Effect of suppression of plasma prolactin on ovulation, plasma gonadotrophins and corpus luteum function in LH-RH-treated anoestrous ewes

Abstract

Nineteen Scottish Blackface ewes were given LH-RH (3 X 30 micrograms i.v., 90-min intervals) during anoestrus when prolactin levels were elevated. Plasma levels of prolactin were suppressed with CB 154 (twice daily, i.m.) on Days -5 to 0 (N = 5), 0 to +5 (N = 5) or -5 to +5 (N = 5) around the day of LH-RH treatment (Day 0). Control animals (N = 4) received saline on Days -5 to +5. Nine animals ovulated forming corpora lutea as judged by laparoscopy on Day +7. No difference in FSH or LH levels was found between treatments and ovulations occurred equally in all treatment groups. Progesterone levels were less than ng/ml in all animals up to Day 14. It is concluded that short-term suppression of prolactin does not affect the incidence of ovulation or corpus luteum progesterone production in LH-RH-treated anoestrous ewes.

Corpora lutea induced by gonadotrophin-releasing hormone treatment of anoestrous Welsh Mountain ewes: reduced sensitivity to luteinizing hormone in vivo and to chorionic gonadotrophin in vitro

“…Extended luteal phases were associated with higher plasma prolactin levels, suggesting that prolactin may affect luteal phase length. However, short-term pharmacological suppression of prolactin failed to alter luteal lifespan in anoestrous GnRH-treated (Group 5) ewes (McNeilly & Land 1979) or pituitary stalk-disconnected ewes (Niswender et al 1986), and pharmacological elevation of prolactin failed to prevent luteolysis induced by prostaglandin F 2a (Sasser et al 1977). Due to small numbers of CL, a direct comparison of the characteristics of 'short' and 'peristent' inadequate luteal phases in the Figure 6 Progesterone secretion by luteal tissue from the different experimental groups on day 4 (A) or day 12 (B) of the luteal phase, incubated with or without 10 IU/ml hCG or 0.5 mM dbcAMP in vitro.…”

“…Induction of ovulation in seasonally anoestrous ewes by the administration of luteinizing hormone (LH) or gonadotrophin-releasing hormone (GnRH; Crighton et al 1973) or GnRH agonist generates inadequate corpora lutea (CL), and such CL have been widely used as a model to study naturally occurring inadequate luteal function. The CL formed tend to be smaller and secrete less progesterone in vivo and in vitro than CL of the breeding season (McNeilly & Land 1979. Increasing the frequency of LH (McNeilly et al 1982) or GnRH pulses (Crighton et al 1975, McLeod et al 1982a, 1982b, Southee et al 1988a, 1988b to mimic the final stages of follicular maturation during the breeding season increased ovulation rate during seasonal anoestrus but still gave rise frequently to abnormal CL.…”

Dinâmica hormonal durante o processo luteolítico nas espécies equina e bovina; com ênfase sobre o papel da prolactina

“…Previous studies in ewes (PICAZO et al, 2000;LAND 1979) and the current study in heifers have not found a direct effect of bromocriptine on the preovulatory follicle, the LH preovulatory surge, or the ovulatory process in ruminants. In a study with daily sampling in cattle, PRL concentrations were low during diestrus and increased during the 3 d before estrus .…”

Ovulation rate in induced oestrous cycles of anoestrous ewes given bromocriptine

“…The reason for this is uncertain but it may be linked to the inhibition of the pre-oestrous prolactin surge described by Kann & Denamur (1974) Previous studies on the effects of short-term treatment with bromocriptine in the ewe have shown no effect on the natural release of LH in cyclic animals (Niswender, 1974), a slight reduction in the release of LH following the injection of LH-RH in anoestrous ewes (McNeilly & Land, 1979) and no effect of oestradiol benzoate on LH release in anoestrous ewes (Land, Carr, McNeilly & Preece, 1980). In the absence of long-term studies on ewes treated with bromocriptine these observations led Land et al (1980) to speculate that, unless hyperprolactinaemia has a long-term effect, its removal by bromocriptine alone is unlikely to eliminate seasonal anoestrus.…”