The test detects compounds which inhibit lipid biosynthesis or stimulate lipid catabolism. Several drugs with ... to performance levels of the screen pre- ... Their tests were of two kinds. In the .... glass tissue grinder at a concentration of 2 mg/ml ...
Triton-Induced Hyperlipidemia in Rats as an Animal Model for Screening Hypolipidemic Drugs P.E. SCHURR, J.R. SCHULTZ and T.M. PARKINSON, Research Laboratories, The Upjohn Company, Kalamazoo, Michigan 49001
ABSTRACT
INTRODUCTION
We describe a screening test for hypolipidemic agents in which compounds are administered orally to fasted rats after a single intravenous injection of 225 mg Triton WR-1339/kg and serum cholesterol and triglycerides are measured 43 hr post-Triton. Conditions for the screen were established by studying interrelationships between serum cholesterol, triglycerides and Triton levels during the post-Triton period and the effects of Triton dose, route of administration and fasting on serum lipid levels and drug hypocholesterolemic activity. The test detects compounds which inhibit lipid biosynthesis or stimulate lipid catabolism. Several drugs with different mechanisms of action which are hypolipidemic in man, i n c l u d i n g nicotinic acid, Dthyroxine, triparanol, nafoxidine HC1 and clofibrate are active in this system. Results with standard hypolipidemic agents are reproducible and conform well to performance levels of the screen predicted from statistical analysis.
A single parenteral administration of Triton WR-1339 to adult rats produces a hypeflipidemia in which cholesterol, triglycerides and phospholipids increase to a maximum in about 20 hr and decrease thereafter. The majority of experimental evidence (1-8) supports the concept that Triton physically alters very low density lipoproteins, rendering them refractive to the action of lipolytic enzymes of blood and tissue. This prevents or delays their removal from blood and secondarily stimulates the synthesis of lipid, enhancing the hyperlipidemia. Garattini et al. (9) and Paoletti (10) suggested the use of Triton-induced hyperlipidemia as an approach to screen for or to differentiate the mechanism of action of hypolipidemic drugs. Their tests were of two kinds. In the "first phase" test the drug was given ip at the same time as Triton, and a decrease in hyperlipidemia 8 hr later compared to controls was taken as evidence of activity resulting from an inhibition of increased synthesis of cholesterol
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FIG. 2, Effects o f Triton dose a n d fasting on serum tfiglycerides.
FIG. 1. Effects o f Triton dose and fasting on serum cholesterol.
68
TRITON-INDUCED HYPERLIPIDEMIC RATS
69
TABLE I Effects of Triton Dose and Fasting on Serum Cholesterol and Triglycerides Serum cholesterol, mg/d 1a
Serum triglycerides, mg/d 1a
Triton dose, mg/kg
Time postTriton, hr
250
Triton dose, mg/kg
350
450
250
350
450
24
Prefasted Not prefasted
374• 389•
455• 490__+7
496• 545•
1526• 1615•
2504• 2944• 3270__+23 4386•
36
Prefasted Not prefasted
302• 220•
504__+22 527•
572• 626•
695• 234•
1808• 2841• 2473__+24 3810•
48
Prefasted Not prefasted
2054"20 141•
436__+21 413•
614• 604__--+9
183• 64•
1106• 853•
2420• 2667•
aMean • % standard deviation. and f a t t y acids. In the " s e c o n d p h a s e " test the drug was given 22-24 h r after Triton, and decreased b l o o d lipids 8 hr later c o m p a r e d t o
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=ontrols was interpreted as an indication of the
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drug's ability t o accelerate lipid removal. In this c o m m u n i c a t i o n we describe a screenhag test for h y p o l i p i d e m i c drugs in w h i c h the agents were a d m i n i s t e r e d orally to rats
immediately following and 20 hr after intraJenous injection of Triton, and activity was determined by measuring serum cholesterol and triglycerides 43 hr post-Triton. Thus one test detects c o m p o u n d s w h i c h affect lipid synthesis, removal, or b o t h . The i n f l u e n c e o f Triton dose, route o f a d m i n i s t r a t i o n and fasting on h y p e r i p i d e m i c r e s p o n s e o f t h e animals, their sensi:ivity t o c h o l e s t e r o l - l o w e r i n g drugs, and the ~bility o f the screen to d e t e c t several drugs ?reviously d e m o n s t r a t e d t o be h y p o l i p i d e m i c in ~xperimental animals or m a n b y d i f f e r e n t aaechanisms o f action were investigated. EXPERIMENTAL PROCEDURES ~,nimals and Diet
Male albino rats derived f r o m the Sprague-
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FIG. 3. Serum levels of cholesterol, triglycerides and Triton following Triton administration. Dawley strain o b t a i n e d f r o m the U p j o h n r o d e n t c o l o n y ( U p j : T U C ( S D ) s p f ) were h o u s e d in groups o f five animals and allowed free access to f o o d and w a t e r for at least 21 days b e f o r e being d i s t r i b u t e d by weight i n t o e x p e r i m e n t a l groups. The diet o f Phillips and Berg (11) was used, w i t h 10% c o c o n u t oil s u b s t i t u t e d for corn
TABLE II Cholesterol Lowering Activity of U-10,387 and U-23,469 in Triton-Induced Hyperlipidemic Rats Serum cholesterol, mg/dl Triton WR-1339 dose, mg/kg
Control
U-10,387, (5 mg/kg)
200 250 300 350 400 450
116 247 340 509 583 619
74 a 157 a 279 414 a 508 a 545 a
U-23,469, (25 mg/kg) 75 a 181 a 307 471 527 592
Standard deviation, % 18 35 27 13 16 7
aSignificantly different from control.
LIPIDS, VOL. "7, NO. 1
70
P.E. S C H U R R , J.R. S C H U L T Z AND T,M. P A R K I N S O N
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