The effects of relaxin on the response of intramammary pressure and mammary blood flow to exogenous oxytocin in the goat.

Lactating goats were given relaxin (50 micrograms) by close-arterial infusion into one mammary gland. The increase in intramammary pressure and in mammary blood flow elicited by exogenous oxytocin i.v. was attenuated by relaxin in goats during pregnancy and early lactation but not in a group studied during the oestrous cycle. Intramammary pressure in both mammary glands was affected at the dose of relaxin used. It is concluded that a change in responsiveness of the mammary myoepithelium to oxytocin is one possible effect of relaxin, acting directly or indirectly, circulating systemically during pregnancy and produced locally by the mammary gland at the onset of and during lactation.