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Biomedical subjects

A L Johnson

Publications and source records attributed to A L Johnson.

At least 163 records · Page 9Linked to original sources
PubMed1991

Cytochrome P450 side-chain cleavage (P450scc) in the hen ovary. I. Regulation of P450scc messenger RNA levels and steroidogenesis in theca cells of developing follicles.

We have recently shown that granulosa cells from hen ovarian follicles, collected at a stage of development 2-3 wk prior to ovulation (e.g. 6-8 mm in diameter) are steroidogenically inactive. Therefore, the hypothesis tested in the present studies was that theca cells from follicles at this stage of development must contain sufficient levels of functional cytochrome P450 side-chain cleavage (P450scc) enzyme to produce the progestin precursor required for the synthesis of androgens and estrogens. Northern blot analysis of total theca RNA collected from 6-8-mm follicles indicated the presence of a single P450scc mRNA transcript of approximately 2 kb whose expression was increased following an 8-h preincubation with 200 ng/ml ovine LH (oLH) or 10 microM forskolin. Western blot analysis of crude mitochondrial protein revealed a band of immunoreactive P450scc protein of approximately 53 kDa that was determined to be capable of converting 25-hydroxycholesterol to pregnenolone in a cell-free system. In the second set of studies, conducted to examine the cellular regulation of steroidogenesis in isolated theca cells of 6-8-mm follicles, theca cells were found to produce measurable basal levels of cAMP, progesterone, androstenedione, and estradiol following a 3-h incubation of 5 x 10(5) cells. Furthermore, significant dose-dependent increases in steroidogenesis were observed in response to oLH (0.2-200 ng/ml), chicken FSH (cFSH; 20-200 ng/ml), cholera toxin (0.002-20 ng/ml), and 8-bromo-cAMP (0.1-3.33 mM). Phorbol 12-myristate 13-acetate (PMA; 10-167 nM) also stimulated dose-dependent increases in basal progesterone, androstenedione, and estradiol production. In addition, while PMA had no effect on oLH (200 ng/ml)-promoted cAMP accumulation, or on oLH (20 ng/ml)- or 8-bromo-cAMP (1 mM)-stimulated progesterone production, it attenuated oLH-induced and 8-bromo-cAMP-induced androstenedione and estradiol accumulation. We conclude that theca cells from 6-8-mm follicles possess mRNA and immunoreactive protein coding for functional P450scc. Furthermore, basal steroidogenesis is increased by both the protein kinase A and protein kinase C pathways, whereas evidence suggests that protein kinase C inhibits LH-induced androstenedione production at a site distal to cAMP and progesterone production, most likely by decreasing C17,20-lyase activity.

Androstenedione↗
PubMed1991

Cytochrome P450 side-chain cleavage (P450scc) in the hen ovary. II. P450scc messenger RNA, immunoreactive protein, and enzyme activity in developing granulosa cells.

Previous studies have indicated that developing avian granulosa cells collected from follicles 2-3 wk prior to ovulation (e.g. 6-8-mm in diameter) are steroidogenically incompetent, apparently due to a lack of functional cytochrome P450 side-chain cleavage (P450scc) enzyme activity. The present studies were designed to test this hypothesis by determining the absence or presence of P450scc messenger RNA, immunoreactive protein, and enzyme activity in granulosa tissue of developing hen ovarian follicles. Additionally, the interactive roles of FSH, the adenylyl cyclase-cAMP system, and the protein kinase C pathway in granulosa cell differentiation were investigated. Granulosa cells collected from developing, 6-8-mm follicles were found to contain extremely low but detectable levels of a single, 2.0-kb P450scc mRNA transcript, as well as immunoreactive P450scc protein (53 kDa). However, this protein was apparently incapable of converting 25-hydroxycholesterol to pregnenolone in a cell-free system. Preincubation of granulosa cells with ovine FSH or forskolin for 24 h rendered the cells capable of converting cholesterol precursor to pregnenolone during a subsequent 3-h incubation. Inclusion of the protein kinase C activator, phorbol 12-myristate 13-acetate (PMA), in the preincubation medium blocked the stimulatory actions of FSH and forskolin on the induction of P450scc activity; however, PMA-preincubation did not alter the ability of granulosa cells to convert exogenous pregnenolone to progesterone compared to vehicle-pretreated cells. These data suggest that steroidogenic incompetency in differentiating avian granulosa cells is primarily due to a lack of active P450scc enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Radiographic and histologic effects of chondroitinase ABC on normal canine lumbar intervertebral disc.

