Protropin rhymes with:
somatotropin, somatotropin, somatotropin, somatotropin, arpin, aspin, backspin, coppin, crespin, crispin, daspin, flippin, galpin, gilpin, halpin, hennepin, jospin, juarez-espin, jupin, lapin, ongpin, pepin, peppin, pippin, ruxpin, somatotropin, steppin', tappin, tippin, toppin, toupin, trupin, turpin, vipin