Adalgisa Bizzi

Comparative studies on the anorectic activity of d-fenfluramine in mice, rats, and guinea pigs

SummaryThe present study compares the anorectic activity of d-fenfluramine and its metabolite d-norfenfluramine in three animal species. d-Fenfluramine and d-norfenfluramine show anorectic activity at increasing doses (ED50) in rats, guinea pigs, and mice, d-norfenfluramine being more active than d-fenfluramine in all three species. Equiactive anorectic activities are reached with different brain levels of d-fenfluramine and d-norfenfluramine, guinea pigs being the most sensitive species, followed by rats then mice. The metabolite most probably plays a major role in the anorectic effect of d-fenfluramine in guinea pigs, contributes to the anorectic activity in rats, but adds little to the action of the parent drug in mice. The different sensitivity to d-fenfluramine and d-norfenfluramine in these three species does not appear to be explained by a number of biochemical parameters, including serotonin uptake or release, receptor subtypes, or 3H-d-fenfluramine binding and uptake.

Valproate, carnitine metabolism, and biochemical indicators of liver function

Summary: The effects of valproate (VPA) on carnitine and lipid metabolism and on liver function were assessed in 213 age‐ and sex‐matched outpatients from five centers, with the following distribution: VPA monotherapy, 54; VPA polytherapy, 55; other monotherapies, 51; and untreated, 53. Mean total and free carnitine levels were significantly lower in patients with polytherapy; acylcar‐nitine was significantly higher for VPA monotherapy and the ratio of acyl‐ to free carnitine was significantly higher in all patients receiving VPA. Ammonia, uric acid, and bilirubin were the only tests selectively impaired with VPA. A significant correlation was found between serum ammonia and VPA dosage. Glucose, B‐lipoproteins, try‐glicerides, acetacetate, and p‐hydroxybutyrate were unchanged in the four groups. Sex and age appeared to interact with total and free carnitine values. Adverse drug reactions were apparently unrelated to carnitine metabolism impairment. Only a few patients had abnormal carnitine values. Our data support the assumption that carnitine deficiency and abnormal liver function due to VPA are mostly subclinical events.

Progress report on the anorexia induced by drugs believed to mimic some of the effects of serotonin on the central nervous system.

Some agents that increase serotoninergic transmission in the brain show anorectic activity at doses that do not interfere with the behavior of rats and other animal species. These agents reduce food intake by a mechanism that clearly differs from that involved in the anorectic activity of d-amphetamine. d-Fenfluramine, fluoxetine, and sertraline are three drugs that have already been tested and are used in man. These compounds accumulate in the brain and are metabolized through N-dealkylation. They affect the uptake and release of serotonin at different concentrations, with mechanisms that do not completely overlap. There is pharmacological evidence that d-fenfluramine and sertraline exert their anorectic activity by enhancing the stimulation of 5-HT1nonA receptors whereas fluoxetine seems to affect at anorectic doses both serotoninergic and dopaminergic systems. The role of serotonin in controlling food intake will be discussed, and the effects of agents that reduce serotoninergic transmission will also be considered.

Amiodarone induced phospholipidosis biochemical, morphological and functional changes in the lungs of rats chronically treated with amiodarone

Amiodarone, an antiarrhythmic drug, causes pulmonary fibrosis in some patients during chronic treatment but the mechanism is unknown. We studied the effects of amiodarone on pulmonary biochemistry, morphology and function at doses of 25 and 50 mg/kg/12 hr given to rats by gavage for four weeks. Plasma and pulmonary phospholipids were significantly augmented, 13% and 88% respectively, in the group given amiodarone 50 mg/kg/12 hr compared to pair-fed controls. Typical phospholipidosis-like light and electron microscopic alterations were seen in the lung, their severity related to the extent of biochemical changes induced by amiodarone. Pulmonary function tests revealed mild but not significant changes in O2 and CO2 alveolar exchange efficiency and lung compliance (P-V curve) of treated animals in comparison to pair fed controls. Plasma average concentrations of amiodarone and its main metabolite, desethylamiodarone, after four weeks were 2.46 +/- 0.18 and 0.73 +/- 0.13 micrograms/ml, respectively, in the 50 mg/kg/12 hr group. In the same group amiodarone and desethylamiodarone concentrations in lung were 163 +/- 26 and 569 +/- 153 times higher than those in plasma. A highly significant correlation was found between amiodarone concentrations in plasma and lung and phospholipid content in the lung. A subgroup of animals received amiodarone 50 mg/kg/12 hr for 8 weeks. The pulmonary phospholipidosis-like lesions were similar to those observed after one month of treatment, no fibrosis was evident on light microscopic examination.

Effect of fenfluramine on the intestinal absorption of triglycerides

Abstract Fenfluramine decreased plasma triglycerides in fed rats but not in fasted rats. When this compound was administered to rats in a post-absorptive state, a diminution in lymphatic flow and in triglyceride concentration was observed. Moreover, pretreatment with fenfluramine inhibited a rise in plasma and lymph triglycerides, normally found after an olive oil load. No alterations were noted in the flow rate and density of bile. The motility of the small intestine was decreased. These data suggest that the lowering of plasma triglycerides, elicited by fenfluramine, is at least partially due to inhibition of the intestianal absorption of triglycerides.

