Hr In Animals Research Articles

Circadian Control of Mouse Heart Rate and Blood Pressure by the Suprachiasmatic Nuclei: Behavioral Effects Are More Significant than Direct Outputs

BackgroundDiurnal variations in the incidence of events such as heart attack and stroke suggest a role for circadian rhythms in the etiology of cardiovascular disease. The aim of this study was to assess the influence of the suprachiasmatic nucleus (SCN) circadian clock on cardiovascular function.Methodology/Principal FindingsHeart rate (HR), blood pressure (BP) and locomotor activity (LA) were measured in circadian mutant (Vipr2 −/−) mice and wild type littermates, using implanted radio-telemetry devices. Sleep and wakefulness were studied in similar mice implanted with electroencephalograph (EEG) electrodes. There was less diurnal variation in the frequency and duration of bouts of rest/activity and sleep/wake in Vipr2 −/− mice than in wild type (WT) and short “ultradian” episodes of arousal were more prominent, especially in constant conditions (DD). Activity was an important determinant of circadian variation in BP and HR in animals of both genotypes; altered timing of episodes of activity and rest (as well as sleep and wakefulness) across the day accounted for most of the difference between Vipr2 −/− mice and WT. However, there was also a modest circadian rhythm of resting HR and BP that was independent of LA.Conclusions/SignificanceIf appropriate methods of analysis are used that take into account sleep and locomotor activity level, mice are a good model for understanding the contribution of circadian timing to cardiovascular function. Future studies of the influence of sleep and wakefulness on cardiovascular physiology may help to explain accumulating evidence linking disrupted sleep with cardiovascular disease in man.

Effect of stimulation of endogenous melatonin secretion during constant light exposure on 6-sulphatoxymelatonin rhythmicity in rats.

When light is presented unexpectedly at night to rats, melatonin production and secretion is acutely inhibited and the time of onset of production on the subsequent night is altered. In a series of experiments, we examined the effects of 6-12 hr light (200 lux) at night on melatonin metabolite excretion (6-sulphatoxymelatonin, aMT.6S). During the light exposure, we administered isoproterenol to stimulate endogenous production of melatonin by the pineal gland to determine if replacement of melatonin would block any phase shifting effects of the light. Exposure to 6 hr of light either during the first or second half of the night suppressed aMT.6S excretion during the light treatment and delayed the onset of melatonin secretion by 3.7 +/- 0.6 and 2.5 +/- 0.6 hr, respectively, compared to a change of 0.5 +/- 0.1 hr in animals maintained in darkness. Twelve hours light exposure (i.e. one night of continuous light) suppressed aMT.6S excretion completely and resulted in a delay in the onset the next night of 2.1 +/- 0.7 hr. When propranolol (10 mg/kg) was administered at 2-hr intervals during darkness, aMT.6S excretion was suppressed throughout the night, but on the subsequent release into constant darkness the onset of excretion was not delayed (0.6 +/- 0.1 hr delay). Administration of isoproterenol (10 mg/kg) to animals in constant light, at the time of expected lights off (CT12), and 5 hr later (CT17) resulted in an increase in melatonin production and aMT.6S excretion that was similar in duration and amount to the control night. The stimulation of endogenous melatonin production failed to block the phase shifting effects of the light exposure and, in fact, appeared to potentiate the delay at least on the first night (4.2 +/- 0.9 hr). The timing of the release into constant darkness following the light treatment had an unexpected effect on melatonin production on the cycle after treatment. Thus, animals exposed to 12 hr light and released into darkness at the normal time of lights off as above had a delay of about 2 hr and excreted 71 +/- 18% of the aMT.6S excreted on a control night. Animals released into darkness at the expected time of lights on failed to excrete more than 20 pmol/hr(i.e. no onset of excretion could be determined) at any time on the first subjective night after light treatment, which was no different from the excretion during the light treatment. On the next subjective night, the onset was delayed as expected and the amount of aMT.6S produced was restored. Treatment with isoproterenol at CT12 and CT17 failed to affect either the amount of aMT.6S excreted on the first subjective night after light treatment or the phase delay on the second night after treatment. The failure to produce melatonin on the first subjective night after 12 hr light exposure and release into darkness at CTO was not due to failure at the level of the pineal gland since injection ofisoproterenol at CT12 and CT17 on the first subjective night after light restored the normal amount of melatonin production. These results suggest that the absence of melatonin during light stimulation at night is not responsible for the phase delay in melatonin production and excretion on subsequent nights. The basis of the failure of the rats to commence melatonin production following 12 hr extended light exposure followed immediately by continuous darkness is not known.

