Portal and aortic blood sampling technique in unrestrained rats

Efficiency and safety of a technique for drawing blood from the hamster cranial vena cava

The authors evaluated the efficiency and safety of a technique for drawing blood from the cranial vena cava of the hamster (Mesocricetus auratus). They collected blood from Golden Syrian hamsters (n = 15) and from epileptic hamsters (GASH/Sal strain; n = 10) that were anesthetized with isoflurane. Four epileptic hamsters constituted a control group that underwent anesthesia but not blood collection. For blood sampling, a needle connected to a syringe was inserted at a site between 0.2 and 0.6 cm from the manubrium; the depth of insertion was 0.3-1.0 cm. Blood collection was successful in all hamsters except one, and the volume of collected blood ranged from 0.2 ml to 1.5 ml. All hamsters recovered quickly from the procedure, and none showed obvious signs of pain or stress. At necropsy (24 h after the procedure), six subjects showed small local hematomas, and eight showed vascular lacerations of limited severity. Lungs and hearts did not show any damage related to vein puncture. This relatively simple blood collection technique seems to be efficient and safe in hamsters.

Opposite effects of bezafibrate and gemfibrozil in both normal and hypertriglyceridemic rats

Chow and sucrose-fed rats were used as animal models to study the dose-responses of bezafibrate and gemfibrozil in normolipidemic and hypertriglyceridemic states, respectively. Although both drugs lowered plasma triglycerides (TG) to about the same extent in chow-fed rats, gemfibrozil lowered liver TG as well as plasma total and LDL-cholesterol (LDL-C), but elevated HDL-cholesterol (HDL-C) and plasma apo E concentrations. Bezafibrate produced opposite effects, namely, decreased HDL-C, apo E and liver TG, and tended to increase LDL-C. TG lowering for both drugs in chow-fed rats was not due to changes in TG secretion (production) in normal rats but was associated with enhanced LPL activity. In hypertriglyceridemic rats both drugs modestly reduced TG secretion rates about 40% at a dose producing maximal TG lowering, but again, gemfibrozil elevated and bezafibrate lowered HDL-C and apo E. Unlike gemfibrozil, bezafibrate induced the appearance of LDL-C in hypertriglyceridemic rats which was not detected in control animals, and also tended to increase rather than decrease plasma apo B levels. Finally, changes in liver TG concentration (mg/g) in hypertriglyceridemic rats were opposite for these drugs, resulting in significant drug-related differences in liver TG content (mg/organ). From these data we postulate that, although similar with regard to TG lowering activity and mechanisms thereof, gemfibrozil and bezafibrate produce fundamentally different effects on LDL, HDL and apolipoprotein metabolism (apo B and apo E) in rats which may relate to potential differential effects on reverse cholesterol transport and atherogenesis.

Role of the direct and indirect pathways for glycogen synthesis in rat liver in the postprandial state

The pathway for hepatic glycogen synthesis in the postprandial state was studied in meal-fed rats chronically cannulated in the portal vein. Plasma glucose concentration in the portal vein was found to be 4.50 +/- 1.01 mM (mean +/- SE; n = 3) before a meal and 11.54 +/- 0.70 mM (mean +/- SE; n = 4) after a meal in rats meal-fed a diet consisting of 100% commercial rat chow for 7 d. The hepatic-portal difference of plasma glucose concentration showed that liver released glucose in the fasted state and either extracted or released glucose after feeding depending on plasma glucose concentration in the portal vein. The concentration of portal vein glucose at which liver changes from glucose releasing to glucose uptake was 8 mM, the Km of glucokinase [E.C. 2.7.1.12]. The rate of glycogen synthesis in liver during meal-feeding was found to be approximately 1 mumol glucosyl U/g wet wt/min in rats meal-fed a 50% glucose supplemented chow diet. The relative importance of the direct vs. indirect pathway for the replenishment of hepatic glycogen was determined by the incorporation of [3-3H,U-14C]glucose into liver glycogen. Labeled glucose was injected into the portal vein at the end of meal-feeding. The ratio of 3H/14C in the glucosyl units of glycogen was found to be 83-92% of the ratio in liver free glucose six minutes after the injection, indicating that the majority of exogenous glucose incorporated into glycogen did not go through glycolysis. The percent contribution of the direct versus indirect pathway was quantitated from the difference in the relative specific activity (RSA) of [3H] and [14C]-glycogen in rats infused with [3-3H,U-14C]glucose. No significant difference was found between the RSA of [3H]glycogen and [14C]glycogen, indicating further that the pathway for glycogen synthesis in liver from exogenous glucose is from the direct pathway. Our results do not support the thesis that the majority of liver glycogen is synthesized from glucose-6-phosphate derived from gluconeogenesis. Reasons for the discrepancy between current findings and other reports supporting the indirect pathway for glycogen synthesis in the liver are discussed.

