Release of LH, FSH and GnRH into pituitary venous blood in mares treated with a PGF analogue, luprostiol, during the transition period

Abstract

Nine mares received cannulae to collect blood from the pituitary venous outflow in the intercavernous sinus (ICS) and the jugular vein; in 4 mares, only jugular cannulae were used. Those 4 mares and 3 of the mares with cannulae in both positions received 7.5 mg luprostiol i.m. and 1 mare with both cannulae was treated with 3.75 mg uprostiol i.v. Blood samples were kept before and after treatment at 2-, 5- or 10-min intervals and concentrations of LH, FSH and GnRH were determined by RIA. Treatments resulted in an immediate sharp rise of LH and FSH in ICS and jugular blood samples within 2-10 min, with ICS concentrations rising earlier, and with peak levels of LH 8 to 100 times higher, respectively. In ICS samples, GnRH was elevated consistently only after LH and FSH had reached peak levels. At both locations, LH and FSH concentrations remained elevated 60-120 min after treatment, but had returned to baseline by 240 min. In 5 untreated mares with cannulae at both locations, sampling at 5-min intervals for 12 or 24h revealed no pulses of LH or FSH in 3 mares, and only one pulse a day, preceded by several small rises of GnRH during the hour before the pulses, in 2 mares.