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C J Kenyon

Publications and source records attributed to C J Kenyon.

At least 55 records · Page 3Linked to original sources
PubMed1995

A calcium-channel homologue required for adaptation to dopamine and serotonin in Caenorhabditis elegans.

Processing and storage of information by the nervous system requires the ability to modulate the response of excitable cells to neurotransmitter. A simple process of this type, known as adaptation or desensitization, occurs when prolonged stimulation triggers processes that attenuate the response to neurotransmitter. Here we report that the Caenorhabditis elegans gene unc-2 is required for adaptation to two neurotransmitters, dopamine and serotonin. A loss-of-function mutation in unc-2 resulted in failure to adapt either to paralysis by dopamine or to stimulation of egg laying by serotonin. In addition, unc-2 mutants displayed behaviours similar to those induced by serotonin treatment. We found that unc-2 encodes a homologue of a voltage-sensitive calcium-channel alpha-1 subunit. Expression of unc-2 occurs in two types of neurons implicated in the control of egg laying, a behaviour regulated by serotonin. Unc-2 appears to be required in modulatory neurons to downregulate the response of the egg-laying muscles to serotonin. We propose that adaptation to serotonin occurs through activation of an Unc-2-dependent calcium influx, which modulates the postsynaptic response to serotonin, perhaps by inhibiting the release of a potentiating neuropeptide.

Amino Acid Sequence↗
PubMed1995

Effects of the glucocorticoid antagonist RU486 in spontaneously hypertensive and Sprague Dawley rats.

The effect of a low dose of the gluco-corticoid receptor antagonist, RU486, was tested in spontaneously hypertensive (SHR) and in Sprague Dawley (SD) rats. In SD rats, RU486 (50 micrograms/day, 18 days) significantly increased growth rate and thymus weight, probably by antagonising the actions of endogenous glucocorticoid hormones. Blood pressure and plasma corticosterone levels were not affected by RU486 at this dose. In leucocytes, RU486 treatment in vivo reduced the number of glucocorticoid binding sites but did not affect binding affinity. In contrast, growth rate and thymus weight were not altered in SHR when treated with the same dose of RU486 for a longer period (60 days). Blood pressure was unaffected as were leucocyte glucocorticoid receptor characteristic. Glucocorticoid receptor binding characteristics for RU486 were similar for liver cytosol of SD and SHR. We conclude that the apparent difference in sensitivity to RU486 between strains is probably not due to differences in interaction of the antagonist with the glucocorticoid receptor but may be caused by differences in pharmacokinetics of RU486 between strains.

Adrenal Glands↗
PubMed1995

Differences in temperature-sensitive receptor binding of glucocorticoids in spontaneously hypertensive and normotensive Wistar-Kyoto rats.

Glucocorticoid receptor binding was compared in liver cytosol preparations from spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats using homologous displacement of [3H]dexamethasone. At 5 degrees C, there was no difference in receptor binding affinity or concentration between strains for dexamethasone, corticosterone or aldosterone. At 37 degrees C, affinity for dexamethasone was lower than at 5 degrees C for both rat strains and decreased with time. However, at this higher temperature, binding affinity in the SHR preparation was consistently higher than in the WKY preparation. The WKY preparation had a higher receptor concentration. The rate of dissociation of the [3H]dexamethasone-receptor complex prepared at 5 degrees C and then incubated at 37 degrees C was rapid but not different between strains. A possible explanation of these results is that the relationship of the heat shock proteins to the receptor heterocomplex is different between strains. Evidence exists of a genetic difference in Hsp 70 between SHR and WKY rats, although its cosegregation with blood pressure has not been established.

Aldosterone↗
PubMed1995

Regulation of adrenocortical steroidogenesis by benzodiazepines.

