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K T Borer

Publications and source records attributed to K T Borer.

At least 37 records · Page 2Linked to original sources
PubMed1987

Rostromedial septal area controls pulsatile growth hormone release in the golden hamster.

Limbic forebrain inhibits growth and growth hormone (GH) secretion in mature golden hamsters as shown by acceleration of growth and increases in serum GH concentrations following the electrolytic lesions of septum, transection of the hippocampus and surgical separation of these two regions. The growth-inhibitory function of this circuit is most probably mediated by somatostatinergic (SRIF) neurons. Such lesions induce hypoactivity possibly due to damage to endogenous opiatergic (EOP) neurons. EOP neurons facilitate spontaneous running in hamsters and mediate exercise-induced acceleration of growth and GH pulses. The coincidence of hypoactivity and growth acceleration after such lesions suggested the coexistence of SRIF and EOP fibers within the growth-inhibitory limbic forebrain circuit which control the rate of growth in mature hamsters by the variable inhibition of SRIF neurons by the EOP neurons. This hypothesis posits that accelerated growth is due to increased GH pulse frequency, and hypoactivity due to damage to EOP neurons, and was tested in this study by measuring pulsatile GH release (and as a measure of specificity, pulsatile prolactin release) in the presence and in the absence of opiate-receptor blocker naloxone in 21 female hamsters which sustained electrocoagulative lesions of rostromedial septum and 30 hamsters subjected to control surgery. Lesions doubled GH but not PRL pulse frequency, neither of which was affected by naloxone. Results support the hypothesis that opiatergic neurons facilitate pulsatile GH release by inhibiting the action of somatostatin neurons.

Animals↗
PubMed1987

Physiological, metabolic and running characteristics of senescent female hamsters.

Metabolic, endocrine and biochemical variables of female hamsters were studied to define age-related alterations in their characteristics. Endurance performance, aerobic capacity and metabolic fuels and hormones were measured and compared in young-adult (2-3 months) and old (16-17 months) hamsters to determine if the storage of substrates used in endurance exercise is altered with age, and if so, its effect on performance. The results indicate that storage of metabolic fuels are not appreciably altered with age, although voluntary running is markedly reduced. Other factors are likely involved in the hypoactivity of senescent female hamsters.

Aging↗
PubMed1987

Melatonin: its antagonism of thyroxine's antisomatotrophic activity in male Syrian hamsters.

The effects of daily evening melatonin injections on serum and pituitary levels of growth hormone (GH) and follicle stimulating hormone (FSH) were investigated in male Syrian hamsters receiving thiourea in the drinking water. Melatonin injections, by themselves, had no significant effect on serum or pituitary GH. Thiourea induced hypothyroidism reduced pituitary GH content but increased serum GH several fold. Daily thyroxin (T4) injections for 3 weeks partially restored pituitary GH content and reduced circulating GH to control values. Melatonin injections prevented T4 from reducing circulating GH levels to normal in hamsters receiving thiourea. As previously reported, FSH levels in serum and pituitary were reduced by melatonin. Thiourea-induced hypothyroidism prevented this effect. Daily T4 injections increased circulating FSH levels above control levels; melatonin injections prevented this increase in serum FSH. These observations show that melatonin and T4 have antagonistic actions on GH and FSH release from the pituitary. We conclude that melatonin influences the release of hypothalamic hormones regulating GH and FSH release from the pituitary. The effects of T4 on the sensitivity to melatonin injections could be accounted for by thyroid hormone regulation of pituitary receptors for hypothalamic hormones. An alternative explanation is that T4 regulates the concentration of melatonin receptors in the central nervous system.

Animals↗
PubMed1987

Hormonal and nutritional determinants of catch-up growth in hamsters.

Exercise accelerates somatic and skeletal growth in mature nondeprived hamsters and induces catch-up growth when food restriction during exercise is followed by ad libitum realimentation. The hypothesis that nutrient availability controls the rate of growth through changes in anabolic hormone release was tested through measurements of serum growth hormone (GH) and insulin concentrations at the same time of day in exercising and sedentary hamsters subjected to acute fasts, chronic food restriction, and to acute and prolonged realimentation. Concentrations of GH and insulin increased in ad libitum-fed exercising hamsters, but these increases were abolished by 12 and 4 h of fast, and restored by 4 and 2 h of refeeding, respectively. Four h of refeeding restored exercise-induced increases in serum GH, but not in serum insulin concentration in chronically food-restricted hamsters. During catch-up growth, the growth rate was double that of ad libitum fed exercising hamsters, but the increases in serum GH concentration in the two situations were similar. I conclude that increases in serum GH rather than in serum insulin concentration are the most probable determinant of exercise-induced growth and catch-up growth because they are relatively refractory to short-term nutritional perturbations.

