Comparison of the discriminative-stimulus effects of SKF 38393 with those of other dopamine receptor agonists

The dopamine D(1)-like receptor agonists have traditionally been defined molecularly by their efficacy in stimulating adenylyl cyclase. However, evidence correlating the effectiveness of these drugs in behavioral assays and their effectiveness biochemically has not been forthcoming. The present study compared the discriminative-stimulus effects of the D(1)-like partial agonist SKF 38393 with several other D(1)-like agonists, an indirect agonist, cocaine, and a D(2)-like agonist, quinpirole. Rats were trained under a fixed-ratio 30-response schedule to discriminate SKF 38393 (5.6 mg/kg) from vehicle. Under this schedule, 30 consecutive responses on one of two keys were reinforced with food presentation after a pre-session injection of 5.6 mg/kg SKF 38393, and 30 consecutive responses on the alternative key were reinforced after saline injection. When daily performances were stable, substitution patterns for several compounds were assessed during test sessions in which 30 consecutive responses on either key were reinforced. Quinpirole and cocaine each produced saline-appropriate responding. In contrast, the D(1)-like agonists, SKF 75670 and SKF 77434, fully substituted for SKF 38393. Curiously, SKF 82958, which is considered a full agonist based on adenylyl cyclase assays, was less effective in substituting for SKF 38393 (maximum drug-appropriate responding 66%) than was the partial agonist SKF 75670. The present results suggest that second messenger effects other than stimulation of adenylyl cyclase may play an important role in the behavioral effects of dopamine D(1)-like agonists.

Tea consumption and the risk of colorectal cancer in Sweden

The association between tea drinking and colorectal cancer risk remains unclear. The evidence for black tea is sparse but may indicate an increased risk with regular use. Because black tea is a common beverage in many populations, the significant twofold increased risk of colon cancer recently reported from a large prospective cohort of male Finnish smokers is disconcerting. Using Cox proportional hazards models to estimate relative risks, we examined this association in a large, population-based prospective cohort study in Sweden. During an average 9.6 years of follow-up of our cohort of 61,463 women (588,270 person-yr), we observed 460 incident cases of colorectal cancer (291 colon, 159 rectal, and 10 with both colon and rectal cancer). We observed no association between tea consumption and combined colorectal cancers in age- or multivariate-adjusted models. With the use of collapsed exposure categories, the multivariate-adjusted relative risk for the highest exposure (> or = cups/day) compared with the lowest (never or seldom) was 0.97 (95% confidence interval = 0.63-1.48, p for trend = 0.34). Examining the association by cancer subsite, we observed no association between tea consumption and proximal, distal, or combined colon cancers. We did, however, observe a nonsignificant positive association with rectal cancers, which became stronger and statistically significant among women > or = 65 years of age at baseline. Our data do not support the strong, dose-dependent positive association with colon cancer found in the Finnish study.

Modulation of the effects of alcohol on driving-related psychomotor skills by chronic exposure to cannabis

RATIONALE

Many previous studies have reported that alcohol and cannabis produce additive psychomotor effects in acute combination, but few have explicitly tested whether chronic exposure to cannabis, in the absence of acute administration, alters the effects of alcohol on psychomotor performance.

OBJECTIVES

To test whether long-term cannabis use modulates the effects of alcohol on psychomotor skills and self-reported mood and sensation.

METHODS

Regular cannabis users (minimum: daily use for at least 3 years) and infrequent users (maximum: once-monthly use for at most 3 years) were matched for sex, age, alcohol intake and other drug use (14 participants in each group). Participants received alcohol (females 0.35 g/kg; males 0.45 g/kg) and placebo drinks. By urinalysis, only regular users tested positive for metabolites of Delta(9)-tetrahydrocannabinol; breath alcohol levels were similar between groups. Participants were tested on a computerised tracking task that has been used to screen drugs for adverse effects on driving. The task involved tracking a moving target on a computer screen while simultaneously responding to occasional presentations of stimuli in the periphery of the screen.

RESULTS

Tracking accuracy was similar for both groups after placebo, but alcohol caused a significant deterioration in performance among infrequent cannabis users relative to regular users. These changes were mirrored by significant changes in self-reported scores for dizziness, measured by visual analogue scales. Alcohol slowed reaction times, but not differentially between groups.

