Pharmacology of Histamine , Histamine receptors and Anti-histamine Drugs : Part 1
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Histamine is a chemical mediator that plays a key role in various physiological processes in the body. It is involved in allergic reactions, regulation of gastric acid secretion, neurotransmission, and immune responses. Histamine exerts its effects by binding to specific receptors, known as histamine receptors, which are present on various cells and tissues throughout the body.
Histamine Receptors:
There are four main subtypes of histamine receptors, designated as H1, H2, H3, and H4 receptors. Each receptor subtype is found in different locations and serves different functions:
H1 Receptors: These receptors are primarily located on smooth muscle cells, endothelial cells, and nerve endings. Activation of H1 receptors leads to smooth muscle contraction, increased vascular permeability, itching, and bronchoconstriction. Antagonists of H1 receptors are commonly used as anti-allergic drugs.
H2 Receptors: H2 receptors are predominantly found in the stomach, where their activation stimulates the secretion of gastric acid. Antagonists of H2 receptors, known as H2 blockers, are used to reduce gastric acid secretion and are commonly used in the treatment of gastric ulcers and gastroesophageal reflux disease (GERD).
H3 Receptors: These receptors are mainly located in the central nervous system, particularly in areas involved in neurotransmission. H3 receptors act as autoreceptors and heteroreceptors, regulating the release of various neurotransmitters, including histamine itself. Modulation of H3 receptors is being explored for the treatment of conditions such as Alzheimer's disease, attention deficit hyperactivity disorder (ADHD), and sleep disorders.
H4 Receptors: H4 receptors are primarily expressed on immune cells, such as mast cells, eosinophils, and T cells. Activation of H4 receptors contributes to immune responses, including chemotaxis and cytokine release. H4 receptor antagonists are being investigated for their potential role in the treatment of inflammatory and allergic disorders.
Anti-Histamine Drugs:
Antihistamines are medications that block the effects of histamine by binding to and inhibiting histamine receptors. They are widely used to relieve symptoms associated with allergic reactions, such as sneezing, itching, runny nose, and hives.
Antihistamines can be classified into two generations:
First-Generation Antihistamines: These drugs, such as diphenhydramine and chlorpheniramine, readily cross the blood-brain barrier, leading to sedative effects. They are effective in alleviating allergic symptoms but are associated with drowsiness and other side effects.
Second-Generation Antihistamines: This group includes drugs such as cetirizine, loratadine, and fexofenadine. Second-generation antihistamines are less likely to cause sedation because they have reduced penetration into the central nervous system. They provide long-lasting relief from allergy symptoms and are generally preferred over first-generation antihistamines.
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I have been hyper sensitive to histamine for long time and have had HB with swelling feet your Vedio makes a lot of sense to me
Thanks again for your support
Which begger dislike the vedio..if u have doubts just ask him.its not the way by dislikeing his efforts and hard work...
At 4:16 what meaning Direct action,i mean what's the mechanism.plz tell me. thnxs for lecture
EXCELLENT CONCEPT SIR,THANK YOU SIR!
A lot of love and thanks from Lahore Pakistan.
Pakistan ki maa ka bhosda nikl gandu
Thank you, sir! It really helped me a lot - from Korea
Very simple and ease to remember. Excellent sir
Sir it's really a good explanation but need more detail plezz sir
Great video man, studying for a pharmacology exam this helped
Mst
Chemical classifications of antibiotics
Best explanation big big thumbs up 👍
I am grateful for your lectures Sir
It's my pleasure
THANK YOU SIR 🙂
What a good explanation
Unspeakable 💛💛💛
Thank u
Need drugs effect GIT and endocrine system lectures 😢
Thank you
Great sir g
clarified butter(desi gee) with bread& chapati used in morning and get rid off this anti hestime i swear i use it’s beneficial
It’s just dry blood issue.
In relation to the Histamine flush from Niacin B3 vitamin, how would you classify histamine intolerance ??
Prolonged high Histamine levels is causing depression , in my opinion ; More of a question than the statement it is ??
Maybe by using Niacin causing small histamine flush can increase the tolerance for food related histamine release ??
Which receptors for Histamine are involved , H1 , H2 , H3 , H4 at the time of Niacin flush ??
DAO involvement etc. Please get it addressed in following presentations.
I think, both H1 and H2
Sir you left some points like enzyme between histamin and histidin
Histidine decarboxylase
L-histidine decarboxylase in presence of pyridine phosphate
Sir I want anti histamine drug explaination... Sir 🙏
Excellent sir...👏👏👏👏👏
sir making more video on. pharmacology
Nice explanation and easy understanding 🤗
Thankyou well explained
Sir can u mention D link of next video in ur description . It ll b easy for many.. TQ
Thanks dear sir
Sir, upload all topics of pharmacology.
Is itching response due to histamine action , kindly clarify?
yes! because there is H1 receptors for histamine on skin.. so when histamine is released and bind to this receptor it stimulate sensory nerve endings and cause itching and pain.
According to you histamine dialate smooth muscle,,what's about bronchial contraction in asthama caused by histamine,,
Good sir
Thank you sir it is really helpfull
Doctor, What is the reason NO is released by Histamine action and subsequent fall in BP? What is the reason for this design?
Bahot Good Sirji 👍
Sir one question
Why histamine has two basic center?
flare due to axon reflex .. is not clear ... please clear it to me sir
Can you answer how does the stimulation of H1 receptors (which are Gq coupled) lead to vasodilation ( since any smooth muscle contracts when it is stimulated via a Gq coupled receptor)?
H1 receptors are typically coupled to Gq proteins and can mediate smooth muscle contraction, the overall effect of H1 receptor activation on vascular tone involves a complex interplay of various signaling pathways, including the release of vasodilatory factors like nitric oxide and prostacyclin, modulation of calcium signaling, and indirect effects on other vasoactive substances.
Sir, Is histidine also stored in mast cell
And from where NO released
Stored in mast cells and released when req
maybe NO is released from endothelial cells
thank u so much sir..
Watching from uganda 🇺🇬
Simple and easy to understand
Sir pls share the link anti cancer drug topic
Histamine is good Or bad human body?
Why antagonists are more when compare to agonist drug which is bad for body
Veeru Veeruyadav depends
Please when I get pdf of this lecture
Sir there is some selective videos of pharma by U why?
You can avail full subscription on Www.medvizz.com
Sir there is no anti histamine videos?
Synthesis of histamine
Sir, you say that Histamine receptors are found on "small blood vessels" and their activation causes vasodilation. But surely vasodilation can only be caused by contraction of their smooth muscle, and this cannot occur in capillaries (which don't have smooth muscle)?
Vasodilation is by relaxation of smooth muscle
capillaries have h1 receptors .release of NO causes relaxation
Good
dilatation nahi dilation hota ha
हिंदी में भी वीडियो बनाओ
Ｗｅｌｌ ｄｏｎｅ
Tysm
😊😊👌
Sir please speak in hindi
Sir hindi english
Tari english k hal b moye moye ki terha h😅
Good
Nice