Animal Nutritional Physiological Phenomena↗
PubMed1986

Ontogenesis of corticotropes and lactotropes in situ in the pituitary gland of the hamster. An immunohistochemical study.

The development of corticotropes and lactotropes was investigated in the golden Syrian hamster using an anti-porcine ACTH antiserum and a homologous anti-hamster PRL antiserum. Oval corticotropes were first visible in the ventral region of the pars distalis at 13 days of gestation. By the end of gestation, corticotropes were found throughout the pars distalis and in the pars intermedia. Corticotropes in the pars distalis of postnatal hamsters were either round or irregularly-shaped, often appearing in clusters. Throughout development, corticotropes often appeared to be surrounding other cells. Scarce, very small lactotropes were first observed in the pars distalis of hamsters on the first postnatal day. The number of these cells, which were either round or polyhedral, increased dramatically between 4 and 20 days of postnatal life. These observations indicate that the sequence of appearance of corticotropes and lactotropes in the hamster is similar to that in other species and that lactotropes are confined to the pars distalis of postnatal hamsters.

Adrenocorticotropic Hormone↗
PubMed1986

Alteration of pulsatile growth hormone secretion by growth-inducing exercise: involvement of endogenous opiates and somatostatin.

Our aim was to examine whether 1) growth-inducing exercise altered the pulsatile pattern of GH release, 2) endogenous opiates mediated these changes, and 3) endogenous somatostatin (SRIF) suppressed pulsatile GH secretion in slowly growing sedentary hamsters. To that end, mature female hamsters were either exposed to 2 weeks of voluntary running or prevented from engaging in running activity. Intracardiac catheters were inserted to allow blood collection every 20 min during 6 h. GH and PRL secretory patterns were determined with homologous RIAs for hamster hormones after administration of saline, naloxone, or anti-SRIF serum. It was found that exercise accelerated somatic growth. GH pulse frequency and amplitude were significantly higher in rapidly growing hamsters. The rate of growth was inversely related to basal trough values of GH and PRL. Opiate receptor blockade reduced GH pulse frequency and amplitude to below sedentary values and did not affect PRL secretion. Anti-SRIF serum increased GH pulse frequency and amplitude in naloxone- as well as in saline-injected animals. Our results are consistent with the conclusions that 1) rapid growth, spontaneous or induced by exercise, is associated with increased GH pulse frequency and amplitude and decreased GH and PRL baseline concentrations in hamsters; 2) endogenous SRIF inhibits pulsatile GH secretion in slowly growing hamsters; and 3) endogenous opiates mediate increases in GH pulse frequency and amplitude in rapidly growing hamsters by antagonizing the endogenous SRIF action.

Animals↗
PubMed1985

Recovery from energy deficit in golden hamsters.

Hamsters feeding at greater than 2-h intermeal intervals (IMI) lose weight but recover from weight losses without hyperphagia if they are allowed to feed at 2-h IMIs (Am. J. Physiol. 236 (Endocrinol. Metab. Gastrointest. Physiol. 5): E105-E112, 1979). To determine the relative importance of changes in energy expenditure and fat synthesis in their energy regulation, measurements were made of resting metabolic rate, respiration by brown adipose tissue (BAT), locomotion, fecal energy content, and insulin and hepatic lipogenic enzyme responses to feeding in underweight hamsters allowed to feed at 2- or 5-h IMIs. Energy deficit suppressed the resting metabolic rate and general locomotor activity and increased the activity of fatty acid synthetase (FAS). Heat production by BAT increased in underweight hamsters. Increase in IMIs blocked the postprandial insulin release, reduced plasma insulin concentration and FAS activity, and increased malic enzyme activity. Thus ad libitum feeding hamsters recover from energy deficit by reducing energy expenditure, whereas failure to add additional meals and impaired insulin and changed lipogenic responses to feeding produce energy deficits in infrequently feeding hamsters.

Adipose Tissue, Brown↗
PubMed1984

Regulation of testicular prolactin and luteinizing hormone receptors in golden hamsters.