Hypersensitivity to lipid mobilizing agents in essential fatty acid (EFA) deficient rats

Abstract Essential fatty acid (EFA) -deficient rats showed a higher sensitivity to lipolytic agents than control animals. Norepinephrine released more free fatty acid in vivo and in vitro , both from adipose tissue slices and isolated fat cells. Similarly, theophylline and cyclic 3′, 5′ AMP (dibutyryl ester) were more active on EFA-deficient fat cells than on control cells. Also, the combination of norepinephrine with theophylline was more effective in EFA-deficient fat cells. PGE 1 was able to inhibit the lipolytic effect of norepinephrine on EFA-deficient fat cells as well as on controls. The results are discussed with reference to the possible physiological role of EFA as precursors of prostaglandins.

Further observations on the attachment of carbohydrate to lipoproteins by rat liver Golgi membranes.

Summary After in vitro incubation of rat liver Golgi membranes with 14C-CMP-sialic acid, the membranes were extracted by treatment with 2 × 10–4 M Tris, pH 8.6, and lipoproteins were isolated by ultracentrifugation. The distribution of labeled lipoprotein was found to be 42% in VLDL, 14% in LDL, and 44% in HDL after sequential isolation of each density fraction. The addition of unlabeled whole rat serum to the extracted Golgi resulted in a decrease in label recovered in VLDL which was attributed to exchange of sialopeptides between VLDL and HDL. However, the addition of serum doubled the amount of recovered labeled lipoprotein and the extra label was associated with HDL. The labeled peptides were similar to those normally found in HDL as judged by DEAE-cellulose chromatography of the apo-HDL peptides. These results suggest the presence of a precursor pool of apolipoproteins within Golgi vesicles.

Effects of amphetamine and fenfluramine on the net release of triglycerides of very low density lipoproteins by slices of rat liver.

Abstract Slices of rat liver, incubated in a medium devoid of very low density lipoproteins (VLDL),† release an average of 0·2 mg of triglyceride (TG)† per 0·1 g liver protein in 3 hr at 37°. Liver slices responded qualitatively in the same manner as the perfused liver with regard to TG release, as judged by (a) enhancement by incubation in rat serum, (b) decreased output after fasting, (c) increased output after fasting and re-feeding, (d) inhibition by norepinephrine and (e) increased output when medium FFA† levels were increased, up to 2 mM. Liver slices differed from the perfused liver in that a net output of FFA was observed. During the incubation, liver slices showed a net loss of phospholipid (PL)† and a net synthesis of TG. The effects of d -amphetamine, dl -fenfluramine, and dl -norfenfluramine on the release of VLDL-TG were studied after in vivo injection or in vitro addition of these drugs. In vivo , the drugs, which elevate serum FFA levels, increased liver TG, decreased serum TG and prevented net synthesis of TG during incubation, but no significant effects on VLDL-TG release were found. When added in vitro , all of these compounds inhibited TG release. Norfenfluramine and norepinephrine were effective inhibitors at 10 −4 M while fenfluramine and amphetamine required higher concentrations. Liver TG synthesis was inhibited by the presence of the drugs in vitro . It is concluded that the liver slice system, while unable to perform at the level of the perfused organ, can nevertheless be useful in studies of the effects of drugs on hepatic lipoprotein metabolism.

Role of 5-HT receptors in the effect of d-fenfiuramine on gastric emptying and feeding behaviour as examined in the runway test

In one experiment, the effect of d-fenfluramine (DF) on gastric emptying was studied in rats treated i.p. with metergoline, a non-selective serotonin (5-HT) receptor antagonist, ritanserin, a selective 5-HT2 and 5-HT1C receptor antagonist, and xylamidine, a 5-HT antagonist which has poor access to the brain. Metergoline (1 mg/kg) but not ritanserin (0.5 mg/kg) or xylamidine (3 mg/kg) blocked the effect of 2.5 mg/kg DF studied 2 and 4 h after injection. In a second experiment, we studied the ability of metergoline to antagonise the effect of DF, administered after a meal, on runway performance, food intake and gastric emptying assessed 4 h later. Metergoline at a dose of 1 mg/kg did not antagonise the effect of DF (2.5 mg/kg) on runway performance but completely blocked the effect on gastric emptying. The data clearly show that DF delays gastric emptying by indirectly activating 5-HT1 receptors; this effect is not important for the ability of DF to reduce runway performance and food intake when the drug is injected after a pre-feeding period. While there is evidence that DF hastens the termination of the meal by a 5-HT mechanism, the data suggest that DF may prolong the satiating effect of food during the post-absorptive phase by mechanisms other than 5-HT.

The hypersensitivity of adipose tissue to norepinephrine and other lipolytic agents during blockade of free fatty acids (FFA) mobilization.

Abstract Adipose tissue of rats pretreated with 5-carboxy-3-methylpyrazole (5C3MP) or nicotinic acid released less glycerol and FFA (basal lipolysis) in their incubation medium. However, they were more sensitive to the lipolytic action of norepinephrine or theophylline. The maximum release of FFA and glycerol due to norepinephrine addition was increased in adipose tissue from 5C3MP pretreated rats. Moreover, the sensitivity to cyclic 3′5′ AMP (dibutyryl ester) was not significantly increased. The hypersensitivity to lipolytic agents already appeared at times when plasma FFA were lowered, but was present also during the rebound phase. Adrenalectomy did not prevent the inhibition of lipolytic activity exerted by these compounds, but almost completely inhibited the hypersensitivity of adipose tissue of treated rats to lipolytic agents. The possibility that these changes in the responsiveness of adipose tissue were correlated with the increased level of plasma corticosterone observed after the administration of 5C3MP or nicotinic acid are taken into consideration. A possible role of the hypersensitivity in the onset of rebound effect is discussed.