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A L Johnson

Publications and source records attributed to A L Johnson.

At least 145 records · Page 8Linked to original sources
PubMed1992

Zinc-induced molt: evidence for a direct inhibitory effect on granulosa cell steroidogenesis.

Results from previous studies indicate that the use of dietary zinc may provide an effective means to initiate an induced molt in laying hens. Although much evidence indicates that high concentrations of zinc (10,000 to 20,000 ppm) cause the cessation of lay primarily by depressing feed intake, recent data suggest that lower concentrations (2,800 ppm) in a calcium-deficient diet may act via a direct action on the ovary. Therefore, a series of in vitro studies was conducted to evaluate whether zinc can affect granulosa cell progesterone production. Incubation of granulosa cells from the largest preovulatory (F1) follicle with zinc as zinc sulfate (.1 to 10 microM) had no effect on basal progesterone production. By contrast, ovine luteinizing hormone-stimulated progesterone production was inhibited (P less than .05) in a dose-related fashion by zinc in both the sulfate and acetate forms (1 to 10 microM). Furthermore, zinc attenuated oLH- and forskolin-induced cyclic adenosine monophosphate (cAMP) formation, and inhibited 8-bromo-cAMP- and calcium ionophore (A23187)-induced progesterone production. Such results indicate both pre- and post-cAMP sites of action for zinc's inhibitory actions on progesterone production in F1 granulosa cells. Finally, ovine follicle-stimulating hormone-stimulated cAMP accumulation and progesterone production in granulosa cells collected from 9- to 12-mm follicles (a stage of development representing the early, rapid growth phase) were suppressed (P less than .05) by co-incubation of cells with zinc.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Methyl-3-isobutylxanthine↗
PubMed1992

Molt induced by dietary zinc in a low-calcium diet.

Three experiments were designed to test the hypothesis that zinc has a specific effect independent of anorexia during induction of molt. In Experiment 1, hens were fed a low-calcium (.08%) basal molt diet to which was added 0, 110, 620, or 1,120 mg/kg (ppm) zinc as zinc sulfate heptahydrate (ZnSO4.7H2O) for 7 days and 0, 1, 400, 2,800, or 4,200 ppm zinc, respectively, for the following 14 days. In Experiment 2, hens were provided ad libitum access to the low-calcium basal molt diet with 2,800 ppm added zinc for 14 days during which a paired control hen received a similar amount of the low-calcium basal molt diet. In Experiment 3, hens were fed the low-calcium basal molt diet on a restricted basis amended with either 0 or 2,800 ppm zinc on a restricted basis for 10 days. In Experiment 1, all hens that consumed zinc had significantly fewer days to last oviposition as compared with control hens, and this occurred without significant differences in body weight or feed consumption for the lowest zinc group. When compared with the control group, higher levels of zinc did decrease body weight and feed consumption. In Experiment 2, the hens consuming the diet with 2,800 ppm zinc (Zn2800) reached last oviposition significantly sooner than control hens, although the Zn2800 hens actually consumed more feed. In Experiment 3, the Zn2800 hens lost more body weight than control hens due partially to earlier reproductive tract regression. Serum luteinizing hormone was increased in the Zn2800 hens.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Cloning DPB3, the gene encoding the third subunit of DNA polymerase II of Saccharomyces cerevisiae.

