Radioimmunoassayable plasma and pituitary oxytocin (ROT) was measured during pregnancy and parturition. The highest mean plasma ROT level was seen in maternal rats on day 20 of pregnancy followed by a non significant decrease on day 21 reaching the basal level just before delivery. Plasma ROT level declined continuously up to the time of delivery of the first pup and then gradually increased until the completion of parturition. The highest maternal mean pituitary ROT level was found on day 21 pregnancy. Just before delivery of the first pup, the mean pituitary ROT level significantly declined by 22%. Pituitary ROT level declined steadily during the delivery of the first five pups. This pattern of reduction was reversed and ROT levels increased between the delivery of the fifth pup and the completion of labor. The increase of maternal pituitary and plasma ROT levels during delivery of the pups suggest that maternal ROT may play a role in normal parturition. Fetal hypothalamic-pituitary ROT does not seem to play any part in parturition.
The neural control of voluntary food intake has been studied for many years ( 1 ) . Little attention has been devoted to a study of the role of the endocrine glands and their hormones and to the effect of reproduction and lactation on food intake. In a preliminary study in this laboratory, wide variation in voluntary food consumption in Sprague-Dawley-Rolfsmeyer female mature rats was observed (2). I t was suggested that the differences observed might be due, in part, to differences in their normal hormone secretion rates. A number of studies have been reported on the effect of removal of various endocrine glands and destruction of B-cells by alloxan and replacement therapy and the effect of various hormones in normal animals In a continuation of these studies, the effect of pregnancy on food consumption is reported. In addition, the extent of mammary gland growth as measured by DNA was estimated a t the end of pregnancy and related to food consumption and weight gain of the dams.Materials and Methods. Eighteen nulliparous mature female rats of the Sprague-Dawley-Rolfsmeyer strain weighing a mean of 229 g were placed in metabolism cages constructed so as to prevent coprophagy and feed wastage. Temperature was maintained at 78 fr 1°F and the rats were artificially illuminated during daylight hours. Purina lab chow with 'an energy value of 4.41 cal/g and 23.4% total protein was fed during a preliminary period of 8 days to determine the mean daily feed consumption of each animal in the group.* Contribution from the Missouri Agr. Expt. Sta.; journal series no. 2915; approved by the Director.
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