Prolactin Cell Activity in Female and Male Syrian Hamsters: An Apparent Sexually Dimorphic Response to Light Deprivation and Pinealectomy

De, Blask; Ca, Leadem; Km, Orstead; Br, Larsen

doi:10.1159/000124242

Cited by 31 publications

(28 citation statements)

References 15 publications

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“…Previous studies [32,33] have indicated that a depres sion in pituitary PRL content, mRNA levels, newly syn thesized PRL and pituitary RIA PRL accompany light deprivation in male hamsters. These studies were based on animals killed during the day (pituitaries [32] were removed between 08.00 and ll.OOh and incubated for 3 h) when, in our experiment, daytime assayable levels are also very low.…”

Section: Discussionmentioning

confidence: 96%

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Circadian Rhythms in Reproductive and Thyroid Hormones in Gonadally Regressed Male Hamsters Exposed to Natural Autumn Photoperiod and Temperature Conditions

et al. 1994

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Two groups of young adult male Syrian hamsters were kept in a vivarium at 22°C and a light :dark cycle of 14.5:9.5 h (lights on 06.30 h; indoor) or in a naturally decreasing photoperiod and fluctuating ambient temperature conditions (outdoor) from October 1 (day length 11 h 50 min) to November 30 (day length 10 h 12 min). Representative animals from each group were killed at 3-hour intervals with additional time points near the onset of light. Weights of the paired gonads and accessory organs revealed that all of the animals kept outdoors and none of those kept indoors underwent reproductive regression. Significant circadian rhythms were observed in serum luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin (PRL), thyrotropin (TSH), thyroxine (T₄), triiodothyronine (T₃) and testosterone in indoor and outdoor-housed hamsters. The 24-hour acrophase in serum LH, TSH, T₄ and T3 occurred between 13.00 and 16.00 h, while that of serum testosterone and PRL occurred between 18.00 and 20.00 h in indoor hamsters. Hormonal variables in which there was a significant alteration in the 24-hour acrophase of outdoor animals relative to that in the indoor animals included pituitary PRL and serum testosterone, PRL, FSH and TSH. Hamsters housed indoors had a significant rhythm in brown adipose tissue type-II 5’-deiodinase activity, but no rhythm was evident in this tissue in outdoor animals. The natural autumnal conditions depressed serum LH and testosterone around the clock, though the depression of serum FSH relative to indoor hamster values was best seen between 09.00 and 21.00 h and that for PRL between 15.00 and 24.00 h. The overall lower T4 and higher T3 and type-II 5’-deiodinase in brown adipose tissue in the outdoor group suggest a role for accelerated peripheral conversion of T₄ in producing the thyroid hormone changes of autumn conditions.

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Section: Discussionmentioning

confidence: 96%

“…These studies were based on animals killed during the day (pituitaries [32] were removed between 08.00 and ll.OOh and incubated for 3 h) when, in our experiment, daytime assayable levels are also very low. However, our study shows that a significant surge in pituitary PRL stores to control levels occurred during the night.…”

Section: Discussionmentioning

confidence: 99%

Circadian Rhythms in Reproductive and Thyroid Hormones in Gonadally Regressed Male Hamsters Exposed to Natural Autumn Photoperiod and Temperature Conditions

et al. 1994

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“…In hamsters, Blask et al [18]found that the suppressive effects of light deprivation and blindness for 14 weeks on PRL cell function seem to be pineal-dependent in males, while these effects would be partially pineal-independent in females. Thus, a dimorphism according to sex was especially evident, since in females a direct retinohypothalamic-suprachiasmatic input in structures of the medial basal tuberal region of the hypothalamus would regulate the function of the lactotropes, without the intervention of the pineal gland.…”

Section: Discussionmentioning

confidence: 99%

“…This may lead to atrophy of the reproductive organs by means of an induction in pineal activity, while pinealectomy (Px) prevents the suppressing effects on the lactotrope cells [1, 16, 17, 18]. This was especially effective in female hamsters, showing a dimorphism in accord with sex [19].…”

Section: Introductionmentioning

confidence: 99%

Influence of Photoinhibition on the Morphology and Function of Pituitary Lactotropes in Male Golden Hamsters

