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Biomedical subjects

A L Johnson

Publications and source records attributed to A L Johnson.

At least 127 records · Page 7Linked to original sources
PubMed1993

Regulation of P450 cholesterol side-chain cleavage messenger ribonucleic acid expression and progesterone production in hen granulosa cells.

Previous studies have shown that granulosa cells from hen follicles < 8 mm in diameter are steroidogenically inactive. We have proposed that cytochrome P450 cholesterol side-chain cleavage (P450scc) enzyme activity within the granulosa layer is first expressed at the time the follicle is selected into the preovulatory hierarchy. The present studies were conducted to evaluate the actions of FSH and of the growth factors epidermal growth factor (EGF), transforming growth factor alpha (TGF alpha), and insulin-like growth factor I (IGF-I) in regulating levels of P450scc mRNA and initiating progesterone production in cultured granulosa cells from 6- to 8-mm follicles. Levels of P450scc mRNA were elevated, and progesterone production initiated, in granulosa cells cultured for 16 h and 8 h, respectively, in serum-free medium containing recombinant human (rh) FSH or the cAMP analog, 8-bromo-cAMP. While both EGF and TGF alpha blocked the ability of rhFSH to increase P450scc mRNA levels and initiate progesterone production, IGF-I failed to alter P450scc mRNA levels or progesterone production in either the presence or absence of rhFSH. Results from these studies indicate that, as in mammals, FSH is a primary factor that mediates the initiation of steroidogenesis in hen granulosa cells at the time of follicle selection. Furthermore, we propose that EGF and TGF alpha are, at least in part, responsible for preventing premature differentiation of granulosa cells in ovarian follicles that have not yet been selected into the preovulatory hierarchy.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1993

Expression and regulation of cytochrome P450 17 alpha-hydroxylase messenger ribonucleic acid levels and androstenedione production in hen granulosa cells.

Studies were conducted to evaluate the expression and regulation of cytochrome P450 17 alpha-hydroxylase (P450 17 alpha-OH) mRNA levels and androstenedione production in 6-8-mm-diameter follicle granulosa cells from the domestic hen. Although P450 17 alpha-OH mRNA was detected within granulosa cells from follicles at all stages of development (3-12-mm and preovulatory follicles), 8-12-fold higher levels were found in small, less developed follicles (3-12 mm in diameter) compared to the three largest follicles within the preovulatory hierarchy (F3 to F1 follicles). By comparison, P450 17 alpha-OH mRNA levels were 25-89-fold higher in theca tissue compared to the granulosa layer at comparable stages of development. Despite detection of P450 17 alpha-OH mRNA in granulosa cells from 6-8-mm follicles, androstenedione production was low to nondetectable when cells were cultured in the presence of exogenous progesterone (10 ng/ml). Treatment with FSH increased levels of P450 17 alpha-OH mRNA (by 6-fold after 16 h of treatment) and induced androstenedione production in cultured granulosa cells; these actions were mimicked by the cAMP analog, 8-bromo-cAMP. By contrast, addition of the growth factors transforming growth factor alpha (TGF alpha), epidermal growth factor (EGF), and basic fibroblast growth factor (bFGF) completely suppressed the stimulatory effects of FSH on both mRNA levels and androstenedione production, while insulin-like growth factor I (IGF-I) inhibited only androstenedione production. We conclude that in the granulosa layer of developing (< or = 12 mm) hen follicles the expression of P450 17 alpha-OH mRNA does not directly reflect P450 17 alpha-OH enzyme activity. Moreover, P450 17 alpha-OH mRNA levels dramatically decrease in granulosa cells from preovulatory (compared to developing) follicles, and in the theca layer from the F1 preovulatory follicle (compared to remaining follicles). It is proposed that FSH initiates P450 17 alpha-OH enzyme activity (and perhaps to a lesser extent regulates mRNA levels) at the time a follicle is recruited into the preovulatory hierarchy, and that this action is mediated, at least in part, by the adenylyl cyclase/cAMP second messenger pathway. On the other hand, growth factors (including TGF alpha, EGF, bFGF, and possibly IGF-I) may act to prevent premature expression of P450 17 alpha-OH activity in the granulosa layer of follicles that have yet to enter the rapid growth phase of follicle development.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1993

A multicopy suppressor gene of the Saccharomyces cerevisiae G1 cell cycle mutant gene dbf4 encodes a protein kinase and is identified as CDC5.