DNA polymerase II purified from Saccharomyces cerevisiae contains polypeptides with apparent molecular masses of greater than 200, 80, 34, 30 and 29 kDa, the two largest of which (subunits A and B) are encoded by the essential genes POL2 and DPB2. By probing a lambda gt11 expression library of yeast DNA with antiserum against DNA polymerase II, we isolated a single gene, DPB3, that encodes both the 34- and 30-kDa polypeptides (subunit C and C'). The nucleotide sequence of DPB3 contained an open reading frame encoding a 23-kDa protein, significantly smaller than the observed molecular masses, 34- or 30-kDa, which might represent post-translationally modified forms of the DPB3 product. The predicted amino acid sequence contained a possible NTP-binding motif and a glutamate-rich region. NTP-binding motif and a glutamate-rich region. A dpb3 deletion mutant (dpb3 delta) was viable and yielded a DNA polymerase II lacking the 34- and 30-kDa polypeptides. dpb3 delta strains exhibited an increased spontaneous mutation rate, suggesting that the DPB3 product is required to maintain fidelity of chromosomal replication. Since a fifth, 29-kDa polypeptide was present in DNA polymerase II preparations from wild-type cell extracts throughout purification, the subunit composition appears to be A, B, C (or C and C') and D. The 5' nontranscribed region of DPB3 contained the MulI-related sequence ACGCGA, while the 0.9-kb DPB3 transcript accumulated periodically during the cell cycle and peaked at the G1/S boundary. The level of DPB3 transcript thus appears to be under the same cell cycle control as those of POL2, DPB2 and other DNA replication genes. DPB3 was mapped to chromosome II, 30 cM distal to his7.

Amino Acid Sequence↗
PubMed1991

Coordination of expression of DNA synthesis genes in budding yeast by a cell-cycle regulated trans factor.

All of the DNA synthesis genes of budding yeast examined so far are periodically expressed and hence under cell-cycle control (Table 1). Expression occurs near the G1/S phase boundary and the genes seem to be coordinately regulated (reviewed in ref. 4). The upstream promoter sequences of these genes have only a hexamer element, ACGCGT (an MluI restriction site), in common. Here we show that this hexamer is able to impart periodic expression to a heterologous gene and, significantly, this expression occurs coincidentally with that of CDC9, one of the DNA synthesis genes (Table 1). We have also identified a protein that binds specifically to these sequences in a similar periodic manner. These ACGCGT sequences and the transcription factor that binds to them therefore seem to be the elements controlling both the periodic expression and coordinate regulation of the DNA synthesis genes.

Cell Cycle↗
PubMed1991

The yeast DNA ligase gene CDC9 is controlled by six orientation specific upstream activating sequences that respond to cellular proliferation but which alone cannot mediate cell cycle regulation.

By fusing the CDC9 structural gene to the PGK upstream sequences and the CDC9 upstream to lacZ, we showed that the cell cycle expression of CDC9 is largely due to transcriptional regulation. To investigate the role of six ATGATT upstream repeats in CDC9 regulation, synthetic copies of the sequence were attached to a heterologous gene. The repeats stimulated transcription strongly and additively, but, unlike conventional yeast UAS elements, only when present in one orientation. Transcription driven by the repeats declines in cells held at START of the cell cycle or in stationary phase, as occurs with CDC9. However, the repeats by themselves cannot impart cell cycle regulation to a heterologous gene. CDC9 may therefore be controlled by an activating system operating through the repeats that is sensitive to cellular proliferation and a separate mechanism that governs the periodic expression in the cell cycle.

Base Sequence↗
PubMed1991

Plasma uric acid in patients receiving anticonvulsant monotherapy.

In newly diagnosed adult patients with epilepsy followed prospectively on monotherapy, carbamazepine and phenytoin were associated with a fall in plasma uric acid, but sodium valproate and phenobarbitone were associated with a rise in plasma uric acid. The mechanisms and significance of these findings are discussed.

Adolescent↗
PubMed1991

Nonpeptide angiotensin II receptor antagonists: the discovery of a series of N-(biphenylylmethyl)imidazoles as potent, orally active antihypertensives.

A new series of nonpeptide angiotensin II (AII) receptor antagonists has been prepared. These N-(biphenylyl-methyl)imidazoles, e.g. 2-butyl-1-[(2'-carboxybiphenyl-4-yl)methyl]-4-chloro-5- (hydroxymethyl)imidazole, differ from the previously reported N-(benzamidobenzyl)imidazoles and related compounds in that they produce a potent antihypertensive effect upon oral administration; the earlier series generally were active only when administered intravenously. It has been found that the acidic group at the 2'-position of the biphenyl is essential. Only ortho-substituted acids possess both high affinity for the AII receptor and good oral antihypertensive potency. The carboxylic acid group has been replaced with a variety of acidic isosteres, and the tetrazole ring has been found to be the most effective. The tetrazole derivative, DuP 753, is currently in development for the treatment of hypertension.