Twelve dogs were divided into two equal groups and given lumbar intradiscal injections of 10, 50, or 100 U/ml of chondroitinase ABC reconstituted in sodium acetate buffer. Radiographs of the lumbar spine were made before and after surgery in both groups. Additional films were made at 5 days after surgery in Group I and at 7, 14, and 21 days after surgery in Group II. All spaces injected with 50 or 100 U/ml chondroitinase ABC demonstrated significant radiographic narrowing in both groups compared with uninjected control and buffer injected discs (P less than 0.001). Discs injected with 10 U/ml of chondroitinase ABC showed increased narrowing over time from 7 to 21 days (P less than 0.05). A zone of safranin O depletion was present in the ventral anulus fibrosus adjacent to the nucleus pulposus in all treated discs, indicating proteoglycan loss. All histologic effects of chondroitinase ABC were confined to intervertebral disc tissues. Chondroitinase ABC appears to be effective for chemonucleolysis in dogs.

Animals↗
PubMed1991

Angiotensin II receptor antagonists. From discovery to antihypertensive drugs.

Some simple N-benzylimidazoles, originally described by Takeda Chemical Industries (Osaka, Japan), were characterized to be very weak but selective nonpeptide angiotensin II (Ang II) receptor antagonists with a competitive mode of action. Chemical modifications of these led to EXP6155 and EXP6803, which showed approximately 10- and 100-fold higher affinity, respectively, but were orally ineffective. Oral activity was obtained for the biphenyl carboxylic acid derivatives EXP7711 and especially EXP9654. A further advance in the design of nonpeptide Ang II receptor antagonists was provided by DuP 753, an analogue of EXP7711 in which the carboxylic acid function is replaced by its tetrazol-5-yl equivalent. DuP 753 (2-n-butyl-4-chloro-5-hydroxymethyl-1-[(2'-(1H-tetrazol-5-yl)bi phe nyl-4- yl)methyl]imidazole, potassium salt) displaces radiolabeled Ang II from its specific binding sites in various tissues, affording IC50 values of approximately 20 nM. DuP 753 competitively antagonizes Ang II-induced responses in various in vitro and in vivo preparations but does not influence those to KCl, norepinephrine, vasopressin, and others, nor does it affect converting enzyme and renin. In high renin animal models of elevated arterial blood pressure, intravenous and oral administrations of DuP 753 produce a sustained decrease in pressure without influencing heart rate. Marked antihypertensive effects are observed in spontaneously hypertensive rats, but no efficacy is noticed in deoxycorticosterone acetate hypertensive animals. DuP 753 showed no agonistic properties in any of the above test systems and has been chosen to undergo clinical trials for the treatment of hypertension. In rats, the 5-carboxylic acid (EXP3174) represents a major metabolite of DuP 753.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗
PubMed1991

Involvement of apoptosis in ovarian follicular atresia and postovulatory regression.

In the ovary, greater than 99% of the follicles present at birth are destined to degenerate during life. In humans, less than 400 of the more than 400,000 follicles found at puberty will eventually ovulate whereas the overwhelming majority of follicles undergo atresia. Although follicular atresia plays a critical role during the recruitment of follicles for ovulation, the exact mechanism of this process is unknown. In chicken and porcine ovaries, atretic follicles can be morphologically distinguished from their healthy counterparts of the same size. Adapting a sensitive 3'-end labeling method for DNA analysis, we identified internucleosomal cleavage of cellular DNA in atretic (but not normal) follicles of both animal species, resembling that found during programmed cell death in embryogenesis, autoimmune T-cell removal and prostate regression. The present findings provide a basis for elucidating the hormonal signals involved in the initiation of follicular atresia during follicle recruitment, reproductive aging and premature ovarian failure.

Animals↗
PubMed1991

Role of calcium in the regulation of theca cell androstenedione production in the domestic hen.