We have isolated a multicopy suppressor of the temperature-sensitive growth phenotype of organisms carrying mutations of DBF4, a gene that is required for the initiation of chromosomal DNA replication in Saccharomyces cerevisiae and that interacts with the CDC7 protein kinase. Nucleotide sequence analysis of the suppressor gene, provisionally named MSD2, revealed an open reading frame encoding a protein with a calculated M(r) of 81,024, with amino acid sequence similarity to the catalytic domains of protein kinases. Both genetic linkage and complementation analyses indicated that MSD2 is identical to the cell division cycle gene CDC5. An activity that phosphorylated exogenously added casein was immunoprecipitated by antiserum against a TrpE-Cdc5 fusion protein from lysates of wild-type cells containing CDC5 on a multicopy plasmid but not of cells bearing a small deletion in the predicted protein kinase domain of CDC5 on the plasmid. Deletion of CDC5 was lethal and resulted in a dumbbell-shaped terminal morphology, with the nuclei almost divided but still connected. Consistent with the function at the G2/M boundary, the CDC5 transcript accumulated periodically during the cell cycle, peaking at the G2/M boundary. CDC5 on a multicopy plasmid also suppresses temperature-sensitive cdc15, cdc20, and dbf2 mutations which affect mitosis during the cell cycle.

Alleles↗
PubMed1993

The Nottingham study of neurotic disorder. Effect of personality status on response to drug treatment, cognitive therapy and self-help over two years.

Repeated assessments of psychopathology, together with personality status, were made over two years on 181 psychiatric out-patients with generalised anxiety disorder (59), panic disorder (66), or dysthymic disorder (56) diagnosed using an interview schedule for DSM-III. Patients were randomly allocated to drug treatment, cognitive and behaviour therapy, or a self-help treatment programme. Although there were no overall differences in compliance rate and efficacy between the three modes of treatment, the psychological treatment methods, particularly self-help, were more effective in patients without personality disorder, and those with personality disorder responded better to drug treatment, primarily antidepressants. The findings suggest that assessment of personality status could be a valuable aid to selection of treatment in neurotic disorders and that self-help approaches are particularly valuable once personality disorder has been excluded.

Adult↗
PubMed1993

Caregivers of children with disabilities: a comparison of those managing "OK" and those needing more help.

A survey was mailed to caregivers of children with disabilities to ascertain how they were managing caregiving. Caregivers reporting they were managing "OK" were compared to those who reported they needed more help or could not manage much longer ("not OK"). Results showed the not OK group of caregivers had children who were more severely impaired and functionally dependent. Their mothers were in poorer physical and mental health, had greater demands placed on their time and finances, and received less emotional support from friends and family. Special programs provided some assistance but not enough to meet their needs.

Adolescent↗
PubMed1993

Apoptosis during luteal regression in cattle.

