Reversible impairment of endothelium-dependent relaxation in golden hamster carotid arteries during hibernation

The effects of hibernation on endothelium-dependent vasodilatation were investigated in the golden hamster carotid artery, paying special attention to hibernating body temperature (10 °C). To record mechanical and electrical membrane responses, we applied pharmacological (organ bath) and electrophysiological (microelectrode) techniques, using acetylcholine (ACh; 0.001–100 μ m ) and ATP (0.01–1000 μ m ) for endothelium-dependent vasodilatation and sodium nitroprusside (SNP; 0.05–10 μ m ) for endothelium-independent vasodilatation. At 34 °C, ACh, ATP and SNP each induced a relaxation or a hyperpolarization, and these responses were similar in all the preparations from control and hibernated animals. At 10 °C, on the other hand, ACh-induced relaxations and hyperpolarizations were reduced to approximately 35 % and 50 % of the euthermic level in controls and 1 % and 4 % of the euthermic level in hibernated animals, respectively. In contrast, at 10 °C, ATP induced only a contraction or depolarization in all preparations with no significant difference between control and hibernated animals. SNP-induced relaxations and hyperpolarizations obtained at 34 °C were not attenuated by cooling to 10 °C. In the presence of a P2X receptor blocker, pyridoxal phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS; 5 μ m ), at 34 °C ATP-induced relaxations and hyperpolarizations were significantly enhanced whereas no responses were induced by ATP at 10 °C. After endothelium removal, on the other hand, ATP induced only a contraction or depolarization at both 34 °C and 10 °C. These results suggest that depression of endothelium-dependent vasodilator responses to ACh and ATP may occur in the hibernating golden hamster carotid artery.     

Electron-immunocytochemical studies of perivascular nerves of mesenteric and renal arteries of golden hamsters during and after arousal from hibernation

Electron immunocytochemistry was used to examine perivascular nerves of hamster mesenteric and renal arteries during hibernation and 2 h after arousal from hibernation. Vessels from cold-exposed but nonhibernating, and normothermic control hamsters were also examined. During hibernation the percentage of axon profiles in mesenteric and renal arteries that were immunopositive for markers of sympathetic nerves, tyrosine hydroxylase (TH) and neuropeptide Y (NPY), were increased 2–3 fold compared with normothermic and cold control animals. This increase was reduced markedly only 2 h after arousal from hibernation. The small percentage of nitric oxide synthase-1-positive axon profiles found in mesenteric (but not renal) arteries was also increased during hibernation and returned towards control values after arousal. In contrast, the percentage of perivascular axons immunostaining for vasoactive intestinal polypeptide (VIP), a marker for parasympathetic nerves, was reduced in mesenteric arteries during hibernation. There was no labelling of perivascular nerves for substance P in either mesenteric or renal arteries. It is suggested that the increase in percentage of TH- and NPY-immunostained perivascular nerves may account for the increased vasoconstriction associated with high vascular resistance that is known to occur during hibernation. The reduction in the percentage of axons positive for VIP in hibernating animals would contribute to this mechanism since this neuropeptide is a vasodilator.     

Physiological and behavioral responses to glucoprivation in the golden hamster

Golden hamsters failed to increase their food intake following food deprivation alone or in combination with insulin or 2-deoxy-D-glucose (2DG) treatment. 2DG also failed to induce feeding in hamsters tested at night. In this latter experiment, there was no effect of 2DG on wheel running or general alertness. Insulin administration significantly decreased plasma levels of glucose and free fatty acids (FFA). 2DG treatment produced a dose-related hyperglycemia associated with increased ketone levels. These data are discussed in terms of cerebral energy status and its relation to food intake and physiological responses.     

Physiological and behavioral responses to starvation in the golden hamster.

Physiological and behavioral responses of adult hamsters to starvation were studied by measuring food intake, weight recovery, serum concentrations of glucose, insulin, free fatty acids and beta-hydroxybutyrate, and ketonuria in animals subjected to different weight losses, diets, and durations of fast. Hamsters were debilitated by fasts longer than 12 h or leading to greater than 20% weight loss. Hamsters' feeding patterns were unmodified by fasts ranging between 5 and 12 h and showed no circadian periodicity. Hamsters predominantly recovered from weight losses without increasing their food consumption (unless they were offered a diet of pellets and seeds) and without changing their meal patterns, at a rate of weight gain proportional to the magnitude of preceding weight loss if provided with uninterrupted access to food. By 8 h of fast, blood metabolites were indicative of mobilization of body fat. Hamsters are thus behaviorally unresponsive to duration of fast, but compensate physiologically for weight losses with proportional increases in the rate of weight gain.     

