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Biomedical subjects

S Murad

Publications and source records attributed to S Murad.

At least 55 records · Page 3Linked to original sources
PubMed1987

Suppression of fibroblast proliferation and lysyl hydroxylase activity by minoxidil.

The effect of minoxidil on lysyl hydroxylase activity and proliferation of human skin fibroblasts in culture was examined. Exposure of cells to minoxidil resulted in a specific loss of lysyl hydroxylase activity, the extent of which was dependent on the concentration of minoxidil from 25 to 500 microM and the duration of the treatment from 6 to 48 h. This phenomenon was unaffected by culture conditions, i.e. ascorbic acid status, serum concentration, and cell density. Minoxidil added directly to cell extracts had no effect on lysyl hydroxylase activity, showing a requirement for intact cells. Mixing experiments with extracts of minoxidil-treated cells and controls gave additive results which rule out the possibility that a metabolite derived from minoxidil could be inhibiting the enzyme activity. The effect of minoxidil on fibroblast lysyl hydroxylase activity disappeared in the presence of cycloheximide, an inhibitor of protein synthesis. Moreover, the recovery of the enzyme activity that occurred after removal of minoxidil from the culture medium could be prevented by actinomycin D, an inhibitor of RNA synthesis. These results indicate that minoxidil may inhibit the synthesis of lysyl hydroxylase in the cell. In addition to suppressing fibroblast lysyl hydroxylase activity, minoxidil caused inhibition of cell growth within 48 h in a manner dependent on the concentration from 10 to 1000 microM, the latter resulting in almost complete cessation of cell proliferation. This effect was not accompanied by cytotoxicity as judged by the criteria of dye exclusion, plating efficiency, growth recovery, and protein synthesis. The inhibition of fibroblast proliferation by minoxidil appeared to be related to its ability to inhibit DNA synthesis measured by incorporation of tritiated thymidine into acid-precipitable material.

Antihypertensive Agents↗
PubMed1987

Induction of collagen synthesis by ascorbic acid. A possible mechanism.

L-Ascorbic acid stimulates procollagen synthesis in cultured human skin fibroblasts without appreciably altering noncollagen protein synthesis. The effect is unrelated to intracellular degradation of newly synthesized procollagen. Levels of mRNA for pro alpha 1(I), pro alpha 2(I), and pro alpha 1(III), measured by hybridization with the corresponding cDNA probes, are elevated in the presence of ascorbic acid, whereas the level of mRNA for fibronectin is unchanged. Levels of functional mRNA for procollagen, measured in a cell-free translation assay, are specifically increased in the presence of ascorbic acid. Thus, ascorbic acid appears to control the expression of three different procollagen genes, each of which is located on a separate chromosome. It is proposed that intracellularly accumulated procollagen in ascorbate deficiency may lead to a translational repression of procollagen synthesis. Ascorbic acid may relieve this block by promoting hydroxyproline formation and, consequently, secretion of procollagen from the cell. The increased level of procollagen mRNA under the influence of ascorbic acid may be secondary to increased synthesis of procollagen polypeptides; the control point may be gene transcription or mRNA degradation.

Aging↗
PubMed1987

Effects of minoxidil on cultured human skin fibroblasts.

Two important findings related to the effect of minoxidil on human skin fibroblasts in culture are reviewed. Treatment of cells with minoxidil is associated with a specific loss of lysyl hydroxylase activity; this loss occurs gradually and is reversed by removing minoxidil from the culture medium. Experiments with inhibitors of protein and RNA synthesis reveal that minoxidil may inhibit the synthesis of lysyl hydroxylase by acting at the transcriptional level. Treatment of cells with minoxidil is also associated with inhibition of proliferation, without any sign of cytotoxicity. This effect of minoxidil is accompanied by inhibition of DNA synthesis. Since collagen is the major product of fibroblast activity and lysyl hydroxylase catalyzes a crucial reaction in collagen biosynthesis, the combined effects of minoxidil offer the potential for its use as an antifibrotic agent. Thus, minoxidil may prove to be beneficial in treating skin conditions associated with collagen accumulation.

Cell Division↗
PubMed1986

Ascorbic acid stimulates collagen production without altering intracellular degradation in cultured human skin fibroblasts.