Theca cells were collected from the second largest preovulatory follicle. Chelation of extracellular calcium with EGTA attenuated LH (10 ng)-induced androstenedione production by theca cells, and this effect was more pronounced in calcium-deficient than in calcium-replete incubation medium. Incubation of theca cells with steroidogenic agonists in the presence of the calcium channel blocker verapamil (100 microM) suppressed androstenedione production stimulated by LH (a 57% decrease), the adenylate cyclase activator forskolin (a 59% decrease) and the cyclic adenosine monophosphate (cAMP) analog 8-bromo-cAMP (a 61% decrease). Furthermore, 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester (TMB-8), a putative inhibitor of intracellular calcium mobilization, suppressed LH-induced androstenedione production in a dose-dependent fashion. The calmodulin inhibitors trifluoperazine (100 microM) and R24571 (50 microM) inhibited androstenedione production stimulated by hormonal (LH) and non-hormonal (forskolin, 8-bromo-cAMP) agonists (decreases ranging from 76 to 98%). While increasing the intracellular calcium ion concentrations with the calcium ionophore A23187 did not affect basal concentrations of androstenedione, treatment of LH-stimulated cells with the ionophore caused dose-dependent inhibition of androstenedione production; these effects were enhanced by coincubation with phorbol 12-myristate 13-acetate (a known activator of protein kinase C). We conclude that the mobilization of calcium is critical for agonist-stimulated steroidogenesis in hen theca cells, apparently requiring the interaction of calcium with its binding protein, calmodulin. Furthermore, increased cytosolic calcium concentrations may be involved in the suppression of androstenedione production, possibly as a result of an interaction with protein kinase C.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1991

Plasma progesterone, luteinizing hormone concentrations, and granulosa cell responsiveness in heat-stressed hens.

Plasma progesterone and luteinizing hormone (LH) profiles were obtained during the first ovulatory cycle of heat-stressed (HS, 35 C; n = 24) and unstressed (US, 17 to 27 C; n = 24) hens using 30-min sampling intervals beginning approximately 6 h prior to ovulation. Progesterone levels from HS hens were lower from 6 h [.07 +/- .01 (SE) versus 1.66 +/- .25 ng/mL; P = .008] to predicted ovulation (.06 +/- .006 versus .70 +/- .18 ng/mL; P = .07). Likewise, LH levels from HS hens were lower from 6 h (1.55 +/- .16 versus 3.86 +/- .34 ng/mL; P = .007) to predicted ovulation (1.63 +/- .18 versus 2.50 +/- .27 ng/mL; P = .01). Eggs from HS hens were more often laid early (less than 24 h) than eggs from US hens (71.42 versus 13.33%, respectively; P = .01), but US hens more often laid eggs of a normal oviposition interval length (24 to 26 h) compared with HS hens (73.34 versus 14.29%; P = .0005). The percentage of delayed eggs (greater than 26 h) was not different (US, 14.29 versus HS, 13.37%; P = .75) between the two treatment groups. Basal production of progesterone by dispersed granulosa cells from US hens was 97.62 +/- 16.01 ng/mL. Challenge by LH increased this to 417.50 +/- 53.38 ng/mL (P = .0001). In contrast, basal progesterone secretion by cells from HS hens was 40.25 +/- 6.60 ng/mL (P = .0001) and LH challenge failed to increase progesterone production.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Platelet [3H]imipramine and alpha 2-adrenoceptor binding in normal subjects during desipramine administration and withdrawal.

The effect of desipramine 150 mg daily on platelet [3H]imipramine and alpha 2-adrenoceptor binding sites was studied over a 6-week period and for 6 weeks after withdrawal. Modest (10%) increases in [3H]imipramine binding site densities during treatment were noted with a decrease between 1 and 4 weeks after withdrawal. No effect was found on alpha 2-adrenoceptors. Time of day appeared to have some effect on the results found. None of the [3H]imipramine binding site effects of desipramine, on treatment or following withdrawal, was comparable in magnitude to trait differences that were also found between subjects.

Adult↗
PubMed1990

National General Practice Study of Epilepsy: newly diagnosed epileptic seizures in a general population.

