ETHANOL AND THE INHIBITION OF OXYTOCIN RELEASE IN LACTATING RATS

1969 ◽  
Vol 62 (3) ◽  
pp. 546-554 ◽  
Author(s):  
Anna-Riitta Fuchs
Keyword(s):  
Mammary Gland ◽  
Dose Level ◽  
Milk Yield ◽  
Complete Inhibition ◽  
Milk Ejection ◽  
Oxytocin Release ◽  
Anaesthetized Rats ◽  
Peripheral Effect ◽  
Higher Doses

ABSTRACT The effect of ethanol on the release of oxytocin in the rat was studied using suckling as the oxytocin releasing stimulus. Milk removal on 30 min suckling by a litter of 8 after 18 h separation from the mother on postpartum day 13–16 was used as a parameter of oxytocin liberation. Under these conditions 25 mU intravenously injected oxytocin permitted normal milk removal in anaesthetized rats, whereas after injection of 10 mU oxytocin only about half of the normal milk yield was obtained. Ethanol in doses varying from 1.0 to 5.0 g/kg was injected intraperitoneally into the dam as 10 to 20 % solution in saline 30 to 60 min before nursing commenced and the milk yield was compared with saline injected control rats. At the dose level of 1.0 g/kg ethanol had no effect on milk removal but 2.0 g/kg caused a significant reduction to about 60 % of normal, and with higher doses a further reduction of the milk yield occurred. At 3.5 g/kg about 14% of normal milk yield was obtained, and at 5.0 g/kg a complete inhibition of milk ejection was observed. Oxytocin administration permitted normal milk removal in all ethanol treated rats indicating that there was no peripheral effect on the mammary gland. The experiments suggest that ethanol inhibits oxytocin release also in the rat.

INHIBITORY EFFECT OF PROSTAGLANDIN F2α ON OXYTOCIN RELEASE AND ON MILK EJECTION IN LACTATING RATS

1976 ◽  
Vol 69 (3) ◽  
pp. 395-399 ◽  
Author(s):  
J. PRILUSKY ◽  
R. P. DEIS
Keyword(s):  
Mammary Gland ◽  
Prostaglandin F2α ◽  
Physiological Saline ◽  
Inhibitory Effect ◽  
Blocking Effect ◽  
Suckling Period ◽  
Milk Ejection ◽  
Oxytocin Release ◽  
Anaesthetized Rats ◽  
Prostaglandin F

SUMMARY The effect of prostaglandin F2α (PGF2α) on milk ejection and on oxytocin release during suckling for one or two periods of 30 min was studied in lactating rats. Doses of PGF2α (20 or 40 μg) were injected i.p. 15 min before the suckling period. Control rats were injected with physiological saline. An inhibition of milk ejection proportional to the dose of drug administered was obtained. A normal milk ejection response was induced with a small dose of oxytocin injected immediately before nursing to mothers treated with PGF2α, indicating that the blocking effect was not due to a lack of mammary gland response. Two groups of mothers were injected with 40 μg PGF2α 2 and 4 h respectively before suckling. In both groups milk ejection was partially but significantly inhibited. In rats pre-treated with sodium pentobarbitone (3·5 mg/100 g body wt) to prevent the release of oxytocin induced by suckling, PGF2α (10 or 20 μg) did not modify the inhibition of milk ejection indicating that PGF2α does not have milk-ejecting activity. The administration of oxytocin to anaesthetized rats, immediately before a second suckling period, induced a normal milk-ejection response while in the rats treated with PGF2α, oxytocin was less effective. The results indicate that PGF2α inhibited milk ejection by a central block on oxytocin release and that the lipid is not able to mimic peripherally the milk-ejecting activity of oxytocin.

ELECTROPHYSIOLOGICAL RECORDINGS FROM OXYTOCINERGIC NEURONES DURING SUCKLING IN THE UNANAESTHETIZED LACTATING RAT

1981 ◽  
Vol 90 (2) ◽  
pp. 255-265 ◽  
Author(s):  
A. J. S. SUMMERLEE ◽  
D. W. LINCOLN
Keyword(s):  
High Frequency ◽  
Action Potentials ◽  
Milk Ejection ◽  
Extracellular Recordings ◽  
Electrophysiological Recordings ◽  
Oxytocin Release ◽  
Anaesthetized Rats ◽  
Freely Moving ◽  
Frequency Burst ◽  
Stimulation Of

