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S J Hughes

Publications and source records attributed to S J Hughes.

At least 19 recordsLinked to original sources
PubMed1999

Differential expression of Hsp27 in normal oesophagus, Barrett's metaplasia and oesophageal adenocarcinomas.

The protein expression patterns of normal, metaplastic and malignant oesophageal tissues were analysed by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) to identify changes associated with Barrett's metaplasia and transformation to oesophageal adenocarcinoma. Heat-shock protein 27 (Hsp27), a small heat-shock protein which is protective against cytotoxic stresses, was abundant in normal oesophagus. However, Hsp27 expression was markedly lower in Barrett's metaplasia and oesophageal adenocarcinomas. This was confirmed by immunohistochemical analysis. Hsp27 protein was most highly expressed in the upper layers of squamous epithelium and exhibited a pattern of expression that corresponded with the degree of squamous maturation. Northern and Southern analysis demonstrated Hsp27 to be regulated at the level of mRNA transcription or abundance. Normal oesophageal tissues were examined for gender differences in Hsp27 expression. Women expressed fourfold higher levels of Hsp27 mRNA, however, this difference was not appreciable in protein expression. Hsp27 protein was inducible by heat shock in Barrett's adenocarcinoma cell lines and an immortalized oesophageal epithelial cell line (HET-1A), but not by oestradiol. These results demonstrate abundant constitutive expression of the stress-response protein Hsp27 in the normal oesophagus, and suggest that low-level expression in Barrett's metaplasia may be one factor which may influence susceptibility to oesophageal adenocarcinoma development.

Adenocarcinoma↗
PubMed1999

Cytochromes P450 are expressed in proliferating cells in Barrett's metaplasia.

The expression of cytochromes P450 (CYP) in Barrett's esophagus and esophageal squamous mucosa was investigated. Esophagectomy specimens from 23 patients were examined for CYP expression of CYP1A2, CYP3A4, CYP2C9/10, and CYP2E1 by immunohistochemical analysis, and the expression of CYP1A1, CYP3A4, CYP1B1, CYP2E1, and CYP2C9/10 in these tissues was further confirmed by reverse transcription polymerase chain reaction. Immunohistochemical analysis of esophageal squamous mucosa (n = 12) showed expression of CYP1A2, CYP3A4, CYP2E1, and CYP2C9/10 proteins, but it was noted that cells within the basal proliferative zone did not express CYPs. Immunohistochemical analysis of Barrett's esophagus (n = 13) showed expression of CYP1A2, CYP3A4, CYP2E1, and CYP2C9/10 that was prominent in the basal glandular regions, which are areas containing a high percentage of actively proliferating cells. Immunohistochemical staining for both proliferating cell nuclear antigen and the CYPs further supported the colocalization of CYP expression to areas of active cell proliferation in Barrett's esophagus, whereas in the esophageal squamous epithelium, CYP expression is limited to cells that are not proliferating. RT-PCR with amplification product sequence analysis confirmed CYP1A1, CYP3A4, CYP1B1, CYP2E1, and CYP2C9/10 mRNA expression in Barrett's esophagus. These data suggest that the potential ability of cells in Barrett's esophagus to both activate carcinogens and proliferate may be important risk factors affecting carcinogenesis in this metaplastic tissue.

Barrett Esophagus↗
PubMed1998

A novel amplicon at 8p22-23 results in overexpression of cathepsin B in esophageal adenocarcinoma.

