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Biomedical subjects

E S Johnson

Publications and source records attributed to E S Johnson.

At least 127 records · Page 7Linked to original sources
PubMed1980

Electrically-evoked release of [3H]-histamine from the guinea-pig hypothalamus.

1 [3H]-histamine was taken up by slices of guinea-pig hypothalamus against a concentration gradient. 2 Electrical field stimulation of the superfused slices resulted in an increased efflux of radioactivity, the major part of which was shown to be associated with histamine by paper chromatography. 3 The evoked release of histamine was dependent on calcium ions in the superfusate and was increased by 56% when the frequency of stimulation was doubled from 5 to 10 Hz.

Animals↗
PubMed1980

Release-modulating acetylcholine receptors in cholinergic neurones of the guinea-pig ileum.

1 Twitch responses of the guinea-pig ileum to electrical transmural stimulation (0.2 Hz) were smaller after a dose of acetylcholine (ACh) than before it. The magnitude of the post-ACh inhibition of twitch was dose-dependent. 2 The post-ACh inhibition of twitch could not be explained in terms of post-junctional desensitization and was not modified by guanethidine, thymoxamine, propranolol or naloxone. Inhibition of twitch also followed high frequency stimulation (10 Hz) but this inhibition, unlike that following ACh, was partially antagonized by naloxone. 3 Hexamethonium (C6) in concentrations known to block contractions to nicotine, potentiated the post-ACh inhibition of twitch and modified the pattern of recovery. An initial rapid phase followed by a slower phase was converted by C6 to an initial slow phase followed by a more rapid rate of recovery. 4 The C6-sensitive (nicotinic) component of twitch recovery after ACh was also dose-dependent and contributed greatly to the rapid recovery during the first minute after ACh washout, whereas during the same period the C6-resistant inhibition remained relatively constant; thereafter both components declined. The C6-resistant inhibition was considered to be due to the activation of prejunctional muscarinic receptors. 5 5-Hydroxytryptamine (5-HT) and nicotine also caused inhibition of twitch but the pattern of response differed from those due to ACh, the maximum inhibition usually being produced 1 min after recommencing stimulation. High doses of 5-HT produced inhibitory responses similar to those following ACh, whereas nicotine produced a characteristic triphasic pattern of response. 6 It is concluded that ACh acts on at least two prejunctional receptors subserving a modulatory role on transmitter release, a nicotinic receptor whose activation enhances ACh output and a muscarinic receptor whose activation leads to an inhibition of transmitter secretion.

Acetylcholine↗
PubMed1980

Modulation by acetylcholine of the electrically-evoked release of [3H]-acetylcholine from the ileum of the guinea-pig.

1 Acetylcholine (ACh) stores within neurones of the myenteric plexus of the guinea-pig were labelled with [3H]-choline and the influence of unlabelled ACh, atropine, or atropine and unlabelled ACh on the electrically-evoked output of [3H]-ACh was evaluated. 2 Electrical transmural stimulation (5 Hz) of the ileum led to an increase in the output of [3H]-ACh over that released spontaneously. Superfusion with unlabelled ACh (6.8 microM) caused a marked reduction in the release of [3H]-ACh which was reversed by atropine (3.5 microM). Atropine itself had no effect on the electrically-evoked [3H]-ACh. 3 These experiments provide further evidence for the existence in the guinea-pig ileum of neuronal muscarinic receptors for ACh subserving an inhibitory role on transmitter release.

Acetylcholine↗
PubMed1978

A basis for migraine therapy- the autonomic theory reappraised.

The concept that migraine results from an initial vasoconstriction due to increased release of noradrenaline from the sympathetic nerves to cranial blood vessels has been reappraised in the light of recently acquired knowledge of the mechanisms of action of drugs used in the treatment of migraine, physiological and pharmacological evidence implicating noradrenaline, and the observations by others that several migraine variants may be associated with some degree of sympathetic overactivity. If the theory is correct, it suggests that both prophylaxis and management of the acute condition should be possible by means of selective alpha-adrenoceptor antagonism. The use of drugs with potentially dangerous vasoconstrictor properties appears to be unnecessary. The suggestion is made that the increased adrenergic activity might result from changes within the hypothalamus.

Adrenergic alpha-Antagonists↗
PubMed1977

High molecular weight DNA intermediates synthesized by permeabilized L cells.

