Hamster Prolactin: Physiological Changes in Blood and Pituitary Concentrations as Measured by a Homologous Radioimmunoassay

Borer, Katarina T.; Kelch, Robert P.; Corley, Kevin P.

doi:10.1159/000123348

Cited by 46 publications

(33 citation statements)

References 23 publications

(32 reference statements)

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“…Our immunohistochemical results revealed similar changes on the pituitary lactotropes in male golden hamsters submitted to short periods, although different from those periods used by Wang et al Other studies have previously shown that both PRL synthesis and release are severely inhibited in hamsters exposed to SP [22, 23]. On the other hand, Massa and Blask [24]found that light deprivation due to blindness or to exposure to SP for 42–56 days depresses the activity of the lactotrope cells in Syrian hamsters, with significant diminution of the pituitary levels of PRL mRNA.…”

Section: Discussionsupporting

confidence: 70%

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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Section: Discussionsupporting

confidence: 70%

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

et al. 2002

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“…The acrophase of serum PRL in the indooranimals(= 20.00 h) is close to the peak in serum PRL observed by Goldman et al [12] in both stressed and non-stressed male hamsters exposed to 14:10 LD (lights on 05.00). Another study [35] examined PRL concentrations throughout a 24-hour fasting and 12-hour refeeding period in male hamsters. However, comparison of our data with their [35] results is impossible since the time of day at which the starvation began was not given, although it is interesting that refeeding was associated with a sharp rise in PRL.…”

Section: Discussionmentioning

confidence: 99%

“…Another study [35] examined PRL concentrations throughout a 24-hour fasting and 12-hour refeeding period in male hamsters. However, comparison of our data with their [35] results is impossible since the time of day at which the starvation began was not given, although it is interesting that refeeding was associated with a sharp rise in PRL.…”

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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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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“…Although certain neuroendocrine responses to stress may be adaptive mechanisms, the analysis of GH secretion in organisms under stressful conditions has an important aspect in understanding the physiology of stress. Numerous observations have shown that stress alters the pattern of GH secretion in a different manner in various species; in hamsters (Borer et al, 1982), monkeys (Brown et al, 1971;Meyer and Knobil, 1987) and men (Schalch, 1967;Schalch and Reichlin, 1968) stress increases GH secretion, while in rats (Day et al, 1983;Armario et al, 1986;Aquila et al, 1991;Benyassi et al, 1992;Franci etal., 1992) GH secretion is inhibited. Little is known about GH secretion under stressful conditions in farm animals.…”

Section: Introductionmentioning

confidence: 99%

Growth hormone secretion in anestrous ewes subjected to prolonged stressful stimuli

Przekop¹,

Krejci²,

Slaba³

1995

J. Anim. Feed Sci.

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The study was performed on 6 three-year-old Polish Merino ewes to examine the effects of prolonged intermittent footshock stimuli on the secretion of growth hormone (GH) in anestrous ewes. The state of stress was induced by electrical footshocks of enduring and repetitive character (20 min/h, 9 h daily during 3 consecutive days, current intensity 3 mA). The blood samples were taken at 2 h intervals on the day prior to stimulation (controls), during 3 days of footshock application, and on the post-stress day. The control levels of plasma GH were quite low (from 1 to 6 ng/ml) and in some samples they were at, or near,the limit of detection. The mean 24 h plasma GH level ranged from 0.51 to 3.70 ng/ml. The mean concentration of GH in all ewes prior to the exposure to footshock stress was 2.12 + 0.55 (SE) ng/ml. Footshock led to marked increase in GH concentration; the mean plasma level of GH in animals reached about 200% of pre-stress values. There were no significant differences between GH responses in the first, second and third day of exposure to footshock stimuli. The mean level of plasma GH on the post-stress day did not differ significantly from the control concentration. However, in 4 out of 6 ewes the mean 24 h plasma GH level was lower as compared to the value found in controls. In conclusion, these results indicate that prolonged intermittent footshock stimulation increases GH secretion in anestrous ewes, after which the concentration of this hormone in the blood plasma in most animals on the post-stress day returns to normal, pre-stress values. It is suggested that changes in GH concentrations, among others, may be to some extent a valuable indicator of the biological cost of environmental challenges.

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Hamster Prolactin: Physiological Changes in Blood and Pituitary Concentrations as Measured by a Homologous Radioimmunoassay

Cited by 46 publications

References 23 publications

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

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

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

Growth hormone secretion in anestrous ewes subjected to prolonged stressful stimuli

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