Cathepsin B (CTSB) is overexpressed in tumors of the lung, prostate, colon, breast, and stomach. However, evidence of primary genomic alterations in the CTSB gene during tumor initiation or progression has been lacking. We have found a novel amplicon at 8p22-23 that results in CTSB overexpression in esophageal adenocarcinoma. Amplified genomic NotI-HinfI fragments were identified by two-dimensional DNA electrophoresis. Two amplified fragments (D4 and D5) were cloned and yielded unique sequences. Using bacterial artificial chromosome clones containing either D4 or D5, fluorescent in situ hybridization defined a single region of amplification involving chromosome bands 8p22-23. We investigated the candidate cancer-related gene CTSB, and potential coamplified genes from this region including farnesyl-diphosphate farnesyltransferase (FDFT1), arylamine N-acetyltransferase (NAT-1), lipoprotein lipase (LPL), and an uncharacterized expressed sequence tag (D8S503). Southern blot analysis of 66 esophageal adenocarcinomas demonstrated only CTSB and FDFT1 were consistently amplified in eight (12.1%) of the tumors. Neither NAT-1 nor LPL were amplified. Northern blot analysis showed overexpression of CTSB and FDFT1 mRNA in all six of the amplified esophageal adenocarcinomas analyzed. CTSB mRNA overexpression also was present in two of six nonamplified tumors analyzed. However, FDFT1 mRNA overexpression without amplification was not observed. Western blot analysis confirmed CTSB protein overexpression in tumor specimens with CTSB mRNA overexpression compared with either normal controls or tumors without mRNA overexpression. Abundant extracellular expression of CTSB protein was found in 29 of 40 (72. 5%) of esophageal adenocarcinoma specimens by using immunohistochemical analysis. The finding of an amplicon at 8p22-23 resulting in CTSB gene amplification and overexpression supports an important role for CTSB in esophageal adenocarcinoma and possibly in other tumors.

Adenocarcinoma↗
PubMed1998

Impaired glucose-stimulated insulin release in islets from adult rats malnourished during foetal-neonatal life.

Poor foetal and neonatal nutrition may impair normal pancreatic beta-cell development and predispose to diabetes in later life. We investigate here the nature of the pancreatic beta-cell dysfunction in sucrose-fed adult offspring malnourished during the foetal-neonatal period and examine glucose metabolism and the generation of signals involved in the secretory mechanism. In islets from sucrose-fed previously malnourished rats, rates of glucose utilisation (production of 3H2O) and oxidation (production of 14CO2), at 2, 6 and 10 mM glucose, were not lower than those of controls. ATP concentrations in islets from previously malnourished rats fed sucrose at 2 and 10 mM glucose were similar to those of controls. Glucose-stimulated insulin release was impaired (by 49-55%) in islets from these animals as was the response to keto-isocaproate (by 70%) and tolbutamide (by 70%). Under conditions in which ATP-sensitive K+ channels were clamped open (40 mM K+ and diazoxide), glucose-stimulated insulin release in islets from previously malnourished rats fed sucrose was reduced. These findings show that defects in insulin secretion in islets isolated from previously malnourished animals are located in both ATP-sensitive K+ channel dependent and independent pathways. They do not involve alterations in the early steps of glucose handling in the beta-cell, including glucose metabolism and ATP generation.

Adenine Nucleotides↗
PubMed1998

Lack of cell surface Fas/APO-1 expression in pulmonary adenocarcinomas.

The Fas receptor and ligand initiate an apoptotic pathway. Alterations in this pathway within tumor cells can result in escape from apoptosis and immune surveillance. We evaluated Fas protein expression in 42 primary pulmonary adenocarcinomas, and Fas expression and function in the lung adenocarcinoma cell lines A549 and A427. Immunohistochemical analysis demonstrated Fas protein expression in 47.6% of the tumors; however, Fas-positive tumors demonstrated cytoplasmic staining without cell surface expression. Northern blot analysis indicated that levels of Fas mRNA were similar in Fas protein-positive tumors to levels in normal lung tissue, but were reduced in Fas protein-negative tumors. Soluble form Fas was not detected in the majority of these tumors either by RT-PCR or Western blot analysis. Cell surface Fas protein expression was minimal in A549 and A427 cell lines as determined by flow cytometry. Both cell lines demonstrated Fas mRNA expression by Northern blot analysis and abundant protein expression by Western blot analysis. Transfection of the Fas cDNA derived from A549 cells induced surface Fas protein in COS cells; however, stable transfection of a native Fas cDNA into A549 cells failed to induce surface Fas protein expression. Parental A549 cells and A549 cells transfected with a Fas expression vector were resistant to Fas-mediated apoptosis. Transgenic expression of a FLAG-tagged Fas cDNA in A549 cells, with visualization of the Fas-FLAG protein using confocal microscopy, demonstrated that the Fas-FLAG protein was retained within cytoplasmic portions of the cell and was not translocated to the cell surface. These findings suggest that the Fas protein is reduced or not present on the cell surface in the primary lung tumors and is sequestered within A549 tumorigenic lung cells, and these alterations directly affect the cells resistance to Fas-mediated apoptosis.