Iodinated ovine PRL (oPRL) was used to detect the presence of PRL receptors in hamster testes. Binding to these receptors was specific for PRL and was saturable and incompletely reversible. Testicular PRL receptors possessed a single class of independent, high affinity binding sites (Ka = 2.4 X 10(10) M-1). The ability of PRL to regulate testicular PRL and LH receptors was measured in experiments wherein mature hamsters were injected daily for 10 days with 600 micrograms bromocriptine, 600 micrograms bromocriptine plus 250 micrograms oPRL, or injection vehicles. Bromocriptine injections, which caused significant reductions in serum PRL, produced commensurate decreases in concentrations (femtomoles per mg protein) of testicular LH and PRL receptors, without affecting binding of PRL to adrenal or liver tissue preparations. Decreases in testicular PRL binding were not always statistically significant, but were consistently measured. The administration of oPRL with bromocriptine significantly increased both concentration and total content (femtomoles per paired testes) of testicular LH receptors and PRL-binding sites above those measured in bromocriptine-injected and control hamsters. Liver PRL-binding sites were, likewise, increased above values measured in controls and bromocriptine-injected hamsters by this latter treatment, which had no significant effect on adrenal PRL-binding sites. Neither bromocriptine nor bromocriptine plus oPRL had any effect on the affinity (Ka) of testicular PRL receptors for labeled oPRL. Serum testosterone and FSH concentrations were unaltered by treatment, thereby suggesting that effects on receptors did not occur secondary to changes in these hormones, but, rather, represent direct effects of PRL. An additional experiment in prepubertal male hamsters (aged 14-30 days) demonstrated that bromocriptine injections for 17 days significantly reduced the total content of testicular PRL receptors. In vitro experiments eliminated the possibility of direct effects of bromocriptine on testicular receptors. The data demonstrate the possibility that PRL is required for maintenance of normal concentrations of testicular LH/hCG and PRL receptors in adult and immature golden hamsters. An increase in putative serum anti-oPRL antibodies was measured in oPRL-injected hamsters. Since such antibodies could contribute, to an unknown degree, to PRL binding measured in tissue preparations, the present data indicate only that increased testicular binding occurs subsequent to injection of heterologous PRL, without demonstrating that this binding is indeed due to increased PRL receptors.

Adrenal Glands↗
PubMed1983

Basis for the hypoactivity that accompanies rapid weight gain in hamsters.

The pattern of hypoactivity that accompanies rapid weight gain following septal lesions in hamsters was characterized. Lesioned hamsters displayed reduced levels of running, shorter and slower running bouts, and longer pauses. We examined whether this hypoactivity was due to reassignment of metabolic fuels from supporting physical activity to anabolism, or due to reduced capacity of running to induce psychomotor arousal and mobilize metabolic fuels. Septal lesions were associated with increased rate of ponderal growth and higher titers of circulating growth hormone and insulin. No difference in concentrations of muscle and liver glycogen, percentage of body fat, or the capacity of muscle homogenates to oxidize substrates were identified. Lesioned hamsters ran as fast and as long as control animals on electrical-shock reinforced treadmill, but were unable to generate as much heat in response to injection (0.8 mg/kg) of norepinephrine. We concluded that hypoactivity that accompanies rapid weight gain in hamsters results either from a reduced capacity of running to induce psychomotor arousal and provide incentives that normally motivate that behavior, or from a failure of running to mobilize metabolic fuels at a rate necessary to sustain normal running speed and duration, and not from reduced availability of metabolic fuels or reduced muscle capacity to oxidize metabolic substrates.

Animals↗
PubMed1983

Opiate-receptor blockade reduces voluntary running but not self-stimulation in hamsters.

Naltrexone HCl, a long-acting opiate receptor blocker was administered to female hamsters at two doses, 10 and 20 mg/kg, IP prior to 12 hr of nocturnal running or every 12 hr during access to hypothalamic self-stimulation to determine whether endogenous opiates played a role in either of these two motivated behaviors. Naltrexone suppressed total running activity and speed, and caused an increase in pause time but did not affect the rate of hypothalamic self-stimulation. Furthermore, weight gain was unaffected by four weeks of self-stimulation but was accelerated during two weeks of voluntary running. Thus stimulation of endogenous opiate receptors helps support high levels of voluntary running but is not involved in initiation of running or in maintenance of intracranial self-stimulation in female hamsters. Furthermore, the association of opiate receptor stimulation and increased somatic growth with voluntary running but not with self-stimulation suggests a possible facilitatory role for endogenous opiates in acceleration of growth by exercise.