Benzodiazepines affect steroidogenesis in at least four ways depending on concentration and adrenocortical cell type. Firstly, at micromolar concentrations, they inhibit steroidogenic enzymes. Competition for microsomal 17- and 21-hydroxylase activity explains the inhibition of ACTH-stimulated aldosterone and cortisol synthesis by diazepam and midazolam. At slightly higher concentrations, we have evidence that 11 beta-hydroxylase activity is also inhibited. Secondly, at sub-micromolar concentrations, calcium influx is inhibited. T-type and L-type calcium channels appear to be blocked, this impairs signal response coupling and, in particular, decreases angiotensin- and K(+)-stimulated aldosterone synthesis in zona glomerulosa cells. Thirdly, the mitochondrion of steroidogenic tissues is a sensitive site for the stimulatory effects of benzodiazepines. Aldosterone synthesis from added HDL-cholesterol by cultured bovine zona glomerulosa cells is stimulated by diazepam, RO5-4864 and PK11195. The fourth site of benzodiazepine's effect on steroidogenesis is particular to zona glomerulosa cells. In addition to cholesterol side chain cleavage, the final part of the aldosterone biosynthetic pathway, the conversion from deoxycorticosterone is controlled. Although high micromolar concentrations of diazepam appear to be inhibitory, lower nanomolar concentrations stimulate the synthesis of aldosterone from added deoxycorticosterone. In vivo, a fifth site of benzodiazepine activity may influence plasma steroid concentrations. Competition between steroids and benzodiazepines for hepatic clearance enzymes may affect half lives of both drugs and hormones.

Adrenal Glands↗
PubMed1995

Colonic spreading of a non-chlorofluorocarbon mesalazine rectal foam enema in patients with quiescent ulcerative colitis.

BACKGROUND: Rectal foam enemas provide for drug delivery to the distal colon for treatment of left sided ulcerative colitis. However, currently available formulations contain chlorofluorocarbons which are due to be phased out in the near future. The objective of this study was therefore to determine the degree of dispersion of a newly developed non-chlorofluorocarbon rectal foam preparation in ulcerative colitis patients. METHODS: This was an open label non-controlled study of a single administration of a mesalazine foam enema (two actuations containing 2 g of mesalazine in approximately 120 mL foam) in 10 patients with quiescent ulcerative colitis. Spreading of the 99mTc-labelled foam enema was assessed over a 4-h period by the non-invasive technique of gamma scintigraphy. RESULTS: All patients retained the enema for the full 4-h imaging period. In nine out of the 10 patients, the enema was observed to spread as far as the descending colon and on average 23% of the dose was present in the descending colon at 4 h post-dose. CONCLUSIONS: The extent of spreading observed in the study supports the use of the formulation in the treatment of left sided ulcerative colitis.

Aminosalicylic Acids↗
PubMed1995

Differences in aerodynamic particle size distributions of innovator and generic beclomethasone dipropionate aerosols used with and without a large volume spacer.

BACKGROUND: The equivalence of generic beclomethasone dipropionate (BDP) formulations with their innovator counterpart must be demonstrated if generic formulations are to be used. This study has examined the aerodynamic particle size distributions of both innovator and generic formulations of BDP and the effect of a large volume spacer (Volumatic) on these distributions. METHODS: Aerosol clouds of three formulations of BDP delivering 250 micrograms per metered dose were characterised using a high precision multistage liquid impinger, and the amount of drug in different particle size bands was determined by spectrophotometric assay. RESULTS: The mean (SD) respirable fractions of Becloforte, Beclazone, and Filair without the spacer (n = 10) were 24.1 (2.1)%, 23.1 (2.7)%, and 23.0 (2.1)% respectively; however, the ratio of deposition on stage 4 of the impinger to that on stage 3 was lower for Beclazone and for Filair than for Becloforte, implying a smaller proportion of fine particles for the generic products. When the three products delivered via the Volumatic spacer device were compared, the respirable fraction for Becloforte (n = 10) was 25.0 (4.0)%, but those of Beclazone (n = 10) and Filair (n = 11) were 16.0 (1.9)% and 14.6 (3.4)%. Repeat testing (n = 5) at a later date showed higher mean respirable fractions for all three products, but a trend towards the highest respirable fraction for Becloforte, and the same rank order for the other two products. CONCLUSIONS: These in vitro findings suggest that the particle size distributions of the two generic formulations of BDP are not equivalent to that of the innovator product. Some differences in particle size distributions might not have been detected by a twin impinger. Clinical testing would be required to assess the therapeutic equivalence of innovator and generic corticosteroid products used with or without spacer devices.

