Interactions between melatonin and prolactin during gestation in mink (Mustela vison)

Abstract

Immature female mink, 8 weeks of age in July, were treated with implants releasing melatonin. Mating, which induced ovulation, took place during the normal breeding season in the following March. Circulating prolactin and progesterone concentrations did not undergo the expected gestational increases, and no embryos implanted. A similar absence of gestational changes in prolactin and progesterone values ensued in primiparous mink treated with the melatonin implant 2-3 days after the second of 2 matings. Administration of exogenous sheep prolactin (0.5 mg/day) by minipump induced precocious elevation of progesterone concentrations in mated mink. Prolactin administration overcame the effects of melatonin, in that the corpora lutea were activated and embryos implanted, but exogenous prolactin resulted in degeneration of implanted embryos both in the presence and absence of chronic melatonin. The results suggest that melatonin has a single effect in alteration of gestation in mink; i.e. the prevention of prolactin secretion. Hyperprolactinaemia may inhibit embryo development in this species.

Embryonic diapause and its regulation

“…The pineal gland was first implicated in studies in which its denervation by cervical sympathetic ganglionectomy disrupted photoperiodic regulation of the termination of diapause (Murphy & James 1974), later confirmed by pinealectomy and melatonin replacement (Bonnefond et al 1990). While chronic melatonin treatment of mink does not interfere with puberty, ovulation or blastocyst formation in mink, it prevents termination of diapause and implantation (Murphy et al 1990). Implantation can be rescued by exogenous prolactin in this species, suggesting a single mechanism for photoperiod induction of implantation.…”

“…Withdrawal of the dopamine agonist (Papke et al 1980) or administration of dopamine antagonists (Murphy 1983) terminates diapause in mink. Indeed, prolactin alone induced implantation in hypophysectomized mink (Murphy et al 1981), as did administration of prolactin to animals in protracted diapause due to chronic melatonin treatment (Murphy et al 1990). In macropod marsupials, prolactin plays an inhibitory role.…”

Embryonic diapause: development on hold

“…It is mediated via the pineal gland by a decrease in the duration of the nocturnal secretion of melatonin (reviewed in Lopes et al, 2004). Increasing photoperiod translates into increased secretion of prolactin from the pituitary (Murphy, 1983), and can be prevented by dopamine agonist treatment (Papke et al, 1980), hypophysectomy (Murphy et al, 1981) and chronic melatonin treatment (Murphy et al, 1990). All three treatments abrogate implantation.…”

Luteotropic Hormone Receptors in the Ovary of the Mink (Mustela vison) during Delayed Implantation and Early-Postimplantation Gestation

“…All samples were evaluated in a single assay in which the intraassay coefficient of variation, determined between duplicates, was less than 10%. Mink serum prolactin concentrations were determined in a double-antibody RIA employing canine antiserum against prolactin, previously validated for the mink [31]. The sensitivity of the assay was 30 pg/ml, and the intraassay coefficient of variation, calculated between duplicates, averaged 9.5%.…”