HISTAMINE AND ANTIHISTAMINE
HISTAMINE is distributed throughout the periphery and in few select areas of the brain periphery: mast cells - in tissue (bronchioles, skin, intestinal mucosa). basophiles - circulatingBRAIN: the majority of the cell bodies of histaminergic neurons are located in the posterior basal hypothalamus and reticular formation , histamine is involved in cortical stimulation
HISTAMINE
powerful tissue substance released during an allergic reaction that dilates capillaries, contracts most smooth muscles, increased heart rate, and stimulates gastric secretionANTIHISTAMINE: any substance capable of reducing the physiologic and pharmacologic effects of histamine.
Histamine receptors
there are 3 types H1:mediate vasodilatation & edema. H2: mediate gastric acid secretion. H3: mediate inhibition of histamine release.WHITE REACTION
when a pointed object is drawn lightly over the skin, the stroke line becomes pale this is because of precapillary sphincter contraction &the blood is drains out of capillaries &small veinsTRIPLE RESPONSE
when the skin is stroked more firmly with a pointed instrument instead of the white reaction there is reddening of the site that appears in 10 seconds-red reaction. this i s followed in a few minutes by local swelling with diffuse mottled reddening around the injuryThe initial redness is due to capillary dilatation due to pressure effect. the swelling-wheal is local edema due to increase capillary permeability with consequent fluid extravasations. The redness spreading out from the injury- flare is due to arteriolar dilatation probably due to axon reflex.
This red reaction, wheal & flare is called triple response. It is produced by histamine or histamine-like substances released from mast cells and mediated via H1-receptors. in rats it is due to serotonin released from mast cells.