They've misspelt prolactin. :)
Perhaps it's the Queen's English version.
Sort of like the guy on FR who insists on the archaic spelling 'insuline'. The -in ending is used to designate a prote
in. The preferred spelling in OED is "insulin", "protein", and "prolactin".
Oldest use listed in OED:
1932 O. RIDDLE et al. in Proc. Soc. Exper. Biol. & Med. XXIX. 1211 We..have identified this same hormone, which we shall here call ‘Prolactin’ as the hitherto undefined pituitary principle which is essential for lactation in mammals.
Thank you for explaining the difference in spelling.. That makes sense. The condition is also called hyperprolactinemia-- the meds for it make people really sick.