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SUMMARY
Cross-circulation experiments were performed on sheep by joining the jugular veins of two animals by anastomoses. One of the two animals (B) was a lactating ewe, and the release of hormones from the neurohypophysis in the other animal A (ewe, ram or wether) was investigated by recording the intramammary pressure in B.
The following types of stimulation were carried out on A: (1) distension of vagina or anus; (2) massage of seminal vesicles (SV) or cervix via the rectum; (3) deep massage of the rectal walls, SV or cervix excluded; (4) direct massage of cervix, SV or uterine horns through the abdomen; (5) manipulations in the deep pelvic cavity; (6) distension of the urinary bladder in rams and wethers and pressure upon the filled bladder.
Direct massage of cervix and uterine horns through the abdomen was ineffective. Stimulation of the urinary bladder by distension and pressure induced milk-ejection responses in some animals. Massage of the SV through the abdomen was hardly effective in rams but was effective in two out of seven wethers. The most efficient stimuli, classified according to their ability to induce milk ejection in B, were: distension of the vagina, stimulation of receptors in the retroperitoneal part of the rectum, manipulation in the deep pelvic cavity.
The hypothesis is advanced that reflex release of neurohormones is induced by stimulation of receptors of the afferent pelvic nerves wherever they are situated in the pelvic region. The release of neurohypophysial hormones, provoked by massage of the cervix or SV via the rectum in sheep, is to be attributed primarily to stimulation of receptors in the rectal wall. Reflex hormone release can be elicited just as well in wethers as in rams.
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Search for other papers by G. Peeters in
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The effects of perphenazine on galactopoiesis were studied in 52 goats in the phase of declining lactation (September–December). At the beginning of September, perphenazine (1 mg) was stereotaxically implanted into the hypothalamus, sham-implantations being performed on control animals. After the operation milk yield decreased and stabilized at a new starting level in most animals of both groups. The average weekly milk yield of the sham-implanted goats gradually fell during the experimental period. This progressive decline in yield was greatly reduced if perphenazine had been implanted in the median eminence (ME). No galactopoietic effects were observed when the implantation was localized outside the ME.
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SUMMARY
During water diuresis in conscious goats, noradrenaline (NA), its antagonists phentolamine, phenoxybenzamine and propranolol and also atropine were administered into the 3rd ventricle. The subsequent effects on water diuresis and on the excretion rates of Na+, K+ and Cl− were investigated.
Infusion of NA into the 3rd ventricle induced a strong and significant antidiuretic response and a decrease in the Na+: K+ excretion ratio; these effects were dose-dependent. High doses of NA produced a significant increase in urinary K+ excretion. Similar results were observed after i.v. administration of arginine-vasopressin.
Pretreatment with phentolamine injected into the 3rd ventricle produced a dose-dependent inhibition of the NA-induced antidiuretic effects. Phenoxybenzamine also blocked the response to NA but a dose-response relationship was not apparent. Atropine and propranolol did not block the response to NA.
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Search for other papers by N. TUYTTENS in
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SUMMARY
Cross-circulation experiments were carried out using either two lactating ewes (six experiments) or one sexually mature ram and one lactating ewe (seven experiments). Under local anaesthesia an anastomosis was established by means of two plastic tubes between a jugular vein of one animal (A) and a jugular vein of the second animal (B) in each pair. The other jugular veins were clamped.
Vaginal distension performed in ewe A by means of an inflated balloon often caused a sharp rise of pressure in the udder cisterns of ewe B after a minimum latency of 30 sec. Many pressure curves could be obtained successively in the same preparation by repeating the vaginal distension stimulus.
Massage of the seminal vesicles and ampullae of the ram often caused a sharp pressure rise in the udder of the ewe after a minimum lag period of 30 sec. This effect could be obtained several times with the same preparation, but considerable individual variation was observed between the different rams used. Massage of the seminal vesicles and ampullae induced emission in many cases but not always. Intravenous injection of a synthetic oxytocin, Syntocinon (500–1000 mu.), in the ram or distension of the vagina in the ewe failed to elicit emission.
Pressure responses were induced by injection of suitable doses of Syntocinon into the plastic tube leading to the ewe in which the cistern pressure was recorded, after a latency of approx. 30 sec. It may be concluded that vaginal distension in the ewe causes the discharge of a hormone from the head. A similar phenomenon occurs in the ram after massage of the seminal vesicles and ampullae. These effects are not abolished by atropine. It is postulated that this hormone is oxytocin in both sexes. The amount of hormone released after one stimulus was usually equivalent to 40–100 mu. oxytocin in the ram and 20–50 mu. oxytocin in the ewe.
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Search for other papers by F. VANSCHOUBROEK in
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SUMMARY
The relation between milk ejection and antidiuretic response was studied on lactating cows using different stimuli.
The stimuli, utilized to induce milk ejection, could be classified according to increasing effectiveness as follows: (1) showing the calf to the mother (visual stimulation); (2) washing the udder with water at 40° C in trained animals; (3) washing combined with visual stimulation; (4) suckling. Experimental conditions (hydration, bladder catheter) exerted a marked inhibiting effect in most animals on the milk-ejecting reflex induced by stimuli 1, 2 and 3. The reactions of domesticated cows under these circumstances are analogous to those of primitive breeds under normal conditions.
Generally, the antidiuretic response seemed to be quantitatively correlated with the release of oxytocin. However, exceptions to this rule were observed.
An antidiuretic response was obtained in cows after milk ejection unaccompanied by withdrawal of milk.
The effect of known amounts of oxytocin on milk ejection was studied, and the dose-response curve was nearly a straight line when log dose was plotted against the volume of milk ejected. The slope of the curves, however, varied in different cows.
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Search for other papers by R. REYNAERT in
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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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Search for other papers by A. HOUVENAGHEL in
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SUMMARY
Distension of the vagina by an inflated balloon induces milk ejection in goats. This reflex (the Ferguson reflex) is based on a neurohormonal mechanism. In three goats the reflex was abolished after bilateral section of the complex pelvic nerves plus caudal rectal nerves. Bilateral section of the pelvic nerves only, caused a complete elimination of the reflex in 11 out of 13 goats; in the two remaining animals, the reflex was abolished after a supplementary section of the pudendal nerve plus caudal rectal nerves. The reflex remained intact in one goat in which first the caudal rectal nerves and subsequently the pudendal nerve were cut. Elimination of the Ferguson reflex was accompanied by a marked reduction of the intensity of straining movements which are normally induced by distension of the vagina. Bilateral section of the pelvic nerves provoked a severe but temporary paralysis of the large intestine with blocking of the defaecation reflex. It is suggested that in ruminants the afferent pelvic nerves are involved in the release of oxytocin and in the intense straining occurring during the phase of expulsion at parturition.
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Search for other papers by G. PEETERS in
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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.