PubMed Health⌕ Search

Biomedical subjects

N B Stamm

Publications and source records attributed to N B Stamm.

At least 19 recordsLinked to original sources
PubMed1999

Conditional transformation of rat embryo fibroblast cells by a cyclin D1-cdk4 fusion gene.

Cyclin D1 gene overexpression is a frequent event in a number of human cancers. These observations have led to the suggestion that cyclin D1 alterations might play a role in the etiology of cancer. This possibility is supported by the finding that transfection of mammalian cells with cyclin D1 can accelerate progression through the G1 phase of the cell cycle. Moreover, cyclin D1 can function as an oncogene by cooperating with activated Ha-ras to transform primary rat embryo fibroblasts (REFs). In addition, cyclin D1 transgenics develop hyperplasia and neoplasia of the thymus and mammary gland. We have constructed a novel fusion gene consisting of full-length human cyclin D1 and cdk4 genes. This fusion gene was expressed in insect cells and the fusion protein was shown to be enzymatically active. The fusion gene was expressed in mammalian cells under the control of tet-repressor. This fusion gene immortalized primary REFs, and cooperated with activated Ha-ras to transform primary REFs, in terms of anchorage-independent growth in vitro and formation of tumors in vivo. Utilizing a tet-regulated gene expression system, we have shown that proliferation of stably transfected primary REFs in vitro and in vivo is dependent on the continued expression of the cyclin D1-cdk4 fusion gene. These cell lines could be useful in the discovery of novel cancer therapeutics to modulate cyclin D1.cdk4 activity.

Animals↗
PubMed1993

LY191704: a selective, nonsteroidal inhibitor of human steroid 5 alpha-reductase type 1.

Androgens, in particular dihydrotestosterone (DHT), play a key role in differentiation, growth, and maintenance of the mammalian prostate. Production of DHT from testosterone is catalyzed by two distinct membrane-bound steroid 5 alpha-reductase [5 alpha-reductase; 3-oxo-5 alpha-steroid delta 4-dehydrogenase; 3-oxo-5 alpha-steroid:(acceptor) delta 4-oxidoreductase, EC 1.3.99.5] isozymes designated types 1 and 2. Benign prostatic hyperplasia (BPH), a disease that occurs almost universally in males, is characterized by obstructive and irritative urinary voiding symptoms and has been associated with an overproduction of DHT. Recently, steroidal inhibitors of 5 alpha-reductase type 2 have been used successfully for treatment of BPH. Described here is a nonsteroidal inhibitor of 5 alpha-reductase type 1, LY191704 (8-chloro-4-methyl-1,2,3,4,4a,5,6,10b-octaahydro-benzo[f]quinol in-3(2H)-one). This compound was identified based on its capacity to inhibit 5 alpha-reductase activity in a human genital skin fibroblast cell line (Hs68). Surprisingly, LY191704 is inactive when tested in freshly isolated prostate cells obtained from subjects with BPH, whereas previously described 4-azasteroids are active. LY191704 is, however, a potent inhibitor of the 5 alpha-reductase activity of BPH cells that have been maintained in culture. Analysis of human and rat 5 alpha-reductases expressed from transfected cDNAs in simian COS cells indicates that LY191704 is a specific noncompetitive inhibitor of the human 5 alpha-reductase type 1. Taken together, the results suggest that prostate cells have the capacity to express both 5 alpha-reductase isozymes and that LY191704 may be useful in treatment of human endocrine disorders associated with overproduction of DHT by 5 alpha-reductase type 1.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
PubMed1993

LY207320 (6-methylene-4-pregnene-3,20-dione) inhibits testosterone biosynthesis, androgen uptake, 5 alpha-reductase, and produces prostatic regression in male rats.