Adenocarcinoma↗
PubMed1998

How effective is the Newport/Aspen collar? A prospective radiographic evaluation in healthy adult volunteers.

BACKGROUND: Cervical extrication collars are used in the evacuation of the injured to minimize secondary injury. These collars were designed for extrication and evacuation, not for longterm use, and complications have been reported when they have been used in the rehabilitation phase. The Newport/Aspen collar was designed specifically for long-term use. METHODS: Using a radiographic method, the effectiveness of the collar in restricting motion was evaluated for the cervical spine as a whole and for constituent segments, occiput to C7, in 15 normal volunteers. RESULTS: Combined flexion-extension was reduced from mean 98.8 to 31.1 degrees (31.5% of normal; p = 0.000000002), lateral bending was reduced from mean 31.1 to 15.9 degrees (51.1% of normal; p = 0.0000001), and overhead rotation was reduced from mean 64.6 to 26.8 degrees (41% of normal; p = 0.000000002). The cervical spine, however, does not move as one unit; paradoxical motion, the phenomenon of "snaking," occurs. Goniometric techniques do not demonstrate this effect. Data are provided for motion by segmental level. CONCLUSION: Full cervical immobilization is a myth. It would seem logical to match the level-specific efficacy of the device to the level of injury. Data are provided for the Aspen collar.

Adolescent↗
PubMed1998

Electrophysiological and metabolic characterization of single beta-cells and islets from diabetic GK rats.

We have used the whole-cell recording technique to determine whether ATP-sensitive potassium (K[ATP]) currents, voltage-dependent Ca2+ currents, and exocytosis are different in single beta-cells from pancreatic islets of Goto-Kakizaki (GK) rats, a novel model of NIDDM, and normal rats. In addition, we have also measured the insulin secretory responses, ATP content, and the rate of glucose metabolism in intact islets. Although the glucose sensitivity of the K(ATP) current was similar between GK rats and controls, in the absence of glucose, K(ATP) current density was larger in GK rats, which resulted in a more hyperpolarized membrane potential. Whole-cell Ca2+ currents were similar. By monitoring the cell capacitance with a fixed intracellular solution, no difference was detected in the exocytotic responses of beta-cells from normal and GK rats. In islets from GK rats, the rates of glucose utilization ([3H]H2O production from 5-[3H]glucose) and oxidation ([14C]CO2 production from U-[14C]glucose) were not significantly different from controls. Insulin secretion, however, was impaired (by 50%), and this was paralleled by a smaller increase in ATP content in response to stimulation by 10 mmol/l glucose in islets from GK rats when compared with controls. Under conditions in which K(ATP) channels were held open and the effects of glucose were independent of membrane potential, insulin release was still significantly lower in GK rat islets than in controls. These findings suggest that the impaired insulin secretion in islets from GK rats does not simply result from a failure to close K(ATP) channels, nor does it result from an impairment in calcium secretion coupling.

Adenosine Triphosphate↗
PubMed1997

Fas/APO-1 (CD95) is not translocated to the cell membrane in esophageal adenocarcinoma.

