Reproductive endocrinology in Hatano high- and low-avoidance rats during the estrous cycle

The high- and low-avoidance animals (HAA and LAA rats) were originally selected from Sprague-Dawley rats for their shuttle-box task. Reproductive endocrinology during the estrous cycle was compared between HAA and LAA rats. All HAA rats showed a regular 4-d estrous cycle, whereas most LAA rats (70.8%) showed a regular 5-d estrous cycle. The peak level of preovulatory luteinizing hormone (LH) surge level was significantly lower in LAA rats than in HAA rats on the day of proestrus. In contrast, the peak level of prolactin surge on the day of proestrus was significantly higher in LAA rats than in HAA rats. Plasma concentrations of follicle-stimulating hormone (FSH) and estradiol-17β were significantly lower in LAA rats as compared with HAA rats at 12 h on the day of estrus and from 24 h on the day of diestrus to 18 h on the day of proestrus. On the other hand, plasma concentrations of progesterone were significantly higher in LAA rats compared with HAA rats on the day of diestrus. The number of antral follicles (300–600 μm in diameter) at 12 h on the day of proestrus was significantly fewer in LAA rats than in HAA rats. The size and number of corpus luteum at 12 h on the day of estrus were significantly greater in LAA rats than in HAA rats. These results clearly demonstrated that apparent differences are observed in reproductive endocrinology between two Hatano strains. These strain differences probably originated from neural regulation of pituitary hormones.     

Differential responses of the hypothalamo-pituitary-adrenocortical axis to acute restraint stress in Hatano high- and low-avoidance rats

The high- and low-avoidance animal (HAA and LAA respectively) strains of Hatano rats were originally selected and bred from Sprague-Dawley rats for their performance in the shuttle-box task. The present study focused on the activity of the hypothalamo-pituitary-adrenocortical (HPA) axis of HAA and LAA rats in response to restraint stress. The restraint stress induced an elevation in plasma concentrations of ACTH, prolactin, corticosterone and progesterone. Peak levels of plasma ACTH during stress conditions were significantly higher in HAA rats than in LAA rats, while peak levels of prolactin were significantly lower in HAA rats than in LAA rats. Under stress conditions, ACTH and prolactin synthesis in the anterior pituitary glands was significantly higher in HAA rats compared with LAA rats. The peak plasma concentrations of corticosterone, during restraint stress, were significantly higher in LAA rats compared with HAA rats. These results indicate that the response of the hypothalamo-pituitary axis to acute restraint stress is greater in HAA rats than in LAA rats, whereas the ACTH-induced adrenal response of corticosterone release is higher in LAA rats than in HAA rats. On the other hand, prolactin secretory activity is higher in LAA rats compared with HAA rats. These differences in endocrine responses to stress may be involved in the regulation of the avoidance responses in the shuttle-box task.     

Gastric ulceration and expression of prolactin receptor in the brain in Hatano high- and low-avoidance rats

Recently, prolactin was shown to inhibit the development of stress-induced ulcers. However, the mechanism for suppression of gastric ulcers by prolactin has not been clarified. Hatano high-avoidance (HAA) and low-avoidance (LAA) strains of rats were originally selected and bred from Sprague-Dawley rats based on shuttle-boxtasks. The present study focused on the relationships among gastric ulceration and endocrine response with special reference to prolactin secretion and restraint stress in water of HAA and LAA rats. The restraint stress induced an elevation of plasma concentrations of ACTH, corticosterone, and prolactin. Peak levels of plasma ACTH during stressful condition were significantly higher in HAA rats than in LAA rats, while peak levels of prolactin were significantly lower in HAA rats than in LAA rats. The gastric erosion inde was significantly higher in HAA rats than in LAA rats 7 h after restraint stress in water. The numbers of prolactin-receptor-positive cells determined by immunohistochemistry in the paraventricular nucleus was significantly increased in LAA rats than in HAA rats 7 h after restraint stress in water. These results indicate that HAA rats were more sensitive than LAA rats to restraint stress in water. The strain differences in gastric ulceration under stress may be involved in peripheral prolactin secretion and central prolactin receptor expression. The expression of prolactin receptor in the paraventricular nucleus may be important in suppressing gastric ulceration.     

