Effects of Ponderosa pine needle ingestion of uterine vascular function in late-gestation beef cows.

Consumption of Ponderosa pine (Pinus ponderosa) needles (PN) by beef cows during late gestation results in premature delivery in association with profound constriction of the caruncular arterial bed. Further, PN extracts and plasma from PN-fed cows increase uterine arterial tone in vitro. Uterine arterial tone is a measure of the arterial resistance to stretch and controls the baseline rate of flow through the vascular bed. Uterine arterial tone results from the uptake of extracellular Ca2+ into smooth muscle cells through specific membrane channels called potential sensitive channels. Functional potential sensitive channels remain open for prolonged periods after activation, allowing a continuous uptake of Ca2+ and the maintenance of uterine arterial tone. Recent evidence from our laboratory has demonstrated that a group of estrogen metabolites produced by the placenta and(or) endometrium, called catechol estrogens, inhibits Ca2+ uptake through the potential sensitive channels. During gestation, progressive decreases in uterine arterial tone are observed, with resultant increases in uterine arterial blood flow. Thus, the continuous production of catechol estrogens may be necessary to maintain the pronounced uterine vasodilation that is required for fetal survival. Ponderosa pine needle extracts exhibit antiestrogenic activity, as evidenced by their inhibition of estrogen-induced uterine hyperemia. Data from our laboratory show that after consumption of PN by beef cows during late gestation, uterine arterial blood flow progressively decreased to less than 50% of prefeeding rates before premature delivery of a live calf.(ABSTRACT TRUNCATED AT 250 WORDS)