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Search for other papers by J. A. EDWARDSON in
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SUMMARY
The role of the peripheral innervation of mammary tissue in the maintenance of lactation has been investigated by the procedure of selective thelectomy combined with denervation of the posterior thoracic nipples.
When suckling is restricted to a single pair of nipples bilateral transection of the three adjacent nerves supplying a nipple arrests lactation completely; partial denervation is associated with a reduced level of lactational performance which is directly related to the concentration of the residual innervation.
Increase in litter size is associated with an overall increase in milk-yield up to a limit beyond which the addition of further young to the litter is without effect.
It is inferred that there is a quantitative relationship between the neural stimulus of suckling and the endocrine response of the hypothalamopituitary system.
Search for other papers by J. A. EDWARDSON in
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Search for other papers by D. GILBERT in
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SUMMARY
A technique is described for the continuous perifusion of rat adenohypophyses. Exposure of the perifused glands to repeated equal 5 min stimuli with hypothalamic extract resulted in a series of equal peaks of corticotrophin secretion, the response was proportional to log dose over the range 0·25–2·0 rat hypothalamic equivalents/ml. Repeated equal stimuli with hypothalamic extract, or with luteinizing hormone releasing hormone (LH-RH) at concentrations of 2 or 10 ng/ml, resulted in a progressively increasing series of peaks of LH secretion, i.e. a self-potentiating or priming effect. The effect took between 30 min and 1 h to develop. A delayed increase in the responsiveness of the glands was also seen with continuous incubation of anterior pituitaries with LH-RH. The relevance of these observations to the physiological control of LH secretion is discussed.
Search for other papers by G. W. BENNETT in
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Search for other papers by J. A. EDWARDSON in
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SUMMARY
Synaptosomes isolated from the sheep and the rat hypothalamus contain corticotrophin releasing factor, vasopressin, prolactin-release inhibiting factor and probably all of the substances which participate in the regulation of adenohypophysial function. Electrical field stimulation or depolarizing concentrations (55 mmol/l) of potassium ions cause a release of these factors from the incubated nerve-endings in a calcium-dependent manner. It is suggested that synaptosomes may provide a valuable approach to the study of mechanisms involved in hypothalamic neurosecretion in vitro.
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Search for other papers by C. A. M. HOUGH in
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SUMMARY
Adult genetically obese (ob/ob) mice which are characterized by adrenal hypertrophy and increased secretion of corticosteroids have considerably increased levels of ACTH in the pituitary gland. At 5 weeks of age there is no difference in the pituitary ACTH content of lean and obese animals and dietary restriction, sufficient to maintain body weight at normal values, reduces the pituitary ACTH content of adult obese mice from 14 times the level found in lean litter-mate controls to almost normal values. Using an in-vitro perifusion system, the release of ACTH from isolated pituitary glands was studied. Pituitaries from lean and obese mice responded similarly to stimulation with a crude extract of hypothalamic tissue containing corticotrophin releasing factor (CRF). The CRF content of the hypothalamus in both groups appears to be similar. In contrast with the high pituitary content, plasma values for ACTH in unstressed obese mice are not increased. The results are discussed in relation to other evidence for a hypothalamic disorder in ob/ob mice.
Search for other papers by ANNE BELOFF-CHAIN in
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Search for other papers by J. A. EDWARDSON in
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Search for other papers by JANET HAWTHORN in
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SUMMARY
The influence of the pituitary gland of lean and genetically obese (ob/ob) mice on insulin secretion from microdissected pancreatic islets of lean and ob/ob mice has been studied by perifusing the pituitaries of these animals in series with the isolated islets and measuring insulin secretion at 5-min intervals over a period of 60 min.
It has been shown that the pituitary perifusate of both lean and obese mice stimulate insulin secretion from lean mouse islets but not from obese mouse islets. The maximum stimulation occurs in the first 10 min and with the lean mouse pituitaries returns to the basal level in about 20 min, whereas with the obese mouse pituitaries insulin secretion is about double that from the control islets even after 40 min.
A concentration of pure porcine ACTH equivalent to about three times the amount released from the pituitary gland under the experimental conditions used, caused only a small stimulation of insulin release. Possible interpretations of these findings and further lines of investigation are discussed.
