Subchronic inhalation of mixtures of cigarette smoke constituents in Xpa-/-p53+/- knock-out mice: a comparison of intermittent with semi-continuous exposure to acetaldehyde, formaldehyde, and acrolein.

We investigated whether inhaling peak concentrations of aldehydes several times daily is more damaging than semi-continuously inhaling low-dose aldehydes. We exposed Xpa-/-p53+/- knock-out mice either intermittently or semi-continuously to mixed acetaldehyde, formaldehyde, and acrolein. The intermittent regimen entailed exposure to the aldehydes 7 min every 45 min, 12 times/day, 5 days/week, corresponding to concentrations inhaled by smokers. Semi-continuously exposed animals received half the dose of aldehydes in 8h/day, 5 days/week. Some mice in each group were sacrificed after 13 weeks of exposure; the rest breathed clean air until the end of 1 year. Mice injected intratracheally with benzo[a]pyrene formed a positive control group. The nasal cavity, lungs, and any macroscopically abnormal organs of all mice were analysed histopathologically. After 13 weeks of exposure, the subacute, overall, histopathological changes induced by the inhalation differed noticeably between the intermittently and semi-continuously treated Xpa-/-p53+/- knock-out mice. After 13 weeks of mixed aldehyde exposure, atrophy of the olfactory epithelium generally appeared, but disappeared after 1 year (adaptation and/or recovery). Respiratory epithelial metaplasia of the olfactory epithelium occurred at a higher incidence at 1 year. Except for a significantly greater number of tumours observed in knock-out mice compared to wild mice (semi-continuous aldehyde exposure and controls), no differences between the semi-continuous and intermittent exposure groups were observed.

Mepyramine but not cimetidine or clobenpropit blocks pertussis toxin-induced histamine sensitization in rats.

The effects of pertussis toxin (PT) and the role of histaminergic H(1), H(2) and H(3) receptor blockade on the actions of histamine on blood pressure, heart rate, blood gas values, and mortality were studied in anaesthetized rats. Four days after treatment with PT, histamine dose-dependently decreased mean arterial blood pressure (MAP) and PT enhanced the histamine-induced decrease in MAP. In the PT but not in the inactivated PT (IPT) or saline treated group three out of six animals died after the highest dose of histamine (300 mg kg(-1), i.v.) In order to determine the type of histamine receptor that mediates HS, 4 days after PT the selective antagonists mepyramine (H(1)), cimetidine (H(2)) and clobenpropit (H(3)) were administered 20 min before the challenge with histamine. Mepyramine completely inhibited both the enhanced histamine-induced decrease in MAP and mortality brought about by PT. Cimetidine and clobenpropit had no protective effects, but rather enhanced the histamine-induced mortality elicited by PT. The present study shows that PT caused HS in rats which is primarily mediated via H(1) and secondarily via H(2) and H(3) receptors. These results are considered to be a first step in the elucidation of the mechanism(s) of the HS test used in the quality control of acellular pertussis vaccine.

Further study of possible direct vascular actions of indapamide in the conduit and renal arteriolar vessels of spontaneously hypertensive rats.

The effect of indapamide on vascular reactivity and its properties as a calcium antagonist were studied in both isolated aorta and perfused renal vasculature of spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) rats. Indapamide was given orally to SHR and WKY rats for 2 weeks at a dose of 5 mg/kg per day. During this period indapamide did not lower blood-pressure in SHR and WKY rats although there was an adequate concentration of indapamide in the blood. There were no differences observed in the vascular reactivity towards noradrenaline and high-K+ in both the above mentioned vessels in either indapamide- or vehicle-pretreated SHR and WKY rats. Verapamil (10(-9)-10(-5) M) caused a concentration-dependent relaxation of high-K+-depolarized aortas and a decrease in the renal-arteriolar perfusion pressure elevated by high-K+ in both strains of rat. However, indapamide (10(-7)-10(-4) M) did not affect the K+-induced effect on either vessel type. Preloading of the vessels in vivo with indapamide for 2 weeks did not influence the results. In conclusion, further evidence has been presented to show that indapamide does not have calcium-antagonist properties in conduit (aorta) or resistance (renal) vessels under hypertensive conditions. Preloading of the vessels with indapamide was not a prerequisite for the demonstration of a pharmacological action of indapamide.

