Structural Requirements for the Action of Neurohypophyseal Hormones upon the Isolated Amphibian Urinary Bladder

Abstract

The response of the isolated amphibian urinary bladder to thirtyfour structural analogs of arginine vasotocin was determined in an effort to define the physiological significance of specific structural groups on the hormone molecule. All but one of the analogs tested possessed full intrinsic activity in this system but varied greatly in their affinity for the receptor site. An analysis of the effect of changes in hydrogen ion concentration upon the response of the bladder to oxytocin was performed in order to determine the number and nature of the ionizable groups involved in hormone receptor interaction. Two ionizable groups with apparent pK's of 7.1 and 7.75 were found to be important in determining the magnitude of the hormonal response. On the basis of the results it was postulated that hormone-receptor interaction can be considered a two-step process: (a) The binding or attachment of hormone to receptor site through ionic, hydrogen, and hydrophobic bonds and (b) a disulfide interchange reaction between hormonal disulfide and receptor sulfhydryl. The latter step is considered to be the reaction which initiates the chain of events leading to the observed change in permeability.Although the distinction between the affinity and intrinsic activity of a drug for its receptor site has received theoretical consideration and application in pharmacology (1), little usefulness has been found for these concepts in the study of hormone-receptor interactions. However, because of the recent developments in the isolation, characterization, and synthesis of polypeptide hormones, they m a y become of practical value in the study of hormonereceptor interactions. The classic work of du Vigneaud and his colleagues on the neurohypophyseal hormone (2-7) has evoked new and exciting possibilities in the study of the correlation between structure and activity of II7I

Role of prostaglandin E2 in mediating the effects of pH on the hydroosmotic response to vasopressin in the toad urinary bladder.

“…An increase in PGE2 synthesis after vasopressin was not seen at any pH. These studies establish that increased basal PGE2 synthesis plays a critical role in the pH dependence of the hydroosmotic response to vaso- INTRODUCTION The inhibitory effect of acidosis on the hydroosmotic response to vasopressin has been well documented by both in vitro and in vivo studies (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)). An effect of media pH on the hydroosmotic response to vasopressin was observed in the first study of water transport in the toad urinary bladder (1).…”

“…In the toad bladder this inhibition has been observed in multiple buffer systems, i.e., when serosal pH is reduced by bubbling with CO2, by addition of strong acid (HCI), or by removal of bicarbonate (1)(2)(3)(4)(5)(6)(7)(8). In addition, acute metabolic acidosis in vivo has been shown to inhibit the response to vasopressin in both the amphibian bladder (9) and mammalian kidney (7).…”

“…An effect of media pH on the hydroosmotic response to vasopressin was observed in the first study of water transport in the toad urinary bladder (1). Subsequent work in this tissue established that acidification of the serosal media (pH 8.4 to 6.9) impairs the hydroosmotic response to vasopressin and theophylline but not to cyclic AMP (2)(3)(4)(5)(6). In the rat, acute metabolic acidosis in vivo inhibits vasopressin-stimulated free-water reabsorption, and in renal medullary slices in vitro, both vasopressinstimulated adenylate cyclase and cyclic AMP accumulation are inhibited by acidification of the media (7).…”

Natriferic and hydrosmotic effects of neurohypophysial peptides and their analogues in augmenting fluid uptake by Bufo melanostictus

“…Values derived from Fig. 1 Dose of peptide required to produce 50 % augmentation of fluid uptake (n-mole/kg) that 8-arginine vasopressin was much less potent-1/50 on frog skin (Jard et al 1960), 1/100 on toad bladder (Rasmussen et at. 1963) and 1/200 on frog bladder (Jard et al 1960)-but in all of these investigations sodium chloride was present and the difference could be ascribed to the greater natriferic action of 8-arginine vasotocin.…”

“…Dose-response curves for each peptide showed that in the case of 8-arginine vasopressin, 8-lysine vasopressin and 8-ornithine vasopressin the augmentation of rate of fluid uptake did not differ in the absence or in the presence of NaCl in the bathing solution; whereas in the case of 8-arginine vasotocin, oxytocin, and 8-ornithine oxytocin the augmentation was greater in the presence of sodium chloride. INTRODUCTION Vasotocin, which is the principal neurohypophysial hormone of the amphibia (Pickering & Heller, 1959;Sawyer, Munsick & van Dyke, 1959) has been shown to promote fluid reabsorption from the bladder (Rasmussen, Schwartz, Young & Marc-Aurele, 1963;Sawyer, 1960) and fluid uptake across the skin (Elliott, 1966;Jard, Maetz & Morel, 1960) of Bufo and Rana. In respect of its action on the skin it has been proposed by Bourguet & Maetz (1961) that it exerts both a hydrosmotic effect, increasing permeability to water, and a natriferic effect, promoting sodium transport with which water movement would also be associated.…”