Lactation and pregnancy effects on blood flow to mammary and reproductive systems in heat-stressed rabbits

This study used radioactive microspheres to examine blood flow distribution in the mammary and reproductive systems of hyperthermic (+1°C), anesthetized laboratory rabbits at different stages of pregnancy and lactation. Ovarian, cervical and oviductal blood flows decreased by 20-30% during heat stress while vulval blood flow rose by 40%, irrespective of pregnancy and/or lactation status. Mammary blood flow was unaltered during heat stress at most pregnancy and/or lactation stages, with the exception of a 35% decrease in non-pregnant rabbits in early lactation. Uterine blood flow in non-pregnant rabbits in early and peak lactation decreased by 42% and rose by 33%, respectively. Uterine blood flow response to heat stress in pregnant animals varied among tissues: no changes occurred in the flow to implantation sites (early pregnancy) or to inter-embryonic segments (mid- to late pregnancy); that to gestation sacs decreased by 12-40% at the different lactation stages; and that to maternal placentas decreased in the lactating state by 18%, and rose in the non-lactating state by 50%. Results indicate that pregnancy and lactation modulate vasomotor responses to heat stress in mammary and reproductive tissues, and that the extent of the modulation depends upon their respective stages.