LY207320 is an in vitro inhibitor (estimated IC50 = 0.06 microM) of steroid 5 alpha-reductase that catalyzes the conversion of testosterone (T) to dihydrotestosterone (DHT). In contrast, LY207320 was only moderately active against rat prostatic 5 alpha-reductase in vivo (32% inhibition at 50.0 mg/kg single dose). LY207320 did, however, inhibit the in vivo uptake of [3H]-T by the prostate. The antiprostatic and endocrine effects of this agent were evaluated following daily (21 days) administration to castrated, androgen-supplemented castrate, and intact rats. LY207320, which has modest progestational competitive binding activity, does not bind to rat prostatic androgen or uterine estrogen cytosolic receptors. In the castrated male rat, subcutaneously (s.c.) administered LY207320 had no androgen agonist activity, as evidenced by a lack of accessory sex organ weight gains. Administration of s.c. LY207320 to intact rats for 21 days at doses greater than 5.0 mg/kg-day produced significant (P < 0.05) reductions of seminal vesicle and ventral prostatic weights (maximal regression = -65% and -40% from control values, respectively at 50.0 mg/kg-day). The compound had no regressive activity on male accessory sex organs when administered orally. LY207320 did not alter circulating prolactin, LH, or corticosterone levels, but at high doses (> or = 50.0 mg/kg-day), lowered circulating T[-67% from intact control levels (P < 0.05)]. Histological analysis of the rat ventral prostates (RVPs) in LY207320-treated rats was consistent with an androgen-deprived state. Decreased circulating androgens and prostatic regression are associated with inhibition of testicular 17 alpha-hydroxy/C17,20-lyase enzyme activity (IC50 = 0.06 microM). These findings support the contention that LY207320 is a physiological antagonist of androgen action in male rats, and that its effects are mediated primarily through inhibition of testicular androgen production rather than accessory sex organ 5 alpha-reductase.

Aldehyde-Lyases↗
PubMed1984

Thermogenesis and weight control.

Compound LY104119, [R-(R*,S*)]-4-[3-[(2-hydroxy-2-phenylethyl)amino]butyl]benzamide monohydrochloride, was found to be a potent beta-agonist in the mouse. Its Ki for displacing the binding of (-)-3H-dihydroalprenolol to beta-receptors on the lung membranes from either viable yellow obese mice (VY/WfL-Avy/a) or their corresponding normal controls (VY/WfL-a/a) was 3 X 10(-7) M, comparable to that of isoproterenol which was 2 X 10(-7) M. LY104119 increased the concentration of cyclic AMP in adipose tissue, stimulated lipolysis in vitro and in vivo and the expiration of CO2 in vivo. When given s.c. or p.o., LY104119 reduced the body weight of Avy/a mice without altering the food consumption. The loss of triacylglycerol accounted for a major portion of the weight loss and the weight was recovered after the treatment was withdrawn. When fed in the diet, LY104119 reduced the weight of Avy/a mice and caused a moderate increase of food intake. Thermogenesis (whole body heat production) of the treated mice increased. An elevated level of hepatic glucokinase activity regularly found in these mice was almost normalized to the level measured in normal mice. The kinetic properties of the beta-receptors were not altered, but the number of beta-receptors on lung membranes was reduced about 25 percent. The lipolytic response of epididymal adipose tissue to LY104119 or isoproterenol, however, was not changed. When slightly overweight a/a mice were treated with LY104119 in the diet, they lost weight, but a similar treatment of normal-weight a/a mice caused a loss of only a small amount of carcass triacylglycerol without affecting the body weight. These normal-weight a/a mice were able to maintain their weight by an exorbitant increase of food intake. When this large increase of food consumption was not allowed, ie by being restricted to normal amounts of food intake, normal-weight a/a mice fed LY104119 did lose weight. Thermogenesis increased in all LY104119-treated a/a mice. However, the increase in the LY104119-treated but diet-restricted a/a mice was smaller than that in the LY104119-treated a/a mice fed ad libitum. We conclude from these observations that: Compound LY104119 was able to decrease weight in Avy/a mice apparently through the stimulation of the beta-adrenergic system. The metabolic responses to LY104119 were not different in obese Avy/a mice and normal a/a mice. The difference between the Avy/a mice and the a/a mice was in their ability to increase their food consumption to compensate for the energy loss caused by LY104119.

2-Hydroxyphenethylamine↗
PubMed1983

Stimulation of cyclic AMP and lipolysis in adipose tissue of normal and obese Avy/a mice by LY79771, a phenethanolamine, and stereoisomers.

