Adipose tissue resistin expression is severely suppressed in obesity and stimulated by peroxisome proliferator-activated receptor gamma agonists.

Elevated levels of the hormone resistin, which is secreted by fat cells, are proposed to cause insulin resistance and to serve as a link between obesity and type 2 diabetes. In this report we show that resistin expression is significantly decreased in the white adipose tissue of several different models of obesity including the ob/ob, db/db, tub/tub, and KKA(y) mice compared with their lean counterparts. Furthermore, in response to several different classes of antidiabetic peroxisome proliferator-activated receptor gamma agonists, adipose tissue resistin expression is increased in both ob/ob mice and Zucker diabetic fatty rats. These data demonstrate that experimental obesity in rodents is associated with severely defective resistin expression, and decreases in resistin expression are not required for the antidiabetic actions of peroxisome proliferator-activated receptor gamma agonists.

Biological-time-dependent differences in effect of verapamil on rat aorta and influence of endothelium.

The biological-time-dependent variation in the vasodilator effect of verapamil on rat thoracic aorta was assessed in both endothelium-intact and denuded preparations. Groups of adult male rats were housed in light from 08:00 to 20:00 and in darkness from 20:00 to 08:00 and sacrificed at six different times of the day (1, 5, 9, 13, 17, and 21 hours after lights on; HALO). Verapamil caused concentration-dependent relaxations in both endothelium-intact and denuded aortic rings precontracted with phenylephrine (Phe). In endothelium-intact rings, neither the AUC nor the EC50 values for verapamil exhibited significant biological-time-dependent effects, as determined by one-way analysis of variance (ANOVA). In endothelium-denuded rings, AUC values did vary in a statistically significant manner according to the biological time of study, while the EC50 values did not. Endothelium denudation led to an increase in EC50 values at almost every time point. Statistically significant interactions between the biological time of study and treatment (intact vs. denuded endothelium) in both AUC and EC50 values were documented by two-way ANOVA; this indicated differences in the clock-time staging of verapamil-induced relaxation in endothelium-denuded versus intact aortic rings.

Circadian-rhythm-dependent effects of L-NG-nitroarginine methyl ester (L-NAME) on morphine-induced analgesia.

Circadian changes in the interactions between L-NG-nitroarginine methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor, and morphine-induced antinociception were investigated by the mouse hot-plate test. Both the basal pain sensitivity and morphine-induced analgesia undergo significant 24 h variations. L-NAME (40 mg/kg, i.p.) alone did not show any antinociceptive activity, but potentiated morphine-induced analgesia when combined with morphine at all injection times. In terms of percentage absolute potentiation (%AP), L-NAME dramatically augmented the analgesic effect of morphine in the late dark period at 19 hours after lights on (HALO). It is concluded that nitric oxide (NO) is involved in the modulation of the analgesic effect of morphine; thus, the L-NAME and morphine combination might be beneficial in alleviating pain.

In vitro susceptibility rhythms. II. Biological-time-dependent differences in effect of beta 1- and beta 2-adrenergic agonists of rat aorta and influence of endothelium.

Time-dependent variations in the vasodilator effects of beta-adrenergic agonists terbutaline (Ter) and dobutamine (Dob) were studied in isolated rings of rat thoracic aorta in both endothelium-intact and endothelium-denuded preparations. Rats were housed in light from 08:00 to 20:00 and in darkness from 20:00 to 08:00 and sacrificed at six different times of the day. In endothelium-intact and endothelium-denuded aortic rings precontracted submaximally with phenylephrine (Phe), addition of Ter and Dob produced concentration-dependent relaxations. Removal of endothelium reduced the relaxant responses and area under curve (AUC) values and augmented the EC50 values to Ter and Dob at most, but not all, time points. Two-way analysis of variance (ANOVA) revealed that AUCs, maximum responses, and EC50 values significantly depended on both treatment (endothelium intact/endothelium denuded) and time of sacrifice. Results of the present study clearly show that in vitro sensitivity of rat thoracic aorta to beta-adrenergic agonists displays temporal variations depending on the time of animal sacrifice, and the presence of endothelium modifies the rhythmicity in beta-adrenergic activity. These variations may be due to the circadian rhythmicity in the adenylyl cyclase-cAMP-phosphodiesterase system that mediates the responses to beta-adrenergic agonists.

In vitro evidence of tissue susceptibility rhythms. I. Temporal variation in effect of potassium chloride and phenylephrine on rat aorta.

In this study, time-dependent variations in the in vitro sensitivity of rat thoracic aorta rings to potassium chloride (KCl) and phenylephrine (Phe) were investigated. Animals were synchronized with a 12h light and 12h darkness (lights on 08:00-20:00) schedule, and thoracic aortas were obtained at six different times of the day (1, 5, 9, 13, 17, and 21 hours after lights on). In order to avoid endothelial influence, all experiments were performed in endothelium-denuded preparations. Responses to KCI showed time-dependent variations in all the concentrations used. Phe-induced contractions also exhibited time-dependent differences. The rhythmic pattern of Phe responses did not change with the presence of the alpha1-adrenergic antagonist prazosin. In addition, both the EC50 values of KCl and Phe, and also the K(B) values of prazosin, displayed rhythmicity. In conclusion, time of obtaining tissues is an important factor for experimental standardization in, at least, vascular smooth muscle preparations.