A method for large volume blood sampling and transfusion in rats

A new protocol that makes it feasible to withdraw large volumes of whole blood from an individual rat within 1 h or less is described. This method involves the use of indwelling catheters for withdrawal of blood from the inferior vena cava with concurrent isovolemic replacement of whole blood into the superior vena cava. Simultaneity of the transfusion and withdrawal, strict equality of volumes, and a smooth exchange of blood are assured by the use of separate channels of the same multiple-channel peristaltic pump for withdrawal and replacement. Validation experiments using both anesthetized and unanesthetized rats indicate that several responses remain essentially undisturbed during large volume blood sampling; these parameters include blood pressure, heart rate, hematocrit, plasma hormones including insulin and glucagon, plasma glucose levels, and feeding behavior. Considerations of technical and physiological limitations of the protocol, including choice of catheters and catheter placement, pump, sampling parameters, and obtaining donor blood, are discussed.

A new technique for hepatic portal vein catheterization in freely moving rats

To perform kinetic studies of pancreatic hormones in freely moving rats, we have designed a new technique for hepatic portal vein catheterization through the left branch of the portal vein. Rats were followed up for 14-38 days. Catheter patency allowed blood sampling in 86% of rats on postoperative day 8 and in 55% on day 12. Rat growth, liver functions, and regional blood flows (measured with radiolabeled microspheres) were normal. In freely moving rats fasted for 16 h, portal venous concentrations in the basal state were: glucose, 112 +/- 4 mg/dl; insulin, 67 +/- 10 microU/ml; and glucagon, 480 +/- 74 pg/ml. These values remained stable for a 1-h period. Intravenous glucose infusion induced a biphasic insulin release, significant from the 1st min of infusion on, and a significant decline in glucagon level. Intravenous arginine stimulated both A and B cells. The portoperipheral hormone concentration gradient, which was detected in the basal state, increased during arginine infusion, particularly in regard to insulin. Ingestion of a mixed meal induced an early glucagon release and a sustained rise in insulin and glucose concentrations.

The effect of anesthesia or restraint on triacylglycerol turnover in the rat

A comparison of triacylglycerol metabolism was made among anesthetized, restrained and unanesthetized-unrestrained rats. The method utilized for the comparison was the determination of triacylglycerol turnover following the intravenous injection of [3H]glycerol. Peak appearance of triacyl[3H]glycerol was 25 min in unanesthetized-unrestrained rats but 35 and 45 min in restrained and anesthetized rats, respectively. Using serial plasma triacylglycerol determinations as an index of steady-state in all three groups, it was found that only the anesthetized and unanesthetized-unrestrained animals could be used for kinetic analysis. In these two animal preparations, apparent fractional catabolic rates were calculated and found to be lower in anesthetized (0.014 min-1) compared to unanesthetized-unrestrained animals with chronic indwelling cannulas (0.029 min-1). Apparent total catabolic rates, calculated from the plasma triacylglycerol mass and estimated plasma volume, were reduced by 50% in anesthetized animals. It is concluded that wide differences in triacylglycerol metabolism exist in these rat preparations which should be considered in the interpretation of future studies. The unanesthetized-unrestrained rat model may represent the closest approximation to the normal physiologic state.

Lipid absorption in unanesthetized, unrestrained rats. Effects of 4-aminopyrazolopyrimidine and ethinyl estradiol

Emulsified triacylglycerol containing [14C]palmitate was infused intraduodenally in unanesthetized, unrestrained animals treated with 4-aminopyrazolopyrimidine or pharmacologic doses of ethinyl estradiol. 4-Aminopyrazolo-pyrimidine practically eliminated the appearance of radioactivity in plasma but in ethinyl estradiol-treated animals the peak of radioactivity and shape of the plasma curve were similar to control, although lower in amplitude. A delayed appearance of radioactivity was also observed in 48-h- compared to 15-h-fasted controls, suggesting a requirement for induction of lipoprotein production prior to fat absorption.