EFFECT OF MAGNESIUM ION ON THE RESPONSE OF THE RAT UTERUS TO NEUROHYPOPHYSIAL HORMONES AND ANALOGUES¹

Abstract

Absolute oxytocic potencies of highly purified neurohypophysial hormones and analogues were determined on isolated rat uteri suspended in van DykeHastings solution. Assays were performed in bath solutions with and without magnesium ions. In a concentration of 0.5 raM/1. magnesium ions were found to augment the response to the U.S.P. Standard, oxytocin, lysine and arginine vasopressins and all the analogues tested, but there was considerable variation between substances in the degree to which this potentiation occurred. Advantages inherent to the solution of van Dyke and Hastings are discussed, and reasons are presented for utilizing this solution without magnesium for assays of oxytocin and posterior pituitary extracts.

Molecular evolution of the neurohypophysial hormones: The active peptides of a primitive bony fish Polypterus bichir

“…The oxytocic activities without and with magnesium [8,13], the pressor activity on the rat [9], and the depressor activity on the chicken * Cystine undergoes partial destruction when the peptide is hydrolyzed after elution from paper; the determination was performed in a separate sample after oxidation into cysteic acid with performic acid. [8] ; OMg2+: oxytocic activity with magnesium [ 13 ]. D: depressor activity in the chicken [14] ; P: pressor activity in the rat [9].…”

The Clearance of Neurohypophysial Hormones From the Circulation of Non‐mammalian Vertebrates

“…The middle part of one uterine horn was suspended in a 3 ml. organ bath containing magnesium-free Munsick (1960) solution and connected to a frontal writing lever with a load of 2 to 3 g. The bath temperature was kept constant at 330 C and a slow stream of 95% oxygen plus 5% carbon dioxide was bubbled through the solution. Assays of standard design of four (2+2) blocks were performed.…”

The Action of 2‐o‐methyltyrosine‐oxytocin on the Rat and Rabbit Uterus: Effect of Some Experimental Conditions on Change From Agonism to Antagonism

“…of the appropriate medium and a current of 95% oxygen-5% carbon dioxide mixture, or of air, was passed through; the pH was checked at intervals. Holton's (1948) medium (NaCI,154;KCI,5.4;NaHCO3,6; glucose, 2.77 mM) and Munsick's (1960) medium (NaCl, 114; KC1, 6.2; NaHCO3, 30; NaH2PO4, 1; glucose, 2.77 mM) were used, CaCI2 and MgCl2 being added to the concentration stated for individual experiments from stock solutions standardized by chelatometric titration. Unless otherwise stated, the temperature of the organ bath was 300 C.…”