This study describes Fas (CD95) expression in Barrett's esophagus, adenocarcinomas of the esophagus, and three esophageal adenocarcinoma cell lines. Immunohistochemical analysis of Barrett's esophagus demonstrated cell surface expression of Fas protein. In contrast, 30.5% of esophageal adenocarcinomas examined by immunohistochemical analysis demonstrated faint cytoplasmic staining, and 69.5% were negative for Fas. Similar levels of Fas mRNA were identified in tumors compared to mRNA levels in esophageal squamous mucosa or Barrett's esophagus. An approximately Mr 48,000 Fas protein was identified by Western blot analysis in tumors that were negative for Fas expression by immunohistochemical analysis. The esophageal adenocarcinoma cell line Seg-1 was negative for Fas expression by immunohistochemical analysis, but Western blot analysis demonstrated abundant, appropriately sized Fas protein. In agreement with the immunohistochemical analysis, flow cytometry of Seg-1 showed minimal amounts of Fas on the cell surface, which correlated with resistance to Fas-mediated apoptosis. No mutations in the Seg-1 Fas coding sequence or exon 1 were identified by sequence analysis. This was confirmed by transient transfection of COS cells with expression vectors generated from the Seg-1 Fas cDNA, which resulted in cell surface expression of the Fas protein. Stable transfection of Seg-1 with a Fas expression vector did not result in efficient Fas expression on the cell surface. Seg-1 cells, transiently transfected with a Fas-FLAG expression vector and examined for protein expression using confocal microscopy and an anti-FLAG antibody, showed that the Fas-FLAG protein was not present on the cell surface but was present in the cytoplasm. Taken together, these results indicate that expression of Fas on the cell surface by esophageal adenocarcinoma is reduced. In an esophageal adenocarcinoma cell line, wild-type Fas protein is retained in the cytoplasm, and this correlates with resistance to Fas-mediated apoptosis. The retention of wild-type Fas protein within the cytoplasm may represent a mechanism by which malignant cells evade Fas-mediated apoptosis.

Adenocarcinoma↗
PubMed1997

Relaxin as a relaxant of the isolated rat uterus: comparison with its mechanism of action in vivo.

1. Glibenclamide, a blocker of ATP-sensitive potassium channels, has been shown to antagonize relaxin as a uterine relaxant in the rat in vivo but not in vitro. The aim, therefore, was to investigate whether the discrepancy between the two studies was a consequence of differences in (1) muscle layers, (2) hormonal conditions or (3) spasmogens utilized. Relaxin was compared with salbutamol and levcromakalim. 2. Relaxin was of similar potency as a uterine relaxant against oxytocin (0.2 mM)-induced spasm with tension measured in the circular or longitudinal muscle layers. Glibenclamide (10 microM) did not antagonize relaxin or salbutamol in these preparations but greatly antagonized levcromakalim (91-fold). Relaxin was a relaxant of tension activated by transmural electrical stimulation in uteri from rats that had been ovariectomized, although the maximal effect was only 30 +/- 15%, and in uteri from rats that had been treated with 17 beta-estradiol benzoate. Glibenclamide was not an antagonist of relaxin in the latter preparation but did antagonize levcromakalim (118-fold). Relaxin also inhibited spontaneous phasic tension development in uteri from ovariectomized rats but again was not antagonized by glibenclamide. 3. Because relaxin was not antagonized by glibenclamide under any of these various conditions, it would appear that the in vivo-in vitro discrepancy in the antagonism of relaxin by glibenclamide is not attributable to the effects of different muscle layers, hormonal conditions or spasmogens. It may be that the mechanism of action of relaxin or glibenclamide or both differs between in vivo and in vitro preparations.

Albuterol↗
PubMed1997

The role of a cAMP-dependent pathway in the uterine relaxant action of relaxin in rats.

