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 degrees 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 nonpregnant 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 beat stress in mammary and reproductive tissues, and that the extent of the modulation depends upon their respective stages. Copyright (C) 1996 Elsevier Science Inc.