Recording electrodes were implanted in contact with the dura mater overlying the parietal cortex of six female goats, four of which were lactating. After recovery from surgery and complete familiarization with the housing conditions, the personnel and the recording technique, each goat was observed continuously for 24 h with simultaneous recording of the cortical electroencephalogram (EEG). Remote blood sampling was carried out every 30 min without disturbing the animal. Apart from the release of growth hormone (GH) associated with morning milking in two of the goats, there was no consistent relationship between the apparently spontaneous, episodic release of GH and behvaiour, stages of sleep, cortical EEG, air temperature, time of day or night, obvious environmental stimuli which arose from the normal husbandry routine, or the levels of porlactin, insulin, glucose or free fatty acids in the blood. There was also no relationship between the release of prolactin and the stages of sleep.

SUMMARY The afferent path of the milk-ejection reflex has been studied in the brain of the anaesthetized lactating rabbit. Electrical stimulation was applied between a monopolar electrode in the brain and an indifferent electrode in the scalp. The brain was transected at the mid-cerebellar level to eliminate sympathetico-adrenal activation, and intramammary pressure and arterial blood pressure were monitored to detect release of neurohypophysial hormones. In the mid-brain, the afferent path of the reflex is compact, lying in the lateral tegmentum of each side and passing forwards to lie medio-ventral to the medial geniculate body. On entering the diencephalon, the pathway on each side bifurcates: a dorsal path passing forwards in association with the extreme rostral central grey and periventricular region, and a ventral path ascending through the subthalamus. The dorsal and ventral paths reunite in the posterior hypothalamus. Delineating the pathway further forward in the hypothalamus, using a simple stimulation technique, was not possible because at this level it intermingles with efferent fibres descending from the paraventricular nucleus to the pituitary stalk. The afferent path of the reflex is concerned with the preferential release of oxytocin from the neurohypophysis, is not a major pathway for the release of vasopressin and its neural substrate in the mid-brain is believed to be the spinothalamic system of fibres.

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%.

SUMMARY Plasma samples from five goats taken during their first pregnancies and subsequent lactation were examined for prolactin concentration by a radioimmunoassay and for total lactogenic activity by a rabbit mammary gland organ culture assay. Prolactin was released in response to suckling and there was a fair correlation between prolactin concentrations as measured by radioimmunoassay and the levels of total lactogenic activity in the plasma samples from the lactating animals. During pregnancy, however, high levels of lactogenic activity were detected in the second and last thirds of pregnancy when the concentration of immunoreactive prolactin was low or even absent. This discrepancy in the results of the two assays suggests that the blood of pregnant goats contains a second lactogen of placental origin which does not cross-react with prolactin.

The direct estimation of oxytocin in blood during suckling in women has only been reported by two groups of workers, who obtained conflicting results. Hawker & Robertson (1957) and Hawker, Walmsley, Roberts, Blackshaw & Downes (1961) failed to detect a change in the oxytocin content of peripheral venous blood during suckling. However, Coch, Fielitz, Brovetto, Cabot, Coda & Fraga (1968) demonstrated the presence of oxytocin (12-25 \g=m\u./ml. plasma) in internal jugular venous blood collected from women during suckling. The present study investigates the possible release of oxytocin during suckling and coitus in man by direct estimation of the hormone in the blood. No previous estimation during human coitus has been reported, but in domestic animals an increase in the oxytocin content of the blood has been claimed after mating (Walmsley, 1963) and after artificial stimulation of the genitalia (Fitzpatrick, 1957;Roberts & Share, 1968).Three suckling experiments, with the same multiparous subject (aged 33), were performed at 6, 14 and 18 weeks post partum. In each, a control sample was taken before suckling began, and further serial samples were taken from the start of suckling. Two experiments were carried out during coitus. In the first, a blood sample was taken 1 min. after male and female orgasm, and in the second, samples were taken 5 min. before and 1 min. after male and female orgasm. A control sample was taken several hours before each experiment.The samples (20 ml.) were collected from the antecubital vein into a polyethylene syringe. The extraction and bioassay were those described by Folley & Knaggs (1965). Three recovery experiments were also performed, in which a known amount of oxytocin was added to blood taken from the lactating mother 18 weeks post partum. These samples, together with a blank control, were assayed in the same way.No oxytocin was detected in the first suckling experiment (6 samples). In the second and third experiments (11 samples) oxytocin was found on one occasion each time. Amounts of 112 and 11 /tu./ml. plasma were found in the samples taken 3 min. and 2-5 min. from the commencement of suckling, respectively. In the third experiment, oxytocin was also found in the control sample taken 1 min. before suckling (see Table 1). Oxytocin was found in both cases in the blood sample taken after female orgasm but no activity was found in any of the samples from the male or any of the controls. From the three blood samples with known amounts of oxytocin added, 77, 85, and 96% of the oxytocin was recovered.