Cigarette smoking and bladder cancer in Washington County, Maryland: ammunition for health educators

To investigate the frequency of cigarette smoking in patients who have been diagnosed with bladder cancer, data were obtained for 1507 subjects listed in the 1975 private census of Washington County, Maryland. Case subjects were defined as persons at least 18 years of age diagnosed with bladder cancer (ICD code = 188.0 to 188.9) between 1975 and 1992 for whom smoking information was available. Control subjects were defined as a random sample of persons frequency matched by age and sex to the cases. Controls were free of bladder cancer and had smoking information available. The odds ratio for current smokers for the association between smoking and bladder cancer adjusted for age and sex was statistically significant (OR = 1.68, 95% confidence intervals, 1.22 to 2.32). The chi-square trend test of the dose-response results was significant (chi-square = 11.69, df = 1, P < .01).

Thermoregulatory and maternal nestbuilding in Syrian hamsters: interaction of ovarian steroids and energy demand

To investigate the relationship between energy demand, ovarian hormones and behavioral thermoregulation, we measured nestbuilding of female Syrian hamsters (Mesocricetus auratus) under conditions where energy demand and circulating ovarian hormone levels varied. Hamsters increased nestbuilding under conditions of chronically elevated estradiol and progesterone levels (late gestation; ovariectomized animals treated with estradiol +/- progesterone) and increased energy demand (late gestation or cold exposure). When hormone treatments were withdrawn, hamsters gained weight and reduced nestbuilding activity. Nestbuilding was not affected by lactation (characterized by low ovarian steroid levels and high energy demand) or by estrous cycle phase (characterized by relatively transient changes in ovarian steroid levels and subtle changes in energy demand). Thus, nestbuilding in Syrian hamsters was responsive to increased energy demand from cold exposure, late gestation, and to ovarian hormones. However, during lactation and estrous cycles, nestbuilding did not always change predictably according to known changes in energy expenditure and steroid hormone levels. Thus, levels of nestbuilding are influenced by factors in addition to ovarian hormones and energy expenditure under some circumstances.

Localization and characteristics of atrial natriuretic peptide receptors in prenatal and postnatal rat brain

We studied the expression of atrial natriuretic peptide (ANP) receptor subtypes during development in the rat forebrain, using quantitative autoradiography. Highest ANP binding was observed in the cortical neuroepithelium at embryonic day 17. Lower ANP binding was found in cingulate and frontal cortices at postnatal day 10, but none was detectable at 8 weeks of age. In the neuroepithelium of the embryonic rat, binding was displaced with a potency of rat ANP-(1-28) (rANP) > porcine type-C natriuretic peptide (pCNP-22) = rat ANP fragment C-ANP-(4-23) (rC-ANP-(4-23)) = rat brain natriuretic peptide (rBNP-32), different from that of any of the well-characterized (ANPA, ANPB, and ANPC) natriuretic peptide receptors. The present results support the hypothesis of a role for ANP during brain maturation and indicate that the ANP receptors highly expressed in the embryonic neuroepithelium may belong to a new ANP receptor subtype not yet characterized.

Energy balance in pregnant hamsters: a role for voluntary exercise?

During pregnancy or after experimental manipulations of ovarian hormone levels, Syrian hamsters exhibit changes in energy balance and body fat content without modifying their food intake. The present experiments determined whether fluctuations in voluntary exercise play a role in these changes in energy balance, as they appear to do in other species. As expected, pregnant hamsters maintained a constant level of food intake and lost approximately 40% of their body fat. These animals did not show the abrupt decrease in activity after mating that is seen in rats. Instead, they maintained their high, premating level of running wheel activity until the last 3 days of pregnancy. Similarly, ovariectomy and replacement therapy with estradiol or estradiol+progesterone caused substantial changes in energy balance in the absence of significant changes in food intake or running wheel activity. These findings indicate that, unlike rats, Syrian hamsters do not exhibit substantial changes in voluntary exercise during pregnancy or in response to manipulations of ovarian steroid levels. Therefore, neither changes in food intake nor in voluntary exercise play any important role in the pregnancy- or steroid-induced changes in energy balance in Syrian hamsters.

