Effects of ethinyl estradiol on hepatic microsomal proteins and the turnover of cytochrome P-450.

The effect of ethinyl estradiol, a steroid commonly used in birth control pills and possibly associated with impaired drug metabolism in humans, on the activity of and turnover of components of the hepatic microsomal mixed-function oxidase system was studied in male rats. After 5 days of ethinyl estradiol, 5 mg/kg/day, there was a significant decrease in the activity of ethylmorphine-N-demethylase and in cytochrome P-450, cytochrome b2, and NADPH cytochrome c reductase. Cytochrome P-450 apoproteins were identified within an SDS-polyacrylamide gel system, and the rate of turnover of cytochrome P-450 apoproteins was studied by double-isotope labeling techniques.

Noradrenergic mediation of the positive reinforcing properties of ethanol: II. Extinction of ethanol-drinking behavior in laboratory rats by inhibition of dopamine-beta-hydroxylase. Implications for treatment procedures in human alcoholics.

Following stabilization of consumption of a 15% (v/v) ethanol solution in a free-choice with water, rats were presented with a forced-choice of ethanol for 10 consecutive alternate days. Prior to each forced-choice presentation experimental animals were injected with the non-toxic dopamine-beta-hydroxylase inhibitor FLA-57 (30 mg/kg i.p.

Stimulation of hepatic sodium and potassium-activated adenosine triphosphatase activity by phenobarbital. Its possible role in regulation of bile flow.

Since phenobarbital administration produces a profound increase in bile flow without changing bile acid secretion, we examined whether this drug increases the activity of hepatic sodium-potassium-activated ATPase [Na+-K+)-ATPase], the postulated regulating enzyme in the secretion of bile salt independent bile flow. After freeze-thawing to increase substrate accessibility, (Na+-K+) ATPase activity was determined by ouabain inhibition of total ATPase activity. Its activity was highest in isolated liver surface membrane fractions enriched in bile canalicult.

Hepatic alkaline phosphatase isoenzymes: isolation, characterization and differential alteration.

Although it is generally believed that hepatic alkaline phosphatase is localized to liver plasma membranes, 63% is present in the cytosol fraction after ultracentrifugation of rat liver homogenates. Divalent cation requirements, heat inactivation, pH optima, Km and chemical inhibition characteristics of partially purified alkaline phosphatase enzymes prepared from membrane and cytosol fractions suggested different structural forms. Furthermore, bile duct obstruction and ethinyl estradiol administration preferentially increased membrane-bound alkaline phosphatase activity, while cytosol activity was unaltered.

Adenosine 3':5'-monophosphate content and actions in the division cycle of synchronized HeLa cells.

The involvement of adenosine 3':5'-monophosphate (cAMP) in the regulation of the cell cycle was studied by determining intracellular fluctuations in cAMP levels in synchronized HeLa cells and by testing the effects of experimentally altered levels on cell cycle traverse. Cyclic AMP levels were lowest during mitosis and were highest during late G-1 or early S phase. These findings were supported by results obtained when cells were accumulated at these points with Colcemid or high levels of thymidine.

Apparent multiple forms of cyclic AMP phosphodiesterase from rat erythrocytes.

Bio-Gel A-5m chromatography has been used to separate apparent multiple forms of cyclic nucleotide phosphodiesterase from rat erythrocytes. Cyclic AMP phosphodiesterase was resolved by gel filtration into three peaks of activity with apparent molecular weights of about 300,000, 225,000 and 100,000, while cyclic GMP phosphodiesterase activity in gel column fractions was too low to permit meaningful estimates of its molecular weight. All three of the separated peaks of cyclic AMP phosphodiesterase activity displayed anomalous kinetic behaviour suggestive of negative cooperativity.

Cellular levels of feedback regulator of adenylate cyclase and the effect of epinephrine and insulin.

We have obtained direct evidence that shows the cellular formation and subsequent release of a potent inhibitor (feedback regulator) of adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.

Concepts for the rational selection of assays to be used in monitoring therapeutic drugs.

As the domain of monitoring therapeutic drugs rapidly expands from experimental investigations to everyday patient care, all clinical laboratory scientists, but especially clinical chemists, must learn to deal with their involvement in this expansion. First, the theoretical concepts underlying clinical pharmacology must be appreciated so that the laboratory's participation in it can succeed. Individual differences cause unpredictable variations of response to the customarily standardized drug dosage.

Action of feedback regulator on adenylate cyclase.

A factor [the feedback regulator (FR)] formed by adipocytes after the stimulation of a cAMP raising hormone has been found to be a potent inhibitor of membrane-bound adenylate cyclase [EC 4.6.1.

Hydrolysis of guanosine and adenosine 3',5'-monophosphates by rat blood.

Cyclic nucleotide phosphodiesterase activity was measured in whole blood, plasma, and suspensions of platelets and erythrocytes from rats. In fresh whole blood, apparent phosphodiesterase activity was low, but it rose strikingly during the hour after blood withdrawal. The apparent phosphodiesterase activity in platelet-free plasma showed no such increase, but that in platelet-enriched plasma increased in parallel with that in whole blood.

The importance of calcium ions for the regulation of guanosine 3':5'-cyclic monophosphage levels.

Guanosine 3':5'-cyclic monosphosphate (cyclic GMP) levels in the ductus deferens of the rat were increased 2- to 3-fold by acetylcholine (10-1000 muM) or by 125 mM KCl, while adenosine 3':5'-cyclic monophosphate (cyclic AMP) levels were not changed. After incubation for 30 min in the absence of Ca(++), cyclic GMP control levels were decreased by 85% and were not affected by acetylcholine or KCl. The readdition of Ca(++) (1.

A new enzymatic assay for guanosine 3':5'-cyclic monophosphate and its application to the ductus deferens of the rat.

A sensitive enzymatic procedure has been developed for the determination of guanosine 3':5'-cyclic monophosphate (cyclic GMP). It is based on the conversion of cyclic GMP to GMP by cyclic nucleotide phosphodiesterase and on the transfer of (32)P from [gamma-(32)P]ATP to GMP by the action of a specific ATP:GMP phosphotransferase (EC 2.7.

Effects of catecholamines and adrenergic-blocking agents on plasma and urinary cyclic nucleotides in man.

Studies were performed in healthy volunteers to determine the effects of catecholamines and adrenergic-blocking agents on plasma and urinary levels of adenosine 3',5'-monophosphate (cyclic AMP) and guanosine 3',5'-monophosphate (cyclic GMP). Plasma cyclic AMP rose in response to infusions of the beta-adrenergic agent, isoproterenol, or in response to infusions of either epinephrine or norepinephrine alone or in combination with the alpha-adrenergic-blocking agent, phentolamine. Although urinary cyclic AMP also rose, the percentage increase was less than that observed in the plasma.