CONCLUSIONS

For psychomotor skills relevant to driving, chronic cannabis use (in the absence of acute administration) does not potentiate the effects of alcohol. In fact, the superior tracking accuracy of regular users relative to infrequent users after alcohol, and their lower scores for dizziness, suggest that chronic cannabis use may instead confer cross-tolerance to specific effects of alcohol on behaviour.

Reflux-inducing dietary factors and risk of adenocarcinoma of the esophagus and gastric cardia

Gastroesophageal reflux (GER) is the strongest known risk factor for esophageal adenocarcinoma. For long-term sufferers with severe symptoms, the excess risk may exceed 40-fold. GER has also been shown to increase the risk of cancers of the gastric cardia more than fourfold. Several foods, including dietary fat, chocolate, mints, coffee, onions, citrus fruit, and tomatoes, have been associated with temporary symptoms of reflux, most likely through a relaxation of the lower esophageal sphincter (LES). Our aim was to determine whether these foods are associated with risk of adenocarcinoma of the esophagus or gastric cardia. We studied intakes of LES-relaxing foods and other dietary habits potentially associated with reflux in a nationwide population-based case-control study in Sweden, with 185 and 258 cases of esophageal adenocarcinoma and gastric cardia adenocarcinoma, respectively, and 815 controls. We found no association between LES-relaxing foods and symptoms of chronic reflux, although this might be due to avoidance of these foods among sufferers. In addition, we found no association between dietary factors known to cause LES relaxation and the risk of adenocarcinoma of the esophagus or gastric cardia. Our findings indicate that dietary factors associated with LES relaxation and transient GER (but perhaps not severe chronic reflux) are not associated with any important risk of esophageal malignancy.

Prospective study of major dietary patterns and colorectal cancer risk in women

A number of prospective cohort studies have examined the relations of individual dietary variables to risk of colorectal cancer. Few studies have addressed the broader eating patterns that reflect many dietary exposures working together. Using data from a prospective study of 61,463 women, with an average follow-up period of 9.6 years (between 1987 and 1998) and 460 incident cases of colorectal cancer, the authors conducted a factor analysis to identify and examine major dietary patterns in relation to colorectal cancer risk. Using proportional hazards regression to estimate relative risks, the authors found no clear association between a "Western," "healthy," or "drinker" dietary pattern and colorectal cancer risk. However, the data suggested that consuming low amounts of foods that constitute a "healthy" dietary pattern may be associated with increased risks of colon and rectal cancers. An inverse association with the "healthy" dietary pattern was found among women under age 50 years, although the number of cancers in this age group was limited and interpretation of this finding should be cautious. In this age group, relative risks for women in increasing quintiles of the "healthy" dietary pattern, compared with the lowest quintile, were 0.74 (95% confidence interval (CI): 0.41, 1.31), 0.69 (95% CI: 0.39, 1.24), 0.59 (95% CI: 0.32, 1.07), and 0.45 (95% CI: 0.23, 0.88) (p for trend = 0.03). The role of overall eating patterns in predicting colorectal cancer risk requires further investigation.

A prospective study of major dietary patterns and the risk of breast cancer

Our aim was to study the broader eating patterns that potentially reflect many dietary exposures working together in their association with breast cancer risk. Using data from a prospective study of 61,463 women with an average follow-up of 9.6 years and 1,328 incident cases of breast cancer, we conducted a factor analysis to identify major dietary patterns. Proportional hazards regression was used to estimate hazard ratios. We found no association between the "Western" dietary pattern (characterized by such foods as red and processed meats, refined grains, fat, and sweets) or the "healthy" dietary pattern (fruit and vegetables, fish and poultry, low-fat dairy, and whole grains) and breast cancer risk. However, women who were in the highest category of the "drinker" dietary pattern (wine, beer, and spirits) had a moderately increased risk (rate ratio = 1.27; 95% confidence interval, 1.06-1.52; P for trend, 0.002). The positive association was somewhat weaker among women below 50 years of age, a finding not inconsistent with chance. Our results are in agreement with the majority of previous studies that show alcohol consumption moderately increases the risk of breast cancer, but our results do not support any association between breast cancer risk and the "Western" or "healthy" dietary patterns.

