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Prostaglandin and thromboxane synthesis by microsomes of inflamed rabbit ciliary body--iris
Abstract:
Microsomes of albino rabbit ciliary body--iris were prepared 6 hr, 24 hr, 3 days, 7 days, and 28 days after intravitreal injection of 10 micrograms of Shigella endotoxin. The microsomal preparations were incubated for 15 min with [1-14C]arachidonic acid. Prostaglandin and thromboxane products (cyclo-oxygenase products) were identified by thin-layer chromatography and quantified by scintillation counting. Synthesis of prostaglandin F2 alpha (PGF2, PGD2, 6-keto-PGF1 alpha (a stable metabolite of PGI2) and thromboxane B2 (TXB2) (a stable metabolite of TXA2) was increased 24 hr, 3 days, and 7 days after endotoxin injection. The greatest increase was in TXB2 synthesis. Cyclo-oxygenase product synthesis returned to normal levels by 28 days. Ciliary body--iris microsomes prepared 15 min after paracentesis synthesized increased amounts of all cyclo-oxygenase products assayed, most notably TXB2 and PGE2. Ciliary body--iris microsomes from albino rabbit treated with topical 1% nitrogen mustard or pigmented rabbits treated with subcutaneous alpha-melanocyte--stimulating hormone (20 micrograms/kg) synthesized normal amounts of cyclo-oxygenase products.
Insights
Shigella endotoxin significantly increases prostaglandin and thromboxane synthesis in rabbit eyes for up to seven days. This inflammatory response, involving cyclo-oxygenase products, returns to normal levels within 28 days.
Area of Science:
- Ocular Pharmacology
- Biochemistry
- Immunology
Background:
- The ciliary body-iris is a key ocular tissue involved in inflammatory responses.
- Endotoxins can trigger significant inflammatory cascades within the eye.
- Prostaglandins and thromboxanes are critical mediators of inflammation.
Purpose of the Study:
- To investigate the impact of Shigella endotoxin on cyclo-oxygenase product synthesis in rabbit ciliary body-iris microsomes.
- To determine the time course of these changes following endotoxin administration.
- To compare these effects with other inflammatory stimuli.
Main Methods:
- Microsomes were isolated from albino rabbit ciliary body-iris at various time points after intravitreal Shigella endotoxin injection.
- Microsomal preparations were incubated with [1-14C]arachidonic acid.
- Prostaglandin and thromboxane products (cyclo-oxygenase products) were identified and quantified using thin-layer chromatography and scintillation counting.
Main Results:
- Intravitreal Shigella endotoxin increased the synthesis of prostaglandin F2 alpha, prostaglandin D2, 6-keto-prostaglandin F1 alpha, and thromboxane B2 (TXB2) at 24 hours, 3 days, and 7 days post-injection.
- The most significant increase observed was in TXB2 synthesis.
- Cyclo-oxygenase product synthesis returned to baseline levels by 28 days.
- Paracentesis also led to increased synthesis of these products, particularly TXB2 and prostaglandin E2.
- Nitrogen mustard and alpha-melanocyte-stimulating hormone did not alter cyclo-oxygenase product synthesis.
Conclusions:
- Shigella endotoxin induces a transient but significant increase in cyclo-oxygenase product synthesis in the rabbit ciliary body-iris.
- Thromboxane B2 is a major product elevated during this endotoxin-induced inflammatory response.
- These findings highlight the role of prostaglandins and thromboxanes in ocular inflammation triggered by bacterial endotoxins.