Effect of nitrite on blood pressure in anaesthetized and free-moving rats.

The effect of nitrite on blood pressure and heart rate was studied in anaesthetized (non-telemetric method) and free-moving rats (biotelemetry system). In anaesthetized rats, NaNO2 (10-1000 mumol/kg), infused over 5 min, induced a dose-related decrease in blood pressure. The maximal decrease in mean arterial blood pressure (MAP), caused by 1000 mumol/kg NaNO2 and measured 15 min after infusion was 55.9 +/- 3.2% (n = 3). After NaNO2 infusion, in the plasma, rapid conversion of nitrite into nitrate was observed. However, sodium nitrate (NaNO3, 100 mumol/kg) did not decrease blood pressure and there was no conversion of nitrate into nitrite. Free-moving rats received KNO2 which was added to drinking water (36 mmol/litre) for a period of 3 days. KNO2 decreased the MAP and increased the heart rate during the rat's activity phase at night but not during their resting phase in the day. An equal concentration of potassium (KCl, 36 mmol/litre added to drinking water) for 3 days did not decrease blood pressure. It is concluded that nitrite decreases blood pressure in rats, which probably induces, by renin-angiotensin system activation, hypertrophy of the adrenal zona glomerulosa.

Disturbance of cardiovascular circadian rhythms by pertussis vaccine in freely-moving rats.

Vaccination of young children with diphtheria, tetanus, poliomyelitis and pertussis (DTPoP) vaccine is effective in preventing outbreaks of whooping cough but adverse events sometimes occur. This pilot study shows that in freely-moving rats, multiple treatment with DTPoP (at day 0 and day 5, 6 ml/kg i.v.) increased heart rate (HR) for 5 days after the first treatment and decreased diastolic blood pressure (DBP) for at least 26 days after the first treatment and inhibited the circadian rhythm of HR and DBP for at least 10 days. DTPo vaccine, containing no pertussis vaccine, was free of such effects. Thus, in rats, the pertussis component of DTPoP acts on the cardiovascular system and disturbs its circadian rhythm. The contribution of these findings to clinical adverse effects is as yet unknown and needs further research.

Toxic doses of rac-, (-)-(S)- and (+)-(R)-propranolol in rats and rabbits.

The contribution of the individual enantiomers ([+]-[R]- and [-]-[S]-propranolol) to rac-propranolol intoxication was studied in anaesthetized, spontaneously breathing (SB) rats and artificially ventilated (AV) rats and rabbits. In the SB rat, propranolol (30 mg.kg-1.h-1 i.v.) decreased heart rate and mean arterial blood pressure and caused hypoventilation, serious hypoxaemia, respiratory acidosis, and death by respiratory arrest. Survival time (ST) in the (+)-(R)-propranolol group (ST 91 +/- 5 min) was significantly longer than in the rac-propranolol group (ST. 68 +/- 6 min). In AV rats and rabbits toxic doses of rac-, (-)-(S)- and (+)-(R)-propranolol, 30 mg.kg-1.h-1 and 15 mg.kg-1.h-1 i.v., respectively, induced comparable effects on haemodynamic variables as in the SB rat. Artificial ventilation lengthened ST by a factor of three to four in rats. In the AV rat, ST's were not significantly different between the rac-, (-)-(S)- and (+)-(R)-propranolol groups. In the rabbit, as in the SB rat, ST in the (+)-(R)-propranolol group was significantly longer than ST's in the rac- and (-)-(S)-propranolol groups. The acute respiratory acidosis in SB rats and the prolonged ST in AV rats suggest that respiratory failure is the primary and cardiovascular failure the secondary cause of death in propranolol intoxication. The potentiation of the toxic effect of the enantiomers observed after dosing the racemate instead of the pure enantiomers could not be explained by a stereoselective difference in plasma propranolol concentration.