Placental Lactogen and Somatotropin: Hormone Binding to the Corpus Luteum and Effects on the Growth and Functions of the Ovary in Heifers1

Abstract

The effects of recombinant bovine placental lactogen (rbPL) and recombinant bovine somatotropin (rbST) on development of ovarian follicles and CL were tested in heifers. Estrus (day = 0) was synchronized and heifers were treated (Days 0-21) with either saline (control; n = 7), rbST (25 mg/day; n = 6), or rbPL. (50 mg/day; n = 8). Blood was collected daily for analyses of progesterone, estradiol, ST, PL, and insulin-like growth factor (IGF)-I; ultrasound was performed daily for measurement of follicles and CL. PL in plasma (mean +/- SE; ng/ml) averaged 4.1 +/- 0.2 for rbPL-treated heifers, and ST in plasma (ng/ml) averaged 2.7 +/- 0.3 for rbST-treated heifers. IGF-I in plasma (ng/ml) was increased for rbST-treated (198 +/- 10; p < 0.001) and rbPL-treated (143 +/- 9; p < 0.06) heifers compared to controls (117 +/- 9). After Day 9 of the estrous cycle, heifers treated with rbPL had larger CL (p < 0.001) and more progesterone in plasma (p < 0.001) than controls, whereas rbST-treated heifers were intermediate for these measures. Largest follicles were decreased in size (mm) throughout the estrous cycle for rbPL-treated heifers (12.9 +/- 0.4) compared to controls (14.2 +/- 0.5; p < 0.06) or heifers given rbST (14.0 +/- 0.5; p < 0.11). After Day 17 (preovulatory period), concentrations of estradiol in serum (pg/ml) were decreased for rbST-treated (2.7 +/- 0.3; p < 0.01) and rbPL-treated (2.9 +/- 0.2; p < 0.02) heifers compared to controls (3.8 +/- 0.3).(ABSTRACT TRUNCATED AT 250 WORDS)

First lactation ovarian function in dairy heifers in relation to prepubertal metabolic profiles

“…Thus the PCL cows maintained their yield with greater dry matter intake, compared with DOV1 cows, without major adverse consequences for the reproductive system. The endocrine profile of high GH levels may, however, be responsible for the extension of the luteal phase, as GH has been shown to be luteotrophic in vitro (Liebermann & Schams 1994, Wathes et al 1995 and some studies have reported that administration of bovine somatotrophin to lactating cows can prolong the luteal phase (Schemm et al 1990, Gallo & Block 1991, Lucy et al 1994, although this effect was not seen in 1-year-old heifers (Yung et al 1996).…”

Pregnancy, parturition, and lactation in hypophyseal stalk-transected beef heifers

“…There is also evidence for bGH-R and bPRL-R transcripts in bovine extra-embryonic membranes and in the glandular uterine endometrium, but much lower levels of both receptor mRNAs in the caruncles (Kolle et al 1997). Recombinant bPL (rbPL) treatment increased the size of bovine corpus luteum, increased concentrations of progesterone in plasma, and specifically bound to luteal membranes, whereas the responses of bovine corpus luteum to recombinant bovine GH (rbGH) were much less than to rbPL (Lucy et al 1994a). Bovine corpus luteum and endometrium have a unique mRNA that hybridizes with a cDNA for bGH-R.…”

“…Bovine corpus luteum and endometrium have a unique mRNA that hybridizes with a cDNA for bGH-R. The giant cells of the bovine corpus luteum have been shown to be rich in GH-R message and to stain positively by immunohistochemistry for the presence of cell surface GH-R (Lucy et al 1993(Lucy et al , 1994a. The administration of rbGH increased both the size of the bovine corpus luteum and progesterone secretion; it also increased the progesterone response to gonadotropin-releasing hormone infusion in bGHtreated animals (Lucy et al 1994b, Adriaens et al 1995.…”

“…Thus, the biological activity of these related hormones not only depends on receptor distribution and affinity of hormone for the receptor, but also on transmission of signal in response to binding (Scott et al 1992, Anthony et al 1995b. The affinity of bPL for its own putative receptor and receptors for PRL and GH indicate that this placental hormone may act via three receptor types (Lucy et al 1994a). Differences in the primary structure of bPL compared with both bPRL and bGH present the possibility that bPL may participate in hormone-receptor dimers in a different manner to that of the pituitary hormones.…”

Superovulatory response and embryo quality of Holstein heifers treated with one or two injections of somatotropin

“…Thus, to increase yield of transferable embryos, selection of donors with high follicular populations must be considered. On the other hand, size of the follicular population can be manipulated by using recombinant bovine somatotropin (rbST), which produces an increase in the number of recruited small follicles (Gong et al, 1993a) and follicular growth after recruitment (De la Sota et al, 1993;Lucy et al, 1994). Pretreatment of the donor with rbST appears to reduce donor superovulatory variability (Gong et al, 1993b).…”