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S. J. FOLLEY and G. S. KNAGGS

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%.

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S. J. FOLLEY and G. S. KNAGGS

SUMMARY

Milk-ejection activity (oxytocin) was assayed in the external jugular vein blood of cows, goats and sows during milking or suckling. 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.

Serial blood samples were taken during machine milking of cows which had been accustomed to the milking routine and blood sampling procedure. The stimulus most consistently followed by a transient appearance of oxytocin in the jugular vein blood was the application of the teat cups. In some cases, there was a second release of oxytocin, later in the milking process, unrelated to any apparent stimulus. There was no evidence in these experiments of any conditioning of oxytocin release to visual, auditory or olfactory stimuli associated with the milking routine.

Serial blood samples were taken during hand-milking of goats which had been accustomed to the milking routine and blood sampling procedure. Oxytocin was detected in jugular vein blood in only a minority of experimental milkings. Irrespective of whether oxytocin was found in the jugular blood the milk yield at the experimental milking did not differ appreciably from the value to be expected from comparable milkings for the preceding week.

Serial blood samples were obtained from sows during suckling, the animals having been accustomed to the presence of the experimenter and the blood sampling procedure. In most of the experimental sucklings oxytocin was found in the blood. The occurrence of the hormone was transient and it was usually released just before the milk-ejection phase. In most of the cases in which no hormone was detected in the blood the piglets obtained no milk as judged by their behaviour.

The results suggest that in the cow and sow the milk-ejection reflex is a neurohormonal reflex involving the release of oxytocin. On the other hand, in the goat, provided the animals are carefully hand-milked, normal milk yields can be obtained without the release of oxytocin.

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G. VAN WAGENEN and S. J. FOLLEY

It is now well known that many androgenic substances possess certain gynaecogenic properties and it is therefore not surprising that administration of androgens has been found to promote mammary development in the rat [Selye, McEuen, and Collip, 1936; Nelson and Gallagher, 1936; Astwood, Geschickter, and Rausch, 1937; Reece and Mixner, 1939], mouse [van Heuverswyn, Folley, and Gardner, 1939], and guinea-pig [Bottomley and Folley, 1938a]. These observations assume added significance in view of recent reports on the clinical use of testosterone propionate for the treatment of certain mastopathic conditions in women [see Turpault, 1937; Desmarest and Capitain, 1937; Loeser, 1938]. The rationale of such treatment must presumably lie in an attempt to reduce the oestrogenic stimulation of the breast by suppression of the gonadotrophic potency of the pituitary. In view of the fact that the agent used for this purpose is known to exert direct growth, and in some cases

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S. J. FOLLEY and F. G. YOUNG

Earlier experiments have shown that when repeated injections of a prolactin preparation are given to cows in declining lactation, a substantial stimulation of milk production occurs, though later this stimulus declines and finally vanishes, despite continued treatment [Folley & Young, 1939]. Further experiments have now been carried out to determine if the initial response would disappear with continued treatment with other pituitary preparations, and if the development of such resistance to the action of the extract was associated with the appearance, in the blood of the treated cows, of anti-prolactin [Young, 1938 c; Bischoff & Lyons, 1939] activity.

Folley & Young [1938] found that the stimulating influence on milk production of cows in declining lactation of a single injection of various anterior pituitary fractions was more closely correlated with their glycotropic (anti-insulin) activities than with their prolactin1 content. It therefore seemed desirable to investigate the influence on milk production

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A. T. COWIE and S. J. FOLLEY

This and a previous investigation of the kinetics of tablet absorption [Folley, 1944] arose out of the use of the implantation technique of Deanesly & Parkes [1937] for the artificial induction of lactation in cows and heifers by prolonged oestrogen treatment [Folley & Malpress, 1944; Hammond & Day, 1944]. The requisite uptake of synthetic oestrogen (diethylstilboestrol or meso-hexoestrol) could be achieved by implanting a few large (1000 mg.) tablets or a considerable number of small (50, 25 or 15 mg.) tablets into the same site or 'pocket', but unabsorbed residues remained to be removed at the end of the treatment period.