Aerosols↗
PubMed1995

Microsatellite polymorphism analysis allows the individual assignment of the rat 11 beta-hydroxylase gene (Cyp11b1) and the rat aldosterone synthase gene (Cyp11b2) to chromosome 7 using rat x mouse somatic cell hybrids and identifies differences between and within various rat strains.

Mouse hepatoma x rat hepatocyte hybrids that segregate rat chromosomes were used to determine the chromosomal location of the rat genes encoding 11 beta-hydroxylase and aldosterone synthase (Cyp11b1 and Cyp11b2 respectively). By means of species-specific restriction fragments and microsatellite markers both genes were mapped to rat chromosome 7. The Cyp11b1 microsatellite marker was subsequently found to vary in length between and within rat strains. Furthermore, we compared the sequences of Cyp11b1 markers in two genetically hypertensive strains of rat with their normotensive counterparts. Previous studies have indicated that 11 beta-hydroxylase activities in Milan and Lyon hypertensive strains are different from their respective genetic controls. The Cyp11b1 microsatellite regions from Lyon hypotensive and normotensive strains of rat were similar and were both shorter by 15 bases than that of the Lyon hypertensive strain. The Cyp11b1 marker in Milan hypertensive (MHS) and normotensive (MNS) strains differ from all the Lyon strains and from each other. The MHS marker is 12 bases shorter than that of MNS rats. These differences in microsatellite length may provide useful polymorphic markers in cosegregation studies of genetic hypertension in rats.

Animals↗
PubMed1995

Vascular structure, smooth muscle cell phenotype and growth in hypertension.

The media of most blood vessels is occupied by vascular smooth muscle cells. In areas they may be replaced by glomus cells, pericytes or renin-secreting myoepithelioid cells. These cells may be regarded as phenotypic variants of vascular smooth muscle cells. In disease, ordinary vascular smooth muscle cells may also assume a spectrum of phenotypes ranging from contractile to largely secretory types. Therefore, the phenotype of smooth muscle cells that is involved in a disease process such as hypertension or one of its complications is likely to affect the structural outcome in blood vessels.

Aging↗
PubMed1995

In vivo and in vitro studies of the role of HDL in platelet activation in normotensive and hypertensive subjects.

The influence of high density lipoproteins (HDL) on platelet function were examined in vivo and in vitro. Intraplatelet, ionised calcium concentrations ([Ca2+]i) were measured using the fluorescent dye Quin-2. In vitro, platelet responses to AVP were measured in the presence or absence of HDL. Pre-treating platelets from normal volunteers with HDL in vitro lowered the [Ca2+]i response to AVP but did not significantly affect basal values. In vivo, plasma lipoprotein profiles in normotensive (13 men, 17 women) and hypertensive (13 men, 11 women) subjects were compared with basal and AVP-stimulated platelet [Ca2+]i values. Plasma [HDL] were not related to basal or stimulated [Ca2+]i. Plasma cholesterol concentrations were higher in the hypertensive patients largely because low density lipoprotein [LDL] were raised in male hypertensive patients. Plasma [LDL] and total plasma cholesterol correlated negatively with basal [Ca2+]i (but not with AVP-stimulated values) only in this subgroup. In hypertensive patients, AVP-stimulated [Ca2+]i (but not basal values) were lower than normotensive controls. From in vitro studies, it may be concluded that the anti-atherogenic properties of HDL might be mediated by inhibition of platelet reactivity. However, ex vivo a negative influence of LDL on basal (not stimulated) [Ca2+]i appears to be paramount.

Adult↗
PubMed1994

Evidence of abnormalities in corticosteroid secretion leading to volume-dependent hypertension in Milan rats.