Antagonism of the discriminative stimulus effects of cocaine at two training doses by dopamine D2-like receptor antagonists

RATIONALE

The relative contributions of different dopamine receptor subtypes to the discriminative stimulus effects of cocaine may be influenced by the training dose of cocaine. Substitution tests with dopamine receptor agonists have suggested that the role of dopamine D2-like receptors is diminished relative to that of D1-like receptors at a training dose of 3 mg/kg cocaine compared with a training dose of 10 mg/kg.

OBJECTIVES

To test whether dopamine D2-like receptor antagonists were differentially effective at attenuating cocaine's discriminative stimulus effects at different training doses, and to test for the first time an antagonist that is selective for the dopamine D2 receptor within the D2-like receptor subfamily.

METHODS

Rats were trained to press one lever after receiving cocaine and another after receiving saline (maintaining >95% drug-appropriate responding). Three dopamine D2-like receptor antagonists (haloperidol, raclopride and L-741,626) were tested in rats trained at 3 mg/kg or 10 mg/kg cocaine. At the lower training dose, the D1-like receptor antagonist SCH 39166 was also tested.

RESULTS

The antagonists were not differentially effective between training groups: they all produced parallel, rightward shifts in cocaine's dose-effect function, indicating surmountable antagonism.

CONCLUSIONS

The results demonstrate that D2-like receptor antagonists with different affinities for the various D2-like receptors can antagonise the discriminative stimulus effects of cocaine at two training doses. Importantly, antagonism by L-741,626 implies that stimulation of D2 receptors alone (not D3 or D4 receptors) is sufficient to mediate cocaine's discriminative stimulus effects. Finally, the claim that D1-like receptors are preferentially involved at low training doses of cocaine is only consistent with the current findings if indirect stimulation of D2 receptors by low doses of cocaine remains necessary for the expression of the D1-like receptor-mediated effect.

Fruit and vegetable consumption in the prevention of cancer: an update

Fruit and vegetables are considered to be important means of preventing cancer through diet. However, several recent large prospective cohort studies and clinical trials have found no associations regarding several major cancers, including cancers of the colon, breast and stomach. Although these results are disconcerting, especially for health-conscious individuals, there is also mounting evidence that people who avoid fruit and vegetables completely, or consume very little, are indeed at increased risk of these cancers. These individuals in particular should be identified, with the goal of helping them find ways to include more fruit and vegetables in their diets.

Fruit and vegetable consumption in the prevention of oesophageal and cardia cancers

The incidence of adenocarcinoma of the oesophagus has increased rapidly in recent decades. In order to appreciate the potential for prevention by means of dietary modification, we estimated the aetiological fractions and the increments in absolute risk attributable to low intake of fruit and vegetables for adenocarcinoma and squamous cell carcinoma of the oesophagus and for adenocarcinoma of the gastroesophageal junction. We conducted a nationwide population-based case-control study in Sweden, with participation of 608 cases and 815 controls. We used unconditional logistic regression to estimate relative risks, from which we calculated aetiological fractions. Individuals in the highest exposure quartile (median 4.8 servings/day) versus the lowest (median 1.5 servings/day) showed approximately 50% lower risk of oesophageal adenocarcinoma and 40% lower risk of oesophageal squamous cell carcinoma, but no risk reduction for gastric cardia adenocarcinoma. Approximately 20% of oesophageal adenocarcinoma, and likewise squamous cell carcinoma, in Sweden was attributed to consuming less than three servings of fruit and vegetables per day. A very large number of individuals (over 25,000) would need to increase their fruit and vegetable consumption moderately in order to prevent one oesophageal cancer per year. Moderate relative risk reductions translate into weak absolute risk reductions for oesophageal cancers in Sweden.

Body weight and colorectal cancer risk in a cohort of Swedish women: relation varies by age and cancer site

The relation between relative body weight and colorectal cancer among women is unclear. In a large prospective cohort study, we found a positive association only for distal cancers among younger women that became attenuated at older ages. These results support previous reports in which results were stratified by age or colorectal cancer site.

Coffee consumption and risk of colorectal cancer in a population based prospective cohort of Swedish women

BACKGROUND

The presumed protective effect of coffee consumption on colorectal cancer, which is supported by case control studies, has not been confirmed in prospective cohort studies. Cohort studies are few in number however and often suffer from a small number of cases, limited attention to confounding variables, and a low percentage of heavy coffee drinkers.