Administration, Oral↗
PubMed1991

The discovery of a new class of highly specific nonpeptide angiotensin II receptor antagonists.

Since angiotensin II (AII) is the effector molecule of the renin angiotensin system, the most direct approach to interfere with this system would be to antagonize AII at the level of its receptor. AII receptor antagonists would represent an ideal species, for regardless of how and where AII is produced, its function could be specifically turned off. However, the AII receptor antagonists currently available have been limited to AII-like peptides and their usefulness as therapeutics and pharmacologic tools has been hampered by their lack of oral bioavailability, metabolic instability, and partial agonistic activity. A detailed pharmacologic characterization of some simple N-benzylimidazoles, originally described by Takeda Chemical Industries (Osaka, Japan), identified this class of compound as very weak but selective AII receptor antagonists with a competitive mode of action. Encouraged by the quality of these lead compounds, we embarked on a synthetic program aimed at designing more potent and orally effective antagonists, while preserving their selectivity for the AII receptor. Our efforts have culminated in the discovery of DuP 753, 2-n-butyl-4-chloro-5-hydroxymethyl-1-[2'-(1H-tetrazol-5-yl)biph eny l-4-yl) methyl]imidazole, potassium salt, a potent, nonpeptide AII receptor antagonist.

Angiotensin Receptor Antagonists↗
PubMed1991

In vitro pharmacology of DuP 753.

DuP 753, 2-n-butyl-4-chloro-5-hydroxymethyl-1-[2'-(1H-tetrazol-5-yl) biphenyl-4-yl)methyl]imidazole, potassium salt, was characterized in vitro with respect to its affinity and specificity for functional antagonism of angiotensin II (AII) receptors. In rat adrenal cortical microsomes and cultured aortic smooth muscle cells DuP 753 inhibited the specific binding of [125I]AII in a concentration-dependent manner yielding IC50 values of 1.7 and 2.0 x 10(-8) mol/L, respectively. In contrast, DuP 753 had no appreciable affinity for other receptor systems as well as for Ca2+ channels. Functional antagonism was demonstrated by its blockade of AII-induced 45Ca2+ efflux in rat smooth muscle cells. The AII-induced contraction of rabbit aortic strips was competitively antagonized by DuP 753 resulting in a pA2 value of 8.48. Responses induced by other agonists, such as norepinephrine and KCl, were not altered. No partial agonistic effect was noted in any of the in vitro assays. In addition, DuP 753 (10(-5) mol/L) had no effect on rabbit lung converting enzyme or rat/human renin activity. These data demonstrate that DuP 753 is a highly potent and specific AII receptor antagonist. DuP 753 represents a useful experimental tool for dissecting the role of the renin-angiotensin system.

Adrenal Cortex↗
PubMed1991

In vivo pharmacology of DuP 753.

A review of the in vivo pharmacology of DuP 753 (2-n-butyl-4-chloro-5-hydroxymethyl-1-[2'-(1H-tetrazol-5-yl)biphen yl-4- yl)methyl]imidazole, potassium salt) is presented. In the pithed rat, DuP 753 exerted a selective and competitive inhibition of the pressor response to angiotensin II (AII). In conscious normotensive rats, DuP 753 inhibited the AII-induced aldosterone secretion and drinking response. DuP 753 lowered blood pressure in conscious normotensive rats pretreated with furosemide but not in untreated normotensive rats. Unlike saralasin, DuP 753 given intravenously did not cause pressor response. In conscious renal hypertensive rats (RHRs), a high renin model, DuP 753 decreased blood pressure with an intravenous ED30 of 0.78 mg/kg and an oral ED30 of 0.59 mg/kg. The antihypertensive efficacy of DuP 753 in RHRs was similar to that of captopril. In DOCA hypertensive rats, a low renin model, DuP 753 did not lower blood pressure. In conscious 18- to 21-week-old spontaneously hypertensive rats (SHRs), DuP 753 given orally or intravenously reduced blood pressure dose-dependently and did not alter heart rate at these doses. The acute antihypertensive efficacy of DuP 753 was greater than that of captopril in SHRs. In contrast, DuP 753 and captopril given orally at 10 mg/kg/day for 15 days in SHRs caused a similar decrease in blood pressure. Bilateral nephrectomy but not inhibition of prostaglandin synthesis abolished the antihypertensive effect of DuP 753 in SHRs. Our study, therefore, indicates that DuP 753 is an orally active, nonpeptide, selective, and competitive AII receptor antagonist lacking agonism. It appears that there is a relationship between basal renin level and the acute antihypertensive effect of DuP 753 in rats. Further, our results suggest that the renin-angiotensin system plays a significant role in the control of blood pressure in conscious SHRs.

