Eugene Geiling, whom we've met before as a mentor to Frances "Thalidomide" Kelsey, was a pioneer in the early days of molecular endocrinology. To get enough material to charactertise the tiny, hyper-dilute, peptide hormones which he discovered he needed a helluva lot of pituitary. Rather than working through hundreds of lab rats, he had the bright idea of using a whale as a one-stop shop and went at a whale's head with an axe and a saw. It was a change from the probes and scalpels he was used to handling, but he was able to show that substances produced in the posterior lobe - ultimately named as oxytocin and vasopressin - had particular, peculiar and pervasive effects on other parts of the body. Not on the whale's body, it was dead to all effects, but on yours and mine.
picture below shows that the genes encoding these proteins are next-door neighbours in the human genome. Once upon a time in this location there was only one gene: millions of years ago there was stutter in the replication process for chromosome 20 and this section was duplicated.
squeezing the smooth muscles on arteries. Remarkably, this hormone has another completely different function and an alternative name - anti-diuretic hormone ADH - which also states its function: ADH squeezes the kidney tubules and stops you peeing; retaining water in this way also cranks up the blood-pressure. That's pretty neat in my book - a double whammy providing redundancy in controlling this vital equilibrium. If your kidneys are shot and ADH has nothing to operate on, vasopressin can still control blood-pressure by its action on the smooth muscles.
Oxytocin is also amazingly versatile. It gets its name from the Greek ὀξύς + τόκος [oxys-tokos] = sharp/quick birth. Same root as oxygen which tends to generate acids (another meaning of sharp). If your pregnancy is more than a week over 9 months, you'll get an intravenous drip of oxytocin which will precipitate the birth process by inducing uterine