The aim of this study was to investigate the role of the adenylyl cyclase pathway, and in particular cyclic AMP-dependent protein kinase A, in the relaxant action of relaxin in the isolated uterus of the nonpregnant rat. The purportedly selective inhibitor of cAMP-dependent protein kinase A N-[2-(methylamino) ethyl]-5-isoquinolinesulfonamide hydrochloride (H-8) (at 100 mumol l-7) antagonized relaxin, salbutamol (an agonist at beta-adrenoceptors) and levcromakalim (a K+ channel opener) to a similar extent (by factors of 3.1, 1.9 and 2.8, respectively), demonstrating that it is not a selective inhibitor. Relaxin and levcromakalim were less potent and had smaller, maximal, relaxant effects in longitudinal myometrium than in intact uterus cut in the longitudinal plane. By contrast, nifedipine (a Ca2+ channel blocker) was equipotent in the two preparations and salbutamol only slightly less potent in the longitudinal myometrium. Relaxin did not alter the cyclic AMP-dependent protein kinase A activity ratio in longitudinal myometrium, but did increase the activity ratio by a factor of 2.0 +/- 0.2 in the intact uterus. Salbutamol, the positive control, increased this activity ratio in both longitudinal myometrium (by 1.9 +/- 0.3 times) and in the intact uterus (by 3.8 +/- 0.3 times), whereas the negative control levcromakalim had no effect. Relaxin seems to act as a relaxant of longitudinal myometrium by a cyclic AMP-independent mechanism but possibly interacts with the circular myometrium or endometrium to release a relaxant factor via a cyclic-AMP-dependent mechanism.

Adrenergic beta-Agonists↗
PubMed1997

The effect of maternal protein deficiency during pregnancy and lactation on glucose tolerance and pancreatic islet function in adult rat offspring.

To test the hypothesis that poor foetal-neonatal nutrition predisposes adult animals to impaired glucose tolerance or diabetes, pregnant and lactating rats were fed a low (5%) protein diet and glucose tolerance and pancreatic islet function then assessed in the adult offspring. To expose any underlying defects the offspring were allowed access to a sucrose supplement (35%) or fed a high fat diet. Offspring born to low protein-fed females had significantly lower body weights than controls. In islets from previously malnourished rats, insulin release in batch incubations or perifusion was not significantly different to controls. In islets from previously malnourished animals fed sucrose, glucose-stimulated insulin release was reduced in perifusion by 66% (P < 0.01) and batch incubations by 26-52% (6-16 mmol/l glucose, P < 0.01). Similarly, impaired secretory responses were found in islets from previously malnourished animals fed a high fat diet. These did not result from a reduced pool of releasable insulin, as arginine-stimulated secretion was not impaired. Rats previously malnourished showed a normal glucose tolerance. Glucose tolerance was impaired, however, in previously malnourished rats fed sucrose (area under the glucose tolerance test curve was increased by 42%, P < 0.05) but despite the reduced islet secretory responses was not significantly different to sucrose-fed controls (area increased by 54%, P < 0.05). Glucose tolerance was impaired in previously malnourished animals fed high fat diet (area increased by 48%, P < 0.05) more so than in high fat fed-controls (28% increase, NS). These data support the hypothesis that poor foetal-neonatal nutrition leads to impaired pancreatic beta-cell function which persists into adult life. Alone this is not sufficient to produce diabetes, but an inability to respond to a highly palatable fat diet may tip the balance towards impaired glucose tolerance.

Animals↗
PubMed1997

Nursing systems '97. Time for new thinking.

The nursing information systems challenge in 1997 is to identify and implement technology and information systems solutions that provide more breadth, depth, flexibility and standardization than ever before, and at a faster pace. To meet the challenge we need more than application checklists. We need to challenge the old approaches to defining needs, implementing systems and training users. Nurses must be educated, involved and accountable for the integration of systems into the patient care process. It's time for new thinking; it's time to ask why we are doing things the same way we did them 20 years ago when everything else about healthcare has changed.

Catalogs, Commercial as Topic↗
PubMed1996

Impaired glucose tolerance and mild hyperglycemia in sucrose-fed rats does not impair insulin secretion.

