Regional Variations in Uterine Blood Flow in the Guinea Pig: Relationship to Pregnancy Site Distribution

Abstract

The alterations which occur in the total uterine blood flow (UBF) during early pregnancy in the guinea pig were determined using electromagnetic blood flow probes. Between days 4 and 6 postcoitum, UBF rose from basal levels of 1.2 ml/min to peak levels of 3.0 ml/min. The elevated levels corresponded temporally with the onset of blastocyst implantation. Between days 7 and 8, UBF declined to basal levels. In guinea pigs possessing three pregnancy sites per uterine horn on days 10–20, obvious regional differences in UBF were observed. Consistently higher UBF measurements were monitored from uterine segmental arteries supplying the tubal and cervical thirds of the uterus than from those distributed to the middle third of the uterus. These data indicate that regional variations in UBF exist in the guinea pig which may be involved in the regulation of pregnancy site selection or subsequent placental-fetal growth.

Uteroplacental Vascular Perfusion and Blood Flow during Pregnancy in the Guinea Pig

“…These findings are in agreement with previous re ports which indicated that regional vascular changes occurred in the guinea pig uterus during early pregnancy [4,8,9,13] and were associated with regional differences in uter ine vascular pressure [14] and flow rates [8] in late pregnancy. The consistent elevation in blood flow to the tubal and cervical re gions of the uterus mimic growth patterns of the guinea pig fetal-placental unit, in which thé middle uterine zones consistently demon strated the lower weight and size parameters of the three uterine zones [8,14].…”

“…The flow probes were connected to a squarewave, electromagnetic blood flow monitor, calibrated for guinea pig body temperature and blood hematocrit [4], The monitor, in turn, was connected to a potentiometric recorder. In this manner, a 10-to 15-min measurement of uterine segmental blood flow was recorded from the corresponding midsegmental artery supplying each of the three uterine pregnancy sites [9], At the termination of each recording period, the seg mental artery was compressed proximal to the blood flow probe location with vascular clamps as an in situ check for probe function [9]. Failure of the probe to indicate a rapid fall in UBF to zero baseline levels was used as a basis for discarding the recording from anal ysis.…”

“…In the guinea pig, regional variations in UBF and blood pressure have been reported to persist throughout pregnancy, with the tu bal and cervical zones the uterus receiving a higher blood flow rate than the middle uter ine region [8,9], The vascular regionalization is associated with intrauterine growth in these regions, in which the 'ischemic' middle uterine zone supports the smallest fetal-pla cental unit in uteri possessing three preg nancy sites in a cornu [8], Reduction of the blood flow rate to the normally hyperemic tubal region results in intrauterine growth retardation of the fetal-placental unit [8], These data suggested that regional, uterine vascular distribution served as a regulator of intrauterine growth expression in this spe cies. However, it was not apparent if the regional blood flow variations persisted in a constant manner throughout pregnancy in the guinea pig or if blood flow to the placen tal unit accurately represented the intraplacental vascular dynamics or vascular volume changes, if any, which occurred during gesta tion.…”

Estrogen-Regulated Uterine Vascularization Modulates the Guinea Pig Intrauterine Environment

“…Growth and expansion of the intrinsic uterine vascular bed has been well documented to occur in association with early blastocyst-endometrial interaction [6][7][8][9][10][11][12] and decidua growth induction [ 10,[13][14][15] and has been implicated as a mandatory requirement for the successful growth and function of the placenta [16][17][18], Acute reductions in uterine blood flow during early pregnancy have been recognized to have deleterious effects on sub sequent fetal-placental development [ 19], The chronic reduction of uterine blood flow by vascular clamping may induce fetal-placental death or resorption, whereas acute reductions in uterine hyperemia during pregnancy pro mote growth retardation of maternal and fetal tissues [20][21][22], These studies demonstrate the essential role of the uterine vascular sup ply in the establishment and maintenance of proper intrauterine environmental conditions necessary for the continued growth and devel opment of the fetal-placental unit. However, the temporal and quantitative relationships between changes in uterine vascular capacity and the associated alterations in the intrauter ine environment supporting fetal-placental development remain to be elucidated.…”

Effects of Exercise on Fetal-Placental Growth and Uteroplacental Blood Flow in the Rat

“…Mild (acute) uterine ischemia has been demonstrated to induce fetal growth retardation, while the prolonged depression of UBF can induce fetal death [2,[5][6][7]. In addition, regional variations in UBF and vascular pressure have also been corre lated with normal variations in fetal-placen tal growth [2,4,[8][9][10], Thus, the factors which regulate uterine vascular dynamics in directly modulate the intrauterine environ ment of the developing conceptus [3,11] and All values are represented as group means (± SEM) for (n) pregnant female rats. Birth weights arc repre sented as the mean ( ± SEM) for all pups born in the respective group, a vs. b or b vs. c: p < 0.05; a vs. c: p < 0.01. may have either a supportive or detrimental effect on intrauterine growth and develop ment of the fetal-placental unit during preg nancy [2,3,7).…”