PHR 241 Exam 3 Histamines

Antagonists of histamine's actions refer to drugs that block the effects of histamine in the body. Histamine is involved in various physiological processes and can cause allergic reactions, inflammation, and gastric acid secretion. By blocking histamine's actions, these antagonists are commonly used in clinical settings to treat allergies, relieve symptoms of allergic rhinitis, reduce gastric acid secretion in conditions like peptic ulcers, and manage symptoms of histamine-mediated conditions like urticaria. Therefore, the statement that antagonists of histamine's actions have important clinical uses is true.

First generation antihistamines, such as diphenhydramine and chlorpheniramine, do possess anti-cholinergic activity. This means that they not only block the effects of histamine, but also block the effects of acetylcholine, a neurotransmitter involved in various bodily functions. This can result in side effects such as dry mouth, blurred vision, constipation, and urinary retention. Therefore, the statement that first generation antihistamines possess anti-cholinergic activity is true.

The correct answer is H2. Histamine receptor H2 has an effect on gastric parietal cells, cardiac muscle, and some smooth muscle. It is Gs coupled, which means it activates the Gs protein and stimulates the production of cyclic adenosine monophosphate (cAMP), leading to various physiological responses.

Second-generation drugs are a newer class of medications that have been developed to improve upon the limitations of first-generation drugs. One of the key improvements is their extended duration of action. This means that these drugs remain active in the body for a longer period of time, allowing for less frequent dosing and potentially improving patient compliance. Therefore, the statement that second-generation drugs have an extended duration of action is true.

Histamine receptors are classified as GPCRs (G-protein coupled receptors). GPCRs are a large family of cell surface receptors that are involved in signal transduction. They are characterized by their ability to activate intracellular signaling pathways through the interaction with G-proteins. Histamine receptors, when activated by histamine, initiate a cascade of cellular responses by activating G-proteins and modulating downstream signaling pathways. Therefore, histamine receptors are categorized as GPCRs.

Antihistamines, despite being commonly used to treat allergies and induce drowsiness, can have the opposite effect on children. This means that instead of causing sleepiness, they may experience insomnia, nervousness, and tremors. Therefore, the statement that antihistamines can have a paradoxical effect on children is true.

Antihistamines are not considered an effective treatment for bronchial asthma. While antihistamines can help with allergies and symptoms such as sneezing and itching, they do not have a significant impact on the airway inflammation and constriction that occurs in asthma. The mainstay of asthma treatment includes bronchodilators (such as inhalers) and anti-inflammatory medications (such as corticosteroids). Therefore, the statement that antihistamines are an effective treatment in bronchial asthma is false.

Edema is the accumulation of fluid in the tissues, and it is mediated by the H1 histamine receptor. Histamine is a chemical released by the body during an allergic reaction or inflammation. When histamine binds to the H1 receptor, it causes blood vessels to dilate and become more permeable, leading to fluid leakage into the surrounding tissues and resulting in edema. The H1 receptor is primarily responsible for the allergic response, including symptoms such as itching, redness, and swelling.

Mainly H1... but some H2 dependency

first generation ones do... 2nd mostly do not...

THey are LOcALLY acting hormones! :)

Histamine does have clinical applications, particularly in the field of medicine. It is involved in various physiological processes and is used in the diagnosis and treatment of certain medical conditions. Therefore, the statement that histamine has clinical applications is incorrect.

It does NOT play a role, however, asthmatic airways still respond greatly to histamine.

WIKI: Physiological agonism and antagonism is the mechanism of substances to induce the same ultimate effects in the body as other substances, as if they were receptor agonists or antagonists, but without binding to the same receptor.

The statement "antihistamines are good decongestants" is false. Antihistamines are medications that are primarily used to relieve allergy symptoms such as sneezing, itching, and runny nose. They work by blocking the effects of histamine, a substance released by the body during an allergic reaction. While antihistamines can help with some symptoms of congestion, they are not as effective as decongestants in relieving nasal congestion. Decongestants work by narrowing the blood vessels in the nasal passages, reducing swelling and congestion. So, while antihistamines can provide some relief for congestion, they are not considered to be good decongestants.

They are Gq coupled

H1 receptors mediate contraction of intestinal smooth muscle
H2 receptors mediate parietal cell acid production in gastric mucosa

It is Gi coupled to N-type calcium channels

They are histamine receptor antagonists... competitive H1 receptor blockers.

The correct answer is H1 because the axon reflex involves the direct action on H1 receptors on sensory nerve endings and/or depolarization of efferent axons. This suggests that H1 receptors play a role in initiating the axon reflex response.

Equally effective

Diphenhydramine, pyrilamine, and promethazine are not second-generation antihistamines because they are first-generation antihistamines. First-generation antihistamines are known to cause drowsiness and have a shorter duration of action compared to second-generation antihistamines. Fexofenadine, loratadine, and cetirizine, on the other hand, are second-generation antihistamines that have a longer duration of action and are less likely to cause drowsiness.

urinary RETENTION
DECREASED GI motility

they are vasoconstrictors
They are are bronchodilators

The cardiovascular effects of histamine that are indicative of histamine release in the skin are heat, redness, and local swelling. These symptoms are commonly associated with an allergic reaction and are caused by the dilation of blood vessels in the skin, leading to increased blood flow and the characteristic redness and swelling. Urticaria or hives, which are also listed as the correct answer, are another common skin manifestation of histamine release and are characterized by itchy, raised welts on the skin.

Phenylephrine, pseudoephedrine, and oxymetazoline are all effective decongestants. Decongestants work by constricting blood vessels in the nasal passages, reducing swelling and congestion. Phenylephrine is commonly found in over-the-counter nasal sprays and oral medications. Pseudoephedrine is also available over-the-counter and is often used in combination with other medications to treat congestion. Oxymetazoline is a nasal spray that provides fast relief from nasal congestion. These decongestants are effective in relieving symptoms of nasal congestion caused by allergies, colds, or sinus infections.

Histamine is found in vesicular granules of mast cells or basophils, neuronal tissue in the brain, enterochromaffin-like cells in the fundus of the stomach, and venoms.

TYPE I Immediate allergic reactions
COLD temperatures!

decreased and thickened secretions