Effects of ingestion of pine needles (Pinus ponderosa) by late-pregnant beef cows on potential sensitive Ca2+ channel activity of caruncular arteries.

Cows were fed either a control (n = 6) or pine needle (n = 12) diet beginning on day 249 of pregnancy. On day 3 and day 5 of feeding, control-fed and pine needle-fed cows were slaughtered and placentomes were collected for in vitro perfusion of the caruncular artery. Potential sensitive Ca2+ channel (PSC) activity as well as the responsiveness to phenylephrine (alpha 1-adrenergic agonist) and adrenaline (alpha 1- and alpha 2-adrenergic agonist) were determined. Selected gravid uterine tissues (endometrium and myometrium, as well as caruncular and cotyledonary tissues) and associated arteries (caruncular, intercaruncular and umbilical) were isolated, minced and portions either extracted immediately for measurement of PSC or frozen at -90 degrees C until assayed for peroxidase activity or number of alpha 2-adrenergic receptors and affinities or for both. In vitro perfused placentomes from day 5 pine needle-fed cows had greater (P < 0.05) PSC activity, as measured by the increase in perfusion pressure in response to a depolarizing dose of KCl, than day 3 pine needle-fed or control-fed cows (10.3 +/- 2.5 versus 6.1 +/- 1.2, and 4.3 +/- 0.7 kPa, respectively). Furthermore, day 5 pine needle-fed cows also exhibited greater (P < 0.05) contractile responses to adrenaline than day 3 pine needle-fed or control-fed cows. Contractile responses to phenylephrine were similar (P > 0.1) for all three treatment groups. The observed increase in PSC activity and responsiveness to adrenaline, however, was not reflected by increasing numbers or affinities of PSC or alpha 2-adrenergic receptors on caruncular arteries.(ABSTRACT TRUNCATED AT 250 WORDS)