Effect of acute and antecedent hypoglycemia on sympathetic neural activity and catecholamine responsiveness in normal rats.

Adrenergic responsiveness to acute hypoglycemia is impaired after prior episodes of hypoglycemia. Although circulating epinephrine responses are blunted, associated alterations in adrenal sympathetic nerve activity (SNA) have not been reported. We examined adrenal nerve traffic in normal conscious rats exposed to acute insulin-induced hypoglycemia compared with insulin with (clamped) euglycemia. We also examined adrenal SNA and catecholamine responses to insulin-induced hypoglycemia in normal conscious rats after two antecedent episodes of hypoglycemia (days -2 and -1) compared with prior episodes of sham treatment. Acute insulin-induced hypoglycemia increased adrenal sympathetic nerve traffic compared with insulin administration with clamped euglycemia (165 +/- 12 vs. 118 +/- 21 spikes/s [P < 0.05]; or to 138 +/- 8 vs. 114 +/- 10% of baseline [P < 0.05]). In additional experiments, 2 days of antecedent hypoglycemia (days -2 and -1) compared with sham treatment significantly enhanced baseline adrenal SNA measured immediately before subsequent acute hypoglycemia on day 0 (180 +/- 11 vs. 130 +/- 12 spikes/s, respectively; P < 0.005) and during subsequent acute hypoglycemia (229 +/- 17 vs. 171 +/- 16 spikes/s; P < 0.05). However, antecedent hypoglycemia resulted in a nonsignificant reduction in hypoglycemic responsiveness of adrenal SNA when expressed as percent increase over baseline (127 +/- 5% vs. 140 +/- 14% of baseline). Antecedent hypoglycemia, compared with sham treatment, resulted in diminished epinephrine responsiveness to subsequent hypoglycemia. Norepinephrine responses to hypoglycemia were not significantly altered by antecedent hypoglycemia. In summary, prior hypoglycemia in normal rats increased adrenal sympathetic tone, but impaired epinephrine responsiveness to acute hypoglycemia. Hence, these data raise the intriguing possibility that increased sympathetic tone resulting from antecedent hypoglycemia downregulates subsequent epinephrine responsiveness to hypoglycemia. Alternatively, it is possible that the decrease in epinephrine responsiveness after antecedent hypoglycemia could be the result of reduced adrenal sympathetic nerve responsiveness.

Production of the cytokines interleukin 1 and 6 by murine brain microvessel endothelium and smooth muscle pericytes.

Murine brain microvessel endothelial cells and smooth muscle/pericytes (SM/P) cells were cultured from newborn BALB/c (normal strain) and SJL/j (autoimmune-prone strain) mice. These cells were evaluated for their ability to produce interleukin (IL)-1 and IL-6 cytokines. The expression of mRNA for IL-1 and IL-6 was shown in highly purified BALB/c endothelial cells and SM/P cells using polymerase chain reaction with specific primers for IL-1 alpha, IL-1 beta and IL-6. IL-6 but not IL-1 mRNA was detected in unstimulated SJL/j brain microvessel cells. The presence of IL-1 and IL-6 mRNA in the BALB/c brain microvessel endothelial cells and SM/P was confirmed by in situ hybridization. By D10.G4.1 assay, unstimulated BALB/c endothelial cells were shown to produce active IL-1 to a higher degree than SM/P. By B9 bioassay, a low amount of active IL-6 was detected in the supernatant of endothelial cells and SM/P. The production of IL-1 and IL-6 in the bioassays was upregulated by lipopolysaccharide (LPS) activation of the cells in a time- and dose-dependent way. IL-6 production was also shown to be upregulated by IL-1 beta activation of the cells. Brain microvessel endothelial cells of SJL/j origin released equivalent amounts of IL-6 compared to endothelial cells of BALB/c origin. However, the production of IL-6 was markedly higher in SM/P of SJL/j origin than in those of BALB/c origin. These observations, together with our previous data showing that brain microvessel SM/P cells produce GM-CSF, emphasize the possibility for active participation of brain microvasculature SM/P as well as endothelium in inflammatory reactions of the central nervous system.

Differential activation of Th1 and Th2 CD4+ cells by murine brain microvessel endothelial cells and smooth muscle/pericytes.

CD4+ Th cell infiltration into the brain and the activation by cellular elements of the central nervous system (CNS) are thought to be important steps in the initiation of CNS autoimmune diseases. T cell activation requires Ag-specific stimulation and additional costimulatory signals provided by the APC. Here we describe how murine brain microvessel endothelial (En) cells and smooth muscle/pericytes (SM/P) selectively induce the Ag-specific activation of different Th1 and Th2 CD4+ T cell clones. Th1 and Th2 cell clones were used that were specific for the same peptide Ag in the context of the same class II allotype. SM/P preferentially activated Th1 cell clones, whereas En cells activated Th2 cell clones better, as reflected by cell proliferation and production of IL-2 by SM/P-activated Th1 clones and IL-4 by Th2 clones. There was no difference in the level of expression of CD4, CD2, or LFA-1 molecules between these Th cell clones, and anti-CD4, CD2, LFA-1 or ICAM-1 mAb did not differentially affect Ag-induced proliferation among the clones. Moreover, antibody to CD28 did not influence Ag presentation by brain microvessel En or SM/P cells to Ag-specific Th1 and Th2 clones. These results suggest that: 1) different The subsets might require different signals for their activation; 2) different APC might provide different costimulatory signals for Th cell subsets; and 3) brain microvessel En and SM/P might play a differential role in induction of autoreactive T cell responses in the CNS.