In the urea cycle, ornithine leads to arginine and urea. Ornithine can also be decarboxylated to yield 1,4-diaminobutane(see here), a precursor to polyamines. 1,4-Diaminobutane is also known as putrescine because it was originally isolated from rotting meat.

Arginine is a precursor to nitric oxide, a novel second messenger and neurotransmitter. The complex conversion of arginine to citrulline and nitric oxide is shown in Figure 21.3 as is the conversion of arginine to creatine phosphate.

In summary:

Ornithine leads to arginine (in the urea cycle);

Ornithine can be decarboxylated to yield putrescine (see Figure 21.10 and here);

Putrescine is a precursor to polyamines;

Arginine is a precursor to nitric oxide and citrulline (Figure 21.3); and

Arginine can be converted to creatine phosphate (Figure 21.3).