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To investigate the mechanism of ovulation in the hen, histological and physiological investigations on the contractility of the follicular wall were carried out. Smooth muscle bundles in the loose connective tissue coat from the stalk to the equator showed spontaneous rhythmic contractions with an alternation of contraction and pausing periods of about 4 min. The administration of prostaglandins F2 alpha (PGF2 alpha), E2 (PGE2), ovarian oviposition inducing factor (OOIF), oxytocin and acetylcholine increased the frequency and amplitude of the contractions. The theca layer showed spontaneous contractions at a frequency of about 30 per 10 min. PGF2 alpha, OOIF, acetylcholine, adrenaline and noradrenaline induced tonic contractions, whereas PGE2, oxytocin and histamine induced relaxation. It is suggested that the contraction of the follicular wall promotes the rupture of the stigma at ovulation and the neurotransmitters as well as prostaglandins and OOIF may be involved in this event.

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The ovarian ruptured follicles larger than 0.2 g. of wet weight were collected from laying hens and an ovarian oviposition-inducing factor (OOIF) was extracted from the follicles. The extract was chromatographed on a column of Sephadex G-75. Material from the active region for inducing premature oviposition was subjected to thioglycollate or trypsin treatment. It was found that oxytocic activity of this material was completely destroyed by thioglycollate buy not by trypsin, when tested on the contractility of the isolated hen's uterus. The OOIF was found to be diffusible through a cellophane bag. It is suggested that the OOIF may be a relatively small molecule have a disulfied bridge and it seems to be a hormone or hormone-like substance resembling the posterior pituitary hormones in the chemical nature.