Harry M. Vars

Biliary Excretion of Cholic Acid and Cholesterol in Hyper-, Hypo-, and Euthyroid Rats.

Summary 1. Hyper- and hypothyroid rats have been prepared and, along with euthyroid control rats, have been subjected to cannulation of the common bile duct and total daily bile collection for 7 days following cannulation, 2, Analysis of this bile for cholesterol and cholic acid revealed that the excretion of cholesterol is a reflection of the level of thyroid activity, and that cholic acid excretion is lowered in both hyper- and hypothyroidism. 3. After the third postoperative day, the ratio of cholic acid to cholesterol excreted in the bile was found to be relatively constant for each type of animal. 4. Cholic acid and cholesterol excretion in the bile was suppressed in both the hyper- and hypothyroid rats in the immediate postoperative period. In 3 or 4 days following cannulation, these levels reached a plateau.

Postoperative Oral and Intravenous Nutrition

Oral and intravenous high calorie-amino acid nutritional therapy postoperatively resulted in significant weight gain, improved colonic wound healing and maintenance of normal intravascular albumin levels. Provision of caloric needs without amino acids minimized weight loss postoperatively. However, infusion of hypertonic dextrose solutions resulted in severe generalized hepatic fatty infiltration and marked hypoalbuminemia. Protein and calorie deprivation by administration of 5% dextrose and water resulted in the greatest postoperative weight loss, reduced intravascular albumin levels and decreased colonic anastomotic strength. Comparison of oral and intravenous diet administration demonstrated that hypertonic dextrose infusion was markedly deleterious to hepatic morphology and serum protein metabolism in normal rats. Further clinical investigation appears indicated in previously well-nourished patients undergoing extensive surgery who will not be able to ingest adequate nutrients in the postoperative period.

Response to fasting of hepatic arginase, alkaline phosphatase, and rhodanese in protein-depleted rats.

Summary When protein-depleted rats were subjected to 4 days of fasting, the arginase content of the liver increased by 58% while the alkaline phosphatase content decreased by a similar percentage. A simultaneous smaller increment of the rhodanese content was limited to the first 2 days of fasting. The experiments indicate that the initial increase in arginase activity was due to a nonspecific increase in hepatic protein while the later rise was a specific response probably related to the increased protein catabolism.

Various plasma expanders in animals.

In the process of evaluating the merits of a plasma expander, its safety and efficacy under various experimental situations must be determined. Attention is focused particularly upon the following: (a) storage, or retention in any particular organ system; (b) blood retention and urinary excretion; (c) metabolic fate; (d) pharmaco-dynamic effects upon the various elements of the circulatory system; and (e) oncotic efficacy as exemplified by its ability to maintain an adequate plasma volume. I n each category, animal experimentation is a necessary precursor of extensive clinical trial. Only in such manner can the potential value or hazards of a suggested plasma expander be assessed. In certain instances, there may be peculiar species-sensitivities to individual substances which limit the usefulness of certain tests. This occurrence, however, is of interest, and may throw light upon unsuspected pharmacologic properties of the material being studied. At present, there are several types of substances available as suggested plasma expanders, some of which have had extensive experimental study. These include (a) gelatin, prepared from bone ossein or pork skin; (b) oxypolygelatin, a gelatin preparation chemically treated to reduce the gelation temperature of the product; (c) dextran, a polysaccharide elaborated by a micro-organism (Leuconostoc mesenferoides) which, after purification, is hydrolysed and fractionated to give a suitable molecular size; (d) polyvinypyrrolidone, a synthetic polymer produced by the controlled polymerization of vinylpyrrolidone with subsequent fractionation. Two materials that have had only preliminary experimental trials are: (a) pectin, a polyuronide, fractionated and purified from natural sources; (b) polyglucose, a product produced by the chemical polymerization of glucose. In our own investigations, attention has been focused particularly upon the efficacy of the various plasma expanders in maintaining the plasma volume after two types of shock procedures involving hemorrhage in the dog. Besides observing their oncotic effect, ancillary data upon a variety of physiologic reactions have been obtained. Investigations have also been made of the plasma retention, urinary excretion, and metabolic fate of certain of the expanders. Two procedures for evaluating plasma expanders in hemorrhagic-shocked dogs have been employed. They were developed during the period 1942 to 1945, and had an extensive trial in our laboratories by Drs. Parkins and HamilCarefully selected, healthy dogs are bled, under light nembutal anesthesia, at a standard uniform rate to a mean blood pressure of 20 mm. Hg, and are infused immediately with a volume of and in the laboratory of Dr. Lawson.4

Comparison of the Induction Course, Biophysical Chemical Interactions and Photochemical Action Spectra of Phenobarbital and 3-Methylcholanthrene Induced Hepatic Microsomal P-450

A comparison has been made of the physical and chemical properties of hepatic microsomal P-450 and associated enzyme systems from rats treated with phenobarbital or with 3-methylcholanthrene and other polycyclic aryl hydrocarbons. The results of these studies, though preliminary in nature, indicate clearly that the aryl-induced mixed-function oxidase systems differ significantly from the PB-induced ones in time course of induction, spectral properties, hyroxylase and demethylase activities, CO-inhibition of these reactions and light-reversal of the inhibition. The results support and extend the findings of other investigators regarding the differential biophysical and biochemical properties of aryl-induced systems and provide an experimental design for studying these properties in greater depth at the maximum of aryl induction.

INDUCTION OF CYTOCHROME P-450 BY LONG-TERM INFUSION OF PHENOBARBITAL

ABSTRACT A procedure is described for studying the induction of hepatic enzyme systems by long-term continuous intraperitoneal infusion of drugs at constant rates into rats. Its purpose is to prevent the fluctuations of the tissue levels of inducers associated with intermittent injections or their uptake with the drinking water. It was found that phenobarbital (PB), the inducer studied, can be infused at a rate of 80 mg/kg/day for at least three weeks without affecting activity, food consumption, and weight gain of the animals. Preliminary data are reported on the induction response to PB with this method in comparison with intermittent intraperitoneal administration. Up to a total dose of 320 mg PB/kg, induction of cytochrome P-450 in terms of specific microsomal concentration as well as total liver content was a linear function of the total dose irrespective of the method of administration used: daily injection of 80 mg/kg for four days, of 40 mg/kg every 48 hours for 16 days or continuous infusion at this dose level for six days–a novel and unexpected finding. The effect of higher accumulative doses of PB, up to 1680 mg/kg, was studied with the infusion technique. Maximal induction of PB was reached after a total dose of 560 mg/kg. The same held true for induction of demethylation activities toward codeine and ethylmorphine. The results indicate that the optimal or limiting dose for induction of PB, as observed by previous investigators, cannot be exceeded by continuous infusion of PB. Exploratory experiments have shown that urinary elimination of PB, which never exceeds 30% of the administered daily dose, drops to 9% when the limiting total dose is being reached, suggesting that conversion of the inducer to an inactive metabolite causes the limiting dose phenomenon. Experiments to establish such a relationship are in progress.