In the present study, the pulsatile serum profiles of prolactin, LH and testosterone were investigated in eight clinically healthy fertile male beagles of one to six years of age. Serum hormone concentrations were determined in blood samples collected at 15 min intervals over a period of 6 h before (control) and six days before the end of a four weeks treatment with the dopamine agonist cabergoline (5 mg kg À1 bodyweight/day). In addition, the effect of cabergoline administration was investigated on thyrotropin-releasing hormone (TRH)-induced changes in the serum concentrations of these hormones.In all eight dogs, the serum prolactin concentrations (mean 3.0 AE 0.3 ng ml À1 ) were on a relatively constant level not showing any pulsatility, while the secretion patterns of LH and testosterone were characterised by several hormone pulses. Cabergoline administration caused a minor but significant reduction of the mean prolactin concentration (2.9 AE 0.2 ng ml À1 , p < 0.05) and did not affect the secretion of LH (mean 4.6 AE 1.3 ng ml À1 versus 4.4 AE 1.7 ng ml À1 ) or testosterone (2.5 AE 0.9 ng ml À1 versus 2.4 AE 1.2 ng ml À1 ). Under control conditions, a significant prolactin release was induced by intravenous TRH administration (before TRH: 3.8 AE 0.9 ng ml À1 ,
Plasma concentrations of beta-endorphin and met-enkephalin were measured, with appropriate radioimmunoassays, in cows during gestation and at parturition and in newborn calves. During pregnancy beta-endorphin immunoreactivity (IR) concentration increased, but values during the last month of gestation were not different from those at parturition. Highest met-enkephalin IR levels were obtained in cows during calving. A term Caesarean section caused an increase in plasma beta-endorphin and met-enkephalin IR concentrations, but no such increase occurred in cases of a preterm Caesarean section. In calves beta-endorphin IR values were lower before umbilical cord rupture than immediately after birth. Values decreased continuously thereafter. This was also the case for met-enkephalin IR concentrations in calves born at term. In preterm calves met-enkephalin IR values were low immediately after delivery and increased during the first hour of life. A significant correlation existed between the degree of acidosis and plasma levels of both opioid peptides in the calves. We conclude that a direct stimulation of peripheral beta-endorphin release by the pain or stress associated with calving does not seem to exist in cattle, whereas met-enkephalin seems to be more directly related to parturition. In calves the change to the extrauterine environment causes an immediate, increased release of both opioids.
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