An attempt to disclose brain histamine localisation in portocaval shunted rats

Abstract

IntroductionRats with portocaval anastomosis (PCA) exhibit 2-10 fold higher cerebral histamine concentrations than do control rats. These high levels seem to result from accumulation of the amine produced in brain due to persistent saturation of histidine decarboxylase with L-histidine and no compensatory changes in histamine utilisation and catabolism [1,2]. Preliminary data [1] suggest that histamine is located in neurones.Recently it was reported that increased amounts of the histamine catabolite, tele-methylhistamine, were found in some brain areas after several months of portocaval shunt [3]. Adaptation to PCA could involve cellular redistribution of brain histamine. We examined this possibility by a biochemical approach. Materials and methodsPCA rats (n = 18) and corresponding controls (SHAM, n = 12) were used 1.5 and 14 months after surgery performed according to Lee and Fisher [4]. The dissected brains were trimmed of cerebellum and brain stem. Subcellular fractionation of the brain was achieved by differential centrifugation using a modification of the Whittaker procedure [5]. Isolation of astrocyte-and neurone-enriched fractions was performed as described by Farooq and Norton [6] employing a discontinuous Ficoll gradient. Histamine concentrations were measured by radioenzymatic assay employing partially purified rat kidney histamine N-methyltransferase as described elsewhere [1] or RIA (Immunotech S.A., Marseille, France). The results are given as means ± SEM. Differences between groups were assessed with the unpaired t-test. Statistical evaluation was performed using an IBM PC with Prizma GraphPad Inc. USA software. Results and discussionShunted rats had significantly lower body and liver weights than their sham operated counterparts (body weight: 1.5 months after surgery 228 ± 20 g vs. 363 ± 26 g, p < 0.01; 14 months after surgery 324 ± 18 g vs. 504 ± 12 g, p < 0.001 and liver weight: 1.5 months after surgery 4.1 ± 0.46 g vs. 10.3 ± 1.89 g, p < 0.01; 14 months after surgery 6.1 ± 0.37 g vs. 14.9 ± 0.40 g, p < 0.001). The liver index (liver to body weight ratio ¥ 100), a measure of the organ atrophy, was approximately 35% smaller in PCA rats at 1.5 months after surgery and remained similar at 14 months, suggesting stabilised shunt conditions (p < 0.001).In the two groups of sham rats, the cerebral histamine distribution and histamine concentrations did not differ and therefore the values were combined as one control. The percent contribution of each subcellular fraction to the total tissue histamine content was very similar between sham and portocaval shunted rats (Fig. 1a). The higher histamine content in the cytosolic fraction indicates more loosely bound amine in shunted rats. When expressed in pmol/mg protein there is a clear difference in histamine levels between sham and PCA groups (Fig. 1b), which supports our previous findings [1,2]. However, the time since the establishment of the portocaval shunt did not have a significant effect, as the histamine values in the two groups overlapped due to h...

Neuronal storage of histamine in the brain and tele‐methylimidazoleacetic acid excretion in portocaval shunted rats

“…1991). The portocaval anastomosis‐associated deposition of histamine preferentially in neurons, which was originally described by us in 1991, was further substantiated in a more recent paper (Fogel et al . 1999a).…”

“…neurons and mast cells, a major contributor of the non-neuronal histamine pool, have been indicated as cerebral histamine sources (see Schwartz et al 1991). The portocaval anastomosis-associated deposition of histamine preferentially in neurons, which was originally described by us in 1991, was further substantiated in a more recent paper (Fogel et al 1999a). The new immunohistochemical evidence provided here shows that the several-fold increase in brain histamine concentration is indeed of neuronal origin.…”

“…From our biochemical studies on the cellular amine distribution, neurons and not mast cells appear to store histamine (Fogel et al 1991a(Fogel et al , 1999a. To further address this issue, in the present study we used immunohistochemical methods.…”