The present studies were conducted to evaluate whether apoptosis occurs during spontaneous and prostaglandin F2 alpha (PGF2 alpha)-induced luteolysis and, if so, to determine the relationship between the onset of luteolysis and oligonucleosome formation (a characteristic of apoptosis). In the first study, nine normally cycling heifers were ovariectomized (ovx) during the midluteal phase (day 10 or 15; day 0 = estrus) or after luteal regression (day 19; n = 3/time point). While there was no evidence of oligonucleosome formation in DNA from corpora lutea (CL) collected on days 10 and 15, each CL collected on day 19 exhibited DNA fragmentation, represented by distinct bands of DNA in approximately 185-basepair multiples. In the second study, heifers were ovx (n = 5; controls) or given 25 mg PGF2 alpha 15-16 days after estrus. Heifers receiving PGF2 alpha were subsequently ovx 4, 8, 12, 24, or 48 h (n = 5/time point) after the injection of PGF2 alpha. The concentration of progesterone in venous sera collected at ovx was not different (P > 0.20) in control and 4 h groups, but was decreased (P < 0.01) in the 8, 12, 24, and 48 h groups. Total CL weight (mean +/- SEM; grams) did not change (P > 0.10) from 0 h (controls) to 24 h after injection (range, 3.2 +/- 0.5 to 4.1 +/- 0.6), but decreased (P < 0.06) to 2.0 +/- 0.3 at 48 h. With ethidium bromide (EtBr) staining, no oligonucleosome formation was detected in CL collected from 0-12 h after PGF2 alpha injection. However, pronounced oligonucleosome formation was observed in all 10 CL collected 24 and 48 h after the injection of PGF2 alpha. The absence of oligonucleosomes in 0 and 4 h samples was confirmed by the more sensitive technique of 3'-end labeling of DNA fragments. Some samples in both the 8 and 12 h groups had slight oligonucleosome formation, while all samples in the 24 and 48 h groups showed evidence of intense oligonucleosome formation. Histological analysis of tissue sections indicated an increase (P < 0.001) in the percentage of degenerated luteal cells in the 24 and 48 h groups compared to that in the 0-12 h groups. These data indicate that apoptosis occurs during both spontaneous and PGF2 alpha-induced luteal regression in cattle; however, apoptosis, as indicated by oligonucleosome formation, is not apparent until after serum progesterone concentrations have begun to decrease.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Regulation of follicle differentiation by gonadotropins and growth factors.

The rate of ovulation is determined by, among other things, the availability of small follicles that can be recruited into the follicular hierarchy. A decrease in the rate of lay with, for instance, aging has been attributed to both an increase in the rate of atresia and a decrease in the number of small, growing follicles that provide the pool from which follicles are selected into the final growth phase (the preovulatory hierarchy). Among the most important endocrine, paracrine, and autocrine factors that mediate follicle growth and differentiation are the gonadotropins and growth factors. A better understanding of gonadotropin-growth factor interactions that occur during follicle selection and differentiation should lead to the development of management practices or genetic manipulations (Mendelian or molecular) that will enhance the rate of lay at times during the production cycle when egg production is suboptimal.

Animals↗
PubMed1993

Pharmacology of 2-amino-1,4-dihydro-4-(2-[4-[4-(2-methoxyphenyl)-1- piperazinyl]butylsulfinyl]phenyl)-6-methyl-5-nitro-3-pyridine carboxylic acid methyl ester (XB513), a novel calcium agonist with alpha-1 adrenergic receptor antagonistic.

2-Amino-1,4-dihydro-4-(2-[-4[4-(2-methoxyphenyl)-1-piperazinyl]- butylsulfinyl]phenyl)-6-methyl-5-nitro-3-pyridine carboxylic acid methyl ester (XB513) was designed to combine the calcium agonistic and alpha-1 adrenergic receptor antagonistic properties in the same molecule. It inhibited the specific binding of [3H] nitrendipine in rat cardiac ventricular membranes with an IC50 of 1.2 microM, which is 20-fold greater than the standard calcium agonist Bay K 8644. It displaced [3H]prazosin in rat brain membranes with an IC50 of 29 nM. XB513 caused concentration-dependent positive inotropic responses in isolated electrically paced guinea pig left atria with an EC50 of 1.2 microM and was 10 times less potent than Bay K 8644. In rabbit aorta, XB513 inhibited the contractile effect of 16 nM norepinephrine with an IC50 of 89 nM. In an acute heart failure dog model produced by an overdose of propranolol, XB513 at 0.3 to 3 mg/kg i.v. dose-dependently reversed the decreased mean arterial pressure, cardiac output and dP/dt as well as the increased left ventricular end diastolic pressure induced by propranolol. In conscious instrumented dogs, XB513 at 0.1 and 0.3 mg/kg i.v. increased dP/dt and heart rate significantly, with a minor effect on mean arterial pressure. In summary, this study demonstrates that XB513 is a novel chemical entity possessing both calcium agonistic and alpha-1 adrenergic receptor blocking properties and thus may represent a new class of agents for the treatment of congestive heart failure.

