The uptake of 131I-iodinated human serum albumin ([131I]HSA) by the ovary and uterus was used as an indicator of capillary permeability in these organs from pro-oestrus through to day 5 of pregnancy. Highest levels of [131I]HSA in the ovary were found on the day of pro-oestrus. Ovarian uptake declined significantly on days 1 and 2, then rose to an abrupt and transient peak at 17.00 hr. on day 3. The two peaks of ovarian uptake coincide with the appearance of ovarian hyperaemia.
Uterine incorporation of [131I]HSA was high at pro-oestrus and declined significantly on days 1 and 2. The first significant increase occurred between 09.00 hr. and 17.00 hr. on day 3 and a further increase was observed between days 4 and 5. Only the pro-oestrous peak was associated with observable uterine hyperaemia.