William C. Lubawy

Impact of Insulin or Tolbutamide Treatment on 14C-Arachidonic Acid Conversion to Prostacyclin and/or Thromboxane in Lungs, Aortas, and Platelets of Streptozotocin-induced Diabetic Rats

Diabetes is associated with a dramatic increase in the risk of thrombotic and atherosclerotic disease. The underlying factors responsible for this predisposition as well as the mechanisms involved have yet to be elucidated. Two endogenous substances, prostacyclin (PGI2) and thromboxane (TXA2), have recently been shown to possess significant vascular and thrombotic activity and are known to be altered in atherosclerosis, thrombotic conditions, and diabetes. We determined the conversion of 14C-arachidonic acid (AA) to PGI2 and TXA2 by lungs, aortas, and platelets obtained from chemically induced diabetic rats. In addition, we investigated the ability of insulin or tolbutamide to reverse these changes. Streptozotocin (STZ)-injected rats developed blood glucose levels 2–4 times that seen in normoglycemic controls. Intact perfused lungs isolated from rats beginning 7 days after STZ treatment synthesized 22–30% less PGI2 from 14C-AA. The ratio of PGI2/ TXA2 was decreased in the diabetic rat lungs and was inversely proportional to plasma glucose levels at the time of death. Platelet TXA2 generation was increased 67% above control in diabetic rats while aortic PGI2 generation was decreased 28% below normoglycemic controls. Ten-day treatment with NPH insulin 20 U/kg s.c. in STZ-pretreated rats lowered plasma glucose toward normoglycemia more effectively than tolbutamide 200 mg/kg orally. Partial correction of the decreased pulmonary PGI2/TXA2 ratio seen in diabetic rats was produced by insulin and tolbutamide in proportion to their ability to lower blood glucose. At the doses employed, insulin caused aortic PGI2 and platelet TXA2 generation from 14C-AA to approach that seen in normoglycemic controls more effectively than tolbutamide. An inverse correlation with plasma glucose levels was observed for pulmonary PGI2/TXA2 ratios as well as aortic PGI2 generation, r = −0.72 and −0.74, respectively. Platelet TXA2 generation correlated posi-tively with plasma glucose, r = 0.69. This study indicates that metabolism of 14C-AA by pulmonary tissue, platelets, and aortas is altered by experimentally induced diabetes. Furthermore, these findings suggest that such alterations can be partially reversed by regulation Of the diabetic condition.

Lung, aorta, and platelet metabolism of 14C-arachidonic acid in vitamin E deficient rats

14C-arachidonic acid metabolism was determined in aortas, platelets, and perfused lungs from rats pair fed a basal diet supplemented with 0 or 100 ppm vitamin E for 11 weeks. Spontaneous erythrocyte hemolysis tests showed 92% and 8% hemolysis for the 0 and 100 ppm vitamin E groups, respectively. Elevated lung homogenate levels of malonaldehyde in the 0 ppm group confirmed its deficient vitamin E status. Aortas from the vitamin E deficient group synthesized 54% less prostacyclin than aortas from the supplemented group (p less than 0.05). Although thromboxane generation by platelets from the vitamin E deficient group exhibited a 37% increase, this difference was not statistically significant compared to the supplemented animals. Greater amounts of PGE2, PGF2 alpha, TXB2, and 6-keto-PGF1 alpha were obtained in albumin buffer perfusates from lungs of vitamin E deficient rats than in those from supplemented rats. Significant differences (p less than 0.05) were noticed, however, only for PGE2 and PGF2 alpha. These studies indicate that vitamin E quantitatively alters arachidonic acid metabolism in aortic and lung tissue but its effect on thromboxane synthesis by platelets is less marked.

Chronic cigarette smoke exposure adversely alters 14C-arachidonic acid metabolism in rat lungs, aortas and platelets.

