LH release in mink (Mustela vison). Pattern of the LH surge and effect of metabolic status

Abstract

-The mink is a seasonal breeder with induced ovulation and delayed implantation. Reproductive processes are strongly influenced by energy supply and body condition. Items for which there is paucity or complete lack of data were the main objectives of this study: the temporal relationship between copulation and the pre-ovulatory LH surge and the influence of energy supply on LH release. A total of 30 yearling female mink with a well defined metabolic status was used. Twelve females kept in the laboratory were measured in six consecutive one-week balance periods each including the measurement of heat production by means of indirect calorimetry, and 18 females were kept under conventional farm conditions. The animals were fed so as to maintain energy balance (CON), flush fed by 2 weeks food restriction followed by 2 weeks refeeding (FLUSH), or kept in a negative energy balance (NEG). Plasma concentrations of the thyroid hormones, IGF-1 and insulin were determined weekly (n = 12), or 1 week after change in energy supply to the FLUSH group (n = 18). On the day of mating, blood samples for LH and oestradiol-17β (E 2 ) were taken before and immediately after mating and then 4, 8, 12, 24, 30 and 48 h thereafter. Frequent blood samplings, each lasting 60 min, were taken during the LH surge from two other females surgically fitted with venous access ports. Peak concentrations of LH were recorded on the first sampling, an average 16 min after mating. The concentrations remained elevated for 12 h, but almost decreased to basal values 24 h after mating. Plasma E 2 was high before mating and peak values were attained 4 h after mating after which it decreased. Energy supply had no significant influence on LH and E 2 , but there was a tendency for a more sluggish LH release in NEG animals. The lack of response in FLUSH animals was explained by these animals having a lower intake of metabolisable energy than CON animals, the total intake not being significantly different from the NEG group. Plasma concentrations of thyroid Reprod. Nutr. Dev. 40 (2000) 229-247 229

High leptin in pregnant mink (Mustela vison) may exert anorexigenic effects: a permissive factor for rapid increase in food intake during lactation

“…We previously demonstrated a high correlation between plasma insulin and leptin in non-pregnant mink dams and during GEST1/3 (r 0•75, P, 0•001; Tauson & Forsberg, 2002). However, because insulin concentrations declined in late gestation when food intake was low, which is in accordance with previous findings in mink demonstrating a close relationship between food intake and plasma insulin (Fink & Tauson, 1998;Fink et al 1998;Tauson et al 2000), the hyperleptinaemia found in the present study could not be explained by the stimulation by high insulin concentrations. Oestrogen seems more likely to have exerted stimulation because high concentrations of oestradiol-17b occur during the late part of gestation in mink (Tauson, 1991).…”

Aging influences steroid hormone release by mink ovaries and their response to leptin and IGF-I

“…Our observations confirm the previous reports ( Sundqvist et al, 1989 ; Tauson et al, 2000 ) of the release of steroid hormones progesterone and estradiol by mink ovaries. These hormones are considered important regulators of reproduction in this ( Tauson et al, 2000 ; Tauson, 2001 ) and other ( Sirotkin, 2014 ) species. The age-dependent changes in the release of progesterone and estradiol and their response to leptin and IGF-I provide the first evidence that these hormones are involved in the control of mink reproductive aging.…”

“…The farm breeding of these fur animals is important from an economical viewpoint, but the hormonal control of mink reproduction is insufficiently studied ( Sundqvist et al, 1989 ; Amstislavsky et al, 2008 ). The release and involvement of several hormones (including progesterone, estradiol and IGF-I) in the control of mink reproduction have been reported ( Sundqvist et al, 1989 ; Tauson et al, 2000 ; Tauson, 2001 ). Nevertheless, the role of leptin and IGF-I in the control of mink ovarian hormones release has not been studied.…”

Body-weight changes are clearly reflected in plasma concentrations of leptin in female mink (Mustela vison)

“…Reproduction in mink is strictly regulated by photoperiod and reproductive outcome is very responsive to nutritional manipulation (Tauson, 2001). In extremely lean animals the pre-ovulatory luteinizing hormone surge and ovulation can be abolished (Tauson et al 2000). None of the mated females was in such a lean condition at mating, but the female remaining barren had been in such condition by the end of the restriction period.…”

“…We have previously shown that insulin changes rapidly in mink in response to changes in energy supply (Fink et al 1998;Tauson et al 2000), which was confirmed here and fits the concept of insulin as regulator of energy-supply-induced changes in leptin secretion (Havel, 2000). However, food restriction may cause an increased sympathetic activity to the white adipose tissue (Migliorini et al 1997), and this regulation mediated via catecholamines and b-agonists seems to be more pronounced than other regulatory factors , so it cannot be excluded that this mechanism was the main cause of the decrease in plasma leptin during food restriction.…”