We examined corticosteroid secretory patterns and their relation to altered salt and water metabolism in Milan hypertensive and normotensive rats. Hypertensive rats had significantly higher blood pressures, exchangeable sodium (hypertensive, 41.2 +/- 0.3 mmol.kg-1; normotensive, 38.4 +/- 0.03 mmol.kg-1, P < .001), plasma volume (hypertensive, 5.39 +/- 0.12 mL.100 g-1; normotensive, 4.84 +/- 0.10 mL.100 g-1, P < .001), and plasma concentrations of atrial natriuretic peptide (hypertensive, 38.8 +/- 4.0 pg.mL-1, normotensive, 22.4 +/- 3.1 pg.mL-1, P < .02). These features coincide with those of mineralocorticoid-induced hypertension. Adrenal venous secretory rates (picomoles per minute) of corticosterone (hypertensive, 1696 +/- 202; normotensive, 873 +/- 139), 18-hydroxycorticosterone (hypertensive, 49.7 +/- 8.3; normotensive, 25.7 +/- 3.3), and aldosterone (hypertensive, 1.16 +/- 0.17; normotensive, 0.52 +/- 0.08) were higher in the hypertensive than the normotensive strain, but that of 11-deoxycorticosterone (DOC) (hypertensive, 94.4 +/- 14.9; normotensive, 114.3 +/- 33.9) was similar in the two strains. The corticosterone-DOC, 18-hydroxycorticosterone-DOC, and aldosterone-DOC ratios were higher in the hypertensive than the normotensive strain (P < .02), but the 18-hydroxycorticosterone-corticosterone and aldosterone-18-hydroxycorticosterone ratios were not. These results indicate increased activity of the "late" aldosterone biosynthetic pathway in the hypertensive compared with the normotensive strain caused by an increased conversion rate of DOC to corticosterone. The comparison of corticosterone secretion between the two strains indicates that 11 beta-hydroxylase rather than aldosterone synthase activity is more active in the hypertensive than the normotensive rats.

18-Hydroxycorticosterone↗
PubMed1994

Inhibition of lysozyme synthesis by dexamethasone in human mononuclear leukocytes: an index of glucocorticoid sensitivity.

Glucocorticoids inhibit translation of the lysozyme gene. This effect may be the basis of an improved method of measuring glucocorticoid responsiveness in human tissues. We have compared lysozyme synthesis in various types of white blood cells and examined the specificity of inhibitory responses to various steroid hormones. The dose-related effects of the glucococorticoid receptor antagonist RU486 on dexamethasone responses were also assessed. Glucocorticoid receptor binding in mononuclear leukocytes (HML) was characterized by homologous displacement of [3H]dexamethasone and compared with the dose-related inhibitory effect of dexamethasone on lysozyme synthesis. Lysozyme activity was measured photometrically as the ability to cause lysis of Micrococcus lysodeikticus in the medium. The greatest effect of dexamethasone was observed after 72 h of culture. Qualitatively similar effects of dexamethasone were observed on cell lysozyme content and lysozyme activity in the medium, but for convenience, activity in medium, rather than cell content, was measured in subsequent assays. Lysozyme activities in various cell types prepared from the blood of healthy volunteers were ranked as follows: polymorphonuclear cells > monocytes > mononuclear cells > lymphocytes. However, dexamethasone inhibited lysozyme synthesis to a similar degree for all types. As mononuclear cells are more conveniently prepared in greater yield compared with other cells, this HML fraction formed the basis of a method of assessing glucocorticoid responsiveness and sensitivity. Lysozyme activity from HML was not significantly affected by incubation with 1 mumol/L estradiol, progesterone, dehydroepiandrosterone, or aldosterone. Dexamethasone and cortisol at 1 mumol/L both inhibited release by 45-50%. Although RU486 when added alone partially inhibited lysozyme activity, the same concentration (1 mumol/L) antagonized glucocorticoid responses and shifted the IC50 and threshold values for the effect of dexamethasone from 1.2 nmol/L to more than 1 mumol/L and from less than 1.0 to 19 nmol/L, respectively. The equilibrium dissociation constants (Kd) for dexamethasone binding to the glucocorticoid receptor ranged from 2.8-12.5 nmol/L and were positively correlated with dexamethasone IC50 values for lysozyme synthesis (r = 0.57; P = 0.002). In conclusion, the inhibition of lysozyme synthesis by dexamethasone in human mononuclear cells is a convenient and specific method of measuring responsiveness to glucocorticoids.

Cells, Cultured↗
PubMed1993

The role of glucocorticoid activity in the inheritance of hypertension: studies in the rat.