Male rats were exposed to freshly generated cigarette smoke once daily, 5 times a week for 10 weeks. Inhalation of smoke was verified by elevated carboxyhemoglobin in blood sampled immediately after smoke exposure and by increased lung aryl hydrocarbon hydroxylase activity 24 hours after the last smoke exposure. Aortic rings isolated from smoke-exposed rats synthesized less prostacyclin (PGI2) from 14C-arachidonic acid than rings from sham rats. Platelets from smoke-exposed rats synthesized more thromboxane (TXA2) from 14C-arachidonic acid than platelets from room controls but not those from sham rats. Lung microsomes from smoke-exposed rats synthesized more TXA2 and had a lower PGI2/TXA2 ratio than lung microsomes from room controls and shams. It is concluded that chronic cigarette smoke exposure alters arachidonic acid metabolism in aortas, platelets and lungs in a manner resulting in decreased PGI2 and increased TXA2, thereby creating a condition favoring platelet aggregation and a variety of cardiovascular diseases.

Streptozocin-induced diabetes decreases formation of prostacyclin from arachidonic acid in intact rat lungs.

Abstract Diminished vascular prostacyclin (PGI 2 ), as well as elevated platelet thromboxane (TXA 2 ) generation is known to occur in diabetes and may be involved in the thrombotic and atherosclerotic complications of this disease. Pulmonary tissue synthesizes both PGI 2 and TXA 2 ; however, alterations in the generation of these substances in diabetic lungs has not been reported. We determined PGI 2 and TXA 2 generation from 14 C arachidonic acid in isolated perfused lungs obtained from male rats 1 and 14 days after a 50 mg/kg i.v. dose of streptozocin or the citrate-buffer vehicle. Compared to controls, lungs from rats made diabetic for 14 days showed a 30% decrease in PGI 2 generation with no change in TXA 2 . A direct inverse relationship of pulmonary PGI 2 TXA 2 ratios to plasma glucose levels for the 14-day diabetic rats occurred ( r 2 = −0.886). The 1-day study showed no difference between control and diabetic rats which suggests that alterations in arachidonic acid metabolism observed after 14 days are the result of the diabetic condition and not streptozocin. These data indicate that pulmonary PGI 2 synthesis is altered by diabetes of short duration in a manner similar to vascular tissue.

Increase of hexobarbital sleeping time and inhibition of drug metabolism by the major metabolite of diphenylhydantoin

Abstract The major metabolite of diphenylhydantoin, 5-(p-hydroxyphenyl)-5-phenylhydantoin, has been shown to inhibit hexobarbital and ethylmorphine metabolism by a rat liver homogenate, and to markedly prolong hexobarbital sleeping time in mice. Such cross-inhibition of metabolism among drugs which are detoxified by formation of hydroxylated metabolites represents an example of a drug-drug interaction which must be taken into account when describing the behavior of drugs in the body.

Cigarette smoke exposure alters [14C] arachidonic acid metabolism in aortas and platelets of rats fed various levels of selenium and vitamin E

Rats were placed on a basal diet supplemented with 0, 0.03, or 3 ppm selenium and 0 or 20 ppm vitamin E for 41-43 wk. Selenium deficiency decreased hepatic glutathione peroxidase activity and lowered both aortic prostacyclin (PGI2) and platelet thromboxane (TXA2) production compared to selenium- and vitamin E-supplemented animals. Vitamin E deficiency increased hepatic lipid peroxidation and decreased aortic PGI2 synthesis. Rats exposed daily for 31-32 wk to fresh smoke from a UK 2R1 reference cigarette had carboxyhemoglobin levels of 0.75 +/- 0.12 and 4.73 +/- 0.12% in sham- and smoke-exposed groups, respectively. Animals chronically exposed to cigarette smoke displayed a nearly twofold increase in pulmonary arylhydrocarbon hydroxylase activity. Smoke exposure produced a 26-33% decrease in aortic PGI2 synthesis compared to shams in the Se3E20, Se0.03E20, and Se3E0 groups. Smoking also increased platelet thromboxane 91% and 98% in the Se3E20 and Se3E0 groups compared to shams. It is concluded that cigarette-smoke exposure and selenium or vitamin E deficiency alter aortic PGI2 and platelet TXA2 production.