METHODS

We examined data from a large population based cohort of Swedish women who were free from cancer at the start of follow up, with a wide range of coffee consumption, information on many potentially confounding variables, and a larger number of cases than any previous cohort study of coffee consumption and colorectal cancer.

RESULTS

During an average of 9.6 years of follow up of 61 463 women aged 40-74 years, we observed 460 incident cases of colorectal cancer (291 with colon cancer, 159 with rectal cancer, 10 with cancer at both sites). We found no association between coffee consumption and colorectal cancer risk. The risk ratio for drinking four or more cups per day compared with none was 1.04 (95% confidence interval 0.63-1.69; p for trend 0.84). The findings were similar for cancers of the distal and proximal colon and rectum.

CONCLUSIONS

The recently published affirmative conclusions regarding the protective effect of coffee consumption may be premature. For patients seeking advice about coffee consumption, the evidence suggests that moderate or even high consumption will probably not influence the risk of colorectal cancer.

Fatty fish consumption and risk of prostate cancer

Consumption of fatty fish might reduce the risk of prostate cancer, although epidemiological studies of fish consumption are rare. We studied the association between fish consumption and prostate cancer in a population-based prospective cohort of 6272 Swedish men. During 30 years of follow-up, men who ate no fish had a two-fold to three-fold higher frequency of prostate cancer than those who ate moderate or high amounts did. Our results suggest that fish consumption could be associated with decreased risk of prostate cancer.

Long-term tobacco smoking and colorectal cancer in a prospective cohort study

Tobacco smoking has consistently been associated with colorectal adenomas, precursors of cancer, but the association with colorectal cancer itself has not been consistent. If colorectal cancer emerges only after a 35-year induction period, an association would unlikely be detected in studies where exposure assessment is of shorter duration. Most previous studies do not examine smoking of such duration and therefore do not account for the hypothesized 35-year induction period. By using the Cox proportional hazards models to estimate relative risks, we studied the association of long-term smoking and colorectal cancer risk in a population-based prospective cohort of 17,118 Swedish twins with up to 30 years of follow-up and information on smoking habits prior to baseline exposure assessment. Long-term heavy smoking was associated with a statistically significant 3-fold increased risk of colorectal cancer compared with never smoking (relative risk 3.1, 95% CI 1.4- 7.1). Examining colorectal cancer sub-sites separately, a non-significant 60% increased risk of colon cancer was observed only for heavy smokers and a statistically significant 5-fold increased risk was observed for rectal cancer. Our data lend some support to the hypothesis that heavy long-term cigarette smoking is associated with increased risk of colorectal cancer. Further elucidation of this association would be valuable from both etiologic and public health perspectives.

Fruit, vegetables, dietary fiber, and risk of colorectal cancer

BACKGROUND

Several recent large prospective cohort studies have failed to demonstrate the presumed protective effect of fruit, vegetable, and dietary fiber consumption on colorectal cancer risk. To further explore this issue, we have examined these associations in a population that consumes relatively low amounts of fruit and vegetables and high amounts of cereals.

METHODS

We examined data obtained from a food-frequency questionnaire used in a population-based prospective mammography screening study of women in central Sweden. Women with colorectal cancer diagnosed through December 31, 1998, were identified by linkage to regional cancer registries. Cox proportional hazards models were used to estimate relative risks. All statistical tests were two-sided.

RESULTS

During an average 9.6 years of follow-up of 61 463 women, we observed 460 incident cases of colorectal cancer (291 colon cancers, 159 rectal cancers, and 10 cancers at both sites). In the entire study population, total fruit and vegetable consumption was inversely associated with colorectal cancer risk. Subanalyses showed that this association was due largely to fruit consumption. The association was stronger, however, and the dose-response effect was more evident among individuals who consumed the lowest amounts of fruit and vegetables. Individuals who consumed less than 1.5 servings of fruit and vegetables per day had a relative risk for developing colorectal cancer of 1.65 (95% confidence interval = 1.23 to 2.20; P(trend) =.001) compared with individuals who consumed more than 2.5 servings. We observed no association between colorectal cancer risk and the consumption of cereal fiber, even at amounts substantially greater than previously examined, or of non-cereal fiber.

CONCLUSIONS

Individuals who consume very low amounts of fruit and vegetables have the greatest risk of colorectal cancer. Relatively high consumption of cereal fiber does not appear to lower the risk of colorectal cancer.