Young (3-week-old) spontaneously hypertensive rats (SHR) had significantly higher basal plasma corticosterone levels than WKY rats and maximum responses to ACTH were also higher. In isolated adrenocortical cells from these rats, corticosterone production was also more responsive to ACTH in SHR. There was no significant difference in aldosterone production. Mononuclear leucocytes from older (10-week-old) SHR had a higher affinity for dexamethasone but a smaller number of binding sites per cell. The SHR therefore has higher circulating glucocorticoid levels and the target cells have a higher apparent affinity for this agonist. However, the target cells also have a smaller binding capacity. The precise resultant effect of these changes on glucocorticoid activity will require additional studies on specific glucocorticoid-dependent variables.

Adrenocorticotropic Hormone↗
PubMed1993

Serotonin-deficient mutants and male mating behavior in the nematode Caenorhabditis elegans.

Defining a behavior that requires the function of specific neurons in the free-living nematode Caenorhabditis elegans can allow one to screen for mutations that disrupt the specification or function of those neurons. We identified serotonin-immunoreactive neurons required for tail curling or "turning" behavior exhibited by C. elegans males during mating. Males mutant in three different genes that reduce serotonin expression, cat-1, cat-4, and bas-1, exhibited defects in turning behavior similar to those of wild-type males in which these neurons were ablated. The turning defect of cat-4 males was rescued by exogenous serotonin, consistent with the idea that their behavioral defect is caused by a lack of serotonin. While the serotonin-deficient mutants we analyzed shared certain behavioral traits, they were blocked for serotonin synthesis at different steps. Analysis of these and additional serotonin-deficient mutants may help us understand how a neuron controls the expression of a serotonergic phenotype.

Animals↗
PubMed1992

Effects of long-term infusions of dopa and carbidopa on renin and steroid secretion in the rat.

Plasma, kidney, and adrenal catecholamine concentrations were varied by infusing rats with L-dopa and/or carbidopa for 2 weeks. L-Dopa infusion (300 micrograms/day) increased dopamine concentrations in plasma, adrenal zona glomerulosa, and kidney by 140%, 74%, and 224%, respectively: the dopamine content of the adrenal inner cortex plus medulla was not increased. Infusion of carbidopa alone had no detectable effect upon endogenous dopamine concentrations. Concomitant infusion (300 micrograms/day) of carbidopa with L-dopa blocked the rise in plasma and adrenocortical dopamine caused by L-dopa alone. Plasma aldosterone and plasma and kidney active renin concentrations were unaffected by L-dopa administration but plasma corticosterone and deoxycorticosterone (DOC) were significantly elevated (P < 0.05); increases in DOC appeared greater than those of corticosterone. These data cast doubt on the theory that dopamine is a physiological tonic inhibitor of aldosterone synthesis in rats. However, in the rat, stimulatory effects of L-dopa on plasma concentrations of precursors of aldosterone might be of physiological significance since DOC is a potent mineralocorticoid.

Adrenal Cortex↗
PubMed1992

Membrane permeability to K+ and the control of aldosterone synthesis: effects of valinomycin and cromakalim in bovine adrenocortical cells.

Stimulation of aldosterone synthesis by angiotensin II (AII) is associated with depolarization of the cell membrane. Since the potential difference of adrenocortical cells is dependent on membrane permeability to potassium ions, the effects of agents which hyperpolarize the cell (by increasing permeability to K+) on the control of aldosterone synthesis were investigated further. Basal and AII-stimulated aldosterone synthesis was increased by 20-70% in cells incubated with 1 or 10 nM of the potassium ionophore valinomycin; higher concentrations markedly inhibited AII-stimulated synthesis. Cromakalim, a potential antihypertensive drug which facilitates the opening of K+ channels in smooth muscle cells, stimulated basal aldosterone synthesis at 2 microM but had no effect at 40 microM. AII-stimulated aldosterone synthesis was not affected by cromakalim except at 40 microM, which was inhibitory. The inhibitory effects of cromakalim, unlike those of valinomycin, were not reversible. Aldosterone synthesis from added hydroxycholesterol and pregnenolone (but not from deoxycorticosterone and corticosterone) was significantly inhibited by 40 microM cromakalim. Potassium efflux from cells preloaded with 43K was unaffected by low concentrations of valinomycin, but was markedly increased by concentrations which inhibited AII-stimulated aldosterone production. Small decreases and increases in 43K efflux, caused by 1 and 40 microM cromakalim respectively, corresponded with increases and decreases in basal aldosterone production; cromakalim did not affect 43K efflux from AII-stimulated cells. We suggest that increasing adrenocortical cell membrane permeability to K+ reduces steroidogenesis, but that valinomycin and cromakalim have other actions which complicate the relationship between 43K efflux and aldosterone production. Cromakalim appears to inhibit 21-hydroxylase activity in the biosynthetic pathway and may also affect 3 beta-hydroxysteroid dehydrogenase activity.

