Calcium triggers the secretion of histamine from mast cells after previous exposure to sodium fluoride. The secretory process can be divided into a fluoride-activation step and a calcium-induced secretory step. It was observed that the fluoride-activation step is accompanied by an elevation of cyclic adenosine monophosphate (cAMP) levels within the cells. The attained high levels of cAMP persist during histamine release. It was further found that catecholamines do not markedly alter the fluoride-induced histamine release. It was also confirmed that the second, but not the first, step in sodium fluoride-induced histamine secretion is inhibited by theophylline.  Vasodilation and increased permeability of capillaries are a result of both H1 and H2 receptor types. 
Allows full 360° rotation of the entire mast at its base. Turning masts have a 360° counter which allows precise rotation and a manual clamp to lock it in the required position. When ordering a manually rotating mast, a rotation hand wheel which clamps around the mast should also be ordered. A rotation upper mounting bracket is also available. This is commonly used to secure the mast when fitted to a vehicle. It clamps the mast but still allows rotation. All our masts have a rubber roof mounting sealing ring fitted as standard - this is simply slid down to meet the roof mounting bracket to create a water tight seal.