The stimulation of cyclic AMP and lipolysis by LY79771, a phenethanolamine antiobesity compound, and its 3 stereoisomers in adipose tissue of obese viable yellow mice and normal mice were studied. Both activities were stereo-specific with LY79771, the R,S isomer, and LY79730, the R,R isomer, being more potent than LY103085, the S,S isomer, and LY103672, the S,R isomer. Propranolol, a nonspecific beta-antagonist, completely inhibited the elevation of cyclic AMP and lipolysis whereas atenolol, a specific beta 1 antagonist, inhibited the elevation of cyclic AMP but did not completely inhibit lipolysis. These findings indicate that the elevation of cyclic AMP was mediated by the beta 1-receptor whereas the stimulation of lipolysis was mediated by both the beta 1 and beta 2 receptors. The adipose tissue of the obese viable yellow mice responded to these compounds less than that of the normal mice.

2-Hydroxyphenethylamine↗
PubMed1981

Constitutive hepatic glucokinase activity in db/db and ob/ob mice.

The specific activity of hepatic glucokinase (ATP: D-glucose 6-phosphotransferase, EC 2.7.1.2) in db/db mice and ob/ob mice was higher than in normal mice. All enzymes had a similar Km and, thus, the difference in activity was not due to differences in the affinity of enzyme molecules to substrates. Mixing liver extracts with high or low enzyme activities yielded additive results, as expected, which ruled out the involvement of an inhibitor or activator of the enzyme. Fasting normal mice of either strain for three days decreased glucokinase activity. However, fasting db/db or ob/ob mice for as long as 10 days had no effect on enzyme activity, indicating that glucokinase in db/db or ob/ob mice was out of regulation or constitutive. The constant, abnormally high glucokinase activity may be a contributing factor to the obesity of ob/or or db/db mice. These mice provide a model system to study the regulation of this rate-limiting enzyme of glucose metabolism.

Animals↗
PubMed1981

Lowering of blood pressure by direct- and indirect-acting serotonin agonists in spontaneously hypertensive rats.

1-(m-Trifluoromethylphenyl)piperazine, a serotonin agonist, lowered blood pressure in spontaneously hypertensive rats (SHR) at doses of 2 to 10 mg/kg s.c. A structurally related compound lacking serotonin agonist activity, 4-(m-trifluoromethylphenyl)piperidine, was ineffective. Quipazine, another serotonin agonist, lowered blood pressure in SHR at doses of 0.1 to 2 mg/kg s.c. Fenfluramine, a serotonin-releasing drug, lowered blood pressure in SHR at doses of 2 and 5 mg/kg s.c. Metergoline (3 mg/kg s.c.), a serotonin antagonist, elevated blood pressure and prevented the decrease by all of the above agents. These findings are consistent with the view that enhancement of central serotonergic function lowers blood pressure in SHR.

Animals↗
PubMed1980

Hepatic insensitivity to glucagon in ob/ob mice.

Hepatic cAMP concentration of normal mice increased 40 fold within 10 min after a single dose of glucagon (2 mg/kg, IP). In contrast, hepatic cAMP increased only 2 fold in ob/ob mice. Glucagon induced hepatic L-phenylalanine:pyruvate aminotransferase and stimulated glycogenolysis in normal mice but failed to elicit these cAMP-mediated responses in ob/ob mice. The insensitivity of ob/ob mice to glucagon was not ameliorated by fasting or by theophylline.

Animals↗
PubMed1966

Feedback inhibition of key glycolytic enzymes in liver: action of free fatty acids.

Increasing concentrations of sodium octanoate were progressively inhibitory to the activities of glucokinase, hexokinase, phosphofructokinase, and pyruvate kinase. Glucose-6-phosphate and 6-phosphogluconate dehydrogenases were also markedly inhibited. Other enzymes of carbohydrate metabolism such as lactate dehydrogenase, phosphohexose isomerase, and fructose-1,6-diphosphatase were not decreased. Among the key glycolytic enzymes, the inhibition of pyruvate kinase by the fatty acid was most marked. The biological significance of the inhibition of the key glycolytic enzymes is interpreted as a feedback inhibitory mechanism in regulation of fatty acid biosynthesis. The mechanism may function for rapid adaptation by which the organism can use the fatty acid level as a metabolic directional switch in decreasing glycolysis and turning on gluconeogenesis.

Animals↗