et al. 2002

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Inhibition of prolactin (PRL) secretion has been previously shown in pituitaries from male and female hamsters exposed to short photoperiods. The purpose of the present study was to analyze the possible quantitative immunohistochemical and ultrastructural changes of PRL cells in male golden hamsters undergoing regression and spontaneous recrudescence, correlating the morphological findings with circulating PRL levels. Thus, adult male golden hamsters were exposed for 8, 16, 22 and 28 weeks to either short photoperiods (SP: 6 h light, 18 h darkness) or long photoperiods (LP: 14 h light, 10 h darkness). Pituitaries were processed for both light and electron microscopy, and serum levels of PRL were assessed by radioimmunoassay (RIA). Volume density (VD = cell area/reference area) and cell density (CD = number of cells/reference area) of lactotropes were measured with an image analysis system (Imaging Technology, Software Optimas 5.2). One hundred lactotropes were recorded for measuring several ultrastructural parameters. When analyzing the lactrotrope cell population from animals submitted to SP, the VD and CD were found to be significantly (p < 0.05) diminished with respect to those of the groups submitted to LP at weeks 8, 16 and 22. However, at week 28 a spontaneous recrudescence appeared. The lactotropes from animals submitted to LP for 8, 16, 22 and 28 weeks exhibited numerous large electrondense secretory granules. The rough endoplasmic reticulum (RER) presented some flat cisternae and numerous free ribosomes. Animals submitted to SP for 8 weeks showed a number of medium and large secretory granules, and the RER exhibited mainly numerous free ribosomes. In those animals submitted to SP for 16 and 22 weeks, lactotropes were found smaller and showed small and medium-sized secretory granules decreased in number. The Golgi complex exhibited some immature granules and dilated cisternae, while the RER did not present differences with respect to the 8-week SP group. The hamsters submitted to SP for 28 weeks presented medium and large secretory granules, and the RER exhibited dilated irregular cisternae. The ultrastructural morphometric parameters showed a decrease (p < 0.05) in the number of secretory granules and exocytotic profiles, as well as a diminution (p < 0.05) in the areas of Golgi complex, RER, secretory granules, and individual mean area of secretory granule during the 16 and 22 weeks of SP. Serum PRL levels were severely reduced under SP. This decrease was greater at 16 weeks than at 8 weeks of exposure. When hamsters were kept for 22 weeks under SP, PRL levels started their recovery. Thus, at the end of the experiment, the PRL values returned to near those of LP group. In summary, we found quantitative immunohistochemical and ultrastructural, as well as biochemical changes that suggest an inhibition of synthesis, storage and release of PRL in male golden hamsters submitted to SP, with a spontaneous recrudescence appearing at the end of the study.

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“…However, not all seasonal fluctuations in circulating PRL levels are solely dependent on the pineal melatonin signal. For example, it has been demonstrated that some of the inhibitory effects of a short-day photoperiod on PRL synthesis and release are still evident in pinealectomized female Syrian hamsters [6]. In addition, hypothalamic knife cuts in the paraventricular nucleus (PVN) region that abolish the rhythm in pineal melatonin activity result in declines in circulating PRL regardless of ambient photoperiod [7].…”

Section: Introductionmentioning

confidence: 99%

Norepinephrine Dialysate Levels in the Hypothalamic Paraventricular Nucleus: Influence on Photoperiod-Driven Prolactin Levels in the Female Siberian Hamster

Dodge¹,

Badura²

2001

Neuroendocrinology

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Basal prolactin (PRL) levels in Siberian hamsters are modulated by ambient photoperiod via the nocturnal melatonin signal. Recent evidence from our laboratory has demonstrated that norepinephrine (NE), a putative neurochemical regulator of PRL secretion shows photoperiod-dependent fluctuations in the hypothalamic paraventricular nucleus (PVN) that are independent of the pineal melatonin signal. NE content in the PVN is elevated under a short-day photoperiod with a time course that follows the short-day-induced decline in PRL. NE could thus modulate the release of a prolactin-releasing factor that subsequently drives PRL synthesis and release rates. In order to determine whether NE release in the PVN correlates with basal PRL levels, this study evaluated the relationship between extracellular NE levels in the PVN and basal PRL under long- and short-day photoperiod conditions. In addition, the profile of NE during the proestrous surge of PRL was investigated. Female Siberian hamsters were housed either in long-day or short-day photoperiods for 8 weeks. After 6 weeks of photoperiod exposure, the animals were implanted with a stainless steel guide cannula aimed at the PVN. Two weeks later, the animals were fitted with a jugular cannula for serial blood sampling and implanted with an indwelling microdialysis probe. Dialysis samples were collected every 20 min for 5 h (12.00–17.00 h) from short-day-exposed animals and from long-day-exposed animals classified as being either in diestrus or proestrus. Blood samples were collected every hour and analyzed for PRL levels by radioimmunoassay. NE and methoxy-4-hydrophenylglycol (MHPG) levels were significantly higher in short-day-exposed animals, correlating with the suppressed basal secretion of PRL. Both long-day groups had lower NE and MHPG levels, and higher PRL, than the short-day group. However, long-day animals showed a significant decline in NE in proestrus just prior to the onset of the afternoon surge of PRL. These data suggest that NE released within the PVN participates in the regulation of photoperiod effects upon PRL secretion, as well as that of the afternoon surge of PRL on proestrus.

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Prolactin Cell Activity in Female and Male Syrian Hamsters: An Apparent Sexually Dimorphic Response to Light Deprivation and Pinealectomy

Cited by 31 publications

References 15 publications

Circadian Rhythms in Reproductive and Thyroid Hormones in Gonadally Regressed Male Hamsters Exposed to Natural Autumn Photoperiod and Temperature Conditions

Circadian Rhythms in Reproductive and Thyroid Hormones in Gonadally Regressed Male Hamsters Exposed to Natural Autumn Photoperiod and Temperature Conditions

Influence of Photoinhibition on the Morphology and Function of Pituitary Lactotropes in Male Golden Hamsters

Norepinephrine Dialysate Levels in the Hypothalamic Paraventricular Nucleus: Influence on Photoperiod-Driven Prolactin Levels in the Female Siberian Hamster

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