Histamine influences the glomerular microcirculation and modulates immune-inflammatory responses. In the rat kidney, histamine is synthesized by glomeruli and stimulates cyclic nucleotide production specifically in glomeruli. We investigated the in vitro effect of histamine on cyclic nucleotide accumulation in rat cultured glomerular mesangial and epithelial cells. Histamine stimulated cyclic AMP (cAMP) accumulation in cultured mesangial cells (64.0±22.1 to 511.4±86.6 pmol/mg protein, n = 0) but had no effect on cAMP accumulation in epithelial cells. This effect was dose-dependent and time-dependent. Stimulation of cAMP accumulation occurred in the range of 5 x 10-6 M-10-4 M histamine with a half maximal stimulatory effect of 2 x 10-5 M. Initial stimulation was noted by 30 s, and maximum stimulation was observed at 5 min. The H2 antagonist cimetidine (10-4 M) abolished the stimulatory effect of histamine (10-4 M), while equimolar concentrations of the H1 antagonist diphenhydramine had no significant effect on cAMP accumulation. Moreover, the specific H2 agonist dimaprit, but not the H1 agonist 2-pyridylethylamine, stimulated cAMP accumulation. Histamine had no effect on cAMP accumulation in epithelial cells or on cyclic guanosine monophosphate accumulation in epithelial or mesangial cells. Since the in vivo infusion of histamine reduces ultrafiltration coefficient and since mesangial cell contraction is thought to be responsible for the reduction in the ultrafiltation coefficient, we examined the effect of histamine on the contractile property of mesangial cells. Histamine (5 x 10-6-10-4 M) contracted mesangial cells, and the H1 antagonist diphenhydramine (10-4 M) but not the H2 antagonist cimetidine (10-4 M) prevented histamine (10-4 M) induced contraction. In addition, the H1 agonist 2-pyridylethylamine, but not the H2 agonist dimaprit, contracted mesangial cells. Histamine and its specific agonists and antagonists induced contraction of isolated glomeruli as assessed by glomerular planar surface area in a manner parallel to their effect on mesangial cells. Cinnarizine (10-5 M), a Ca++ channel blocker, or Ca++,Mg++-free medium prevented histamine (10-4 M) induced mesangial cell and glomerular contraction. This, histamine enhances cAMP accumulation specifically in mesangial cells via an H2 receptor. In contrast, histamine contracts mesangial cells and glomeruli via an H1 receptor, an effect that is dependent on extracellular Ca++ entry. These findings show that histamine potentially influences intraglomerular hemodynamics via effects on mesangial cell contraction. Moreover, our findings considered with the in vivo observation that histamine reduces k(f) via an H1 receptor provide further support for the hypothesis that mesangial cell contraction regulates the glomerular capillary surface area available for filtration. Our studies also show that this contractile effect of histamine is dependent on extracellular calcium. The presence of a cAMP system sensitive to histamine may have major implications in the pathogenesis of inflammatory glomerulopathies. Mesangial cells possess characteristics similar to circulating and tissue immune effector cells, including lysosomal enzyme release, oxygen radical production, and release of a number of immunomodulatory factors. Histamine and cAMP have been shown to modulate such characteristics of inflammatory cells. It is therefore conceivable that histamine, via its interaction with H2 receptors and subsequent generation of cAMP, may have profound effects on such properties of mesangial cells, suggesting that this autacoid may modulate not only glomerular hemodynamics but also immune, inflammatory responses within the glomerulus.
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