The effect of metyrapone on granuloma induced by carrageenan-impregnated sponges in normal and essential fatty acid deficient rats

Systemic response to thermal injury in rats. Accelerated protein degradation and altered glucose utilization in muscle

Negative nitrogen balance and increased oxygen consumption after thermal injury in humans and experimental animals is related to the extent of the burn. To determine whether defective muscle metabolism is restricted to the region of injury, we studied protein and glucose metabolism in forelimb muscles of rats 48 h after a scalding injury of their hindquarters. This injury increased muscle protein degradation (PD) from 140 +/- 5 to 225 +/- 5 nmol tyrosine/g per h, but did not alter protein synthesis. Muscle lactate release was increased greater than 70%, even though plasma catecholamines and muscle cyclic AMP were not increased. Insulin dose-response studies revealed that the burn decreased the responsiveness of muscle glycogen synthesis to insulin but did not alter its sensitivity to insulin. Rates of net glycolysis and glucose oxidation were increased and substrate cycling of fructose-6-phosphate was decreased at all levels of insulin. The burn-induced increase in protein and glucose catabolism was not mediated by adrenal hormones, since they persisted despite adrenalectomy. Muscle PGE2 production was not increased by the burn and inhibition of prostaglandin synthesis by indomethacin did not inhibit proteolysis. The increase in PD required lysosomal proteolysis, since inhibition of cathepsin B with EP475 reduced PD. Insulin reduced PD 20% and the effects of EP475 and insulin were additive, reducing PD 41%. An inhibitor of muscle PD, alpha-ketoisocaproate, reduced burn-induced proteolysis 28% and lactate release 56%. The rate of PD in muscle of burned and unburned rats was correlated with the percentage of glucose uptake that was directed into lactate production (r = +0.82, P less than 0.01). Thus, a major thermal injury causes hypercatabolism of protein and glucose in muscle that is distant from the injury, and these responses may be linked to a single metabolic defect.

The use of essential fatty acid deficient rats to study pathophysiological roles of prostaglandins. Comparison of prostaglandin production with some parameters of deficiency

In a retrospective study on essential fatty acid deficient (EFAD) rats used to study pathophysiological roles of prostaglandins (PGs), slight increases in the linoleic acid content of the diet were found to gradually restore the depressed growth rate and to increase the reduced endogenous PG production. These apparently poorly deficient animals had a serum triene tetraene (omega9:omega6) ratio much higher than the value of 0.4 used as a criterion for EFA deficiency by nutritionists. Changes in body weight, serum omega9:omega6 and platelet PG production were not correlated with each other. Feeding rats on a diet containing less than 0.1 mg/g/linoleic acid led to decreasing platelet PG production as the degree of EFA deficiency increased. At this high level of deficiency, a serum omega9:omega6 ratio of 6 or over was achieved. This high ratio may be taken as an indicator of the degree of EFA deficiency required for studies on PG deprivation, but PG production by the tissue investigated or by platelets should preferentially be measured.

Time-dependent stimulatory and inhibitory effects of prostaglandin E1 on exudative and tissue components of granulomatous inflammation in rats

1 The effects of prostaglandin (PGE(1)), following local administration during different phases of developing sponge-induced granulomata, were studied in normal and essential fatty acid deficient (EFAD) rats.2 In normal rats, a single dose of 1 mug PGE(1) on implantation (day 1) increased exudate production without altering total leucocyte counts after 6 h and stimulated granulomatous tissue formation after 8 days.3 Repeated daily administration of the same dose of PGE(1) on days 1 to 3 had no effect, while administration on days 4 to 7 (i.e. when tissue growth is already in progress) inhibited granuloma formation.4 In EFAD rats, which are known to produce only very small amounts of endogenous prostaglandins, acute (6 h) exudate formation was unaffected by 0.05 mug PGE(1). However, early stimulatory and later inhibitory effects of 0.05 mug PGE(1) per day were obtained on the granulomatous tissue, similar to those obtained with the 20 fold higher dose in normal rats.5 The early stimulatory action of PGE(1) on granulomatous tissue formation was enhanced, in normal rats, by concomitant administration of 10 mug theophylline. This latter compound did not influence the later inhibitory effect of PGE(1).6 These results indicate that PGE(1) exerts either pro- or anti-inflammatory actions on the proliferative (tissue) component of the inflammatory process, depending on the time of administration. While the stimulatory effect following early administration may have been secondary to an initial cyclic adenosine 3',5'-monophosphate-mediated, vascular response, such a mechanism is unlikely to have been responsible for the later anti-inflammatory action of PGE(1).7 The implications of these results are discussed in relation to the postulated negative-feedback role of endogenous PGE in chronic inflammation.