Endocrinological and pathological effects of anabolic-androgenic steroid in male rats

Many athletes use drugs, especially anabolic androgenic steroids (AAS), but there are few reports on the endocrinological and pathological changes in AAS abusers. In this study we reported the results of endocrinological examinations in rats administered AAS and also physical changes. We separated 37 male Wistar rats (7 weeks old) into 3 groups: Group A was medicated with nandrolone decanoate, metenolone acetate, and dromostanolone; Group B with nandrolone decanoate and saline; and Group C was given only saline. They were given subcutaneous injections of the medications or the control vehicle once a week for 6 weeks. Medications were stopped for 4 weeks, and then resumed for another 6 weeks. After that, rats were sacrificed. Serum testosterone level in Group A was significantly higher than that in Group C. Serum dihydrotestosterone in Group A was significantly higher than that in both Groups B and C. Serum estradiol-17beta levels in Groups A and B were significantly higher than that in Group C. In pathological evaluation, heart, testis, and adrenal gland were severely damaged. These findings indicate that there is a high degree of risk related to the use of AAS.     

Prolactin release and milk ejection in rats suckling underfed pups

Mother rats chronically exposed to underfed pups (obtained daily from nonlactating mothers) show increased milk production which is associated with increased consumption of food and water. The purpose of the present study was 2-fold: to examine whether the magnitude of maternal PRL discharge is related to the nutritional state of the pups and to differentiate between the role of the mother and that of the pups themselves in the regulation of milk intake. PRL release in response to reunion with pups (preceded by 4-h separation from pups) was measured between days 12 and 14 postpartum; each mother was tested twice, once with hungry pups (deprived of food for 24 h) and once with satiated (normally fed) pups. The magnitude of PRL discharge elicited by hungry pups in lactating as well as in thelectomized rats was twice as large as the discharge elicited by satiated pups. For each type of stimulus pups, the magnitude of PRL release was smallest in thelectomized rats, largest in rats that had nursed normally fed pups before testing, and intermediate in rats that had nursed underfed pups. The frequency of milk ejection was considerably reduced in mothers that were chronically exposed to underfed pups compared with mothers that had nursed normally fed pups. Regardless of the mother's previous history, and independent of the milk ejection frequency or maternal food and water intake, hungry pups ingested more milk than did satiated pups over the same suckling period even when both types of pups were suckled simultaneously by the same female. Milk ingestion in satiated pups was not enhanced by the vigorous sucking exerted by hungry littermates. It is suggested that hungry pups are able to meet their increased nutritional demands both directly, by withdrawing a larger portion of the milk available in the mammary glands, and indirectly, by enhancing maternal PRL secretion which in turn may promote maternal consummatory behavior and milk production.     

Caerulein stimulates pancreatic growth and somatic growth in suckling rats

This study deals with the stimulatory effect of caerulein on pancreatic and somatic growth in CFY suckling rats before weaning. After birth, caerulein (0.25, 0.5, 1, 3, 10 and 30 micrograms/kg) was given subcutaneously (s.c.) 3 times daily for 10 days. Saline-treated newborn rats were used as control. Caerulein increased pancreatic weight and total pancreatic trypsin activity reaching the maximum at 1 microgram/kg dose; higher doses did not cause higher values. On this basis 1 microgram/kg caerulein was applied s.c. 3 times daily for 3, 5, 10 and 20 days. At the end of the treatment pancreatic weight, total pancreatic protein, DNA content, trypsin and amylase activity was measured. Increases in body weight due to caerulein treatment were found from 6 days of treatment. Caerulein treatment increased pancreatic weight, total pancreatic DNA and protein content, and trypsin and amylase activity when applied for 5, 10 and 20 days. Treatment for 3, 5, 10 and 20 days with caerulein preferentially increased pancreatic trypsin activity compared to amylase activity. Trypsin activity per mg DNA increased with time in each caerulein-treated group demonstrating that the effect of caerulein increases with duration of treatment. In the saline-treated control group, however, pronounced increase in pancreatic amylase activity compared to that of trypsin activity was found in the age between days 11 and 21. This may be explained by the observation that the plasma corticosterone level increased during this period of postnatal life. The effect of caerulein in promoting pancreatic and somatic growth of suckling rats before weaning may be attributed to a specific enhancing effect of the peptide on proteolytic (e.g. trypsin) enzyme production of the pancreas.     