Physiologic responses of cross-linked hemoglobin in endotoxin-treated rats.

Purified human cross-linked hemoglobin (alpha alpha Hb) as well as recombinant human hemoglobin is undergoing clinical trials in the setting of acute blood loss and perioperative hemodilution. We have previously demonstrated that in rabbits with circulating plasma Hb, such as alpha alpha Hb, infusion of endotoxin (LPS) impairs myocardial contractility which results in hypotension, tissue hypoperfusion and increased mortality. The untoward cardiovascular effects occurring after the combined infusion of LPS and alpha alpha Hb in this model are similar to those reported for other agents that inhibit nitric oxide (NO) availability. To determine if the deleterious effects of alpha alpha Hb and LPS were species specific, we performed similar studies in rats. Anesthetized Sprague-Dawley rats received LPS (4 mg/kg or 40 mg/kg) alone or in combination with alpha alpha Hb (0.7 g/kg). Mean arterial blood pressures (MAP) increased in the group that received alpha alpha Hb alone (105 +/- 8 to 120 +/- 7 mm Hg, p = 0.2) and a decrease was noted in the groups that received low dose LPS (4 mg/kg, p = 0.5) and high dose LPS (40 mg/kg, p = 0.016). MAP in rats treated with the LPS at either dose combined with alpha alpha Hb remained unchanged. Levels of urine nitrite, which was measured as a surrogate marker for plasma NO, were significantly decreased at 2 hr in groups that received the combination of alpha alpha Hb and LPS at 4 mg/kg (p = 0.022) and 40 mg/kg (p = 0.003). No significant decrease was observed in animals treated only with alpha alpha Hb (p = 0.21) or LPS (4 mg/kg; p = 0.78 and 40 mg/kg; p = 0.65). Survival was evaluated during 72 hr in animals that were infused with high dose LPS (40 mg/kg) alone or in combination with alpha alpha Hb and then allowed to recover. The survival of rats treated with LPS alone or the combination was 29% at the end of 24 hr and was 100% for rats receiving only alpha alpha Hb. The data suggest that the toxicity of alpha alpha Hb appears to be a species specific phenomenon.

Pharmacokinetic Profile of a New Matrix-Type Transdermal Delivery System: Diclofenac Diethyl Ammonium Patch

A transdermal delivery system containing the anti-inflammatory analgesic diclofenac diethyl ammonium in an ethyl hexyl acrylate and vinyl acetate pressure-sensitive adhesive system was developed for percutaneous absorption. These patches were subjected to in vitro permeation and permeation enhancement studies through rat skin using a specially designed diffusion cell. Further, the work deals with percutaneous absorption studies carried out on both animals and human volunteers. The pharmacokinetic parameters calculated from the blood levels of the drug reveal a profile typical of a sustained-release formulation, with the ability to maintain adequate plasma levels for 24 hr (i.e., up to the next application). (Area under the curve [AUC]: 4.356 ± 1.3 mcg/ml.hr in animals and 0.442 ± 0.053 mcg/ml.hr in humans; Tmax was 8 hr in both the cases, whereas Cmax was 0.288 ± 0.088 mcg/ml in animals and 0.034 ±. 008 mcg/ml in human volunteers.) The amount of the drug bioavailable for targeting the sites of action is lower than via the oral route, but the absorbed dose appears to be adequate for therapeutic use, particularly because of the absence of side effects.

