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SUMMARY
The rate of excretion of antidiuretic activity in the urine of anaesthetized, water-loaded cats and of rats with familial diabetes insipidus after injection of single doses of lysine vasopressin (LVP) and of the long-acting analogue Nα-glycyl-glycyl-glycyl-[8-lysine]-vasopressin (triglycylvasopressin) has been studied by assays in water-loaded rats.
The excreted antidiuretic material in all experiments resembled LVP and differed from triglycylvasopressin in the time course of the recorded response, the slope of the log dose—response relationship, and the index of persistence. The total antidiuretic activity excreted was a fraction of that of the injected LVP but equalled or exceeded the assayable activity of the dose of triglycylvasopressin injected.
It is concluded that the excreted antidiuretic activity is due to LVP and that the excreted hormone originates from the triglycylvasopressin by enzymic activation in vivo.
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SUMMARY
The contractile response of mammary-gland strips from lactating rats to oxytocin varied with the concentration of calcium ions in the organ bath; calcium could be partially substituted by strontium but not by magnesium. High concentrations of potassium did not substantially affect the response to oxytocin. In these and several other respects the mammary gland myoepithelium resembles uterine smooth muscle, notwithstanding the differences in morphology and embryonal origin.
The effects of 12 synthetic analogues of oxytocin modified in sequence positions 1, 2, and 3 of the peptide chain on the rat mammary-gland strip were examined. None of the analogues showed a higher potency than oxytocin. However, the mammary-gland strip was less sensitive to the structural changes represented in this series of analogues than the rat uterus in vitro. The action of some of the analogues on the mammary-gland strip differs from that of oxytocin in the time-course of the response.