Caerulein stimulates pancreatic growth and somatic growth in suckling rats

Summary This study deals with the stimulatory effect of caerulein on pancreatic and somatic growth in CFY suckling rats before weaning. After birth, caerulein (0.25, 0.5, 1, 3, 10 and 30 μg/kg) was given subcutaneously (s.c.) 3 times daily for 10 days. Salinetreated newborn rats were used as control. Caerulein increased pancreatic weight and total pancreatic trypsin activity reaching the maximum at 1 μg/kg dose; higher doses did not cause higher values. On this basis 1 μg/kg caerulein was applied s.c. 3 times daily for 3, 5, 10 and 20 days. At the end of the treatment pancreatic weight, total pancreatic protein, DNA content, trypsin and amylase activity was measured. Increases in body weight due to caerulein treatment were found from 6 days of treatment. Caerulein treatment increased pancreatic weight, total pancreatic DNA and protein content, and trypsin and amylase activity when applied for 5, 10 and 20 days. Treatment for 3, 5, 10 and 20 days with caerulein preferentially increased pancreatic trypsin activity compared to amylase activity. Trypsin activity per mg DNA increased with time in each caerulein-treated group demonstrating that the effect of caerulein increases with duration of treatment. In the saline-treated control group, however, pronounced increase in pancreatic amylase activity compared to that of trypsin activity was found in the age between days 11 and 21. This may be explained by the observation that the plasma corticosterone level increased during this period of postnatal life. The effect of caerulein in promoting pancreatic and somatic growth of suckling rats before weaning may be attributed to a specific enhancing effect of the peptide on proteolytic (e.g. trypsin) enzyme production of the pancreas. Preliminary results were presented at the 17th Meeting of the European Pancreatic Club, Manchester, 15–17 September, 1985.     

Dexamethasone and indomethacin treatment during endotoxicosis in the suckling rat

Gram negative sepsis/septic shock continues to be a major cause of morbidity and mortality in newborns. We studied the effects of anti-inflammatory drugs, indomethacin (IND) and dexamethasone (DX), on glucoregulation, body weight, and mortality in 10-day-old suckling rats administered Salmonella enteritidis lipopolysaccharide (LPS). IND (1.5 mg/kg) or DX (4 mg/kg) was intraperitoneally (ip) administered immediately after highly lethal LPS injection. Both IND and DX attenuated the LPS-induced hypoglycemia and lactacidemia, and decreased the mortality, IND did not alter body weight changes in rats with septic shock. DX continued a catabolic state and reduced their body weights. In rats fasted for 24 hr before LPS injection, DX, but not IND, increased the mortality. We concluded that IND and DX improved the LPS-induced glucose dyshomeostasis and decreased the mortality of endotoxic shock in 4-hr-fasted 10-day-old rats. Per contra, DX was detrimental in 24-hr-fasted 10-day-old endotoxic rats.     

Reduction of salt sensitivity in stroke-prone spontaneously hypertensive rats administered an AT1 receptor antagonist during suckling

BACKGROUND: In this study, antihypertensive therapy was started during suckling and the effect on blood pressure (BP) and salt sensitivity of stroke-prone spontaneously hypertensive rats (SHRSP) was determined. METHODS: The SHRSP were treated with an AT1 receptor antagonist (losartan: 100 mg/L in drinking water) from 2 to 4 weeks of age. After stopping treatment at 4 weeks of age, the control group and the losartan group were fed a commercial diet with tap water ad libitum until 10 weeks of age. Both the control and losartan groups were switched to 1% saline at the age of 10 weeks. RESULTS: Salt loading was started at 10 weeks of age, with BP levels of 203+/-3 and 199+/-6 mm Hg for the control group and the losartan group, respectively, at that age. After 4 weeks of salt loading, BP levels were 253+/-7 mm Hg in the control group and 242+/-5 mm Hg in the losartan group, showing a mild elevation in the losartan group. The life span of the losartan group (104+/-78 days) was significantly greater than that of the control group (37+/-17 days). Plasma aldosterone concentrations of the losartan group were lower than those of the control group at 4 and 15 weeks of age. CONCLUSIONS: We have demonstrated the renin-angiotensin-aldosterone system may play a key role in the establishment of end-organ salt sensitivity, and the period of lactation in critical for salt sensitivity in later life.     

