional cardiac beta 2-adrenoceptors in man, we studied the responses to intracoronary injections of salbutamol in three groups of six patients. We injected salbutamol, a selective beta 2-adrenoceptor agonist, into the right coronary artery to avoid peripheral vasodilator action and to stimulate the sinoatrial node directly. Salbutamol injections caused a sinus tachycardia. The same doses of salbutamol injected into the aortic root caused no change in heart rate, ruling out a systemic effect. The mean dose required to cause an increase in heart rate of 30 beats/min (IHR30) was 2.6 micrograms in the first group of six patients. In 12 other patients salbutamol was given after beta-blockade to confirm the beta 2-selectivity of the responses. Doses of practolol (beta 1-selective blockade) and of propranolol (beta 1- and beta 2-blockade) that had equal beta 1-blocking activity were used. In six patients who were given practolol, the mean IHR30 dose was 2.1 micrograms. In six patients who were given propranolol, the mean IHR30 dose was significantly greater at 64 micrograms (p less than 0.001, practolol vs. propranolol). This study demonstrates that direct cardiac beta 2-adrenoceptor stimulation in man has a positive chronotropic effect.

Binding sites for 125I-labelled endothelin-1 in the kidneys: differential distribution in rat, pig and man demonstrated by using quantitative autoradiography

1. Quantitative receptor autoradiography in vitro has been used to determine the distribution and density of specific binding sites for 125I-labelled endothelin-1 in human, porcine and rat kidneys. Immunocytochemistry was used to visualize von Willebrand factor-positive endothelial cells in adjacent sections to those used for autoradiography. 2. High levels of specific binding were detected in the vasa recta and papilla of all three species with lower levels in the medulla and cortex. 3. A major difference between the species was observed within the glomeruli, where high levels of binding were found in the rat but no detectable binding sites in pig or man.