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SUMMARY
In the in-vitro assay of Brown & Munro (1967) thyroid-stimulating hormone (TSH) increased the release of radioactive iodine from mouse thyroid glands labelled with 131i during life. Paper chromatography showed that TSH increased the 131I-labelling of thyroxine and tri-iodothyronine both in the culture medium and in hydrolysates of the thyroids.
Cyclic 3′,5′-adenosine monophosphate (cyclic AMP) also increased 131I release in this assay and increased the 131I-labelling of thyronines in the culture medium. The effects on thyroid hydrolysates were less striking.
Theophylline potentiated the influence of TSH and cyclic AMP in the assay and, by itself, increased 131I release and the labelling of iodothyronines in the thyroid without altering the distribution of 131I in the culture medium.
The implications of these results are discussed.
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The pituitary of the cyprinodont fish Poecilia secretes a hormone that is essential for tolerance of freshwater. Intact fish are euryhaline, but when hypophysectomized cannot tolerate fresh water, though living indefinitely in sea water or dilute sea water. In a typical experiment, ten hypophysectomized P. latipinna, transferred from dilute sea water (12 parts/1000) to fresh water at 25°, displayed severe distress symptoms within 8–46 hr. (mean, 22 hr.). When distressed in fresh water, hypophysectomized fish die in a few hours, but recover if returned immediately to dilute sea water (Ball, unpublished).
The pituitary factor essential for freshwater life is probably not a neurohypophysial hormone, since it is secreted by ectopic pituitary transplants in P. formosa (Ball, Olivereau, Slicher & Kallman, 1965), in which the neurohypophysis is involuted and virtually devoid of histologically detectable neurosecretion (Olivereau & Ball, unpublished observations). Histological studies of the adenohypophysis of P. latipinna and of the
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SUMMARY
The pituitary prolactin levels were measured in the domestic duck (Anas platyrhynchos) and in juvenile gulls from a mixed population of herring and lesser black-backed gulls. In the domestic duck the pituitary prolactin levels increased on the 2nd and 3rd days of maintenance on 0·3 m-NaCl, but by the 5th day they had fallen appreciably below the control levels. Maintenance of gulls with 0·3 m-NaCl produced no change in pituitary prolactin levels after 5 days, but a marked fall in prolaction levels when the birds were maintained on 0·7 m-NaCl for 5 days. This difference in response between the two species may be related to their degree of adaptation to a marine environment.
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The development of trophic hormones in foetal pituitary cells has been shown by the use of fluorescent antibodies, differential staining techniques and bioassay of pituitary homogenates. In foetal rat pituitaries, growth hormone, thyrotrophin and adrenocorticotrophin have been detected by radioimmunoassay and bioassay (Contopoulos & Simpson, 1957; Phillips & Schmidt, 1958; Milkovic & Milkovic, 1962; Birge, Peake, Mariz & Daughaday, 1967); but prolactin has not been detected by these techniques.
During experiments involving disc electrophoresis of rat pituitary homogenates the pituitaries from foetal rats were examined and a protein band appeared in the gel in a position almost identical with that of prolactin in the maternal pituitary (Plate). Rat pituitary hormones separated by disc electrophoresis according to the method of Davis (1964) have been identified by Jones, Fisher, Lewis & Vanderlaan (1965). Prolactin is the hormone that has the greatest mobility in this system; maternal prolactin had an R F value
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ABSTRACT
An in-vitro perifusion system was devised in order to examine the secretory profiles of isolated islets of Langerhans, derived from different physiological states, when subjected to various stimuli relevant to lactation. Islets from pregnant rats secreted more insulin than did those from virgin animals; however, islets from lactating and virgin animals secreted similar amounts of insulin with all stimuli, including glucose, amino acids, cations and neurotransmitters. When virgin rats were pretreated for 5 days in vivo with GH or prolactin, insulin responses in vitro were unchanged. Cannulation of the hepatic portal vein and inferior vena cava in vivo revealed that both insulin and glucose concentrations were lower in the portal vein of the lactating rat compared with the virgin animal. It was therefore concluded that insulin concentrations are depressed during lactation as a consequence of the pancreas receiving a diminished glycaemic stimulus rather than because of any change in β-cell sensitivity.
Journal of Endocrinology (1990) 125, 81–88
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ABSTRACT
A highly specific antiserum to rat GH (anti-rGH) was used to assess the role of GH in lactation in the rat. When administered alone, anti-rGH had no effect on litter weight gain, whereas bromocriptine reduced serum prolactin concentrations and litter weight gain for up to 7 days when given on day 4 of lactation. When bromocriptine and anti-rGH were given in combination, however, litter weight gain declined even more dramatically so that pups were receiving virtually no milk 2–3 days after treatment. Daily litter exchange failed to prevent this effect. Concurrent injections of highly purified GH (prolactin contamination undetectable) prevented the dramatic decline in litter weight gain induced by combined bromocriptine and anti-rGH treatment, so that these litters grew as well as those receiving bromocriptine alone. Growth hormone did not act by influencing serum prolactin concentrations, which remained low during GH therapy.
Direct effects of anti-rGH or GH on the pups (transferred through the milk) were ruled out since virtually identical results were obtained when milk yield was estimated during a 30-min suckling period after a 3-h separation of mother and pups.
Lactation had virtually ceased 3 days after treatment with both bromocriptine and anti-rGH, but it could be reinitiated by a single injection of prolactin or GH, and subsequent recovery was virtually complete.
The results of this study show that (1) prolactin can maintain a full milk yield in the absence of GH, (2) milk yield is reduced by approximately 50% in the absence of prolactin and (3) milk yield is totally stopped in the absence of prolactin and GH.
Growth hormone therefore appears to play an auxiliary role in lactation which may be important in times of prolactin insufficiency.
J. Endocr. (1986) 111, 117–123
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SUMMARY
The McKenzie (1958) assay method and an in-vitro assay method (Brown & Munro, 1967) for the determination of long-acting thyroid stimulator have been compared. Differences in the results were not great: the in-vitro method is simpler to perform and more precise. The sensitivity of the two methods is similar.
The in-vitro method, when used with antiserum to thyroid-stimulating hormone in the medium, provided a satisfactory and simple means for the assay of long-acting thyroid stimulator in the serum of thyrotoxic patients.
