**Core Concept**
Prostaglandins are a group of lipids that have hormone-like functions in the body. They play a crucial role in various physiological processes, including inflammation, pain modulation, and smooth muscle contraction. Prostaglandins are synthesized from arachidonic acid through the action of cyclooxygenase enzymes.

**Why the Correct Answer is Right**
Prostaglandin was first discovered by Ulf von Euler in 1935 from the seminal fluid of bulls. The name "prostaglandin" is derived from the Greek word "prostatikos," meaning related to the prostate gland, as it was initially thought to be secreted by the prostate gland. However, it was later found to be present in various tissues and fluids, including seminal fluid. The presence of prostaglandin in seminal fluid is thought to play a role in the liquefaction of semen and the regulation of sperm motility.

**Why Each Wrong Option is Incorrect**
**Option A:** Tear fluid is not a primary source of prostaglandin discovery.
**Option B:** Saliva does not contain significant amounts of prostaglandin, and it was not involved in its initial discovery.
**Option D:** While prostaglandins are present in blood, it is not the source from which they were first discovered.

**Clinical Pearl / High-Yield Fact**
It's essential to note that prostaglandins are not produced by the prostate gland itself but are rather found in various tissues and fluids, including seminal fluid.

**✓ Correct Answer: C. Seminal fluid**