Adaptive Responses to Neurohypophyseal Fractions in Vertebrates

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Abstract
The distr. of responses to posterior pituitary fractions among representative vertebrates was investigated. Frogs (Rana pipiens and R. catesbiana) show antidiuretic, "water-balance," chloruretic and vasodepressor responses to pitocin. Pitressin exerts a weak pressor effect. Bullfrog pituitaries injd. intraven. produce a weak vasodepressor response by the bullfrog consistent with content of oxytocic activity. Very small doses of pitressin produce a glomerular antidiuretic effect in the toad Bufo marinus. Pitocin exerts a weak vasodepressor effect but no pressor response could be demonstrated. In the alligator pitressin produces a marked glomerular antidiuretic effect but a very weak pressor response. Pitocin causes a vasodepressor response. On the basis of the phyletic distr. of responses it is concluded that the effects related to regulation of body water are important homeostatic mechanisms in amphibians, reptiles, birds and mammals. The effects on blood pressure in cold-blooded vertebrates are so slight that it appears highly improbable that they are of importance in the maintenance of normal vascular tone.