The relation among vessel injury, thrombus formation, and platelet survival in rabbits

Continuous or repeated injury of rabbit aortae by indwelling vascular catheters caused the deposition of platelets on the injured vessels and the formation of thrombi rich in platelets and fibrin at sites where flow was most disturbed and injury was most extensive. Incorporation of 51Cr platelets into the thrombi reached a maximum between 3 and 24 hr. The platelet-fibrin-rich thrombi remained reactive to circulating platelets for at least 14 days. Continuing reactivity of thrombi and the turnover of platelets in the thrombi were accompanied by an increase in the proportion of platelets that separated in the least dense fraction on Stractan density gradients. Platelet survival was also shortened (43.5 ± 5.9 hr in animals with catheters, compared with 62.6 ± 4.5 hr in animals with a sham operation), indicating that some platelets that had taken part in thrombus formation or had interacted with the injured vessel wall were rapidly cleared from the circulation. Platelets from rabbits that had had indwelling aortic catheters in place for 3 or 6 days survived significantly longer than those from animals with a sham operation upon injection of the platelets into normal animals; thus, continuous turnover of platelets on injured vessels and thrombi, and the clearance of altered platelets, leads to a population of younger platelets that survive longer. The continuing reactivity of thrombi may in part account for repeated occlusive episodes in vascular disease. The contribution of thrombin generation and fibrin formation to the platelet-rich thrombi is substantial and warrants the ongoing evaluation of treatment with a combination of anticoagulant and antiplatelet agents in arterial thrombosis and in thrombus formation on vascular catheters.

Effect of vinblastine on the cell cycle and migration of ameloblasts of mouse incisors as shown by autoradiography using 3H-thymidine.

The effects of vinblastine on the cell cycle and the migration of ameloblasts were studied in the lower incisors of mice by labelling the cells with 3H-thymidine ([3H]TdR) and radioautography. A group of mice received 2 micrograms/g of body weight vinblastine intraperitoneally and 6 hr after these animals and those of a control group were injected with 1 microCi/g body weight of [3H]TdR, and sacrificed at time intervals from 0.75 hr to 15 days. The generation time of ameloblasts in the progenitor compartment was 14.8 hr in animals treated with vinblastine and 17 hr in the controls, using the FLM curve method; with the grain dilution method the duration was respectively 29.25 hr and 25.96 hr. The thymidine labelling index of the treated animals was 50% higher than the controls. The velocity of ameloblast migration, determined either by the displacement of the most incisally labelled cell or by the grain dilution method, was lower in the experimental group (2.48 cell positions/hr and 9.18 microns/hr respectively) as compared with the control (3.21 cell positions/hr and 18.88 microns/hr respectively). The results on the ameloblast production rate are contradictory but the slowing down in the velocity of cell migration is compatible with a decrease of the rate of cell production in the progenitor compartment as a vinblastine effect.

Cell Population Kinetics and Dna Content During Thyroid Carcinogenesis

The proliferation kinetics and DNA content of thyroid follicular cells in rats were studied by autoradiography and cytophotometry. Continuous treatment of animals with methylthiouracil (MTU) results in hyperplasia followed by tumour growth in the thyroid gland. The mitotic index (MI) increases from 0.006 +/- 0.002% in controls to 0.13 +/- 0.06% in hyperplasia and to 0.09 +/- 0.03% in malignant cells. The same is true for the labelling index (LI) which rises from 0.08 +/- 0.003% in controls to 1.4 +/- 1.1% in hyperplasia and to 1.0 +/- 0.6% in follicular adenomas. The S-phase duration (TS) is shortened from 8.0 +/- 1.2 hr in controls to 6.0 +/- 1.4 hr in animals treated for 9 months with MTU and prolonged to 15.4 +/- 2.1 hr in papillary carcinomas. In all MTU-treated animals a decrease in the value of the potential population doubling time (TPD) and thyroid weight doubling time (TD) was observed. The cell loss factor (phi) decreases in animals treated for 3 months with MTU and increases during the stage of tumour growth in the gland (animals treated 12-15 months with MTU). DNA measurements in the nuclei of hyperplastic and neoplastic thyroid tissues reveal cells with values exceeding that in control animals. However, no difference was found in the DNA content between thyroid adenomas and carcinomas, nor between thyroid hyperplasia and neoplasia.