Enhanced vasoconstrictor effect of endothelin in cerebral arteries from rats with subarachnoid haemorrhage

The contractile response to endothelin has been examined in cerebral arteries from rats subjected to a prior subarachnoid haemorrhage (SAH) and compared with saline-injected controls. Endothelin elicited concentration-dependent contractions of rat basilar artery segments. The endothelin-induced contractions were much stronger in the SAH compared to control animals, which suggests a role in the pathophysiology of cerebral vasospasm.     

Voluntary ethanol consumption during pregnancy and lactation in the golden hamster

Golden hamsters voluntarily consume substantial amounts of ethanol without developing dependence, apparently because ethanol metabolism is rapid and efficient. Six adult female hamsters were given continuous free access to Purina chow, water and a 20% (v/v) ethanol solution before and during pregnancy and during lactation; six control females did not receive the ethanol solution. Intakes of food and water were not elevated during pregnancy, but increased markedly for both groups during lactation. Ethanol consumption remained substantial but unchanged throughout the experiment, with ethanol consumers taking an average of 3.8 g (4.4 kcal) of ethanol solution daily. No significant differences were observed in the size and weight of litters either at delivery or at 16 days postpartum.     

Endothelium-independent potentiation by neuropeptide Y of vasoconstrictor responses in isolated arteries from rat and rabbit

An endothelium-dependent action of neuropeptide Y (NPY) has been implicated in studies on various vascular beds. In the present study, the requirement of an intact endothelium for NPY-evoked potentiation of the response to sympathetic nerve stimulation was determined in the small mesenteric arteries of the rat and in the central ear artery of the rabbit. Further, NPY-mediated inhibition of relaxing influences was determined in small mesenteric arteries of the rat. Vascular segments were mounted in a double myograph, where one of the two suspended vessels was denuded of endothelium by gently rubbing the intimal surface. Removal of endothelium was verified by en-face silver staining. In both species, the response to bursts of transmural field stimulation eliciting 10% of maximal contraction was potentiated 2-4 times in the presence of 10 nM NPY, whether the endothelium was present or not. In small mesenteric arteries precontracted with noradrenaline, addition of acetylcholine (I microM) caused relaxation only in vessels with an intact endothelium. Subsequent addition of 10 nM NPY enhanced vasoconstriction in both intact and endothelium-denuded vessels. The endothelium-independent beta-adrenergic agonist isoprenaline (I microM) relaxed both intact and denuded small mesenteric arteries, and in both further addition of 10 nM NPY increased the contraction to about the same extent. The results demonstrate that NPY potentiates the responses to sympathetic field stimulation in small mesenteric arteries from the rat and in central ear artery from rabbit whether the endothelium is present or not. NPY inhibits both endothelium-dependent and -independent relaxations in small mesenteric arteries from rat.     

Inhibitory effect of hypertonic mannitol on vasoconstrictor and vasodilator responses of isolated coronary arteries.

The effect of hypertonic mannitol on pressor responses to vasoactive agents was studied in isolated canine coronary arteries perfused with physiologic salt solution at a constant flow. When perfusion pressure was increased with 60 mM KCl, mannitol (50 mosM) consistently caused a decrease in perfusion pressure that lasted for at least 1 h. Withdrawal of mannitol from the perfusion media was associated with a vasoconstrictor response that was not prevented by alpha- or beta-adrenoceptor blockade or by the presence of either nitroglycerin or norepinephrine. Hypertonic mannitol also reduced the responsiveness of the isolated smooth muscle preparations to several different mechanistically unrelated vasodilator agents. The mechanism(s) responsible for the paradoxical ability of hypertonic mannitol to reduce vascular responsiveness to both vasoconstrictor and vasodilator interventions in isolated canine coronary arteries is not known, but future studies should be directed at elucidating it as well as determining whether similar phenomena occur in vivo.     

