title: Role of LH in the progesterone increase during the bromocriptine-induced prolactin decrease in heifers.
abstract: The luteotrophic effect of bromocriptine in heifers was studied to determine if the reported posttreatment increase in progesterone (P4) just before or at the beginning of luteolysis was attributable to loss of a luteolytic effect of prolactin (PRL) or to the stimulation of LH, a known luteotropin. Four treatment groups (n = 7) were used: control (Ct), bromocriptine (Bc; 16 mg/heifer), acyline (Ac; 3 μg/kg), and bromocriptine and acyline combined (BcAc). Bromocriptine (inhibitor of PRL) and acyline (antagonist of GnRH and therefore blocker of LH) were given at Hour 0 on Day 16 postovulation, and blood samples were taken hourly at Hours 0 to 8. Concentration of P4 was greater (P < 0.05) in the Bc group than in the Ct group at each of Hours 1 to 8. Concentration of LH increased (P < 0.05) between Hours 0 to 2 in the Bc group but not in the other three groups. The peak of the first posttreatment LH pulse occurred earlier in the Bc group than in the Ct group. Average concentration of PRL was lower (P < 0.05) and number of PRL pulses was less (P < 0.05) in the Bc group than in the Ct group. Acyline inhibited LH in the Ac and BcAc groups as indicated by a decrease (P < 0.05) in concentration between Hours 0 and 2 and a decrease (P < 0.001) in number of pulses/heifer during the 8 h. A decrease in PRL but not an increase in P4 and LH occurred in the BcAc group. Results supported the hypothesis that the P4 increase associated with PRL suppression by bromocriptine treatment is attributable to an increase in LH.
authors.affiliation: Eutheria Foundation, Cross Plains, Wisconsin, USA. ginther@vetmed.wisc.edu
authors.forename: O J
authors.initials: OJ
authors.lastname: Ginther
authors.forename: V G
authors.initials: VG
authors.lastname: Santos
authors.forename: R A
authors.initials: RA
authors.lastname: Mir
authors.forename: M A
authors.initials: MA
authors.lastname: Beg
mesh_terms: D000818:Animals; D001971:Bromocriptine / Q000494:pharmacology*; D002417:Cattle / Q000502:physiology*; D006727:Hormone Antagonists / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000378:metabolism*; D009842:Oligopeptides / Q000494:pharmacology; D011374:Progesterone / Q000097:blood / Q000378:metabolism*; D011388:Prolactin / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D006727:Hormone Antagonists; D009842:Oligopeptides; D001971:Bromocriptine; D011374:Progesterone; D011388:Prolactin; D007986:Luteinizing Hormone; C109238:acyline