Gonadotrophins and ovarian steroids in cattle. II. Pulsatile changes of concentrations in the jugular vein throughout pregnancy.

Short-term secretion patterns (derived from samples collected from jugular vein cannulae every 20 min for 12 h) of LH, FSH, progesterone, oestradiol-17 beta, oestrone and prolactin were studied every 30 days during gestation in heifers. LH pulse frequency and amplitude was greater during the early (months 1-3) and end (months 8-9) than during mid-gestation when pulsatile LH secretion was almost abolished. The frequency of pulsatile FSH release, which was already twice as fast than of LH during early pregnancy, did not change throughout the whole gestation period. Mean, basal and maximal progesterone concentrations were highest during the first 3 months of gestation, were slightly reduced during mid-gestation and decreased further during the last 2 months preceding parturition. Pulses of progesterone occurred concomitantly with the parallel LH/FSH as well as the separate FSH pulses. Average oestradiol-17 beta concentrations during the first months of gestation were slightly higher than during the mid-luteal phase of the cycle and exceeded during mid-gestation concentrations measured at oestrus. Free oestrone could be detected as early as day 60 of pregnancy. Frequency and amplitude of short-term changes of oestrone increased after the 5th month. Discontinuous secretion of oestrone as well as oestradiol-17 beta was only arbitrarily but never consistently correlated with either each other or with pulsatile gonadotrophin release. Apart form an occasional coincidence with pulsatile release of other hormones prolactin concentrations seemed to depend rather on the season of the year and time of the day than on the individual pregnancy stage.(ABSTRACT TRUNCATED AT 250 WORDS)