Grating acuity of the golden hamster

Summary Twelve golden hamsters learned visual discriminations in a Y-maze for a food reward. After initial training on a light/dark task, the hamsters learned to discriminate a grating from a uniform grey field of the same mean luminance as the grating; grating orientation was varied among hamsters. Those animals trained with the grating vertical or horizontal learned significantly faster than those trained on obliques. Acuity, measured by varying the spatial frequency of the grating according to the descending method of limits or the method of constant stimuli, was determined to be about 0.7 c/deg at 50% correct or 0.5 c/deg at 70% correct for all orientations tested (0 °, 45 °, 90 °, 135 °). Acuity was relatively constant within the human photopic range, but decreased to about 0.35 c/deg at 5 × 10^-4cd/m². The change in acuity as a function of luminance suggests that the hamster has a rod-dominated retina.     

Biochemical and histopathological alterations in golden hamster during infection with Ancylostoma ceylanicum

Ancylostoma ceylanicum infection in golden hamsters (Mesocricetus auratus) caused marked biochemical and histopathological derangements. Jejunum, the primary site of infection, showed pronounced alterations compared with liver. Though the biochemical composition of jejunum was not significantly altered, activities of a few lysosomal enzymes were enhanced during hookworm infection. Marked damage to mitochondrial and microsomal membranes was reflected in changes in the activities of the marker enzymes from jejunal tissue. Lipid content, especially phospholipids and neutral lipids of hepatic tissue, exhibited marked elevation. Levels of hexokinase, phosphofructokinase, and lactate dehydrogenase were enhanced in jejunal as well as hepatic tissues, indicating activation of the glycolytic machinery during hookworm infection. A decrease in the levels of mucosal disaccharidases indicated damage to intestinal brush border membranes. However, alkaline phosphatase activity was increased in intestinal mucosa during the infection. Light microscopic examination of jejunal tissue revealed peeling off of the upper epithelial layer, activation of the goblet cells, and thickening of muscularis mucosa. However, hepatic tissue did not show gross alterations, except for slight necrosis in the centrilobular region.     

Neurokinin A in the hypothalamus and anterior pituitary during the estrous cycle in the golden hamster

The fluctuations in the neurokinin A concentrations in the hypothalamus and anterior pituitary of female golden hamsters were studied in the different stages of the estrous cycle, and they were correlated with the changes in serum estradiol levels. Neurokinin A levels in the hypothalamus were lowest at day 4 of the cycle (proestrus), when serum estradiol levels were highest. Neurokinin A levels in the hypothalamus of hamsters in day 1 (estrus), day 2 (diestrus I), and day 3 (diestrus II) were not significantly different from each other. In the anterior pituitary, the highest neurokinin A concentrations were found during day 1 of the cycle (estrus), the levels in day 2 (diestrus I), day 3 (diestrus II), and day 4 (proestrus) were significantly lower than at estrus, again showing the lowest levels during proestrus, when estradiol levels were maximal. These results show that neurokinin A levels in the hypothalamus and anterior pituitary of the female hamster undergo significant changes during the estrous cycle.     

Characteristics of insulin-induced hyperphagia in the golden hamster

Two experiments were performed to investigate in some detail the behavioural and metabolic effects of the administration of regular insulin to golden hamsters. In Experiment 1 dose-response curves describing the effects of insulin upon both food intake and plasma glucose (PG) were generated. Dosages of less than 20 units/kg did not cause increases in food intake, while dosages of 10 units/kg or greater produced significant hypoglycemia at +6 hr post-injection. There was also a significant inverse linear relationship (r=?.528) between individual hamsters' food intakes and PG levels over the range of insulin dosages. It Experiment 2, insulin (30 units/kg) caused increases in meal frequency but not in meal size, and hyperphagia developed within +3 hr of insulin administration. When food was not available, insulin caused PG levels to fall below control levels at +1 hr and to remain depressed until at least +6 hr post-injection. However when hamsters were allowed to eat, PG did not fall significantly below control levels until +3 hr and began to recover at +5 hr post-injection. Results are discussed in relation to several apparent peculiarities in the hamster's behavioural response to regular insulin, specifically the small magnitude and the slow development of insulin-induced hyperphagia, and the hamster's relative insensitivity to the hyperphagic effect of insulin.