We fed normal rats a high sucrose diet in order to test the hypothesis that mild hyperglycemia can induce defects in pancreatic beta-cell function and impair glucose-stimulated insulin release. Rats provided with free access to a sucrose solution (35%) voluntarily consumed 50% more carbohydrate than control per day. After 7 days of sucrose feeding, glucose tolerance was significantly impaired; the area under the glucose tolerance test curve (GTT) was 683 +/- 61 mmol/120 min compared with 472 +/- 56 mmol/120 min in controls (P < 0.05). Impaired glucose tolerance was still present after a further 12 days (area under the GTT: 749 +/- 99 mmol/120 min). Sucrose-fed rats were significantly (P < 0.05) hyperglycemic by 1.5 mmol/l over controls. When insulin secretion was assessed in vivo and in vitro in control and sucrose-fed rats, no significant differences were apparent in plasma samples collected over a 1-h period or in statically incubated or perifused isolated pancreatic islets. In addition, the rates of glucose utilisation and oxidation were normal in islets from sucrose-fed rats. These data do not support the hypothesis that minimal hyperglycemia is sufficient to impair glucose-stimulated insulin release.

Animals↗
PubMed1996

The lack of a role for potassium channel opening in the action of relaxin in the rat isolated uterus; a comparison with levcromakalim and salbutamol.

1. The effects of relaxin in vitro in the isolated uterus from the non-pregnant rat were compared with those of levcromakalim and salbutamol in tissue bath, 42K+ -efflux and electrophysiological studies, to determine whether relaxin exhibits the characteristics of an opener of KATP-channels. 2. In uterus exposed to oxytocin (0.2 nM), tetraethylammonium (TEA, 10 mM) and glibenclamide (10 microM) produced large rightward shifts of the log10 concentration-effect curve to levcromakalim (125 fold and 118 fold, respectively). TEA (10 mM) caused only small rightward shifts of the log10 concentration-effect curves to salbutamol and relaxin (5.2 fold and 7.5 fold respectively). Glibenclamide did not antagonize salbutamol or relaxin. 3. Levromakalim (0.2 and 2 microM) suppressed the spasm evoked by low ( < or = 40 mM) but not high ( > 40 mM) concentrations of KCl. Salbutamol (1.5 nM) inhibited the spasm evoked by low concentrations of KCl ( < or = 40 mM). Salbutamol (15 nM) and relaxin (3 and 30 nM) inhibited the spasm evoked by low and high concentrations of KCl (10-80 mM). 4. Relaxin (0.12 microM) did not produce an increase in 42K+-efflux from longitudinal segments of rat myometrium. Exposure of tissues to relaxin (0.12 microM), in the presence of diltiazem (1 microM) plus KCl (20 mM), resulted in a small increase in 42K+-efflux of short duration. 5. Electrophysiological recording showed that the phasic spasms of the uterus exposed to oxytocin (0.2 nM) were accompanied by bursts of spiking activity superimposed upon a plateau potential. Inhibition of the mechanical activity of the uterus by levcromakalim (2 and 10 microM), salbutamol (30 nM) or relaxin (0.18 microM) was accompanied by a reduction in the duration of the plateau potential and the number of spikes without membrane hyperpolarization. 6. Unlike levcromakalim, relaxin did not selectively inhibit the spasm evoked by low concentrations of KCl and was not markedly antagonized by TEA or glibenclamide. Under conditions where a cromakalim-induced increase of the 42K+-efflux rate has been demonstrated, relaxin had only a very small effect. In isolated uterus from the rat, in contrast to observations in vivo, relaxin did not exhibit the characteristics of an opener of KATP-channels suggesting that another mechanism accounts for its inhibitory action.

Adrenergic beta-Agonists↗
PubMed1995

Insulin secretion from islets of GK rats is not impaired after energy generating steps.

