Acetic acid extracts of hypothalamic tissue of pigs, cattle, and sheep were subjected to gel filtration on Sephadex and other purification procedures. Several vasodepressor fractions were obtained. The activity of one of these fractions was clearly due to oxytocin. However, another fraction, which is present in significant amounts in hypothalamic extracts of domestic animals, lowered the blood pressure of chickens and rats and relaxed isolated rat duodenum, but had no effect on isolated rat uterus. The vasodepressor property of this material was not abolished by treatment with thioglycolate, trypsin, pepsin, papain, chymotrypsin, carboxypeptidase, or leucine aminopeptidase. Data presented show that this fraction is not oxytocin, vasopressin, substance P, angiotensin, bradykinin, acetylcholine, 5-hydroxytryptamine, histamine, γ-aminobutyric acid, epinephrine, or norepinephrine. Many of its pharmacologic and chemical characteristics suggest that it is. adenosine monophosphate. We suggest that in studies of hypothalamic extracts, it is unwise to equate vasodepressor activity with the presence of oxytocin.
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