The National General Practice Study of Epilepsy is a prospective population-based cohort study of 1195 patients with newly diagnosed or suspected epileptic seizures. At the time of initial classification (6 months after notification), 104 patients were excluded. Of the remaining 1091 patients, 220 (20% [95% confidence interval 18-23%]) had febrile seizures, 564 (52% [49-55%]) definite epileptic seizures, and 228 (21% [19-23%]) possible epilepsy. In the definite epilepsy group the proportions of males and females were similar, 25% (21-28%) were younger than 15 years and 24% (21-28%) were 60 years or older. The definite seizures were classified as cryptogenic in 62% (58-66%), remote symptomatic in 21% (18-25%), and acute symptomatic in 15% (12-18%). The aetiology of epilepsy was vascular disease in 15% (12-18%) and tumour in 6% (4-8%). Among older subjects the proportion with an identifiable cause was much higher: 49% (41-58%) were due to vascular disease and 11% (6-16%) to tumour. Only 252 (45% [41-49%]) of the 564 patients with definite epileptic seizures were registered at the time of their first seizure. 52% (48-56%) of the patients had partial or secondarily generalised seizures, and only 39% (35-43%) seizures generalised from the outset.

Adolescent↗
PubMed1990

National General Practice Study of Epilepsy: recurrence after a first seizure.

In the National General Practice Study of Epilepsy 564 patients classified as having definite seizures have been followed up for 2-4 years. 67% (95% confidence interval 63-71%) had a recurrence within 12 months of the first seizure, and 78% (74-81%) had a recurrence within 36 months. Seizures associated with a neurological deficit presumed present at birth had a high rate of recurrence (100% by 12 months), whereas seizures that occurred within 3 months of an acute insult to the brain, such as head injury or stroke, or in the context of an acute precipitant such as alcohol, carried a much lower risk of recurrence (40% [29-51%] by 12 months). Other factors affecting the risk of recurrence were age-the highest risk being for patients under the age of 16 (83% [77-89%] by 36 months) or over the age of 59 (83% [76-90%] by 36 months-and type of first seizure-the risk of recurrence being much higher for patients with simple partial or complex partial seizures (94% [90-99%] by 36 months) than for those with generalised tonic clonic seizures (72% [67-77%] by 36 months).

Actuarial Analysis↗
PubMed1990

Expression of the yeast DNA primase gene, PRI1, is regulated within the mitotic cell cycle and in meiosis.

Mitotic cultures synchronised either by a feed-starve protocol or by elutriation have been used to show that the Saccharomyces cerevisiae DNA primase I gene is periodically expressed in the cell cycle. The transcript increases many-fold in late G1 and reaches a peak at the same time as four other genes essential for DNA synthesis, CDC8, CDC9, CDC21 and POL1. The primase I transcript is also regulated in meiosis, reaching maximal levels during premeiotic DNA synthesis.

DNA Primase↗
PubMed1990

Influence of androgens on plasma concentrations of growth hormone in growing castrated and intact chickens.

Castrated chicks implanted with testosterone or 5 alpha-dihydrotestosterone (5 alpha-DHT) had circulating concentrations of the respective androgen similar to or less than in sham-operated chicks. In castrated chicks, 5 alpha-DHT or 19-nortestosterone (19-NorT) inhibited growth as indicated by body weight, while testosterone and 5 beta-dihydrotestosterone (5 beta-DHT) were without effect. In intact male or female chicks, growth was inhibited by either testosterone or 5 alpha-DHT but was unaffected by 5 beta-DHT or estradiol-17 beta. Plasma concentrations of luteinizing hormone (LH) were reduced in castrated chicks receiving implants of either testosterone or 19-NorT. Only the highest dose of 5 alpha-DHT depressed the circulating concentration of LH; lower doses of 5 alpha-DHT being without effect. During the first 6 weeks of growth, plasma concentrations of GH were unaffected by most steroid treatments (5 alpha-DHT, 5 beta-DHT, low doses of testosterone, estradiol-17 beta) in castrated or in intact male or in female chicks. Similarly, 19-NorT did not affect plasma concentrations of GH in castrated chicks. The high dose of testosterone, however, depressed plasma concentrations of GH in castrated chicks between 2 and 6 weeks of age. Between 8 and 12 weeks of age, all steroids tested, except 5 alpha-DHT, were without effect on plasma concentrations of GH. Plasma concentrations of GH were increased in 5 alpha-DHT-treated chickens. This effect was observed irrespective of dose of 5 alpha-DHT or whether the androgen was administered to castrated or to intact male or to female chicks.

Androgens↗
PubMed1990

The Nottingham Study of Neurotic Disorder: relationship between personality status and symptoms.

