Levels of Oxytocin in the Jugular Vein Blood of Goats During Parturition

Abstract

SUMMARY Oxytocin has been assayed in the jugular vein blood of goats during parturition; for comparison a few measurements were also made during pregnancy. The hormone was extracted from blood plasma by gel filtration, followed by lyophilization and then assayed in the lactating guinea-pig by the increase in intramammary pressure after intra-arterial injection. No oxytocin could be detected in the blood during pregnancy and it was found in only one of eight goats studied during the first stage of labour. The hormone was present in appreciable quantities in blood taken during the second stage of labour, and in general, the concentration rose to a maximum when the head presented. In cases of twin births oxytocin was usually present in the blood during the birth of the second kid but at a concentration lower than during delivery of the first. After expulsion of the kid the blood oxytocin titre diminished rapidly, suggesting that secretion of oxytocin ceased as soon as the kid was born. In three experiments the total release of oxytocin during a considerable portion (2·7–11·0 min.) of the second stage labour was estimated as 223–726 m-u. The results are consistent with the view that oxytocin is not essential for the induction of labour. Rather the hormone is released in response to stimuli arising from distension of the vagina and vulva, and by virtue of its contractile effect on the uterus assists parturition. The half-life of intravenously injected oxytocin in the lactating goat was found to be 1 min. 22 sec. After storage of lyophilized blood extracts at −15° for 5 months milk-ejection activity had declined by only 27%.

Milk-Ejection Activity (Oxytocin) in the External Jugular Vein Blood of the Cow, Goat and Sow, in Relation to the Stimulus of Milking or Suckling

“…In later experiments the indwelling cannula technique was used. There are no internal jugular veins in the goat (see Folley & Knaggs, 19656) and it seems likely that most of the blood draining the pituitary region travels down the external jugular veins, although it is conceivable that some may pass by way of the longitudinal vertebral venous sinuses.…”

The Relationship Between Lactation and the Release of Prolactin and Growth Hormone in the Goat

“…Using radioimmunoassays for ovine/caprine prolactin (Hart, 1972a(Hart, , 1973b (Folley & Knaggs, 1965) fig. 1), finally reaching a concentration which was 2-6 to 4-5 times higher than the lowest concentration of prolactin found earlier in gestation (Hart, 1972a Hart, 1972a.…”

“…The measurement of prolactin levels in blood collected throughout par¬ turition presented an ideal opportunity to test, in a physiological situation, the validity of the hypothesis that in certain circumstances oxytocin may stimulate the release of prolactin from the anterior pituitary (Benson & Folley, 1956 Despite extremely large increases in the concentration of oxytocin (2 to 745 pg/ml), the increases in the circulating level of prolactin were relatively small in comparison with the magnitude of the release that usually occurs at milking (Bryant, Greenwood & Linzell, 1968;Johke, 1969;Hart, 1972b) when the quantity of oxytocin released is often less than that released during parturition (Folley & Knaggs, 1965;McNeilly, 1972 Hart, 1973b). The average levels determined in blood samples taken at 30 min intervals throughout a single 24 hr period were higher in four castrated males than those measured in four virgin females.…”

Identification of neurohypophysial hormones with their antisera

“…4) [5](P > 0.5) [7] [4](P < 0.01) [5](P < 0.01) 100 <25 100 <25 <25 [3] [3](P <0.02) [6] [3](P <0.05) [3](P <0.05) 100 13 ±13 100 26 ±13 <25 [4] [4](P < 0.01) [7] [3](P < 0.05) [5](P < 0.01) 100 8 ±8 100 30 ±13 <25 [6] [6](P <0.01) [4] [3](P <0.01) [4](P <0.01) [3][4][5]. The complete inactivation of the milk-ejection activity of 1000 iU of arginine vasopressin with 8-lysine-vasopressin antiserum indicates that the purified beef vasopressin contained very little or no oxytocin.…”

“…These substances are histamine, catecholamines, 5-hydroxytryptamine, acetylcholine, angiotensin, bradykinin, and other nonspecific peptides (3,4). Hence, to identify tentatively a neurohypophysial peptide by its pharmacologic actions, one must use a highly purified preparation or one with so much of the hormone present that other contaminating, extraneous, pharmacologically active substances can be diluted out of consideration.…”