Adrenergic alpha-Antagonists↗
PubMed1992

Novel piperidine sigma receptor ligands as potential antipsychotic drugs.

sigma receptor ligands represent a new class of potential antipsychotic drugs. This paper presents the structure-activity relationships leading to novel disubstituted piperidine sigma ligands, which have little or no affinity for dopamine D2 receptors. Selectivity for sigma sites over dopamine D2 or serotonin 5-HT2 receptors appears to be governed by the chemical nature of the piperidine nitrogen substituent, its distance from the basic nitrogen, and its orientation relative to the other piperidine substituent. Several of these compounds have good oral potency in some animal models used to evaluate potential antipsychotic drugs. The N-cyclopropylmethyl ketones and ethers (e.g. 6i (DuP 734), 6q, 18a, and 18n) have the best in vivo potency. Compounds 6i (DuP 734) and 6q did not cause catalepsy in the rat, even at very high doses. On the basis of the pharmacology profiles of these sigma ligands, we propose these compounds may be effective antipsychotic drugs, which do not induce extrapyramidal side effects or tardive dyskinesia.

Animals↗
PubMed1992

SWI6 protein is required for transcription of the periodically expressed DNA synthesis genes in budding yeast.

In budding yeast many genes are expressed under cell-cycle control in late G1. These include a large group of DNA synthesis genes, the HO gene involved in mating-type switching, CTS1 (chitinase) and also CLN1 and CLN2 (ref. 4) encoding G1 cyclins. Two factors, encoded by the SWI4 and SWI6 genes, are required for HO (ref. 5), CLN (refs 6, 7) and CTS1 (ref. 3) gene expression and, at least in the HO promoter, bind to CACGA4 upstream sequences (CCBs). This motif is not found upstream of the DNA synthesis genes, which instead have a hexamer element, ACGCGT1 (MCB), an MluI restriction site, that is recognized by a cell-cycle regulated transcription complex DSC1 (ref. 1). This MluI-activation system consisting of the MCBs and DSC1 is conserved in fission yeast where a DSC1-like complex controls the cdc22+ ribonucleotide reductase gene. The Schizosaccharomyces pombe cdc10+ gene encodes a component of DSC1 (ref. 10) and, significantly, this has homology with both the Swi4 and Swi6 proteins. Here we show that Swi6 is an essential component of DSC1 and that deletion of SWI6 impairs the cell-cycle regulation of the DNA synthesis genes, as well as CLN1 and CLN2. Thus Swi6 is the common factor in regulation of all the above genes and may therefore be responsible for the timing of their expression in late G1.

Base Sequence↗
PubMed1992

Control of DNA synthesis genes in fission yeast by the cell-cycle gene cdc10+.

In the budding yeast Saccharomyces cerevisiae, cell-cycle control over DNA synthesis occurs partly through the coordinate expression in late G1 phase of many, if not all, of the genes required for DNA synthesis. A cis-acting hexamer element ACGCGT (an MluI restriction site) is responsible for coordinating transcriptional regulation of these genes at the G1/S phase boundary and we have identified a binding activity, DSC1, that recognizes these sequences in a cell-cycle-dependent manner. In the distantly related fission yeast Schizosaccharomyces pombe, only one of the known DNA synthesis genes, cdc22+, which encodes a subunit of ribonucleotide reductase, is periodically expressed in late G1 (ref. 6). The promoter region of cdc22+ has two MluI sites and five related sequences, suggesting that similar controls over DNA synthesis genes could occur in fission yeast. We report here a binding activity in fission yeast that is very similar to DSC1 in budding yeast. We also show that the fission yeast cdc10+ gene product, which is required for Start and entry into S phase, is a component of this binding activity.