The influence of ascorbic acid on intracellular degradation of collagen synthesized by cultured human-skin fibroblasts was examined. In confluent cells maintained in 0.5% serum-supplemented medium, ascorbic acid had no significant effect on collagen degradation measured with hydroxyproline as the marker. Similar results were obtained when collagen degradation was measured with the marker hydroxylysine, the cellular synthesis of which is independent of ascorbic acid. The stimulatory effects of ascorbic acid on collagen production therefore cannot be explained by a change in the rate of degradation. Ascorbic acid acts at some as yet undetermined level to increase the rate of collagen synthesis.

Ascorbic Acid↗
PubMed1986

1, 25-Dihydroxycholecalciferol stimulates conversion of androstenedione into oestrone by human skin fibroblasts in culture.

Pre-incubation of monolayer cultures of human skin fibroblasts with 1,25-dihydroxycholecalciferol (1,25-D3; 0.1-10 nmol/l) increased the rate of conversion of androstenedione into oestrone (aromatase activity) when measured subsequently in the presence of a 5 alpha-reductase inhibitor (10 mumol/l). Maximal stimulation (14- to 89-fold with 10 nmol 1,25-D3/l) occurred 12 h after addition of the hormone and was maintained for up to 48 h. Stimulation was prevented by cycloheximide. In one cell line high 1,25-D3 concentrations (greater than 30 nmol/l) prevented the increase in aromatase activity; this did not appear to result from direct enzyme inhibition by 1, 25-D3. The possibility is considered that 1,25-D3 could act as a physiological regulator of peripheral aromatase. As oestrogens can prevent postmenopausal bone loss, it is speculated that 1,25-D3 might protect against bone resorption by maintaining peripheral oestrogen biosynthesis.

Androstenedione↗
PubMed1985

A paradoxical effect of hydralazine on prolyl and lysyl hydroxylase activities in cultured human skin fibroblasts.

The effect of hydralazine on several parameters of collagen biosynthesis has been studied in cultured human skin fibroblasts. Cells treated with hydralazine synthesized procollagen which was severely deficient in hydroxyproline and hydroxylysine, indicating inhibition of prolyl and lysyl hydroxylase reactions in the cell. Assays of prolyl and lysyl hydroxylase activities, however, revealed markedly increased levels in hydralazine-treated cells. The stimulatory effect of hydralazine could not be simulated in cell extracts, demonstrating its requirement for intact cells. The effect occurred slowly over a period of 96 h and was dependent on hydralazine concentration between 10 and 100 microM. This phenomenon was also observed in lysyl hydroxylase-deficient mutants. In both normal and mutant cells the relative magnitude of the hydralazine effect could be modified by ascorbic acid in the culture medium. Ascorbic acid increased the response of prolyl hydroxylase to hydralazine from 1.5- to 2-fold to 3- to 7-fold, whereas it decreased the response of lysyl hydroxylase to hydralazine from 4- to 8-fold to 2- to 3-fold. Total collagen synthesis was substantially reduced in hydralazine-treated cells; the time course and the dose-response relationship were similar to those observed for the hydroxylases. alpha, alpha'-Dipyridyl, an iron chelator, mimicked these effects of hydralazine. The studies suggest the existence in cultured cells of a compensatory mechanism for overproduction of these crucial enzymes in collagen biosynthesis, a mechanism which remains functional in cells derived from patients afflicted with hydroxylysine-deficient collagen disease.

Ascorbic Acid↗
PubMed1985

Water excretion in preeclampsia: behavior as nephrotic syndrome.

Decreased free water excretion and the development of interstitial edema are recognized characteristics of preeclampsia. However, the pathophysiology of decreased urine excretion in preeclampsia is presently controversial: diminished glomerular filtration, renal arteriolar spasm, elevated plasma vasopressin levels, and plasma volume contraction have been suggested as etiologies. We studied seven pregnant patients with a diagnosis of mild preeclampsia to assess the role of vasopressin, serum protein, and glomerular function in the renal excretion of water. The ability to excrete a water load was significantly and directly correlated with serum albumin (P less than 0.05) and protein (P less than 0.02) concentrations. Neither plasma vasopressin nor creatinine clearance correlated with water excretion. The similarity of preeclampsia and the nephrotic syndrome with regard to the renal excretion of water is discussed.

Anuria↗
PubMed1985

Serum stimulation of lysyl hydroxylase activity in cultured human skin fibroblasts.

