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Some aspects of the physiological adaptation of lower vertebrates to marine environments McBean, Ralph Lachlan

Abstract

I STUDIES ON THE GLOMERULAR FILTRATION RATE OF RAINBOW TROUT (SALMO GAIRDNERI) Upon adaptation of rainbow trout to 80% sea water, the glomerular filtration rate, as measured by the method of inulin clearance, was reduced from 156 ± 8.9 to 10.0 ± 2.6 ml./kg. body weight/day. Return to fresh water after one month in sea water was accompanied by a rapid re-establishment of the high glomerular filtration rate. This lability of the glomerular filtration rate in the trout is probably an important factor contributing to the reduction of urine flow associated with the adaptation of the euryhaline form to sea water. The effects of adrenocortical and mammalian neurohypophysial hormones on the glomerular filtration rate were studied. Vasopressin and oxytocin, when administered either separately or together, significantly increased the filtration rate, aldosterone had no effect, while corticosterone caused a significant reduction. II STUDIES ON ELECTROLYTE EXCRETION IN THE GREEN TURTLE (CHELONIA MYDAS) The extracellular concentrations of sodium and potassium in the marine turtle, Chelonia mydas mydas, were unchanged after adaptation to a fresh water environment. At the same time the urinary concentrations of these ions were significantly reduced. In addition, the "salt glands" of fresh water adapted juvenile turtles showed a 38% regression in absolute weight. Feeding and saline-loading of sea water adapted turtles elicited rates of sodium and potassium excretion greatly in excess of those possible via the kidney. Failure to detect significant changes in these rates following occlusion of the cloaca further indicated that the major site of electrolyte excretion after feeding or saline-loading was the salt gland. Suppression of adrenocorticosteriod synthesis by treatment with amphenone "B" immediately after feeding or saline-loading reduced the excretion of sodium and potassium to unfed or non-loaded levels. The normal pattern of sodium excretion but not of potassium excretion could be restored in the amphenone-treated animals by the simultaneous administration of corti-costerone. The significance of the ingestion of sea water is discussed in relation to the high electrolyte intake associated with the diet of these turtles.

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