Preliminary studies of the effects of bromocriptine on testicular regression and the spring moult in a seasonal breeder, the male blue fox (Alopex lagopus)

Smith, A. J.; Mondain-Monval, M.; Simon, P.; Berg, K. Andersen; Clausen, O. P. F.; Hofmo, P. O.; Scholler, R

doi:10.1530/jrf.0.0810517

Cited by 27 publications

(14 citation statements)

References 22 publications

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“…Chronic bromocriptine treatment interferes with the coat growth and moult cycle of several seasonal species (Duncan & Goodman, 1984;Martinet et al 1984;Smith, Mondian-Monval, Simon et al 1987; present study), and in the Djungarian hamster the effects of bromocriptine can be reversed by con¬ comitant administration of prolactin (Duncan & Goodman, 1984). In mink, the moult from winter to summer coat is advanced by injection of prolactin in the spring (Martinet et al 1981) and treatment with bromocriptine in midsummer induces early growth of the winter coat (Martinet et al 1984).…”

Section: Discussionmentioning

confidence: 54%

Effects of chronic long-acting bromocriptine treatment on liveweight, voluntary food intake, coat growth and breeding season in non-pregnant red deer hinds

Curlewis

Loudon²,

Milne³

et al. 1988

Journal of Endocrinology

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Seventeen red deer hinds were housed in individual pens and from 28 February until 11 November were injected each week with vehicle (group A; n = 6) or 5 (group B; n = 6) or 12.5 mg (group C; n = 5) of a long-acting formulation of bromocriptine. Liveweight and voluntary food intake (VFI) were recorded for each hind, and blood was collected for determination of progesterone, prolactin, tri-iodothyronine (T3) and cortisol concentrations by radioimmunoassay. Treatment with the high dose of bromocriptine was associated with a significant (P less than 0.05) reduction in VFI, with the effect being greatest between March and July. There was no treatment effect on liveweight, but there was a significant (P less than 0.01) interaction between time and treatment due to the faster rate of weight gain in control animals at the beginning of the experiment. Changes in liveweight could be explained by changes in VFI rather than by changes in the efficiency of utilization of intake. Termination of the breeding season was significantly (P less than 0.01) delayed by 54 days in group C hinds. Growth of the summer coat and subsequent winter coats was delayed by 1 and 3 months respectively in group C hinds, and in groups B and C the duration that animals were in summer coat was increased by about 1 month. The seasonal increase in prolactin concentrations was seen in all groups, but levels were significantly (P less than 0.05) lower in group C hinds. Concentrations of T3 and cortisol were not affected by bromocriptine.

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Section: Discussionmentioning

confidence: 54%

Effects of chronic long-acting bromocriptine treatment on liveweight, voluntary food intake, coat growth and breeding season in non-pregnant red deer hinds

Curlewis

Loudon²,

Milne³

et al. 1988

Journal of Endocrinology

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“…However, chronic treatment of red deer hinds with bromocriptine from midwinter onwards significantly delays the seasonal rise in prolactin concentration and the onset of anoestrus (Curlewis et al 1988). Using the same long-acting preparation of bromocriptine, Smith, Mondain-Monval, Simon et al (1987) have reported that suppression of the springtime rise in prolactin is associated with a significant effect on the timing of testicular regression in the seasonally breeding blue fox. Thus while most authors have concluded that prolactin plays little or no role in regulating the timing of seasonal breeding, the effects of chronic bromo¬ criptine administered from the winter or springtime onwards on prolactin and the breeding season warrant further investigation.…”

Section: Discussionmentioning

confidence: 99%

“…In fur-bearing mammals such as the mink and blue fox, blockade of prolactin secretion with chronic bromocriptine treatment interferes with the normal moult of the winter coat and growth of the summer coat (Martinet, Allain & Weiner, 1984;Smith et al 1987). Experiments on the Djungarian hamster have demonstrated that the action of bromocriptine on coat moult can be counteracted by simultaneous administration of prolactin (Duncan & Goldman, 1984).…”

Section: Discussionmentioning

confidence: 99%

A comparison of the seasonal hormone changes and patterns of growth, voluntary food intake and reproduction in juvenile and adult red deer (Cervus elaphus) and Père David's deer (Elaphurus davidianus) hinds