Angiotensin II↗
PubMed1991

Angiotensin II receptor heterogeneity.

The possibility of receptor heterogeneity in the angiotensin II (AII) system has been suggested previously, based on differences in Kd values or sensitivity to thiol reagents. One of our earliest indications was the frequent observation of incomplete inhibition of the binding of AII to adrenal cortical membranes. Autoradiographic studies demonstrated that all of the labeling of the rat adrenal was blocked by unlabeled AII or saralasin, but not by DuP 753. The predominant receptor in the rat adrenal cortex (80%) is sensitive to dithiothreitol (DTT) and DuP 753, and is designated AII-1. The residual sites in the adrenal cortex and almost all of the sites in the rat adrenal medulla are insensitive to both DTT and DuP 753, but were blocked by EXP655. These sites have been confirmed by ligand binding studies and are designated AII-2. The rabbit adrenal cortex is unique in yielding a nonuniform distribution of AII-2 sites around the outer layer of glomerulosa cells. In the rabbit kidney, the sites on the glomeruli are AII-1, but the sites on the kidney capsule are AII-2. Angiotensin III appears to have a higher affinity for AII-2 sites since it inhibits the binding to the rabbit kidney capsule but not the glomeruli. Elucidation of the distribution and function of these diverse sites should permit the development of more selective and specific therapeutic strategies.

Animals↗
PubMed1991

Stage of ovarian follicular development associated with the initiation of steroidogenic competence in avian granulosa cells.

Previously described models for avian ovarian steroidogenesis, using mature, 25-40-mm preovulatory follicles as the source of tissues, were based on the assumption that interaction of the granulosa layer, as the predominant source of progesterone, with adjacent theca cells is required for maximal production of C21, C19, and C18 steroids. In the present study, we evaluated the steroidogenic capacity of ovarian cells isolated from less mature, 6-8-mm and 9-12-mm follicles in the chicken ovary (representative of a stage of development 2-3 wk prior to ovulation) to determine at which stage of follicular development granulosa and/or theca cells become steroidogenically competent. Granulosa cells collected from 6-8-mm follicles were found to be virtually incompetent to produce steroids, containing extremely low basal levels of progesterone (12 pg/5 x 10(5) cells) and failing to respond with increased steroid output following a 3-h exposure to ovine LH (oLH; 0.1 and 100 ng/0.5 ml), ovine FSH (oFSH; 100, 500, and 1,000 ng/0.5 ml), 8-bromo-cyclic adenosine monophosphate (8-bromo-cAMP; 0.33 and 3.33 mM) or 25-hydroxycholesterol (250 and 2,500 ng/0.5 ml). However, addition of pregnenolone (20 and 200 ng/0.5 ml) to granulosa incubations resulted in significantly increased progesterone levels. Granulosa cells of 6-8-mm follicles also failed to increase cAMP formation in the presence of oLH (10, 100, and 1,000 ng/0.5 ml) and 3-isobutyl-1-methylxanthine (IBMX; 10 microM), but responded to stimulation with 1,000 ng oFSH (4.4-fold increase over basal) or 10 microM forskolin (32-fold increase over basal) in the presence of IBMX. In contrast, granulosa cells isolated from 9-12-mm follicles and incubated for 3 h in vitro were found to contain basal progesterone levels 200-fold higher than those found in granulosa cells of 6-8-mm follicles. Furthermore, granulosa cells of 9-12-mm follicles markedly increased progesterone production following incubation in the presence of oFSH (100-1,000 ng/0.5 ml), 8-bromo-cAMP (0.33 and 3.33 mM), or 25-hydroxycholesterol (250 and 2,500 ng/0.5 ml). However, these granulosa cells remained unresponsive to oLH (0.1, 10, and 100 ng/0.5 ml), failing to increase cAMP accumulation (in the presence of IBMX) and progesterone output. Theca cells of small yellow follicles were found to produce measurable basal levels of progesterone, androstenedione, and estradiol, and levels of each steroid were significantly increased following a 3-h challenge with oLH, 8-bromo-cAMP, 25-hydroxycholesterol, and pregnenolone.(ABSTRACT TRUNCATED AT 400 WORDS)