In the absence of ascorbic acid, confluent human skin fibroblasts incubated in 0.5% serum-supplemented medium had one-third of the level of lysyl hydroxylase activity of cells incubated in media containing high serum concentrations (5-20%). This difference appeared to be due to a decline in the enzyme activity following serum deficiency, and was largely abolished by addition of ascorbic acid to the medium. The effect of serum deficiency was slow, manifesting in 48 h at the earliest, and was completely reversed by replenishing the medium with serum. Prolyl hydroxylase activity was independent of serum concentration, both in the absence and in the presence of ascorbic acid in the culture medium.

Blood↗
PubMed1984

Circulatory and renal effects of beta-adrenergic-receptor stimulation in pregnant sheep.

The effects of beta-adrenergic-receptor stimulation with ritodrine on systemic and pulmonary hemodynamics and on renal handling of water and electrolytes were studied in unanesthetized, chronically instrumented pregnant sheep. Each animal was studied during control, ritodrine, and recovery periods, each lasting 60 minutes, with the use of three different modes of hydration. beta-receptor stimulation produced a significant increase in heart rate and cardiac output and a decrease in systemic vascular resistance. Pulmonary arterial and wedge pressures tended to increase. These circulatory effects were similar for the three types of hydration and they persisted after cessation of infusion. In terms of its renal effects, beta-receptor stimulation elicited a profound decrease in urine flow and in the excretions of sodium and potassium, irrespective of the mode of hydration. The antidiuresis and antinatriuresis were accompanied by no changes in plasma osmolality and sodium concentration, whereas plasma potassium levels decreased. All of these effects persisted for 60 minutes after the cessation of infusion. In the water-loaded experiments, the antidiuresis seemed to be related to increased antidiuretic hormone secretion; in the saline-loaded experiments, however, both the antidiuresis and antinatriuresis appeared to be related to increased renal reabsorption. The changes in renal hemodynamics seemed to have an insignificant role. The amount of fluid retained in the body was greater when ritodrine was infused with saline solution than with dextrose solution. These cardiovascular and renal studies suggest that a circulatory overload may be the major factor in the pathogenesis of pulmonary edema observed during beta-adrenergic-receptor stimulation.

Animals↗
PubMed1983

A comparison of lysyl hydroxylation in various types of collagen from type VI Ehlers-Danlos syndrome fibroblasts.

Type I, type III, and type V collagens were isolated from type VI Ehlers-Danlos syndrome fibroblasts. Five different alpha chains were separated and their degrees of prolyl and lysyl hydroxylations were determined. Lysyl hydroxylation in all collagen types was low in the mutant fibroblasts compared to age-matched controls, with no significant change in prolyl hydroxylation. The degrees of lysyl hydroxylation in type I, type III, and type V collagens were 52%, 73%, and 76% of controls, respectively.

Adult↗
PubMed1983

Collagen synthesis in cultured human skin fibroblasts: effect of ascorbic acid and its analogs.

In confluent human skin fibroblasts maintained in 0.5% serum-supplemented medium. L-ascorbate specifically stimulated the rate of incorporation of labeled proline into total collagenase-sensitive protein, without changing the specific activity of the intracellular free proline. This influence of ascorbate reached a maximum at 30 microM and continued for at least 4 days, resulting in a 4-fold increase. The ascorbate effect occurred in cells at both confluent and subconfluent densities and was evident at all serum concentrations from 0.5-20%. The effect was independent of duration of the radioactive pulse between 2-6 h. D-Ascorbate, D-isoascorbate, and L-dehydroascorbate also stimulated collagen synthesis but at considerably higher concentrations, i.e., 250-300 microM. The stimulation of collagen synthesis by ascorbate and its analogs was accompanied by a decline in prolyl hydroxylase activity and a rise in lysyl hydroxylase activity; again L-ascorbate was found to be most effective. Dimethyltetrahydropterine and L-lactate failed to produce these effects.

Ascorbic Acid↗
PubMed1982

Circulatory effects of chemical sympathectomy in fetal, neonatal, and adult sheep.

