Changes in serum prolactin concentrations and ovarian prolactin receptors during embryonic diapause in mink
Rose, J.; Oldfield, J.E.; Stormshak, F.
Biology of Reproduction 34(1): 101-106
ISSN/ISBN: 0006-3363 PMID: 3006805 DOI: 10.1095/biolreprod34.1.101
Experiments were conducted to determine if prolactin receptors were present in the mink ovary, and to examine the relationship between receptor numbers and serum levels of prolactin (PRL) during embryonic diapause and blastocyst reactivation. For analysis of the physicochemical properties of prolactin receptors, ovaries were obtained from anestrous mink. All binding determinations were made using 125I-ovine prolactin (125I-oPRL), and 20 .mu.g of tissue protein from the 100,000 .times. g particulate fraction. To quantify prolactin receptors during gestation, 20 primiparous mink were mated twice on consecutive days between 4 and 10 March and assigned randomly to one of two groups. Mink in Group 1 (N = 8) were killed on 13 March when blastocysts were completing their migration into the uterus and entering a state of diapause. Animals in Group 2 (N = 10) were killed on 26 March during the period of blastocyst reactivation, just prior to implantation. To determine serum levels of prolactin during gestation, an additional 20 primiparous mink were similarly mated and bled every 4 days from 15 March to 8 April, and then every 7 days until 23 April. Prolactin concentrations were determined by a heterologous double antibody radioimmunoassay using porcine PRL for both tracer and standards. Optimum conditions for binding 125I-oPRL to ovarian membranes were attained at 25.degree. C after 12 h. Scatchard analysis receptors during anestrus was 85 fmol/mg protein, which increased significantly during embryonic diapause to 484 fmol/mg protein, then declined to 16 fmol/mg during blastocyst reactivation. Serum levels of prolactin began to increase soon after the vernal equinox (21 March) and were significantly elevated by 27 March. In view of the established role of prolactin as a luteotropin in mink, the observed reduction in number of receptors during blastocyst reactivation may have been due to the occupancy of these sites with endogenous prolactin. These data provide additional evidence that prolactin is an important regulator of ovarian function in mink.