Inhibition of Regulated Neuropeptide Secretion from Mouse Pituitary Cells by Propofol

Inhibition by propofol of intracellular calcium mobilization in cultured mouse pituitary cells

Propofol inhibited regulated secretion of the neuropeptide beta-endorphin from AtT-20 cells, a pituitary tumor cell line. Neuropeptide secretion depends on an increase of intracellular calcium (Ca(2+)) levels. We investigated the hypothesis that propofol altered intracellular Ca(2+) levels in AtT-20 cells. Propofol (100 microM) did not inhibit Ca(2+)-induced secretion of beta-endorphin from digitonin-permeabilized cells. Thus, propofol did not inhibit neuropeptide secretion by blocking the effects of increased intracellular Ca(2+). Intracellular Ca(2+) was measured in intact cells using a Ca(2+)-sensitive dye. Ca(2+) transients were generated by depolarization with KCl or by incubation with thapsigargin (an inhibitor of Ca(2+) uptake into the endoplasmic reticulum). Propofol inhibited generation of Ca(2+) transients in intact cells by KCl (half-maximal inhibitory concentration of 14.9 microM; P < 0.05). Nitrendipine also inhibited potassium-induced Ca(2+) peaks. Propofol 50 microM reduced the thapsigargin-induced Ca(2+) peak to 47% of control (P < 0.05). Thapsigargin-induced Ca(2+) peaks were not affected by calcium channel blockade by nitrendipine. Propofol inhibited the stimulus-induced increase in intracellular Ca(2+). Propofol inhibited thapsigargin-induced Ca(2+) transients, but nitrendipine did not, indicating that propofol had effects on intracellular Ca(2+) independent of blockade of L-type Ca(2+) channels. Propofol may inhibit release of Ca(2+) from intracellular stores. These results are consistent with the hypothesis that propofol inhibits neuropeptide secretion by inhibiting the stimulus-induced increase in intracellular Ca(2+).

IMPLICATIONS

Propofol may block both entry of calcium into cells and release of calcium from intracellular stores, thereby inhibiting regulated secretion of neuropeptides. Study of the effects of propofol on intracellular calcium metabolism may increase understanding of how propofol alters brain function and may aid development of better IV anesthetics.

Plasma and cerebrospinal fluid concentrations of neuropeptide Y, serotonin, and catecholamines in patients under propofol or isoflurane anesthesia

Propofol is a widely used anesthetic for both induction and maintenance of anesthesia during surgery. A strong feeling of hunger has been reported during the early recovery period after propofol anesthesia. We have investigated the effect of propofol on appetite in 10 patients undergoing a craniotomy and in parallel measured neuropeptide Y (NPY), catecholamines, and serotonin levels in the cerebrospinal fluid and plasma during anesthesia. Ten patients anesthetized with a volatile agent (isoflurane) served as a control group. Plasma NPY and catecholamines levels were not affected by surgery at any time. We observed a strong increase in NPY concentrations in the cerebrospinal fluid independently of the anesthetic technique agent used, whereas catecholamines were unchanged. We found that serotonin concentrations decreased significantly in the plasma (but not in the cerebrospinal fluid) of patients treated by propofol when compared with the control group; this decrease was associated with an increase of hunger early postoperatively. We concluded that the proappetite effect of propofol is mediated through a decrease of serotonin at the peripheral level.Key words: catecholamines, serotonin, neuropeptide Y (NPY), cerebrospinal fluid, serum, appetite.

The effect of midazolam and propofol on interleukin-8 from human polymorphonuclear leukocytes

Anesthetics and sedatives contribute to postoperative immunosuppression. Interleukin-8 (IL-8) is a chemotactic and activating factor that mediates neutrophil adhesion and margination and is essential for host defense. We investigated the effect of anesthetics on isolated human polymorphonuclear leukocyte production of IL-8. Healthy human polymorphonuclear leukocytes were isolated using a single-step density gradient and stimulated with lipopolysaccharide in the presence of varying concentrations of propofol or midazolam for up to 20 h. IL-8 was measured in both culture supernatants and cell lysates using enzyme immunoassay, and IL-8 mRNA in cells was measured using Northern blotting and phosphorimaging. Data were analyzed using Kruskal-Wallis analysis of variance or the Mann-Whitney U-test as appropriate. Lipopolysaccharide increased extracellular accumulation of interleukin-8, which was suppressed by both propofol (P = 0.025) and midazolam (P = 0.028). However, intracellular IL-8 increased with exposure to lipopolysaccharide (P = 0.028) and remained increased with both anesthetics. Northern blot analysis also revealed increased IL-8 mRNA levels in the presence of both midazolam and propofol, which was confirmed by molecular imaging. These data strongly suggest that the anesthetics modulate transport or secretion of IL-8 protein from the cell. Suppression of IL-8 by anesthetics and sedatives may predispose postoperative and intensive care patients to infection.

IMPLICATIONS

Anesthesia causes immune suppression and alters neutrophil function. We investigated the effect of propofol and midazolam on interleukin-8, a neutrophil chemotactic agent in human neutrophils. Both anesthetics decreased extracellular interleukin-8 accumulation, but intracellular levels and mRNA remained high. This suggests that propofol and midazolam alter interleukin-8 secretion from cells.