It was pointed out by Folley, Stewart & Young [1944] that the whole procedure would be simplified if conditions could be found under which tablets yielding a suitable daily dose of oestrogen would be completely absorbed in the required time, thus obviating the necessity for a second minor

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S. J. FOLLEY and A. L. GREENBAUM

It has been known for many years that milk secretion markedly decreases after adrenalectomy [see Cowie & Folley, 1947a]. Recent work indicates that the decrease in milk yield in the rat is due partly to metabolic effects of anorexia resulting from the operation, and partly to more direct effects of the loss of the adrenal hormones [Cowie & Folley, 1947b]. Folley & Cowie [1944] and Cowie & Folley [1947a] were able partially to restore lactation after adrenalectomy in their rats by administration of deoxycorticosterone acetate (doca). The mammary glands of such treated animals were noticeably heavier even than those of normal sham-operated controls which of course were lactating somewhat better. Since doca will cause growth of the mammary duct and alveolar systems [Van Heuverswyn, Folley & Gardner, 1939; Speert, 1940; Nelson, Gaunt & Schweizer, 1943; Mixner & Turner, 1942], it seemed possible that the increased weight of

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A. T. COWIE and S. J. FOLLEY

In previous studies of the effects of adrenalectomy on lactation in the rat [Folley & Cowie, 1944; Cowie & Folley, 1947a, b] we have shown, in agreement with others [Gaunt, 1941; Gaunt, Eversole & Kendall, 1942], that the operation causes a serious secretory decline but not the complete abolition of lactation. As is well known [see Ingle, 1944; Young, 1945], adrenalectomized animals, at any rate in the absence of salt therapy, may show a reduction in appetite, and since a diminution in food intake would adversely affect lactation, it is pertinent to inquire how far the lactational decline following adrenalectomy is due to anorexia, and how far to the disruption of some more direct functional relationship between the adrenals and mammary glands. We have attempted to answer this question by means of the paired-feeding technique. The experiments described in this paper give a partial answer to this question, but

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S. J. FOLLEY and F. H. MALPRESS

The important role played by oestrogens in mammary development has been established by numerous experiments on small animals [for review see Folley, 1940]. Similar results for the ruminant were reported by de Fremery [1936, 1938] who caused mammary growth in virgin goats by inunction of the udder site with ointment containing oestradiol monobenzoate; lactation was subsequently induced in these animals, but only after further treatment with anterior-pituitary extract containing prolactin. This work agreed with current views according to which the effects of oestrogens on lactation, both potential and established, were regarded as purely inhibitory. The adequacy of this theory was first seriously called in question by the experiments of Folley, Scott Watson & Bottomley [1940, 1941a], who showed that copious lactation could be produced in virgin goats by inunction of the udder region with ointment containing diethylstilboestrol. No anterior-pituitary extract was necessary, and lactation was initiated and the yield

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S. J. FOLLEY and F. H. MALPRESS

In the preceding paper [Folley & Malpress, 1944] it has been shown that lactation can be induced in maiden heifers or dry cows by the subcutaneous implantation of tablets of diethylstilboestrol (hereinafter called stilboestrol) or hexoestrol. Dodds, Golberg, Lawson & Robinson [1938] found that stilboestrol was almost as active in the rat, by the vaginal-smear test, when given by mouth as when subcutaneously injected. It was therefore interesting to see whether lactation could be induced in cows and heifers by oral administration of synthetic oestrogens, since the feeding method possesses obvious practical advantages. Induction of lactation in goats by oral administration of stilboestrol was reported by Lewis & Turner [1942].

MATERIAL AND METHODS

Experimental animals

(a) A series of preliminary experiments was carried out on seven maiden heifers and one heifer (Regality) which had aborted early in pregnancy, each of which received individual treatment. Four of these (three Shorthorns and

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S. J. FOLLEY and F. G. YOUNG

Our previous investigations of the influence of injected anterior-pituitary extract on the milk yield of cows in declining lactation have shown that over a period of 3 weeks such treatment may induce a 16–25% rise in milk production [Folley & Young, 1938, 1939, 1940]. The series of investigations now described was undertaken at the beginning of the present war to determine more precisely the conditions under which an increase of milk yield under pituitary stimulation could be consistently obtained, and to ascertain whether such a process provided a means of producing a significant increase in the total milk yield in Great Britain.

Before field trials were undertaken it was necessary to determine whether animals of known reactivity under first class management would consistently respond to treatment, to ascertain the minimum dose of pituitary extract required to induce an adequate response, and to estimate the minimum frequency of pituitary injection necessary