Phytoestrogens, largely formononetin and genistein, are produced in the leaves of stunted desert annuals in a dry year. When ingested by California quail, these compounds apparently inhibit reproduction and prevent the production of young that will not have adequate food. In a wet year, forbs grow vigorously and phytoestrogenic substances are largely absent. Quail then breed prolifically and the abundant seed crop carries the enlarged population through the winter.
It is routinely assumed that the force of gravity can cause blood pooling in the dependent limbs, as venous return from the body region is reduced. However, the effects of postural alterations on blood flow to and from the limbs have not been directly compared or quantified. In the present study, blood flow in the femoral artery and vein of conscious cats were measured using transit‐time ultrasound technology as the animals were rotated head‐up by amplitudes up to 60°. 60° head‐up rotations produced significant (ANOVA, p<0.05) decreases in venous blood flow beginning ≈3 sec following tilt onset, which became maximal at ≈5 sec, with an alteration of 55‐65% from pre‐tilt values. As the animals were maintained head‐up, venous blood flow began to increase, and was 18‐29% lower than pre‐tilt values by 40 sec following rotation initiation. This recovery of venous flow was accompanied by a 17‐34% decrease in arterial blood flow that peaked ≈9 sec after tilt onset. These data confirm that venous return from the dependent limb is greatly attenuated during postural alterations, and the magnitude may be larger than expected. However, the largest perturbation in venous return is transient, and this combined with accompanying decreases in arterial blood flow limits peripheral pooling.
Prior studies showed that vestibular signals influence cardiovascular regulation by eliciting vasoconstriction in the dependent limbs during postural changes. These findings led to the hypothesis that loss of vestibular inputs would exacerbate blood pooling in the body regions below the heart during alterations of body position. We tested this hypothesis by comparing blood flow measured using transit‐time ultrasound technology from the femoral vein and artery in conscious cats subjected to head‐up tilt (HUT) at amplitudes up to 60°. Responses were recorded before and after bilateral ablation of vestibular afferents. Before vestibular lesions, blood flow decreased 24‐35% in the femoral artery by ≈9 sec following 60° HUT, presumably due to vasoconstriction, while venous blood flow decreased 55‐65%. After lesions, arterial blood flow dropped only 0‐14% at the time maximal vasoconstriction previously occurred, while venous blood flow decreased 57‐87%. The alterations were shown to be significant by ANOVA (P<0.05). Because vestibular lesions resulted in more blood flow to the leg in the femoral artery and less venous return in the femoral vein, we concluded that the lesions resulted in hindlimb blood pooling during HUT.
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