Mouse L cells rendered permeable to deoxynucleoside triphosphates synthesize DNA as an extension of replication forks that were active in the intact cells. The permeabilization process does not affect the size of the bulk cell DNA. Intermediate molecular weight DNA, synthesized in the intact cells, is neither degraded to small molecular weight DNA nor processed into bulk cell DNA following the permeabilization process. DNA synthesized by the permeable cells demonstrates a heterogenous distribution in alkaline sucrose gradients, with peaks at 26 S and 71 S. Pulse-chase experiments demonstrate that these two classes of DNA intermediates do not have a precursor product relation. They appear to be synthesized independently and at the same rate. The results are compatible with continuous synthesis of DNA along one template strand and discontinuous synthesis along the opposite strand. DNA synthesis in isolated L cell nuclei was compared to the process in permeabilized cells with the results demonstrating that the rate of DNA synthesis is slower in the nuclei than it is in the permeable cells. Alkaline sucrose gradient studies demonstrate that the DNA synthesized by isolated nuclei is smaller than the DNA synthesized by the permeable cells.

Buffers↗
PubMed1977

Myoglobin concentrations and muscle-enzyme activities in serum after myocardial infarction and cardiac arrhythmia.

Sera from patients with myocardial infarction and cardiac arrhythmias were analyzed for myoglobin concentration and the activities of total creatine kinase, creatine kinase isoenzyme-2, and lactate dehydrogenase isoenzyme-1 at the time of hospital admission and during the first few days of hospitalization. The nine patients with a final diagnosis of myocardial infarction had abnormally high values for total creatine kinase, creatine kinase-2, lactate dehydrogenase-1, and myoglobin. Myoglobin concentrations were highest on admission in six patients and on the day after admission in the other three patients. Creatine kinase-2 manifested maximum activity on the day after admission for all patients with myocardial infarction. Lactate dehydrogenase-1 did not reach maximal values until the second or third day after admission. The six patients with arrhythmias did not show any significant increases in creatine kinase-2 or lactate dehydrogenase-1. Myoglobin and total creatine kinase, however, were increased in the four patients who had received cardioversion. The specificity and diagnostic usefulness of these serum measurements are discussed.

Arrhythmias, Cardiac↗
PubMed1976

Endocrine-dependent rat mammary tumor regression: use of a gonadotropin releasing hormone analog.

Long-term administration of [D-Leu6, des-Gly-NH210, Pro-ethylamide9]-GnRH, an analog of gonadotropin releasing hormone, caused regression of neoplastic tissue in a rat bearing a spontaneous mammary adenocarcinoma and in rats in which tumors had been induced by treatment with dimethylbenzanthracene (DMBA). During two separate treatment periods with the analog, the tumor in the single animal regressed although it had previously grown spontaneously. After a third period of growth, ovariectomy also induced regression, suggesting endocrine dependency of the tumor. These observations were confirmed in the DMBA-induced tumor system, where tumor regression in the analog-treated rats was comparable to that observed in the ovariectomized rats, and in both cases the tumor regression was significant when compared to untreated controls.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1976

Efficacy of antihypertensive drugs.

The magnitude of the fall in blood-pressure in response to an antihypertensive drug depends on the level of the pretreatment pressure, and there is a direct relationship between the two in that the higher the pretreatment pressure the greater the fall in pressure in response to treatment. This simple relationship is inherent in the practical situation of titrating the diastolic blood-pressures of a group of hypertensive patients to a predetermined level. It is assumed that notionally the dose of an antihypertensive drug can be increased in all patients until the diastolic pressure is reduced to the predetermined level. When the fall in diastolic pressure (deltaD.P.) is plotted against pretreatment diastolic pressure (P.T.D.P.), the points for all patients lie on a straight line of slope unity and negative deltaD.P.-intercept numerically equal to the predetermined diastolic-pressure level. This straight-line relationship is termed the predetermined ideal response line. Analysis of data from clinical trials shows that, despite the variability inherent in the practical situation, the data appear to conform to this straight-line relationship. The method of assessing the efficacy of antihypertensive agents is essentially a comparison of each experimental point with the theoretical predetermined response line. In its simplest form the method consists in constructing a scatter diagram of deltaD.P. against P.T.D.P. for all patients. Patients can then be classified as responders or non-responders according to their position on the diagram relative to the predetermined response line. This method of assessing the efficacy of antihypertensive agents has several advantages, the most important of which is that it provides a simple method for displaying all the relevant information in a readily comparable form.