Animals↗
PubMed1983

A role for somatostatin in the control of hamster growth.

Concentrations of somatostatin-like immunoreactivity (SRIF-LI) were measured in cerebral cortex, hippocampus, septum-POA, median eminence, gastric antrum, fundus and pancreas in adult female hamsters to determine whether changes in somatostatin could be related to increased growth hormone (GH) secretion and somatic growth that follow bilateral transections of hippocampus (n = 18; 17 controls). In addition, choline acetyltransferase (CAT) activity was measured in the four brain regions in hippocampectomized (n = 10) and control hamsters (n = 10) to gain insight into the relationship between these two neurotransmitters. Hippocampal transections induced: significant acceleration of somatic growth; increased serum GH concentrations; increased concentrations of SRIF-LI in septum-POA and gastric antrum; reduced concentrations of SRIF-LI in hippocampus and pancreas; and reduced CAT activity in the hippocampus. These results suggest that somatostatinergic and cholinergic projections to hippocampus via fornix suppress GH and somatic growth in adult hamsters and that reduced release of SRIF-LI in the gastric antrum may contribute to the acceleration of somatic growth through facilitated nutrient digestion and entry.

Acetylcholine↗
PubMed1983

Exercise reverses photoperiodic anestrus in golden hamsters.

In contrast to the inhibitory effects of endurance exercise on reproductive function in women athletes, voluntary running induces estrous cyclicity in anestrous female hamsters maintained in the nonstimulatory short-day photoperiod. Increased concentrations of circulating prolactin (Prl) seen in these animals are not responsible for the reversal of photoperiodic anestrus as demonstrated by experimental manipulations of prolactin secretion. Voluntary running also facilitates growth hormone (GH) release and somatic growth in hamsters independently of the photoperiod. Thus, it appears that endurance exercise can have facilitatory as well as inhibitory effects on the reproductive function in female mammals.

Adipose Tissue↗
PubMed1983

Testicular prolactin receptors and serum growth hormone in golden hamsters: effects of photoperiod and time of day.

Investigations were conducted to determine effects of exposure to short photoperiod--with its accompanying reductions in serum prolactin (Prl) concentrations--for various durations on testicular Prl receptors. An additional study investigated the possibility of nyctohemeral fluctuations in testicular Prl receptors and serum growth hormone (GH) concentrations and their alteration by photoperiod. After 10 and 28 days of exposure to a short photoperiod consisting of 5 h of light and 19 h darkness (5L:19D) (and prior to changes in testicular weight), there were progressive and significant reductions in the concentration of testicular Prl receptors (fmol/mg protein) when compared with long-photoperiod controls (14L:10D). After 12 weeks of 5L:19D, when testicular weights were dramatically decreased, Prl receptor concentration was reduced to 39% of long-photoperiod controls in one study, without alteration of affinity of Prl receptors for their labeled ligand. When measured at 6-h intervals in hamsters on 14L:10D, and on 5L:19D for 12 weeks, there were no significant changes in concentration or total content (fmol/testes) of testicular Prl receptors throughout the day. Although serum GH concentrations fluctuated markedly in hamsters on both photoperiods, no definitive nyctohemeral patterns were detected. These data provide indirect evidence for the ability of Prl to regulate its own testicular receptors, and demonstrate that diurnal fluctuations in testicular sensitivity to injected Prl are not a consequence of changes in Prl receptors. The data also suggest the absence of effects of photoperiod on serum GH concentrations in male golden hamsters.

Animals↗
PubMed1982

Metabolic alterations induced by voluntary exercise and discontinuation of exercise in hamsters.

A study was conducted to determine the possible biochemical mechanisms responsible for the rapid increase in body weight and body fat during the early phase of exercise-retirement. Thirty-two adult female hamsters were allotted to four groups of eight each. One group served as sedentary controls. Other groups had access to voluntary disc-running during a 35-day period of the 76-day experimental period and were retired from running for 0, 8, and 41 days, respectively, before the termination of the experiment. Disc-running reduced body fat and body weight. Discontinuation of running led to a fast gain of body fat and body weight. Disc-running decreased serum triacylglycerol levels but had no effect on serum cholesterol levels. Serum high-density lipoprotein-cholesterol concentration was significantly elevated at 8 days after retirement but was not changed during exercise or at 41 days after retirement. Exercise or discontinuation of exercise had no effect on serum T-3 or T-4 levels. The rate of fatty acid synthesis and the activities of malic enzyme and fatty acid synthetase in the liver were increased during running and during the early phase of retirement. Liver glucose-6-phosphate dehydrogenase activity was increased at 8 days after discontinuation of running. Disc-running enhanced food intake which was not reduced to the sedentary level until about 10 days after retirement, suggesting a delay in adaptation to reduced energy expenditure. Results of the present study suggest that both the delay in food intake adaptation and the enhanced lipogenic activity play a role in the rapid gain of body weight and body fat during the early phase of exercise-retirement.

