Characterization of muscarinic M4 binding sites in rabbit lung, chicken heart, and NG108-15 cells

We have carried out an extensive pharmacological characterization of muscarinic binding sites in rabbit lung and chicken heart in parallel with M1, M2, and M3 sites, [3H]Pirenzepine, a selective antagonist at M1 receptors, bound saturably and reversibly to membranes from chicken heart and rabbit lung. These binding sites were not M1 receptors, however, because the cardioselective antagonist himbacine had 10-fold higher affinity at these sites than at [3H]pirenzepine sites in rat and rabbit cortex (true M1 sites). We measured the inhibitory potency of 28 antagonists at [3H]N-methylscopolamine-labeled sites in chicken heart, rabbit lung, rat heart (M2 sites), and rat submandibular gland (M3 sites) and at M1 sites in rat cortex. The sites in rabbit lung were different from M1, M2, and M3 sites, because they had moderate to high affinity for M1-selective compounds (pirenzepine and telenzepine), M2-selective compounds (himbacine and methoctramine), and M3-selective compounds (hexahydrosiladifenidol and 4-diphenylacetoxy-N-methylpiperidine methiodide). The sites in chicken heart resembled most those in rabbit lung, with similar high affinity for secoverine, but they were not the same because tropicamide, diphenylacetoxybutynyl dimethylamine, and [3H]-N-methylscopolamine were more potent in rabbit lung. In a further series of experiments, we compared the affinity of six of the most discriminating antagonists in membranes from rabbit lung and NG108-15 cells, a neuroblastoma-glioma cell line reported to express the muscarinic m4 receptor gene. The antagonists had very similar affinities in the two tissues, the largest discrepancy being that pirenzepine was twice as potent in rabbit lung as in NG108-15 cells. Northern blots using probes designed to discriminate between five species of muscarinic receptor RNA detected only m4 mRNA in rabbit lung. We conclude that rabbit lung contains a muscarinic M4 binding site with a quite distinctive pharmacology and that chicken heart contains a receptor with similarities to the M4 sites. This is the first report to characterize native M4 binding sites in a nonneuronal mammalian tissue.     

Seasonal differences in serum vitamin D binding protein in exclusively breast-fed infants: negative relationship to sunshine exposure and 25-hydroxyvitamin D

Vitamin D binding protein (DBP) is the major carrier for vitamin D and its metabolites in serum. DBP increases in pregnancy and decreases in cirrhosis; no seasonal variation has been reported in adults. We observed significant seasonal differences in 41 exclusively breast-fed infants who were less than 6 months of age. Winter DBP concentrations exceeded summer DBP concentrations: 398 +/- 22 versus 297 +/- 20 micrograms/ml (mean +/- SEM). The mean concentration for spring and fall was 329 +/- 25 micrograms/ml. Maternal DBP concentrations did not differ by season. A sunshine exposure score, previously verified, was used to document time and body surface exposed to the sun. DBP was inversely related to sun exposure (r = -0.46, p = 0.005). Infant DBP was significantly and negatively correlated with 25-hydroxyvitamin D concentrations (r = - 0.38, p = 0.02). We speculate that serum DBP fluctuations are a response to varying vitamin D needs: increased serum DBP occurs in low vitamin D status to maximize uptake of vitamin D from skin.     

A case-control study of risk factors for hepatoblastoma. A report from the Childrens Cancer Study Group

Parents of 75 children with hepatoblastoma, registered with the Childrens Cancer Study Group, and 75 age-matched controls, who had been identified through random digit dialing were interviewed. No evidence was found to support the primary study hypotheses relating to hepatitis infection, maternal estrogen exposure, alcohol consumption, smoking, or potential sources of nitrosamines. Case mothers were more likely to report occupational exposure to metals (odds ratio [OR] = 8.0, P = 0.01), petroleum products (OR = 3.7, P = 0.03), and paints or pigments (OR = 3.7, P = 0.05). Metal exposures were commonly to welding or soldering fumes, and most occurred daily, before and during the index pregnancy. Petroleum product exposures were predominantly to lubricating oils or protective greases. The only significant paternal exposure was to metals (OR = 3.0, P = 0.01) and the risk with exposure to petroleum products was marginally significant (OR = 1.9, P = 0.06). These findings provide further evidence that occupational exposures may increase the risk of cancer in offspring.     

Paget's disease of the breast: What the radiologist may expect to find

Paget's disease of the nipple is characterized by the presence of Paget's cells in the epidermis of the nipple or areola. Two case reports of Paget's disease are described and used to highlight unusual features of the disease. The literature on the radiographic and pathologic findings of this disease is reviewed.