Insulin secretory responses of intact and electrically permeabilised islets of Goto-Kakizaki (GK) rats, a novel model of non-insulin dependent diabetes mellitus, and Wistar (control) rats were compared to investigate the mechanism of the impairment of insulin secretion from pancreatic islets of GK rats. Insulin secretion from intact islets in response to glucose, glyceraldehyde, succinate monomethylester and tetramethyl p-phenylenediamine, which reduces cytochrome c directly, was significantly impaired in GK rats compared to control rats (P < 0.05, P < 0.01, P < 0.05 and P < 0.05, respectively). However, Ca(2+)-induced insulin release from electrically permeabilised islets of GK rats was higher than that of control rats. Moreover, insulin secretion from intact islets in response to 50 mM KCl, which depolarises islet cells, was not impaired in GK rats. These results indicate that insulin secretion from islets of GK rats is not impaired after energy generating steps of metabolism.

Animals↗
PubMed1995

Cellular localization of the inhibitory action of relaxin against uterine spasm.

1. The aim of this study was to determine whether the site of action of relaxin as a relaxant of rat myometrium is at the cell membrane or at an intracellular-site. Therefore, the potency of relaxin was determined against spasms reliant predominantly upon either extracellular Ca2+ or intracellular Ca2+. Uterine spasms dependent upon extracellular Ca2+ were elicited by (i) oxytocin (0.2 nM) (ii) Bay K 8644 (1 microM) in 10 mM K(+)-rich PSS and (iii) KCl (80 mM). Uterine spasm dependent upon intracellular Ca2+ was elicited by oxytocin (20 nM) in the presence of nifedipine (500 nM). The effects of relaxin against these spasmogens were compared with those of levcromakalim, nifedipine and salbutamol. 2. Relaxin (0.2-6.3 nM), levcromakalim (25-800 nM), salbutamol (1-63 nM) and nifedipine (1-250 nM) caused concentration-dependent inhibition of the spasm evoked by oxytocin (0.2 nM) and relaxin was the most potent relaxant. 3. Relaxin and nifedipine were slightly less potent against the spasm induced by Bay K 8644 (1 microM) than against spasm induced by oxytocin (0.2 nM) (15 fold and 13 fold respectively). Levcromakalim and salbutamol were equipotent against the spasm evoked by Bay K 8644 (1 microM) and that evoked by oxytocin (0.2 nM). 4. Relaxin induced only 47 +/- 7% inhibition of the KCl (80 mM)-evoked spasm at a concentration of 0.8 microM. Levcromakalim was much less potent (427 fold) against the spasm evoked by KCl (80 mM) than against the spasm evoked by oxytocin (0.2 nM). The potency of salbutamol against the spasm evoked by KCl (80 mM) was modestly reduced (14 fold) compared to that against the spasm evoked by oxytocin (0.2 nM). The potency of nifedipine against the KCl (80 mM)-evoked spasm was not different from that against the oxytocin (0.2 nM)-evoked spasm. 5. The potencies of relaxin and levcromakalim against the spasm evoked by oxytocin (20 nM) + nifedipine (500 nM) were greatly reduced (74 fold and 234 fold respectively) compared to their potencies against the spasm evoked by oxytocin (0.2 nM). The potency of salbutamol against these two spasmogens was not different. 6. Relaxin was much less potent against the spasm dependent upon intracellular Ca2+ (that induced by oxytocin (20 nM) + nifedipine (500 nM)) than against the spasms dependent upon extracellular Ca2+, those induced by oxytocin (0.2 nM) and Bay K 8644 (1 microM). In this regard, relaxin resembled levcromakalim and nifedipine rather than salbutamol. Therefore, the major site of action of relaxin appears to be located at the plasma membrane rather than at an intracellular level. The observation that relaxin was less effective against the KCl (80 mM)-induced spasm than against the oxytocin (0.2 nM)-evoked spasm may indicate that relaxin has a minor action involving K(+)-channel opening. 7. High concentrations of relaxin (up to 1 microM) induced significant inhibition of the spasm dependent upon intracellular Ca2+. Thus at high concentrations relaxin also appears to have an additional intracellular action.

Adrenergic beta-Agonists↗