Adipose Tissue↗
PubMed1982

Hamster prolactin: physiological changes in blood and pituitary concentrations as measured by a homologous radioimmunoassay.

A specific and sensitive homologous radioimmunoassay (RIA) for determination of hamster prolactin is described and compared to heterologous hamster prolactin RIA and to the homologous and heterologous RIAs for rat prolactin. With this method, we have determined that, in the golden hamster, diurnal plasma prolactin fluctuations have a mean interpeak interval of 1.5 h, that serum prolactin concentrations are influenced by day length, by ether vapors, by animal's gender, and by refeeding following a fast but not by neurosurgical procedures which increase somatic growth and serum GH concentration in adult hamsters. Variations in day length influenced pituitary prolactin content and concentration, and pituitary removal abolished prolactin secretory responses to ether stress. A heterologous RIA for hamster prolactin which utilizes radioiodinated rat prolactin and rabbit antihamster prolactin serum (RK1-15) represents the most advantageous method for the measurement of hamster prolactin because of its high sensitivity (0.14 ng/ml), high antiserum binding to iodinated rat prolactin, and the ability to measure both hamster and rat prolactin.

Animals↗
PubMed1982

Hamster growth hormone. Species specificity and physiological changes in blood and pituitary concentrations as measured by a homologous radioimmunoassay.

A specific and sensitive homologous radioimmunoassay (RIA) for determination of golden hamster growth hormone (GH) is described and compared to a heterologous hamster GH RIA. Using the homologous system, cross-reactivity experiments between golden hamster GH on one hand, and pituitary extracts from two other hamster species, and purified GHs from several rodent and mammalian species, suggested that hamster GH differs from other rodent and mammalian GHs to a greater extent than rat GH. Using the homologous method, we have determined that, in the golden hamster, diurnal plasma fluctuations have a mean interpeak interval of 70-80 min, that serum GH concentrations are affected by nyctohemeral differences in lighting, by ether vapors, by animal's gender, and by starvation and refeeding. Basal GH concentrations were not influenced by exposure to different photoperiods or by removal of the gonads. A heterologous hamster GH RIA, which utilizes a radioiodinated rat GH and monkey antihamster GH serum, represents the most advantageous method for the measurement of hamster GH because of its high sensitivity (0.3 ng/ml), low limit of detection (46 pg/ml), high antiserum binding to iodinated rat GH, and the ability to measure rat and mouse GHs in addition to hamster GH. Immunological differences between hamster, rodent, and other mammalian GHs are diminished when heterologous, rather than homologous, tracer is used.

Animals↗
PubMed1981

Somatic, endocrine, and serum lipid changes during detraining in adult hamsters.

Effects of abrupt discontinuation of chronic exercise on body composition and serum lipid, insulin, and glucagon concentrations were examined in adult female hamsters. Thirty-six hamsters (100 to 120 g) were randomly allotted to two groups of 18 each for an 84-day study. One group served as controls and were sedentary throughout the experimental period; another group had access to voluntary running on horizontal discs during the first 42 days of the experimental period. Six hamsters from each group were killed at the end of the exercise period and at 12 and 42 days after retirement. Results showed that hamsters engaged in high levels of voluntary activity increased food intake by about 10 to 20% and this effect persisted for about 10 days after retirement. Voluntary running resulted in a 60% reduction in body fat content and a 30% decrease in serum triglyceride levels. Exercise was also associated with an increase in body cholesterol level, a decrease in glucagon concentration, and a suggestive increase in serum insulin level. Increased food consumption and changes in serum insulin and glucagon may reflect compensatory adjustments to increased energy expenditure of exercise. Discontinuation of exercise resulted in a reversal of exercise effects on body fat, body cholesterol, and serum triglyceride levels.

Animals↗