Effect of an Estrogen Antagonist (Tamoxifen) on Cloprostenol-Induced Luteolysis in Heifers

Abstract

Experiments were conducted to determine the role of estrogens on endogenous PGF2 alpha secretion and luteolysis following injection of cloprostenol in heifers. In Exp. 1, eight luteal-phase heifers were used to evaluate tamoxifen (T) as an estrogen antagonist. Heifers received T (35 mg i.v.) or ethanol:saline vehicle (ES) every 4 h for 44 h. All received cloprostenol (500 micrograms i.m.) immediately after the start of T or ES, and received estradiol-17 beta (500 micrograms i.m.) 12 h later. Each ES heifer had a surge of luteinizing hormone (LH) within 48 h of estradiol injection, whereas T-treated heifers did not. Estrus was observed in three ES-treated heifers, but not in T-treated heifers. In Exp. 2, 10 heifers received T (35 mg i.v.) or ES every 4 h for 64 h beginning on d 15 postestrus. Cloprostenol (500 micrograms i.m.) was injected 16 h after the start of treatment. Concentrations of LH were similar (P greater than .05) in both groups. In ES heifers, concentrations of 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) increased; in T-treated heifers, PGFM remained at pre-cloprostenol levels. Luteolysis was induced in all heifers. Progesterone (P4) decreased to less than or equal to 1 ng/ml at similar (P greater than .05) rates in ES-treated and T-treated heifers. Mean concentration of P4 288 h post-cloprostenol was greater (P less than .05) in ES-treated than in T-treated heifers. Three ES-treated heifers, but no T-treated heifers, were in standing estrus. We conclude that T effectively antagonizes estrogen in cattle.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of Oestrogen Antagonist (Tamoxifen) on Steroid Hormone Levels, Maturation Process of Placentomes and Course of Late Pregnancy in Cows

“…By contrast, the secretion of progesterone was significantly lower in experimental cows, which is in agreement with Bowen et al (1988) and Jahn et al (1993). This decrease could be a consequence of reduced gonadotrophin secretion, observed in cyclic heifers and ovariectomized ewes (Clarke 1983;Jacobs et al 1988), but a direct effect of tamoxifen on the corpus luteum cannot be excluded.…”

“…Tam o x ifa n because it is believed that oestrogens are essential for the secretion of prostaglandins, preparation of the birth canal and maturation process of the placenta (Thorburn 1979;Taverne 1992). The anti-oestrogenic activity of tamoxifen in cyclic heifers has been demonstrated by Jacobs et al (1988). By contrast, there was no evidence in this study that tamoxifen antagonizes oestrogens in late pregnant cows.…”

“…By contrast, there was no evidence in this study that tamoxifen antagonizes oestrogens in late pregnant cows. The course of pregnancy was physiological and mature placentas were expelled, although in this study, compared with the experiment described by Jacobs et al (1988), the treatment period was much longer and the dose administered was higher. Further- Days before a n d after parturition Fig.…”

“…The antioestrogenic activity of this compound in the human and animals, mainly in the laboratory, has been demonstrated (Harper and Walpole 1967;Wakeling 1982;Patterson et al 1982;Sanford 1987). Jacobs et al (1988) observed inhibited behavioural estrus in cyclic heifers, lower secretion of LH, and lack of ovulation after intravenous treatment with 35 mg of this substance, every 4 h, during the 2 days after cloprostenol-induced luteolysis.…”

Ontogeny of the Epidermal Growth Factor Receptor during Development of the Fetal Bovine Mesonephros and Associated Organs of the Urogenital Tract1

“…9). In addition, tamoxifen, previously shown to be an antiestrogen in cattle [36], did not affect EGF receptor levels. These results, in addition to observations that estrogen did not specifically bind to a putative estrogen receptor or induce DNA synthesis in these cells [37], suggest that functional estrogen receptors are not present in these primary bovine mesonephric cells.…”