Table of Contents
Tetracycline Photosensitivity
Photosensitivity is a sensitivity to sunlight. It can be a physical reaction, such as a rash, or an emotional reaction, such as feeling anxious or uneasy in sunlight. Tetracycline is a medication that can cause photosensitivity.
Primary Photosensitization and Secondary Photosensitization
Primary photosensitization is the process whereby a chemical agent, when first introduced into the body, causes the production of active oxygen species that can injure tissue. These oxygen species are produced by the interaction of the chemical agent with normal body constituents such as hemoglobin, water, and lipids.
Secondary photosensitization is the process whereby the initial injury caused by the chemical agent leads to the production of additional active oxygen species that can injure additional tissue. These oxygen species are produced by the interaction of the chemical agent with normal body constituents such as hemoglobin, water, and lipids.
Photosensitivity in Sheep
Photosensitivity is an abnormal response of the skin to sunlight. It can be caused by a wide variety of factors, including medications, infections, and skin disorders.
Photosensitivity in sheep is most commonly caused by an infection with a type of bacteria called rickettsia. These bacteria are spread by ticks, and can cause a skin infection called rickettsialpox. Rickettsialpox is characterized by a rash that develops when the skin is exposed to sunlight. Other symptoms of rickettsialpox include fever, headache, and muscle aches.
Photosensitivity in sheep can also be caused by a condition called pemphigus. Pemphigus is a skin disorder that causes blisters to form on the skin. These blisters can be very painful, and can easily become infected.
There are a number of other factors that can cause photosensitivity in sheep, including certain medications and skin disorders.
Mechanism of Tetracycline Phototoxicity
The mechanism of tetracycline phototoxicity is not fully understood, but is thought to involve the generation of reactive oxygen species (ROS) by the photosensitizer tetracycline. These ROS can damage cellular components, including DNA, leading to cell death. Additionally, tetracycline can inhibit the repair of DNA damage, further exacerbating the phototoxic effects.
Clinical Signs of Photosensitization
in Horses
Photosensitization in horses can produce a wide variety of clinical signs, depending on the severity of the condition. In mild cases, horses may only have a transient rash or skin irritation. In more severe cases, horses may suffer from extensive skin lesions, and in some cases, may even develop life-threatening complications such as kidney failure.
Methylene Blue Photosensitizer
Methylene blue (MB) is a blue dye that is used as a photosensitizer in photodynamic therapy.
MB has been used as a photosensitizer for more than a century. It is a cationic dye that can cross the cell membrane and bind to DNA. When MB is activated by light, it produces singlet oxygen, which can damage DNA and kill cells.
MB is typically used in combination with a light source, such as a laser, to treat cancer and other diseases. MB can also be used to treat vascular diseases, such as atherosclerosis, by targeting the damaged blood vessels.
The use of MB in photodynamic therapy is limited by its toxicity. MB can cause skin and eye irritation, and it can also be toxic to the liver and other organs.
Photosensitization in Sheep
Sheep are particularly susceptible to photodynamic therapy (PDT) because they have a high concentration of hemoglobin in their blood. When a photosensitizer is injected into the sheep, it is taken up by the hemoglobin and carried to the tumor. When the tumor is exposed to light, the photosensitizer is activated and produces a toxic reaction that destroys the tumor.