Antihypertensive Agents↗
PubMed1976

DNA synthesis in permeabilized mouse L cells.

Mouse L cells are rendered permeable to nucleoside triphosphates by a cold shock with a near isotonic buffer. These cells retain their morphologic integrity and use exogenously supplied nucleotides and deoxynucleotides to synthesize RNA and DNA. The newly synthesized DNA is nuclear and is the product of semiconservative replication. Incorporation of deoxynucleotides into DNA by thymidine kinase-deficient cells were used to conform rigorously that the exogenously supplied deoxynucleotides were incorporated into DNA without intermediate processing through nucleosides. DNA synthesis requires the presence of Na+, ATP, all 4 deoxynucleotides, and Mg2+. The reaction is inhibited by N-ethylmaleimide, p-hydroxymercuribenzoate and actinomycin D. Hydroxy-urea and arabinosylcytosine do not inhibit the reaction whereas cytosine arabinoside triphosphate shows competitive inhibition with the deoxynucleotides. These findings indicate that the permeable cell system can be used for in situ evaluations of the replicative DNA polymerase using the endogenous DNA template.

Biological Transport↗
PubMed1976

Delay of puberty and inhibition of reproductive processes in the rat by a gonadotropin-releasing hormone agonist analog.

Studies were performed in immature and mature female rats to determine the effects of chronic administration of [D-Leu6,des-Gly-NH210, Pro-ethylamide9]-gonadotropin-releasing hormone (GnRH) upon maturation and maintenance of reproductive function. Treatment of immature rats inhibited normal overian growth and maturation as evidenced by arrest of uterine growth, delay of vaginal opening, and absence of normal cycling. The primary responses in the mature animal were cessation of cycling, atrophy of the ovaries to a "prepuberal" size, and uterine weight regression. In both groups termination of treatment was followed by prompt restoration of normal ovarian mass and function, including support of breeding processes. The results presented here suggest that chronic administration of the GnRH analog inhibits ovarian steroid output either by direct action of the analog on the ovary or indirectly through qualitative or quantitative changes in levels of luteinizing hormone and follicle-stimulating hormone.

Animals↗
PubMed1976

Regression of corpora lutea in the rabbit after injection of a gonadotropin-releasing peptide.

We have shown that a potent agonist of the luteinizing hormone injected on either Day 11 of pseudopregnancy of Day 15 of pregnancy causes luteinization of ovarian follicles and a rapid regression of functional corpora lutea. Serum levels of progesterone declined markedly within 3 days of peptide injection in pregnant animals. In the presence of regressing corpora lutea, fetal resorption occurs which can be prevented by estradiol (500 ng, twice a day) or progesterone. Daily levels of estradiol below 4 mug did not maintain either corpora lutea weight or fetal survival, whereas 4 mug of the steroid maintained corpora lutea weight, but not pregnancy.

Animals↗
PubMed1976

Regression of rat mammary tumors effected by a gonadoliberin analog.

A synthetic analog of gonadoliberin (gonadtropin-releasing factor of luteinizing hormone/follicle-stimulating hormone-releasing hormone), designated A-43818, was evaluated for its ability to effect regression of carcinogen-induced mammary tumors in the Sprague-Dawley rat. This analog, specifically (D-leuyl6, desglycyl-NH210, prolyl ethylamide9), gonadoliberin, is a potent synthetic luteinizing hormone/follicle-stimulating hormone-releasing hormone at low dose levels but, at the higher dose levels used in these studies, the effect appears to be that of a potent gonadoliberin antagonist. Administration of 5 or 20 mug of A-43818 per day to tumor-bearing rats was essentially as effective as ovariectomy in causing mammary tumor regression. At least 80% of the tumors in the A-43818-treated animals underwent regression; about one-half of the regressing tumors disappeared in the 6-week period of continuous treatment, and, unlike the 0.9% NaCl solution control group, no new tumors appeared during the treatment period. A subsequent 4-week period of drug withdrawal resulted in the regrowth of palpable tumors and the appearance of new tumors, most of which again regressed on further A-43818 administration.

Animals↗