Autologous regulation of pancreatic glucocorticoid receptors in suckling rats.

The exact mechanism of glucocorticoid action in pancreatic ontogeny is not fully understood. To investigate whether glucocorticoid receptors are subjected to autologous regulation during the early stage of life, the effects of glucocorticoid administration and adrenalectomy (Adx) were examined. Rat pups adrenalectomized on day 10 were given either dexamethasone (DX, 20 micrograms/100 g body weight) or vehicle daily for 3 days before being killed at 15 days of age. Adx increased and DX replacement decreased glucocorticoid receptor binding in the developing rat pancreas. Scatchard analysis showed that Adx led to an increase in receptor number without changing its affinity (Bmax, from 0.385 +/- 0.073 to 0.553 +/- 0.086 pmol/mg protein; Kd, from 2.2 +/- 0.5 x 10(-8) M to 2.7 +/- 0.6 x 10(-8) M), whereas DX down-regulated its own receptor by decreasing the receptor number and lowering the affinity (Bmax, from 0.553 +/- 0.086 to 0.140 +/- 0.025 pmol/mg protein; Kd, from 2.7 +/- 0.6 x 10(-8) M to 8.8 +/- 2.5 x 10(-8) M). The degree of down-regulation was dependent on the dose of DX. Maximal down-regulation (80%) was found at 20 micrograms/100 g body weight, whereas a dose of 1 microgram/100 g body weight caused only 40% down-regulation. Down-regulation was also ligand specific. DX was the most effective, whereas even at 100 times the DX dose, corticosterone had only 70% of the effect of DX. DX-induced down-regulation occurred rapidly (within hours), whereas up-regulation in Adx occurred relatively slowly (days), suggesting these two phenomena involve different mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)     

Enhanced host defense mechanisms with levamisole in suckling rats.

Levamisole, a synthetically produced anthelminthic agent, was administered to suckling rats that were challenged with bacterial and viral pathogens. There was no in vitro antibacterial or antiviral effect of the drug. However, enhanced survival was demonstrated in those animals treated with levamisole and challenged with Staphylococcus aureus or herpes simplex virus. The mechanism for protection against the bacteria appears to be enhancement of the primary inflammatory response. The mechanism for protection against herpes simplex virus is not yet understood.     

Induction and reversibility of thyroid proliferative changes in suckling rats given thiocyanate

Potassium thiocyanate given in the drinking water of pregnant rats led to decreased body weight in their 14-day-old offspring (27%) without altering thyroid weight. Reduction of the suckling rat's body weight could be explained be defective thyroxinemia (38). Plasma FT3 and TSH were unchanged after thiocyanate treatment. The biochemical changes were in agreement with the histological aspects of the hypothyroid animals. The typical pattern was hyperplastic goiter. Colloid volume was reduced compared with controls. Presence of resorbed peripheral vacuoles, a sign of thyroid hyperactivity, was disclosed by a three-fold increase in radioiodide (131I) uptake compared with controls. When the antithyroid drug was removed from the mother's milk, the pups'weight increased but did not reach control values. Plasma thyroid hormone levels returned to normal and even exceeded control values in spite of partial recovery of thyroid iodine content when thiocyanate treatment was stopped for ten days.     