Androstenedione↗
PubMed1991

Possible role for arachidonic acid in the control of steroidogenesis in hen theca.

Studies were conducted to evaluate if arachidonic acid (C20:4) could function as a second messenger within theca cells from the second largest preovulatory (F2) follicle from the ovary of the domestic hen. Arachidonic acid stimulated basal progesterone and androstenedione production, but inhibited LH-induced androstenedione production. The stimulatory effects of arachidonic acid were not altered by either cyclooxygenase or lipoxygenase pathway inhibitors (indomethacin and nordihydroguaiaretic acid, respectively), but were blocked by agents that prevented mobilization and/or efflux of calcium (TMB-8 and verapamil). The inhibitory effects of arachidonic acid on LH-stimulated steroidogenesis were determined to occur both prior and subsequent to cAMP formation. Fifty and 100 microM arachidonic acid attenuated LH- (10 ng) and forskolin- (0.2 microM) induced cAMP levels, and decreased androstenedione and estradiol production following treatment with 8-bromo-cAMP. Phospholipase A2 (PLA2) and the calcium ionophore, A23187, stimulated the release of 3H from theca cells prelabeled with [3H]arachidonic acid, and both PLA2 and the closely related fatty acid, eicosatrienoic acid (C20:3), could replicate the inhibitory effects of arachidonic acid on LH-stimulated androstenedione production. Finally, neither indomethacin nor nordihydroguaiaretic acid blocked the inhibitory effects of arachidonic acid on LH-promoted androstenedione production. We conclude that arachidonic acid can be released within theca cells in response to physiologic (PLA2) and pharmacologic agents (A23187), and accordingly, that it may act directly as a second messenger to modulate both basal and LH-stimulated steroid production.

Androstenedione↗
PubMed1991

Second messenger pathways mediating chicken luteinizing hormone secretion from dispersed pituitary cells.

A series of studies was conducted to evaluate the ability of several second messengers/second messenger systems to stimulate LH secretion from dispersed chicken pituitary cells. [Gln8]-LHRH-(cLHRH) stimulated LH secretion in a dose-dependent fashion; this effect was potentiated in the presence of the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, and was mimicked by the cAMP analog, 8-bromo-cAMP. These data indicate that the production of cAMP in response to cLHRH can stimulate LH secretion, but do not necessarily provide evidence that such production is prerequisite. The tumor-promoting phorbol ester, phorbol 12-myristate 13-acetate (PMA), and diacylglycerol analogs, 1-oleoyl-2-acetylglycerol (OAG) and 1,2-dioctanoyl-sn-glycerol (DOG), also stimulated LH release; however, only PMA (and not cLHRH or DOG) promoted an accumulation of cAMP. The putative protein kinase C inhibitor, staurosporine, completely blocked LH release stimulated by PMA, but failed to block cLHRH-induced LH secretion. Such results indicate that protein kinase C activation can promote LH secretion, but also suggest that additional second messengers may exist to fully mediate the effects of cLHRH. Both the calcium ionophore, A23187, and the intracellular calcium mobilizing agent, thapsigargin, caused a dose-dependent increase in LH secretion; furthermore, thapsigargin augmented the stimulatory effects of PMA. These data are consistent with a role for calcium in the regulation of LH release, and indicate that the mobilization of intracellular calcium alone can affect such an action.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Methyl-3-isobutylxanthine↗