Alleles↗
PubMed1992

DNA polymerase II, the probable homolog of mammalian DNA polymerase epsilon, replicates chromosomal DNA in the yeast Saccharomyces cerevisiae.

Two temperature-sensitive DNA polymerase II mutants (pol2-9 and pol2-18) of the yeast Saccharomyces cerevisiae were isolated by the plasmid shuffling method. DNA polymerase II activity partially purified from both mutants was thermolabile, while DNA polymerase I and III activities remained thermotolerant. At the restrictive temperature, the pol2 mutants were defective in chromosomal DNA replication and exhibited the dumbbell terminal morphology typical of DNA replication mutants. The POL2 transcript accumulated periodically during the cell cycle, peaking at the G1/S boundary in the same manner as the transcripts of more than 10 other DNA replication genes. These results indicate that DNA polymerase II participates in nuclear DNA replication. The similarities in structure and activities between the DNA polymerases of yeast and mammals make it likely that mammalian DNA polymerase epsilon too is required for chromosomal DNA replication.

Amino Acid Sequence↗
PubMed1992

Treatment of growth deformities with external skeletal fixation.

Growth deformities of the long bones are usually caused by premature closure of the physis. The most commonly affected bones are the radius, ulna, and tibia. Premature closure of the physis can result in shortened, angular, and rotational bone deformities, especially when one bone of a paired bone system like the radius and ulna is affected. Adjacent joints may develop osteoarthritis. Corrective osteotomy to realign in joint surfaces is indicated in mature animals. Bilateral or type II external fixation frames are used to stabilize the osteotomies. The advantages of ESF are: (1) The transfixation pins can be used as guide pins to realign joints. (2) The fixation allows rigid stabilization of the osteotomy site. (3) Postoperative correction of alignment can be achieved. (4) Implant removal after bone union is simple.

Animals↗
PubMed1992

Rationale for the chemical development of angiotensin II receptor antagonists.

The renin-angiotensin system (RAS) has been demonstrated to be a key element in blood pressure regulation and fluid volume homeostasis. Since angiotensin II (AII) is the effector molecule of the RAS, the most direct approach to block this system is to antagonize AII at the level of its receptor. Therefore, at Du Pont Merck the working hypothesis has been that the identification of metabolically stable and orally effective AII-receptor antagonists would constitute a new and superior class of agents useful in treating hypertension and congestive heart failure. Our program began with a detailed pharmacologic evaluation of some simple N-benzylimidazoles, originally described by Takeda Chemical Industries in Osaka, Japan. They were found to be a series of weak but selective AII-receptor antagonists with a competitive mode of action. We embarked on a program aimed to design and synthesize more potent and orally effective nonpeptide antagonists, while attempting to preserve their selective affinity for the AII receptor. The first major breakthrough in our efforts to increase the potency of these compounds came with the development of a series of N-benzylimidazole phthalamic acid derivatives. Although effective at lowering blood pressure when administered intravenously, the phthalamic acids were devoid of oral activity. The first orally active AII antagonists came with the discovery of the biphenyl carboxylic acids. Although these compounds are absorbed after oral dosing, their bioavailability was less than desired. In the hope of improving the oral absorption of these biphenyls, we investigated a variety of acidic groups as bioisosteric replacements for the carboxylic acid. The key to the discovery of nonpeptide AII-receptor antagonists with improved oral activity and duration of action resulted from replacing the carboxylic acid group with the isosteric but more lipophilic tetrazole ring. Hence, our efforts culminated in the discovery of losartan (2-n-butyl-4-chloro-5-hydroxymethyl-1-[(2'-(1H-tetrazol-5-yl) biphenyl-4-yl)methyl]imidazole, potassium salt), a highly potent angiotensin type 1 (AT1) selective receptor antagonist with a long duration of action. Losartan is currently undergoing clinical investigation for the treatment of hypertension. The history, including the rationale for the design of the compounds, and ensuing structure-activity relationships of losartan and related analogs will be described. Many of the newer compounds exceed the potency of losartan, and the best compounds in the series rival the affinity of the endogenous ligand, AII, for its receptor.(ABSTRACT TRUNCATED AT 400 WORDS)

Angiotensin II↗
PubMed1992

Plasminogen activator activity and thymidine incorporation in avian granulosa cells during follicular development and the periovulatory period.