Two hundred and ten psychiatric patients with one of three DSM-III diagnoses, generalized anxiety disorder (N = 71), panic disorder (N = 74) or dysthymic disorder (N = 65), were included in a clinical trial in which diazepam, dothiepin or placebo tablets, cognitive and behaviour therapy, or a self-help package were given over ten weeks. Personality status was assessed independently using a structured interview, the Personality Assessment Schedule. One hundred and ninety-eight patients had personality assessments, 89% with a close informant. Thirty-six per cent had a personality disorder and these patients had more severe psychopathology than those with no personality disorder. Personality disorder was more common in patients with dysthymic disorder and this group responded less well to treatment. The category of personality disorder had no apparent influence on symptoms.

Anxiety Disorders↗
PubMed1990

The discovery of potent nonpeptide angiotensin II receptor antagonists: a new class of potent antihypertensives.

A new class of potent antihypertensives has been discovered that exert their effect through blockade of the angiotensin II (AII) receptor. Most AII antagonists reported so far are peptide mimics of the endogenous vasoconstrictor octapeptide angiotensin II. The compounds of this paper are nonpeptides and therefore constitute a new class of potent AII receptor antagonists. Based on the overlap of a conformation of AII with literature lead 3, a hypothesis was developed suggesting the need for an additional acidic functionality to increase the lead's potency. The substitution of an additional carboxylic acid resulted in a 10-fold increase in binding affinity observed for diacid 4. The binding affinities for subsequent compounds were eventually increased 1000-fold over that of the literature leads through a systematic SAR study. Thus the AII receptor binding affinity [IC50 (microM)] of 15 microM for literature lead 1, for example, was increased to 0.018 and 0.012 microM for compounds 33 and 53. A structure-affinity relationship has been found requiring the presence of four key elements for good activity: (1) an additional phenyl ring at the N-benzyl para position of the benzylimidazole nucleus, (2) an acidic functionality at the ortho position of the terminal aromatic ring, (3) a lipophilic side chain at the imidazole 2-position of three to five carbon atoms in length, and (4) a group at the imidazole 5-position capable of hydrogen bonding. The synthesis as well as the pharmacological activity of the compounds in this new series of AII receptor antagonists are presented.

Angiotensin II↗
PubMed1990

Nonpeptide angiotensin II receptor antagonists: N-[(benzyloxy)benzyl]imidazoles and related compounds as potent antihypertensives.

A series of compounds has been synthesized and demonstrated to be antagonists of the angiotensin II (AII) receptor. These compounds are structurally related to the N-(benzamidobenzyl)imidazoles and extend the scope of this new class of nonpeptide AII antagonists. It has been found that the amide linkage (X = NHCO) in the N-(benzamidobenzyl)imidazoles can be replaced successfully by a variety of groups (X = single bond, O, S, CO, OCH2, CH = CH, NHCONH); linkers of 0-1 atoms in length are most effective. When administered intravenously to awake renal hypertensive rats, these compounds are potent antihypertensives.

Adrenal Cortex↗
PubMed1990

Nonpeptide angiotensin II receptor antagonists.

Although the most direct way to interfere with the renin-angiotensin system (RAS) is at the level of the angiotensin II (AII) receptor, the currently available AII receptor antagonists are peptides still retaining significant agonistic properties with the obvious drawbacks of limited stability and lack of oral activity. We have characterized simple N-benzylimidazoles as weak, but selective AII receptor antagonists with a competitive mode of action. Chemical modification of these early leads led to EXP6155 and EXP6803, which show approximately 10- and 100-fold higher affinity. Oral activity was obtained for EXP7711, and in particular for EXP9654. This class of compounds displaces 3H-AII from its specific binding sites in various tissues. They competitively antagonize AII-induced responses in various in vitro and in vivo preparations, but do not influence AII-induced responses to KCl, norepinephrine, and vasopressin, nor do they affect converting enzyme or renin. In high renin models of elevated blood pressure, such as the renal hypertensive rat and sodium-depleted dog, these substances produce a sustained decrease in arterial pressure without changing heart rate after intravenous and oral (EXP7711 and EXP9654) administration. None of these compounds showed agonistic activity in any of the above test systems. In conclusion, the nonpeptide structures described herein are selective and competitive AII receptor antagonists and add another dimension to the arsenal of drugs manipulating the RAS.

Angiotensin II↗