In isolated trout heads, perfused at constant pressure, epinephrine (10(-6) M) was found to double water and urea efflux but increased Ringer perfusion rate by only 33%. Drastic changes in perfusion rate (by clamping) produced smaller changes of both efflux rates. Epinephrine-stimulated increase in water and urea efflux, and perfusion rate, was blocked by propranolol (beta-blocker) but not by phentolamine (alpha-blocker). Both blockers together canceled out all epinephrine effects. Epinephrine increased water influx across isolated unperfused gill arches, the effect again being blocked by propranolol but not by phentolamine. Both blockers together canceled any epinephrine effect. We conclude that epinephrine alters branchial vascular flow and functional surface area via alpha- and beta-adrenergic receptors, but also increases branchial permeability to water and probably urea, via beta-adrenergic receptors. To test the validity of the perfused head technique, water and urea efflux rates were compared with in vivo values.
Presented here are the results of a preliminary investigation into ionic and osmotic regulation by the kidneys and rectal gland of the striped dogfish, Poroderma africanum. Fish with ligated rectal glands showed an increase in blood concentration of sodium and chloride within a short time period, reaching a maximum after four days. The blood concentration of the two ions then decreased over the following ten days. Control animals showed relatively unchanged blood-sodium and chloride levels, over the entire 14-day period. After salt loading, both control animals and those with ligated rectal glands showed initial rise in blood sodium and chloride levels, but these returned towards initial values within seven hours of injection. Comparison of the two groups indicates that the rectal gland may control blood-chloride levels more so than -sodium, although its action as a salt regulator does not seem very pronounced in either case. Urine and rectal gland fluid, were collected as a compound fluid, from normal fish, and the estimated cloacal salt loss is discussed. Urine from normal fish was also collected separately and was analysed for its contribution to salt loss. Results are discussed and compared with previous relevant findings.
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