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  • Author: G. W. HARRIS x
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1. Nursing and suckling behaviour of rabbits is described, and evidence given that an active process of milk ejection ('let-down') occurs in this as in other species.

2. Intravenous injection of posterior pituitary extracts in anaesthetized rabbits resulted in ejection of milk from a cannulated teat duct. The threshold dose was about 5 mU. and maximal responses were produced by 200 mU. of extract. Whole posterior pituitary extract was more effective than the oxytocic fraction, which was in turn more effective than the vasopressor fraction.

3. Stimulation of the supraopticohypophysial (s.o.h.) tract in anaesthetized rabbits also resulted in ejection of milk from a cannulated duct. Kymographic records of this response were similar to those obtained after injection of appropriate doses of posterior pituitary extract.

4. Lesions in the s.o.h. tract in lactating rabbits caused a marked diminution in the quantity of milk obtained by their litters in standard suckling tests, and incomplete evacuation of the mammary glands. Intravenous injection of posterior pituitary extract (30–200 mU.) into the does immediately before nursing gave a marked increase in the amount of milk obtained by the young and complete evacuation of the mammary glands. Stimulation of the region of the s.o.h. tract in these animals failed to elicit milk ejection from cannulated teat ducts.

5. Rabbits with hypothalamic lesions that did not involve the s.o.h. tract showed a normal milk-ejection reflex when suckled by their young, and a milk-ejection response after electrical stimulation of the s.o.h. tract.

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There is little doubt that the secretory activity of the adenohypophysis is to some extent under the control of the nervous system [see Marshall, 1936, 1942; Brooks, 1939]. Two hypotheses have been advanced by various authors to explain this neural control: first, that the glandular cells possess a direct secretor-motor nerve supply, or secondly, that a humoral relay transmits the nervous stimuli from the hypothalamus by means of the hypophysial portal vessels.

The nerve supply of the hypophysis is derived from several sources. A sympathetic supply was first described by Bourgery in 1845. It consists of a few fine twigs passing from the carotid plexus to the pars distalis. The method of termination of these fibres and their function remain doubtful. Possibly they end on gland cells and are secretomotor, but more probably they end on blood vessels and are vasomotor. It is certain, however, that they do not subserve

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B. Chatterjee, W. F. Demyan, J.-Å. Gustafsson, M. W. Harris, T. Hökfelt, G. Norstedt and A. K. Roy


Anterior hypothalamic deafferentation and infusion of human GH (hGH) in the normal male rat caused a marked reduction in the hepatic concentration of α2u-globulin, an androgen-dependent protein. Although s.c. injections of hGH (twice-daily) resulted in more than a 50% reduction in the hepatic level of α2u-globulin, the same dose of hGH when administered continuously through osmotic minipumps caused a threefold greater inhibition. The decreased hepatic concentration of α2u-globulin after hGH administration was associated with corresponding changes in the hepatic level of translatable α2u-globulin messenger RNA. Continuous infusion of hGH through osmotic minipumps and removal of the anterior hypothalamic influence on GH secretion by deafferentation also caused a marked reduction in the cytoplasmic androgen-binding activity of the rat liver. These results suggest that alterations in the level and pattern of GH secretion may influence hepatic androgen-binding activity and α2u-globulin synthesis.

J. Endocr. (1986) 108, 351–355