To elucidate prey preferences, we quantified stomach contents of 1,231 salmonines collected from inshore (21 m or shallower) southeastern Lake Michigan during 1973–1982. Predators ate 12 species of fish. Alewife Alosa pseudoharengus made up 48–79% by weight of the diet of brown trout Salmo trutta, chinook salmon Oncorhynchus tshawytscha, coho salmon Oncorhynchus kisutch, lake trout Salvelinus namaycush, and rainbow trout Salmo gairdneri. Alewives eaten ranged from 23 to 245 mm total length; 46% were 150–200 mm. Rainbow smelt Osmerus mordax eaten were 21–245 mm long and made up 4–11% of the salmoninesˈ prey. There were significant direct linear relationships between lengths of alewives and rainbow smelt eaten and lengths of the five predators. Alewives are currently declining in Lake Michigan. If their population collapses, there should be a shift to alternative prey species. We have seen no such shift through 1982, although more recent data of other investigators show a decline in the importance of alewife in salmonine diets. Diets of the midwater‐feeding chinook and coho salmon were heavily dominated by the pelagic alewife, whereas brown and lake trout diets were more diverse. This suggests that trout should have better survival and growth than salmon, because trout would be able to utilize the more benthic yellow perch, Perca flavescens, rainbow smelt, and, to some degree, bloater Coregonus hoyi. The latter species are becoming more abundant with the decline in alewife. Under the current salmonine stocking regime, alewives will continue to supply a lower and variable portion of the salmonine diet, and predatory pressure on alewife should lead to increases in endemic prey speciesˈ populations.

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Atrial distension, rather than change in intra-atrial pressure, has been suggested as a principal mediator of release of atrial natriuretic factor (ANF). During cardiac tamponade, atrial pressures rise whereas transmural pressures and atrial stretch may not be affected. The roles of atrial pressure and atrial distension were investigated in six open-chest dogs subjected to cardiac tamponade and rapid volume expansion as disparate means of affecting intra-atrial pressures and atrial stretch. Hemodynamic measurements, immunoreactive ANF (ir-ANF), plasma renin activity, antidiuretic hormone, epinephrine, and norepinephrine were monitored before, during, and after three interventions:(1) tamponade, (2) rapid volume loading followed by tamponade, and (3) volume loading during tamponade. Volume expansion increased right atrial pressure and caused a significant rise in ir-ANF. Elevations of right atrial pressure caused by tamponade were comparable to those induced by volume infusion, but an increase in ir-ANF was not elicited during tamponade, and the ir-ANF response to volume loading was abolished when performed during tamponade. The relation between the change in ANF concentration and change in right atrial pressure were highly significant in the absence of tamponade, when atrial stretch was freely responsive to volume expansion (r = .73, p < .0001), but not when stretch was inhibited (r = -.16, p = NS). These observations underscore the importance of considering the modulating effects of atrial compliance, transmural pressure, and atrial stretch on the relation between atrial pressures and ANF release.Circulation 76, No. 4, 884-890, 1987. ABUNDANT EVIDENCE suggests a prominent role for atrial distension as a major stimulus for secretion of atrial natriuretic factor (ANF). Indeed, reports of natriuretic and diuretic responses to experimental and pathophysiologic atrial distension predate discovery of the hormone by decades. [1][2][3][4] Numerous recent studies have demonstrated a strong relationship between atrial pressure elevation and ANF secretion,5-l but because both stretch and pressure changes occurred in these investigations it has not been possible to distinguish between the individual effects of these two variables.

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