Circulatory effects of chemical sympathectomy with 6-hydroxydopamine (6-HD), including changes in vascular sensitivity to neurotransmitters, were investigated in chronically instrumented unanesthetized fetal, neonatal, and adult sheep. In all animals acute response to 6-HD consisted of hypertension and tachycardia, which lasted 2-3 h. Chronic phase of sympathetic ablation then followed during which arterial pressure and heart rate of sympathectomized fetus and neonate returned to and remained at levels observed in intact animals, whereas adult sheep were slightly hypotensive throughout this period. In all animals supersensitivity of peripheral circulation to norepinephrine occurred, but only the fetus exhibited supersensitivity to acetylcholine and isoproterenol. Our conclusions are as follows: 1) acute phase of chemical sympathectomy in fetal, neonatal, and adult sheep simulates strong adrenergic stimulation; 2) absence of significant alteration in arterial pressure of fetus and neonate during the chronic phase of sympathectomy suggests a minor role for the adrenergic system in the maintenance of resting tone of peripheral circulation; and 3) on the basis of present and previous data, we postulate that the supersensitivity of fetal circulation to acetylcholine and isoproterenol may be secondary to changes occurring in pulmonary vascular bed.

Acetylcholine↗
PubMed1981

Regulation of collagen synthesis by ascorbic acid.

After prolonged exposure to ascorbate, collagen synthesis in cultured human skin fibroblasts increased approximately 8-fold with no significant change in synthesis of noncollagen protein. This effect of ascorbate appears to be unrelated to its cofactor function in collagen hydroxylation. The collagenous protein secreted in the absence of added ascorbate was normal in hydroxylysine but was mildly deficient in hydroxyproline. In parallel experiments, lysine hydroxylase (peptidyllysine, 2-oxoglutarate:oxygen 5-oxidoreductase, EC 1.14.11.4) activity increased 3-fold in response to ascorbate administration whereas proline hydroxylase (prolyl-glycyl-peptide, 2-oxoglutarate:oxygen oxidoreductase, EC 1.14.11.2) activity decreased considerably. These results suggest that collage polypeptide synthesis, posttranslational hydroxylations, and activities of the two hydroxylases are independently regulated by ascorbate.

Ascorbic Acid↗
PubMed1980

Mechanisms of beat-to-beat variability in the heart rate of the neonatal lamb. II. Effects of hypoxia.

The effects of acute hypoxia on the resting arterial pressure as well as on heart rate and its beat-to-beat variability were studied in chronically instrumented, unanesthetized newborn lambs at 2 to 8 weeks of neonatal life. Lung ventilation with a gas mixture containing 10% oxygen and 3% carbon dioxide decreased arterial blood PO2 by about 50% in all animals regardless of age without significantly altering blood pH and PCO2. This degree of hypoxia produced a mild pressor response, accompanied by a significant tachycardia; the pattern of these changes, however, differed somewhat according to neonatal growth. The impact of hypoxia on beat-to-beat variability of the neonatal heart rate also varied with age. When the lambs were 2 to 3 weeks old, both the long- and short-term variabilities decreased progressively during hypoxia and the decrement reached a maximum at 10 minutes of oxygen deprivation. As the lambs became older, however, there was some initial and transient increase in the long- and short-term variabilities in the early period of hypoxia but thereafter the changes were inconsistent. The significance of these observations is discussed in terms of our knowledge of the pathophysiologic alterations in the cardiovascular system produced by acute hypoxia.

Aging↗
PubMed1980

Prolyl and lysyl hydroxylase activities of human skin fibroblasts: effect of donor age and ascorbate.

Prolyl and lysyl hydroxylase activities in cultures of human skin fibroblasts from fetal to 94-yr-old donors were measured. In contrast to earlier studies with whole skin, neither prolyl nor lysyl hydroxylase activity was found related to donor age. Prolyl hydroxylase activity increased 3- to 6-fold when cell extracts were incubated with ascorbate and other hydroxylation cofactors before assay. A similar increase in prolyl hydroxylase activity occurred when cells were incubated with ascorbate. Lysyl hydroxylase activity remained unaltered under these conditions.

Adolescent↗
PubMed1980

Midazolam and diazepam: maternal and fetal effects in the pregnant ewe.

Maternal and fetal hemodynamic effects and placental transfer of midazolam (RO 21-3981, Hoffman-LaRoche) and diazepam were studied in chronically instrumented pregnant ewes. Diazepam administration resulted in greater increases of maternal and fetal heart rates and maternal blood pressure, and greater alteration of total uterine blood flow than did administration of comparable doses of midazolam. Neither drug altered fetal mean arterial pressure or maternal and fetal respiratory gases. Although the absolute blood concentrations were higher, the fetal:maternal drug concentration ratios were consistently less for midazolam than for diazepam, suggesting less placental permeability of midazolam.

Animals↗