Adrenal Cortex↗
PubMed1992

Effects of dexamethasone on G protein levels and adenylyl cyclase activity in rat vascular smooth muscle cells.

Dexamethasone administration in vitro has been shown to increase adenylyl cyclase activity in vascular smooth muscle cells (VSMC) from renal arteries and in non-vascular cell lines. To investigate whether G proteins are involved in this response, cultured VSMC from mesenteric arteries of Sprague-Dawley rats were incubated in the presence and absence of 10 nM dexamethasone for 24 and 48 h. Basal and stimulated adenylyl cyclase activities were increased by approximately 50% after treatment with dexamethasone. The changes were neither specifically associated with ligands which stimulate adenylyl cyclase catalytic unit via Gs (isoproterenol and prostaglandin E1) nor with guanylylimidodiphosphate (0.1 nM), which inhibits the catalytic unit via Gi. This suggests that dexamethasone enhances adenylyl cyclase activity through changes at the level of the catalytic unit, rather than through the G proteins which modulate its activity. No differences were seen in immunoblotting studies of the levels of Gi alpha 2, Gs alpha, Gi alpha 3 and beta subunits. Similarly, dexamethasone had no effect on the expression of mRNA for Gi alpha 2 and Gs alpha. The results indicate that glucocorticoid-induced increases of adenylyl cyclase activity are due to changes at the level of the adenylyl cyclase catalytic unit rather than alteration of the levels or turnover of Gs alpha, Gi alpha 2, Gi alpha 3 and beta subunits in the membranes of VSMC.

Adenylyl Cyclases↗
PubMed1992

Inhibition of bovine adrenocortical steroidogenesis by benzodiazepines: a direct effect on microsomal hydroxylation or an inhibition of calcium uptake?

We have previously reported that benzodiazepines inhibit microsomal steroid hydroxylases. We have now studied their effects at much lower drug concentrations and have also addressed the suggestion that benzodiazepines alter cellular calcium metabolism. We investigated the in-vitro effects of midazolam on microsomal steroid hydroxylation by measuring basal and ACTH-stimulated cortisol and 17 alpha-hydroxyprogesterone (17-OHP) synthesis. Threshold inhibition of basal cortisol production was achieved by 3.4 mumol midazolam/l while ACTH-stimulated production required 13.6 mumol/l. This was accompanied by a biphasic response of 17-OHP production, rising to a maximum at 13.6 mumol midazolam/l for basal and 6.8 mumol midazolam/l for ACTH-stimulated synthesis suggesting a preferential inhibitory effect on 21-hydroxylase activity at < 6.8 mumol/l and additional effects on 17 alpha-hydroxylation at higher drug concentrations. This explains the inhibition of ACTH-stimulated cortisol synthesis by midazolam (50% inhibitor dose (IC50) 22 mumol/l). Using 21-deoxycortisol as substrate, we have demonstrated that midazolam is a competitive inhibitor of 21-hydroxylase (inhibitory constant (KI) 35 mumol/l). Both midazolam and diazepam inhibited K(+)-stimulated aldosterone synthesis, with IC50 values of 1.2 mumol/l and 0.8 mumol/l respectively, which are far lower than those observed for ACTH-stimulated cortisol synthesis. With 11 beta-hydroxyprogesterone as substrate, the KI for the inhibition of aldosterone synthesis by midazolam was 54 mumol/l. Potassium stimulates aldosterone biosynthesis at least partly by changing intracellular free calcium levels. To investigate possible antagonistic effects of benzodiazepines on calcium metabolism, we measured 45Ca uptake in the presence of midazolam.(ABSTRACT TRUNCATED AT 250 WORDS)

17-alpha-Hydroxyprogesterone↗