Physical activity and risk of renal cell cancer

The relation between physical activity and renal cell cancer is unclear. High occupational physical activity has been associated with a decreased risk of renal cell cancer among men-but not among women-in two previous studies, while no association has been found for leisure time physical activity. Our aim was to investigate the association between occupational and leisure time physical activity in a prospective cohort of 17,241 Swedish twins. Information on physical activity and a wide range of potential confounding factors was obtained through a mailed questionnaire. During follow-up from 1967 through 1997 we identified 102 cases of renal cell cancer. We found no evidence of an inverse association between either occupational or leisure time physical activity and risk of renal cell cancer in this prospective cohort.

Long-term tobacco smoking and colorectal cancer in a prospective cohort study

Tobacco smoking has consistently been associated with colorectal adenomas, precursors of cancer, but the association with colorectal cancer itself has not been consistent. If colorectal cancer emerges only after a 35-year induction period, an association would unlikely be detected in studies where exposure assessment is of shorter duration. Most previous studies do not examine smoking of such duration and therefore do not account for the hypothesized 35-year induction period. By using the Cox proportional hazards models to estimate relative risks, we studied the association of long-term smoking and colorectal cancer risk in a population-based prospective cohort of 17,118 Swedish twins with up to 30 years of follow-up and information on smoking habits prior to baseline exposure assessment. Long-term heavy smoking was associated with a statistically significant 3-fold increased risk of colorectal cancer compared with never smoking (relative risk 3.1, 95% CI 1.4- 7.1). Examining colorectal cancer sub-sites separately, a non-significant 60% increased risk of colon cancer was observed only for heavy smokers and a statistically significant 5-fold increased risk was observed for rectal cancer. Our data lend some support to the hypothesis that heavy long-term cigarette smoking is associated with increased risk of colorectal cancer. Further elucidation of this association would be valuable from both etiologic and public health perspectives.

Inverse association between intake of cereal fiber and risk of gastric cardia cancer

BACKGROUND & AIMS

Recent data show that salivary nitrites form carcinogenic nitrosamines, especially at the gastric cardia. Wheat fiber has been shown to neutralize such mutagen formation. Our aim was to evaluate the association between dietary fiber and cancers of the esophageal and gastric cardia.

METHODS

We examined data from a large-scale population-based case-control study of risk factors for adenocarcinoma of the gastric cardia and esophagus and squamous cell carcinoma of the esophagus.

RESULTS

We found a strong dose-dependent inverse association between total dietary fiber intake and risk of gastric cardia adenocarcinoma, which was driven mainly by intake of cereal fiber. The odds ratio among individuals in the highest quartile of cereal fiber intake compared with the lowest was 0.3 (95% confidence interval, 0.2-0.5; P trend < 0.0001). High intake of cereal fiber was also associated with a moderately decreased risk of esophageal adenocarcinoma, but no linear dose-risk trend was observed. There was no association between dietary fiber and esophageal squamous cell carcinoma.

CONCLUSIONS

High intake of cereal fiber may significantly lower the risk of gastric cardia cancer.

Inverse association between intake of cereal fiber and risk of gastric cardia cancer

BACKGROUND & AIMS

Recent data show that salivary nitrites form carcinogenic nitrosamines, especially at the gastric cardia. Wheat fiber has been shown to neutralize such mutagen formation. Our aim was to evaluate the association between dietary fiber and cancers of the esophageal and gastric cardia.

METHODS

We examined data from a large-scale population-based case-control study of risk factors for adenocarcinoma of the gastric cardia and esophagus and squamous cell carcinoma of the esophagus.

RESULTS

We found a strong dose-dependent inverse association between total dietary fiber intake and risk of gastric cardia adenocarcinoma, which was driven mainly by intake of cereal fiber. The odds ratio among individuals in the highest quartile of cereal fiber intake compared with the lowest was 0.3 (95% confidence interval, 0.2-0.5; P trend < 0.0001). High intake of cereal fiber was also associated with a moderately decreased risk of esophageal adenocarcinoma, but no linear dose-risk trend was observed. There was no association between dietary fiber and esophageal squamous cell carcinoma.

CONCLUSIONS

High intake of cereal fiber may significantly lower the risk of gastric cardia cancer.