Effects of pregnancy and ovarian steroids on fatty acid synthesis and uptake in Syrian hamsters

The effects of pregnancy and ovarian steroids on the in vivo distribution of newly synthesized fatty acids (incorporation of tritium from 3H2O into fatty acid) in Syrian hamsters (Mesocricetus auratus) were examined. During late, but not early, gestation hamsters had reduced levels of newly synthesized fatty acids in heart, liver, uterus, and white adipose tissues (parametrial and inguinal fat pads). Treatment of ovariectomized hamsters with estradiol + progesterone significantly decreased fatty acid synthesis-uptake in heart, liver, and inguinal white adipose tissue. Treatment with either estradiol or progesterone alone was without significant effect in any tissue. Pretreatment of hamsters with Triton WR-1339 (tyloxapol), an inhibitor of lipoprotein lipase activity and tissue triglyceride uptake, abolished the effects of estradiol + progesterone in white adipose tissue and heart but not in liver. Thus hamsters lose body fat during pregnancy in part because of decreased de novo lipogenesis. The effect of pregnancy on lipogenesis is mimicked by treatment with estradiol + progesterone but not by either hormone alone. Furthermore, it appears that the liver is the principal site of estradiol + progesterone action on lipogenesis in Syrian hamsters.

Response to chronic insulin administration: effect of area postrema ablation

The effects of daily administration of protamine zinc insulin (PZI) on plasma insulin and glucose levels and on food intake and body weight of rats with lesions of the area postrema and adjacent caudal-medial portions of the nucleus of the solitary tract (APX rats) were examined. Prior to insulin treatment, APX rats weighted less and had lower plasma immunoreactive insulin (IRI) levels than nonlesioned controls but did not differ from controls in plasma glucose levels. Five daily injections of 5 U/kg PZI raised plasma IRI and lowered plasma glucose levels similarly for both lesioned and nonlesioned rats. When injected with increasing doses of PZI over a 30-day period, both lesioned and nonlesioned rats showed increases of food intake and rate of weight gain in response to 8 U/kg PZI. These data indicate that APX does not affect either physiological or behavioral responses to chronic peripheral insulin administration.

Progesterone can either increase or decrease weight gain and adiposity in ovariectomized Syrian hamsters

We examined the effects of estradiol and progesterone on weight gain, food intake, and carcass composition in Syrian hamsters (Mesocricetus auratus). In ovariectomized (OVX) hamsters injections of 5 micrograms/day estradiol benzoate (EB) alone decreased weight gain and adiposity, whereas treatment with progesterone alone (1 or 5 mg/day) resulted in increased weight gain and adiposity. However, concurrent treatment with progesterone and EB reduced body fat content to levels significantly below those of hamsters treated with EB alone. In a second experiment, 17 beta-estradiol and progesterone were administered via subcutaneous Silastic capsules in doses which produce physiological levels of steroids. Implants of estradiol significantly decreased body weight gain and fat content. As in the first experiment, these effects of estradiol were exaggerated by concurrent progesterone administration. Implants of progesterone alone did not affect body weight or fatness in OVX hamsters. These data indicate that estradiol and progesterone interact to decrease body lipid stores in hamsters, whereas in rats progesterone reverses the adiposity-reducing actions of estradiol. This species difference in responses to progesterone could help to explain why rats increase, whereas hamsters decrease, their body lipid stores during pregnancy, when circulating progesterone levels are elevated.

Body weight of rats following area postrema ablation: effect of early force-feeding

This study examined the effect of intragastric force-feeding of a milk diet on body weights of rats with lesions of the area postrema/caudal medial nucleus of the solitary tract (AP/cmNTS). Force-feeding was conducted over the first 10 days after the ablation. Body weight was monitored both during and after force-feeding. Food intake was measured during all ad libitum feeding periods. During force-feeding, rats with AP/cmNTS lesions gained weight at the same rate as force-fed sham-lesioned rats or sham-lesioned rats that voluntarily ingested an equal amount of the milk. When returned to ad libitum feeding, lesioned rats that had been force-fed were not hypophagic and did not lose weight. Body weights of such rats remained above those of lesioned rats that were not force-fed and similar to those of nonlesioned rats throughout this study. Despite their normal weights, preliminary analysis indicated that body fat of the force-fed lesioned rats may have been reduced. These findings suggest that the effects of AP/cmNTS ablation are multiple and that reduction of body weight need not be the primary effect of such lesions.