The hormonal and second messenger regulation of plasminogen activator (PA) activities in avian granulosa and theca cells has been documented. However, the physiological role(s) of PAs in the avian ovary remains poorly understood. The present studies were designed to evaluate PA activity in hen granulosa cells collected from the most mature (F1) preovulatory follicle at three discrete time points relative to a spontaneous ovulation and from follicles collected at various stages of follicular development. Levels of PA activity in the granulosa layer of the F1 follicle declined by greater than 90% as follicles were collected closer to their anticipated time of ovulation (e.g., from 17-16 h to 0.75-0.15 h; p less than 0.05). Timing of tissue collection was confirmed by evaluation of serum progesterone levels, which peaked as expected at the 6-5-h time point. During follicular development, PA activity was several times greater in rapidly growing follicles (6-12 mm, 1-3 wk prior to ovulation) than in slowly growing (1-5 mm) or preovulatory (F3 and F1) follicles (p less than 0.05). Granulosa cells of these rapidly growing follicles also incorporated significantly higher levels of 3H-thymidine than did granulosa cells of mature follicles (p less than 0.05), suggesting a higher level of DNA synthesis. Similarly, granulosa cells of the mitotically active germinal disc region of the F1 granulosa layer were found to possess at least 3-fold higher (p less than 0.05) levels of PA activity and a 2-fold greater level of 3H-thymidine incorporation than the more mature granulosa cells isolated from the remaining F1 granulosa layer.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Do prophylactic anticonvulsant drugs alter the pattern of seizures after craniotomy?

A total of 276 patients with a high risk of developing postoperative seizures were randomised to treatment with carbamazepine or phenytoin for six or 24 months, or to no treatment. No significant differences were found (though the confidence limits were fairly wide) between the regimes in respect of the incidence of seizures or death. In a substantial proportion of the patients postoperative epilepsy remained a continuing disability. A high incidence of drug-related side effects was found in the treatment groups. Prophylactic anticonvulsants cannot therefore be recommended routinely following supratentorial craniotomy.

Actuarial Analysis↗
PubMed1992

Effects of gonadotropin-releasing hormone infused in a pulsatile or continuous fashion on serum gonadotropin concentrations and ovulation in the mare.

Studies were conducted to compare continuous vs pulsatile i.v. infusion of GnRH on serum gonadotropin concentrations and ovulation in seasonally anestrous mares and in cycling mares. Anestrous mares (Exp. 1) received no treatment (control; n = 3), 2, or 20 micrograms of GnRH/h continuous infusion (CI) (n = 4 and n = 6, respectively), or 20 micrograms of GnRH/h pulsatile infusion (PI) (n = 5). After initiation of GnRH infusion, serum LH levels increased earlier, and to a greater extent, in the PI group than in other groups (P less than .05). In contrast, serum FSH concentrations did not differ among groups. The number of days to development of the first 35-mm follicle was not different among GnRH treatment groups; however, mares receiving PI ovulated on d 9.4 of treatment, 2.8 d earlier than those receiving 20 micrograms of GnRH/h CI (P less than .05). Mares given 2 micrograms of GnRH/h CI failed to ovulate spontaneously after 16 d of treatment, but each one ovulated within 2 to 4 d after injection of 2,000 IU of hCG on d 16. Control mares did not ovulate or show any significant follicular development throughout the experiment. Cycling mares (Exp. 2) received no treatment (control; n = 6), 20 micrograms of GnRH/h CI, or 20 micrograms of GnRH/h PI (n = 4) beginning on d 16 of an estrous cycle (d 0 = day of ovulation). Serum LH concentrations in all groups increased after initiation of treatment; however, on the day of ovulation LH concentrations were lower in the CI group than in the PI or control groups (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