Stimulation of anterior pituitary galanin and prolactin gene expression in suckling rats

Recent evidence suggests that galanin, may regulate prolactin (PRL) secretion during lactation. In this article, we describe the regulation of anterior pituitary galanin and PRL gene expression during pregnancy and after parturition in the rat. Expression of galanin and PRL in the anterior pituitary were significantly higher at d 20 of pregnancy compared to diestrus. One day after parturition, galanin mRNA levels increased a further 4.5-fold. This post partum increase in gene expression was not observed for PRL. The increase in galanin gene expression was maintained above the diestrous level for at least 10 d after parturition. PRL mRNA expression, on the other hand, was largely unchanged after parturition. Although the increase in galanin gene expression 1 d after parturition was independent of suckling, subsequently, galanin, gene expression was significantly higher in nursing mothers. Anterior pituitary galanin gene expression was 12-fold higher in nursing mothers compared with those that were not, 3 d after parturition. Similarly, PRL gene expression was significantly lower in mothers who were not suckling their pups 3 d after parturition. Initiation of suckling alone was insufficient to stimulate galanin and PRL expression. Despite suckling for 2 d, removal of the suckling stimulus subsequently resulted in a rapid decrease in galanin gene expression. Hence, the stimulatory effect of suckling on galanin expression requires a sustained suckling stimulus. In conclusion, the data support the hypothesis that anterior pituitary galanin plays an important role during lactation, likely acting to amplify lactotroph stimulation through paracrine and autocrine mechanisms.     

Insulin determines leptin responses during a glucose challenge in fed and fasted rats

OBJECTIVE: Leptin secretion has been shown to respond acutely to changes in blood glucose and insulin. Nutritional state also has a marked effect on both the level of circulating leptin protein and leptin gene expression. The aim of this study was to assess whether the prior nutritional state altered the leptin secretory response to an acute glucose challenge, and to determine potential mechanisms. DESIGN: Male fed or fasted rats (200-250 g) were administered a single intravenous glucose bolus (1, 4 or 7 g/kg). The serum leptin, glucose, insulin and free fatty acid responses were studied over the following 5 h. The level of leptin gene expression and leptin protein was then determined in the epididymal fat pads, and in fed and fasted untreated rats for basal comparison. RESULTS: Leptin secretion in response to glucose was suppressed in fasted rats following all glucose doses. The total leptin response was correlated with the total insulin response in all conditions (r = 0.85) and with the glucose response in fed rats (r = 0.69). Both leptin gene expression and leptin protein content were lower in basal fasted rats. Leptin gene expression and leptin protein content still remained lower 5 h following a glucose bolus but there was partial reversal of the effects of fasting following the 7 g/kg glucose dose. CONCLUSIONS: Leptin secretion in response to an intravenous glucose bolus was determined by the insulin response and was significantly suppressed in fasted compared to fed rats. In addition to differences in the total insulin response of the animals, lower leptin responses may be facilitated by lower levels of both leptin gene mRNA and pre-existing leptin protein in epididymal adipose tissue of fasted rats.     

Effects of 1,25-dihydroxycholecalciferol and calcium on calcitonin mRNA levels in suckling rats

The chronic administration of 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) to 9-day-old suckling rats induced no change on day 13 in the calcitonin (CT) mRNA steady-state level of thyroid glands measured by Northern hybridization. Thyroidal CT contents were decreased in relation to increased plasma calcium levels in animals treated with 0.1 or 1 microgram 1,25-(OH)2D3/kg. Using a lower dose (0.01 microgram/kg), neither plasma calcium, nor thyroidal CT contents were changed. No correlation was found between CT mRNA levels and thyroidal CT contents as well as for plasma CT levels and thyroidal CT contents since hormone in blood remained unchanged after treatment by the active vitamin D3 metabolite. Intraperitoneal calcium administration in fasted 13-day-old rats was associated with a 5-fold increase in plasma CT 30 min after injection, but CT mRNA levels were unchanged within 240 min. By contrast, stomach gavage with calcium in fasted 13-day-old rats induced a sustained increase in plasma CT (X2), and a 4-fold increase in the steady-state level of CT mRNA. Calcium per se is a potent stimulator of CT release in suckling rats, but did not change the amount of CT mRNA. However, gastrointestinal factors may be implied directly or indirectly in the increased CT mRNA level after calcium gavage. In conclusion, 1,25-(OH)2D3 which is known to affect CT gene expression in adult rats is ineffective in 13-day-old suckling rats. This observation may be related to developmental changes in the amount of 1,25-(OH)2D3 receptors of C cells.     