Acute tissue response to cerebral ischemia in the gerbil: An ultrastructural study

The Mongolian gerbil, because of the uniqueness of the anatomical features of its circle of Willis, has become an increasingly useful model in the study of cerebrovascular disease. The present work defines acute changes at the ultrastructural level following ischemic insult. The pathomorphological responses include initial astrocytic involvement and, when the degree of insult is increased, a progression of morphological changes is evident in neuronal and other parenchymal elements. Animals with vessels occluded for more than 3 hr without neurological signs suggestive of ischemia exhibited limited perivascular edema. Contralateral changes (perivascular astrocytic) were observed in the basal ganglia at 24 hr in animals with neurological deficit. Astrocytic and basal ganglia susceptibility to ischemia was consistent with previous findings in primate models. An additional association was found in that limited edematous involvement could exist in animals without neurological deficit but neuronal changes were only present in animals with signs of ischemic neurological deficit.

The effect of bile and of sodium taurocholate on the epithelial cell dynamics of the rat small intestine.

The absence of bile from the intestinal lumen of rats for a period of 48 hr led to: a decreased proliferative cell pool, reduced cell shedding, and a 50% decrease of the labeling index in the ileum. The constant duodenal perfusion of Na taurocholate for periods of 48, 60, 72, and 96 hr in animals with a biliary diversion was associated with: deepening of crypts and decreased crypt/villus ratios as well as with acceleration of the epithelial cell migration rate on the crypt-villus units. The data suggest that bile and bile acids constitute important regulatory factors influencing enterocyte proliferation, migration and loss.

Influence of Sodium Taurocholate, Cholestyramine, and Mylanta on the Intestinal Absorption of Glucocorticoids in the Rat

Abstract A micellar solution of sodium taurocholate has been shown to increase the solubility of cortisol and prednisolone crystals in vitro. That this enhanced solubility confers little physiological advantage to the rat has been demonstrated in in vivo studies on the intestinal absorption of these compounds. Tritiated crystals of cortisol and prednisolone were delivered intraduodenally to rats with complete biliary diversion receiving an intraduodenal infusion of either 37 mm taurocholate or normal saline. The excretion of the metabolic products of the steroids in bile and urine was used as a measure of the intestinal absorption of the parent compound. Excretion was greater in the first 2 hr after the administration of either cortisol or prednisolone in rats receiving bile salts than in bile salt-deficient animals. By 4 hr, however, no significant differences were found in the excretion values between the two groups of rats. More than 70% of the administered steroid was recovered in bile and urine within 4 hr in animals with a complete bile-salt deficit. Despite the demonstration, in vitro, that both steroid compounds are bound by cholestyramine, no significant decrease in the intestinal absorption of cortisol was observed when either cholestyramine or an antacid containing aluminum hydroxide were administered concomitantly.

Paradoxical enhancement of S-adenosylmethionine decarboxylase in rat tissues following administration of the specific inhibitor methyl glyoxal bis(guanylhydrazone)

Treatment of rats with large but sublethal doses of methyl glyoxal bis(guanylhydrazone), a potent in vitro inhibitor of animal S-adenosylmethionine decarboxylases, causes marked increases in the enzyme activity of extracts of kidney, ventral prostate, and testis which had been extensively dialyzed to remove any remaining drug. One day after administration of the inhibitor to female rats, the renal S-adenosylmethionine decarboxylase activity was 12 times the normal level and remained greatly enhanced for a further 24 hr. As indicated by decline in decarboxylase activity following depression of protein biosynthesis by injection of cycloheximide, the apparent half-life of the kidney enzyme in normal female rats is roughly 2 hr; in contrast, the apparent half-life of the enzyme is elevated to a value of more than 20 hr in animals that were previously treated with methyl glyoxal bis(guanylhydrazone). The increased renal S-adenosylmethionine decarboxylase activity following administration of the specific enzyme inhibitor in vivo may thus be due, at least in part, to stabilization of the enzyme against intracellular inactivation as a result either of direct combination of the enzyme protein with the inhibitor, or with substance(s) in the tissue whose levels are influenced by treatment with methyl glyoxal bis(guanylhydrazone).