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 be ginning on day 249 of pregnancy. On day 3 and day 5 of feeding, contro l-fed and pine needle-fed cows were slaughtered and placentomes were c ollected for in vitro perfusion of the caruncular artery. Potential se nsitive Ca2+ channel (PSC) activity as well as the responsiveness to p henylephrine (alpha1-adrenergic agonist) and adrenaline (alpha1- and a lpha2-adrenergic agonist) were determined. Selected gravid uterine tis sues (endometrium and myometrium, as well as caruncular and cotyledona ry tissues) and associated arteries (caruncular, intercaruncular and u mbilical) were isolated, minced and portions either extracted immediat ely for measurement of PSC or frozen at -90-degrees-C until assayed fo r peroxidase activity or number of alpha2-adrenergic receptors and aff inities or for both. In vitro perfused placentomes from day 5 pine nee dle-fed cows had greater (P < 0.05) PSC activity, as measured by the i ncrease in perfusion pressure in response to a depolarizing dose of KC l, 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 p ine needle-fed cows also exhibited greater (P < 0.05) contractile resp onses to adrenaline than day 3 pine needle-fed or control-fed cows. Co ntractile responses to phenylephrine were similar (P > 0.1) for all th ree treatment groups. The observed increase in PSC activity and respon siveness to adrenaline, however, was not reflected by increasing numbe rs or affinities of PSC or alpha2-adrenergic receptors on caruncular a rteries. Peroxidase activity (pg mg-1 tissue) was higher (P < 0.05) in caruncular tissue of pine needle-fed cows (299 +/- 39) than in contro l-fed (186 +/- 40) cows. The observed increase in peroxidase activity in caruncular tissue of pine needle-fed cows may function to increase local catechol oestrogen synthesis, in an attempt to inhibit the vasoc onstrictor effects of the substance(s) in pine needles.