SUPEROVULATORY TREATMENTS DO NOT ALTER PULSATILE LH-SECRETION IN OVARIECTOMIZED CATTLE

Previous work has shown a suppressive effect of superovulatory treatme nts on pulsatile LH release in cattle. This study tested the hypothesi s that this suppression may be caused, at least in part, by a direct e ffect of commercial gonadotropin preparations on the hypothalamus/pitu itary gland. Crossbred Holstein heifers, ovariectomized 20 d before th e start of the experiment, received 6 injections of FSH: (50 mg Folltr opin) at 12-h intervals (n = 6); a single injection of 2500 IU eCG fol lowed by 5 injections of sterile saline at 12-h intervals (n = 6); or 6 injections of saline at 12-h intervals (controls; n = 5). Blood samp les were taken every 10-min for 8 h the day before and 3 d after the b eginning of treatment to assess LH pulsatility. At the end of these sa mpling periods, a bolus injection of GnRH (7ng/kg) was given to assess pituitary responsiveness. There were no effects of the superovulatory drugs on mean LH concentrations, nor on LH pulse frequency or amplitu de (P>0.05). The pituitary response to GnRH was significantly elevated in eCG- but not FSH-treated animals (paired t test; P<0.05). These da ta demonstrate that superovulatory preparations do not suppress pulsat ile LH secretion independently of the ovaries in cattle.