Twenty-four-hour variations in the effect of nitrodilators in rat aorta: lack of influence of the endothelium.

Time-dependent variations of the vasodilator effects of sodium nitroprusside and glyceryl trinitrate on isolated smooth muscle have been studied on rings of rat thoracic aorta, both endothelium-intact and endothelium-denuded. For most of the concentrations of sodium nitroprusside used the induced relaxations were significantly dependent on the time the tissues were obtained. However, significant temporal differences were obtained for glyceryl trinitrate-induced relaxations at lower concentrations only for both endothelium-intact and endothelium-denuded preparations. EC50 values of sodium nitroprusside and glyceryl trinitrate (i.e. the concentrations inducing half the maximum response) were also significantly different and they had quite similar rhythmic features both in endothelium-intact and in endothelium-denuded preparations. These results clearly show that the in-vitro sensitivity of rat thoracic aorta to nitrodilator agents varies over a 24-h period and thus depends on when the animals were killed; the presence of endothelium does not change the rhythm of nitrodilator activity. These variations might be a result of circadian rhythm in the guanylate cyclase-cGMP system which mediates responses to nitrodilator agents.

Circadian reactivity rhythm of rat gastric mucosa to restraint-cold stress and indomethacin: temporal variation in the protective effect of iloprost.

In this study, the time-dependent ulcerogenic effects of restraint-cold stress and indomethacin on the gastric mucosa and the temporal variation in the protective effect of iloprost, a synthetic stable analog of prostacyclin, were investigated in rats synchronized to 12h light and 12h darkness, lights on at 08:00. The severity of gastric ulceration produced by either stress or indomethacin showed marked circadian variation; it was greatest at 11 HALO (hours after lights on) for restraint-cold stress and at 23 HALO for indomethacin. The severity of the induced ulcerogenesis was least at 7 HALO for both stimuli. The protective effect of iloprost against restraint-cold stress was most prominent at 15 HALO and 19 HALO with an approximately 80% protection score. On the other hand, pretreatment with iloprost reduced the indomethacin-induced mucosal injury only at 23 HALO. The circadian variation in the effect of iloprost and in the rhythmic modalities of these two experimental ulcer models are indicative of differences in their underlying mechanisms. In experimental models of ulceration, the circadian time of application of the ulcerogenic stimulus must be considered as an important experimental factor. Moreover, the protective effectiveness of antiulcer drugs can express time-dependent differences and must also be taken into account in investigative research.

Effects of auro-detoxin treatment on vascular responses in mouse aorta.

1. In this study, we investigated the effects of chronic Auro-detoxin treatment for 5 and 10 weeks on reactivity to vascular agonists in the mouse aorta. 2. The maximum contractile responses to and the -log EC50 values of phenylephrine (Phe) were not changed with Auro-detoxin treatment. 3. The maximum contractile responses to 5-hydroxytryptamine (5-HT) were not changed over 5 weeks but were significantly increased with Auro-detoxin treatment during a 10-week period. The -log EC50 values of 5-HT were found to be significantly decreased in both treatment groups. 4. The maximum relaxation responses to acetylcholine (ACh) were decreased in both treatment groups. The -log EC50 values of ACh were not changed in 5 weeks but significantly decreased in 10 week-treated animals. 5. Neither the maximum relaxation responses not the -log EC50 values of sodium nitroprusside (SNP) were changed with Auro-detoxin treatment. 6. These results suggest that chronic gold treatment affects vascular responses in the mouse aorta.

Twenty-four-hour variations in the sensitivity of rat aorta to vasoactive agents.

The presence of time-dependent variations in the in vitro sensitivity of aorta preparations to either vasoconstricting or relaxing agents was investigated in rats maintained in light for 08:00 to 20:00 and in darkness from 20:00 to 08:00. Rat thoracic aorta rings were obtained from animals sacrificed at four different times of the day. The rat aorta was found to be sensitive to the constricting effect of phenylephrine at 15:00, and of 5-hydroxytryptamine at 21:00. On the other hand, both endothelium-dependent and -independent relaxations were more remarkable at 03:00 than at other times of the day. These variations represented significant circadian rhythms when analyzed by analysis of variance. Different in vitro responsiveness to these agents might reflect changes in the sensitivity and/or number of related receptors in vascular preparations. In conclusion, the circadian time of animal sacrifice to obtain vascular preparations constitutes an important aspect of the research method and a key determinant of findings.

Temporal variation in the interaction between calcium channel blockers and morphine-induced analgesia.

Circadian variations in the interaction between calcium channel blockers and morphine-induced analgesia were determined by the mouse hot-plate test. Calcium channel blockers diltiazem, verapamil, or nicardipine alone did not display any significant analgesic effect, but all of them potentiated morphine-induced analgesia when injected 30 min prior to morphine at most of the injection times. In terms of percent absolute potentiation, they produced more potentiation during the light period than darkness. Their potentiating effects decreased abruptly during darkness, and around the midtime of the dark period no significant potentiation of morphine-induced analgesia was observed. It is concluded that these fluctuations in the magnitude of interaction between calcium channel blockers and morphine must be taken into consideration particularly in studies dealing with the role of calcium in analgesia.