Enhanced galactose metabolism in isolated perfused livers of folate-treated suckling rats

Folic acid (1 mg/day) was administered intraperitoneally to seven-day-old suckling rats for a period of seven days. Livers of folate-treated animals took up galactose rapidly during the first 35 minutes of perfusion, whereas uptake was delayed in the controls (sham-injected and untreated). More glucose was released by all groups when galactose was perfused than when other substrates were used. With each hexose tested, livers of the folate group consistently released less glucose but more lactate than the controls. The specific activity of galactose-1-phosphate uridyltransferase was elevated in livers of the folate group compared to the controls perfused with either galactose or glucose. A similar finding was made for ATP levels in perfused livers of this group. The differences in transferase and ATP levels in perfused livers of folate-treated over the control groups may explain the enhanced galactose uptake pattern.     

Repeated sleep restriction in rats leads to homeostatic and allostatic responses during recovery sleep

Recent studies indicate that chronic sleep restriction can have negative consequences for brain function and peripheral physiology and can contribute to the allostatic load throughout the body. Interestingly, few studies have examined how the sleep-wake system itself responds to repeated sleep restriction. In this study, rats were subjected to a sleep-restriction protocol consisting of 20 h of sleep deprivation (SD) followed by a 4-h sleep opportunity each day for 5 consecutive days. In response to the first 20-h SD block on day 1, animals responded during the 4-h sleep opportunity with enhanced sleep intensity [i.e., nonrapid eye movement (NREM) delta power] and increased rapid eye movement sleep time compared with baseline. This sleep pattern is indicative of a homeostatic response to acute sleep loss. Remarkably, after the 20-h SD blocks on days 2-5, animals failed to exhibit a compensatory NREM delta power response during the 4-h sleep opportunities and failed to increase NREM and rapid eye movement sleep times, despite accumulating a sleep debt each consecutive day. After losing approximately 35 h of sleep over 5 days of sleep restriction, animals regained virtually none of their lost sleep, even during a full 3-day recovery period. These data demonstrate that the compensatory/homeostatic sleep response to acute SD does not generalize to conditions of chronic partial sleep loss. We propose that the change in sleep-wake regulation in the context of repeated sleep restriction reflects an allostatic process, and that the allostatic load produced by SD has direct effects on the sleep-wake regulatory system.     

Transforming growth factor-alpha delays gastric emptying and small intestinal transit in suckling rats

Transforming growth factor-alpha (TGF-alpha) is a biologically potent polypeptide detected in the gastrointestinal tract in suckling rats. The major goal of the present study was to test the hypothesis that the administration of TGF-alpha affects gastric emptying and small intestinal transit in suckling rats. Suckling (12-day-old) rats fasted 16 h received rat TGF-alpha subcutaneously (s.c.) or orogastrically in varying doses (0, 0.5, 1.0 microg/rat in 0.1% BSA). Control animals received 0.1% BSA only. Poly R-478 dye was used as a motility marker. Rats were decapitated 45 min after marker administration and the amount of dye in the stomach and the small intestine was measured by spectrophotometry. Subcutaneous administration of TGF-alpha significantly delayed stomach evacuation. In controls, the stomach contained 21.4 +/- 1.4% (mean +/- s(x)) of the Poly R-478 marker, whereas in TGF-alpha treated rats the stomach contained 37.2 +/- 2.8% of the total Poly R-478 dye given to animals. The delaying effect of TGF-alpha was time- and dose-dependent. Small intestinal transit was also significantly delayed. The proximal jejunum of TGF-alpha treated rats contained a 1.4-fold higher amount of marker in comparison with control rats. Orogastrically administered rTGF-alpha did not affect gastric emptying or intestinal transit. In conclusion, s.c. administration of rat TGF-alpha significantly delayed the gastrointestinal motility in vivo in suckling rats.