Loudon¹,

Milne²,

Curlewis³

et al. 1989

Journal of Endocrinology

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Non-domesticated seasonally breeding ungulates exhibit marked seasonal changes in metabolic rate, voluntary food intake (VFI), pelage growth and moult and hormone secretion. It is not known whether these seasonal rhythms are regulated by the same central processes which control the onset and termination of the breeding season. Here we compare two closely related deer species which have significantly different mating and calving seasons. Seasonal changes in VFI, liveweight, coat growth, plasma prolactin and tri-iodothyronine (T3), and the timing of the breeding season were examined over a 15-month period in six adult post-pubertal red and Père David's deer from January to April the following year. The timing of the seasonal changes in prolactin, T3, VFI and coat growth were all significantly advanced by 56, 23, 60 and 54 days respectively in the Père David's deer. The times of onset and termination of the breeding season of Père David's deer were also significantly advanced by 90 days, but in both species, the breeding season was of similar duration (160 +/- 5 (S.E.M.) days). Changes in liveweight of adult red deer could be explained by changes in VFI rather than efficiency of utilization. This was not the case in Père David's deer and may indicate seasonal changes in the efficiency of energy utilization. In order to establish whether these species differences develop with age, we undertook a second study in which seasonal changes in VFI, growth, plasma prolactin concentrations and the timing of the onset of the breeding season were recorded for ten red deer and six Père David's deer from 6 to 18 months of age. Both species exhibited a similar decline in VFI in the first autumn of life. Subsequently, the Père David's deer exhibited an advance in the timing of the seasonal peak in VFI and prolactin (21 and 66 days respectively); puberty occurred 3 months earlier than in red deer. The earlier breeding season of the Père David's deer was associated with a significant advance in a range of seasonal endocrine and physiological parameters. These species differences may develop with age. Our data indicate that seasonal patterns of metabolism and growth may be closely linked to those mechanisms which also regulate the onset and termination of the breeding season.

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“…There is also very little known about the role of PRL in seasonal reproduction. In some species such as the blue fox [5] and red deer hind [6], PRL appears to inhibit repro duction although this is not a general finding [7].In the non-seasonally breding laboratory rat, PRL secretion is controlled by short-loop feedback [see ref. 8 for a review] and, Received: August 27, 1990 Accepted after revision: February 18, 1991 in conditions where there is a marked increase in plasma PRL concentrations such as during lactation [9] and in ageing rats [10], high PRL concentrations are due to the absence of PRL short-loop feedback control of PRL secretion.…”

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confidence: 99%

Prolactin Short-Loop Feedback and Prolactin Inhibition of Luteinizing Hormone Secretion during the Breeding Season and Seasonal Anoestrus in the Ewe

Curlewis

McNeilly²

1991

Neuroendocrinology

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In seasonally breeding mammals, plasma prolactin (PRL) concentrations vary on an annual basis with levels high in summer and low in winter. In this study of the ewe, we determined, first, whether PRL secretion is regulated by short-loop feedback and, second, whether the high summer levels of PRL are due to a change in sensitivity or loss of this feedback loop. Because the high summer levels of PRL coincide with the period of seasonal anoestrus in the ewe and could therefore be involved in the seasonal suppression of gonadotrophins, the effects of intracerebroventricular PRL on pulsatile LH secretion were also determined. Ovary intact ewes received intracerebroventricular injections of ovine PRL (oPRL; 50 µg) or anti-PRL serum. From 3 to 13 h after central administration of oPRL, plasma PRL concentrations were significantly reduced compared with the vehicle-treated controls. In contrast, following injection of anti-PRL serum, plasma PRL levels increased significantly. To determine whether there was a seasonal change in sensitivity to PRL feedback, a series of experiments were conducted in July and November when PRL concentrations are high and low, respectively. At each time of year, ovariectomized oestradiol-implanted ewes were injected intra-cerebroventricularly with 10 and 50 µg oPRL with control animals receiving the vehicle. At both times of year there was clear evidence of PRL short-loop feedback with no indication that sensitivity was reduced in the July trial. Luteinizing hormone (LH) pulse frequency, pulse amplitude and mean LH were not affected by intracerebroventricular oPRL at either time of year. These results indicate that the high PRL concentrations of summer are not due to the absence of PRL short-loop feedback and that suppression of pulsatile LH secretion during seasonal anoestrus is unlikely to be due to inhibition by PRL.

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Preliminary studies of the effects of bromocriptine on testicular regression and the spring moult in a seasonal breeder, the male blue fox (Alopex lagopus)

Cited by 27 publications

References 22 publications

Effects of chronic long-acting bromocriptine treatment on liveweight, voluntary food intake, coat growth and breeding season in non-pregnant red deer hinds

Effects of chronic long-acting bromocriptine treatment on liveweight, voluntary food intake, coat growth and breeding season in non-pregnant red deer hinds

A comparison of the seasonal hormone changes and patterns of growth, voluntary food intake and reproduction in juvenile and adult red deer (Cervus elaphus) and Père David's deer (Elaphurus davidianus) hinds

Prolactin Short-Loop Feedback and Prolactin Inhibition of Luteinizing Hormone Secretion during the Breeding Season and Seasonal Anoestrus in the Ewe

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