The effect of acute tobacco smoke exposure on pulmonary benzo[a]pyrene metabolism

Abstract The influence of whole tobacco smoke or the gas phase from smoke on the pulmonary metabolism of [14C]benzo[a]pyrene was examined. [11C]Benzo[a]pyrene disappears from plasma-perfusing isolated rabbit lungs according to first-order kinetics. When these lungs are ventilated with freshly generated whole cigarette smoke, the slope of [14C]benzo[a]pyrene disappearance curves are altered dramatically; the amount of this alteration is dependent on the dose of smoke administered. If the particulate phase is filtered out of the smoke and the resulting gas phase is administered to the lung, relatively little effect is seen. These results suggest that the acute effect of whole smoke on benzo[apyrene metabolism by the isolated perfused lung is inhibition and that this effect is primarily due to the materials present in the particulate phase of smoke.

Influence of pretreatment with tobacco smoke condensate or 3-methylcholanthrene on [14C] benzo (A) pyrene metabolism in the isolated perfused rabbit lung

Pretreatment 24 h before sacrifice with i.p. tobacco smoke condensate (TSC) or 3-methylcholanthrene (3MC) increased the rate of disappearance of [14C]benzo(a)pyrene (BP) from an isolated perfused rabbit lung model. Both pretreatments significantly increased the amount of most metabolites formed. This study indicates that rabbits tend to resemble rats, mice and hamsters in that increased rates of pulmonary BP metabolism are a consequence of exposure to TSC.

Increasing lipid peroxidation by vitamin E deficiency does not augment adriamycin-induced inhibition of hepatic drug metabolism☆

Adriamycin treatment in vivo or addition to incubation mixtures in vitro inhibits hepatic drug metabolism. It has been suggested that adriamycin-induced membrane lipid peroxidation may be a mechanism responsible for this activity in vitro. To determine if similar mechanisms operate in vivo, adriamycin inhibition of drug metabolism was compared in rats whose tissue lipid peroxidizability was altered by manipulating dietary levels of vitamin E. Weanling rats maintained on vitamin E deficient (0 ppm) or supplemented (10 or 100 ppm) diets for 12 weeks were given either adriamycin, 5 mg/kg/week, or equal volumes of the saline vehicle for 3 weeks intraperitoneally. Vitamin E deficiency alone (0 ppm, saline pretreatment) produced a 37% increase in hepatic lipid peroxidation without any appreciable alteration in hepatic aniline hydroxylase, ethylmorphine N-demethylase or aryl hydrocarbon hydroxylase activities. Adriamycin pretreatment altered hepatic lipid peroxidizability over corresponding saline pretreated controls dependent on dietary vitamin E. No increase was seen in the 100 ppm group, while 44% and 500% increases occurred at 10 and 0 ppm vitamin E, respectively. Adriamycin pretreatment decreased drug-metabolizing enzyme activity by an average of 32% for aniline hydroxylase, 26% for ethylmorphine N-demethylase and 63% for aryl hydrocarbon hydroxylase. Statistically, decreases in drug metabolism were independent of dietary vitamin E and did not correlate with lipid peroxidizability. These data would suggest that in vivo adriamycin-induced depression of hepatic drug-metabolizing enzymes is not mediated by elevated lipid peroxidation.

A Novel Question-based Framework for Writing Assessment Plans to Facilitate Their Understanding and Acceptance in Pharmacy Education

To the Editor. For over half my 40 years in pharmacy education the word “assessment” and the phrase “assessment planning” have prompted my colleagues’ eyes to glaze over and their ear canals to close. Two colleagues even told me those words activated their autonomic nervous system and immediately tightened several sphincters. I was no different.