No abstract

The effects of diet on the rate of triglyceride synthesis by rat liver homogenates was measured. Changes in triglyceride synthesis were correlated with the level of activity of L-aglycerophosphate acyltransferase, the enzyme catalyzing the first specific reaction in hepatic glycerolipid synthesis.Fasting for 48-72 hr depressed the synthesis of triglyceride from L-a-glycerophosphate. High carbohydrate diets, fed to rats for 6 days, resulted in increased triglyceride synthesis. Diets high in starch were less effective than high glucose, sucrose, or fructose diets in increasing triglyceride synthesis. Diets high in corn oil did not alter triglyceride synthesis. These studies established the importance of dietary factors in the regulation of hepatic triglyceride synthesis.L-a-GlycerophOsphate acyltransferase activity was measured after the same dietary changes. Both high carbohydrate and high fat diets resulted in increased enzyme specific activity. Fasting for 72 hr did not decrease activity. Thus, the specific activity of this enzyme did not correlate well with the measured rate of triglyceride synthesis indicating that other factors must participate in the regulation of triglyceride biosynthesis.

Renal function was studied in rats treated with cyclosporin A (CyA). Peroral CyA 25 mg kg-1 day-1 depressed glomerular filtration rate (GFR) from 1284 +/- 429 to 500 +/- 228 microliters min-1 g-1 kidney weight (KW) (P less than 0.01). Absolute rate of proximal tubular reabsorption (APR) decreased from 1075 +/- 437 to 468 +/- 203 microliters min g KW-1 (P less than 0.01). Proximal tubular fractional reabsorption (PFR) was 67.7 and 68.5% measured with the TT/OT and fractional lithium-clearance methods, respectively. Amiloride had no effect on lithium-clearance in CyA treated rats. Acute isotonic volume expansion increased GFR and APR towards normal, while PFR remained increased. Increased sodium clearance did not normalize renal function. CyA intravenously (12.5 mg kg-1) depressed GFR and APR acutely, while PFR increased. Proximal intratubular pressures were low normal (mean 11.6 mmHg). Proximal transit times were prolonged (mean 25.2 s, P less than 0.01). Renal morphology was normal. The data are evidence against a primary tubular damage of CyA, and makes it less likely that the major lesion is located to the glomerular membrane. The results suggest that CyA nephrotoxicity mainly is due to a haemodynamic effect.

The contention that cyclosporin A (CyA) nephrotoxicity may be due to renal afferent arteriolar constriction was inferred from rat studies showing CyA to increase renal vascular resistance, to reduce glomerular filtration rate (GFR) and delivery of tubular fluid from the end of the proximal tubule to the loop of Henle (Vprox), and to increase proximal fractional reabsorption. In order to test whether the mechanism of human CyA nephrotoxicity is similar to its rat analogue, and whether CyA treatment causes prolonged renal malfunction after drug withdrawal, renal function was investigated with clearance techniques including lithium clearance (CLi) as a measure of Vprox. The subjects were patients (n = 11) with previously normal renal function, given CyA in the treatment of ocular manifestation of extrarenal disease, or bone-marrow transplant recipients. Nine out of these eleven patients were investigated before and during CyA treatment: GFR (P less than 0.05) and Vprox (P less than 0.005) decreased while proximal fractional reabsorption increased (P less than 0.01). In six patients investigated before CyA was given, and re-examined a mean of 273 days (range 84-384 days) after CyA withdrawal, CLi was reduced (P less than 0.05) while mean GFR was not significantly lowered (0.5 greater than P greater than 0.2). In one of these six patients GFR was reduced to a subnormal value of 26 ml min-1 (1.73 m2 body surface)-1. In conclusion, human and rat CyA nephrotoxicity have the same pattern of renal functional deterioration. Cyclosporin A nephrotoxicity was evident in patients investigated a mean of 9 months after CyA withdrawal.