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SUMMARY
An almost specific release of neurophysin II with only minor release of neurophysin I was found during venous or arterial haemorrhage in five cows. Our data confirm the results of experiments in vitro in which vasopressin has been found to be associated with neurophysin II within neurosecretory granules.
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SUMMARY
Using continuous blood sampling a specific release of neurophysin I without a significant release of neurophysin II was found during hand-milking and suckling in seven out of eight cows. Hand-milking appeared to be a slightly more powerful stimulus than suckling.
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SUMMARY
The influence of intravenous injections or infusions of insulin (0·2 i.u./kg), propranolol (150 mg), 3,5-dimethylpyrazole (3 mg/kg), 3,5-dimethylisoxazole (0·08 mg/kg), glucose (0·5 g/kg), nicotinic acid (120 mg/kg), arginine (0·5 g/kg) or butyrate (0·5 mmol/kg) on plasma glucose levels, and on serum concentrations of growth hormone and free fatty acids of lactating cows was investigated. In all of these experiments we noted an increase in the level of growth hormone. This increase was not a direct consequence of alterations in the glucose concentration, since the growth hormone peak occurred both during a decrease (insulin, 3,5-dimethylisoxazole, nicotinic acid and butyrate tests), and during an increase of the glucose level (glucose, arginine and propranolol tests), whereas the glucose concentration remained unchanged during the 3,5-dimethylpyrazole experiments. However, in each instance a precipitous fall of the free fatty acid level was noted.
The glucose, growth hormone, and free fatty acid levels of lactating cows were not affected by either i.v. injection or infusion of saline.
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Oxytocin and bovine neurophysin I (bNpI) were estimated by radioimmunoassay in jugular vein plasma which was collected continuously from 18 bulls. No release of peptides was observed during successive matings with a cow in oestrus or during successive mountings on a cow with ejaculations into an artificial vagina. Stimulation with an electro-ejaculator or, to a smaller extent, massage of the seminal vesicles and ampullae per rectum caused an increase of oxytocin accompanied by a release of bNpI. It is speculated that the release of these peptides is due to stimulation of afferent pelvic nerves in the rectal wall. Basal molar ratios of bNpI/oxytocin in the plasma were highly variable, often showing a large excess of either bNpI or oxytocin. After the onset of peptide release induced by stimulation, molar ratios approached 1:1. This might indicate that hormone release is by exocytosis. Basal bNpI does not provide a good reflection of the oxytocin level.
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SUMMARY
Bovine neurophysin I and neurophysin II (bNpI and bNpII) have been assayed by radioimmunoassay in the jugular venous blood of cows during parturition.
In general, low bNpI levels were detected on the day before labour began and during the first stage of labour. Neurophysin I was present in appreciable quantities in blood taken during the second stage of labour and in most cows the concentrations rose to a maximum during the expulsive stage. After delivery, the concentration of bNpI in the blood diminished. This pattern of release is similar to that reported for oxytocin at parturition in cows.
As with bNpI, maximum levels of bNpII occurred during the expulsive stage of labour in some animals. In others, bNpII concentrations were very low or absent. Low concentrations of bNpII were found at the other stages of labour. Examination of the results from individual animals indicated that the release of the two neurophysins can be independent.