We focus on the first handler markets where oligopsony structures are most pervasive and public policy issues concerning buyer market power are most acute, given ongoing concerns about low farm prices and incomes.

Public information regarding economic concentration, both aggregate and market, has declined since 1982. The Census no longer publishes a concentration report for its Economic Census, which is done every five years for manufacturing industries. Using purchased data from Census Special Tabulations, this paper documents advanced aggregate and market concentration in U.S. food and tobacco processing markets. The data are much more useful for studying output markets and fail to provide much guidance regarding oligopsony issues, which are perceived to be widespread in food processing. In output markets, evidence suggests that a market's use of media advertising contributed to advanced market concentration prior to 1977, but subsequently concentration has been rising in all industries. Producer good industries have posted the largest increases in concentration as they narrowed the difference in average concentration between themselves and the group of advertising‐intensive industries. [EconLit codes: L110, L660] © 2001 John Wiley & Sons, Inc.

Urea has a critical role in urinary concentration. Mice lacking the inner medullary collecting duct (IMCD) urea transporter A1 (UT-A1) and urea transporter A3 (UT-A3) have very low levels of urea permeability and are unable to concentrate urine. To investigate the role of UT-A1 in the concentration of urine, we transgenically expressed UT-A1 in knockout mice lacking UT-A1 and UT-A3 using a construct with a UT-A1 gene that cannot be spliced to produce UT-A3. This construct was inserted behind the original UT-A promoter to yield a mouse expressing only UT-A1 (UT-A1 +/+ /UT-A3 2/2 ). Western blot analysis demonstrated UT-A1 in the inner medulla of UT-A1+/+ /UT-A3 2/2 and wild-type mice, but not in UT-A1/UT-A3 knockout mice, and an absence of UT-A3 in UT-A1 +/+ /UT-A3 2 /2 and UT-A1/UT-A3 knockout mice.Immunohistochemistry in UT-A1 +/+ /UT-A3 2/2 mice also showed negative UT-A3 staining in kidney and other tissues and positive UT-A1 staining only in the IMCD. Urea permeability in isolated perfused IMCDs showed basal permeability in the UT-A1 +/+ /UT-A3 2/2 mice was similar to levels in wild-type mice, but vasopressin stimulation of urea permeability in wild-type mice was significantly greater (100% increase) than in UT-A1 +/+ /UT-A3 2/2 mice (8% increase). Notably, basal urine osmolalities in both wild-type and UT-A1+/+ /UT-A3 2/2 mice increased upon overnight water restriction. We conclude that transgenic expression of UT-A1 restores basal urea permeability to the level in wild-type mice but does not restore vasopressin-stimulated levels of urea permeability. This information suggests that transgenic expression of UT-A1 alone in mice lacking UT-A1 and UT-A3 is sufficient to restore urine-concentrating ability.

No abstract

This study develops an intertemporally linked market model to explore the relationships between price-cost margins, market concentration, and advertising outlay. The study used data from 48 four-digit SIC (standardized industrial classification) codes for the Food and Tobacco Processing Industries during the 1970s, 1980s, and 1990s. The authors' findings provide evidence that both high and low levels of performance provide signals to industries to consolidate, but for obvious and different reasons. Further, increased consolidation leads to increased entry barriers (advertising) and higher profits to the industry. Our findings are supportive of both Chicago and Traditionalist Schools of thought about antitrust enforcement: Neither emerges in a dominant position. Endogeneity issues and findings within the intertemporal structure cast considerable doubt about overly simplistic structure-performance paradigms of firm behavior. [JEL Code: L11, L40, L66]. r