A method is described for making extracellular recordings of the spontaneous activity of single hypothalamic neurones in unanaesthetized, freely moving, lactating rats using chronically implanted micro-wire electrodes. Extracellular recordings taken from individual neurones were maintained for periods of between 1 and 12 days. These records were not affected by any normal movement of the animal. As several micro-wires were implanted into each animal it was possible to make simultaneous recordings from several different hypothalamic sites in the same animal. Some recordings were identified as those from magnocellular neurones in the paraventricular nucleus on the basis of antidromic invasion after electrical stimulation of the neurohypophysis. Milk ejection in response to the prolonged sucking of ten or more pups was intermittent, and individual milk ejections recurred at intervals of 2–10 min throughout each period of nursing. The rise in intramammary pressure at milk ejection was associated with a vigorous extensor response from the pups. This was monitored by radar to provide an index of milk ejection in the unanaesthetized rat. Eleven antidromically identified neurones were recorded through 321 milk ejections. Eight of these neurones displayed a transient (2–6 s) and very substantial acceleration in discharge at the time predicted for oxytocin release, i.e. 10–12 s before milk ejection. The background discharge of these cells was 0·1–2·6 action potentials/s; this increased to 16–50 action potentials/s during the brief period of accelerated activity. Twenty-five neurones were studied during 365 milk ejections in rats which did not have a stimulating electrode implanted in the neurohypophysis. Thirteen of these neurones displayed a burst of high frequency discharge before each milk ejection, similar to that described for the antidromically identified neurones. Two of the non-responsive cells displayed a phasic pattern of discharge, characteristic of vasopressinergic neurone discharge recorded in anaesthetized rats. These observations of putative oxytocinergic neurones in unanaesthetized, freely moving rats are identical with those previously made on anaesthetized rats, and establish that the high frequency burst of electrical activity displayed by magnocellular neurones some 10–12 s before milk ejection is responsible for oxytocin release under normal physiological circumstances.

LACTATION AND INTRA-MAMMARY PRESSURE IN RATS BEARING OESTROGEN, PROGESTERONE OR NORETHINDRONE MAMMARY IMPLANTS; EFFECTS OF OXYTOCIN

1973 ◽  
Vol 73 (4) ◽  
pp. 713-720 ◽  
Author(s):  
J. D. Bruce ◽  
X. Cofre ◽  
V. D. Ramirez
Keyword(s):  
Mammary Gland ◽  
Milk Yield ◽  
Deleterious Effect ◽  
Inhibitory Action ◽  
Pressure Effect ◽  
Milk Ejection ◽  
Ejection Mechanism ◽  
Mammary Implants

ABSTRACT A study was made of the effect on lactation of progesterone, oestrogen or norehindrone implanted directly into the mammary gland of lactating rats compared to that in control animals. The results showed that progesterone did not disturb the milk yield of the mothers, growth of the pups or the action of oxytocin upon intra-mammary pressure. On the contrary, confirming earlier results, oestrogen showed a definitive deleterious effect upon lactation probably through an alteration of the milk ejection mechanism, since oestrogen reduced the mammary pressure effect of oxytocin. Norethindrone, a weak oestrogenic progestational compound, also showed an inhibitory action on lactation. These results support the hypothesis that oestrogen and progesterone have different direct actions upon the mammary function during lactation.

Lactational changes in oxytocin release, intramammary pressure and milking characteristics in dairy cows

1991 ◽  
Vol 58 (2) ◽  
pp. 159-169 ◽  
Author(s):  
Harald Mayer ◽  
Rupert Bruckmaier ◽  
Dieter Schams
Keyword(s):  
Dairy Cows ◽  
Milk Yield ◽  
Maximum Flow ◽  
Pressure Increase ◽  
Maximum Pressure ◽  
Early Lactation ◽  
Milk Ejection ◽  
Milk Flow ◽  
Oxytocin Release ◽  
Almost All

SummaryTwo experiments were conducted to investigate possible changes of milking-related oxytocin release (Expt 1) and of intramammary pressure and milking characteristics (Expt 2) throughout entire lactations in German Braunvieh dairy cows. Mean oxytocin concentrations after stimulation at onset of milking increased from 18·3 ± 15·9 to 30·7 ± 24·1 pg/ml in Expt 1 and decreased from 23·9 ± 17·6 to 15·4 ± 9·1 pg/ml in Expt 2, respectively, but remained above the level necessary to elicit complete milk ejection in both trials. Premilking baseline intramammary pressure had its maximum in early lactation until about month 4 and then decreased to ∼50% of its initial level. Ejection pressure followed a similar pattern, but dropped only to ∼75% of its maximum. This was due to the constant elevation of pressure increase, reaching its highest level in late lactation. Time from commencement of stimulation until maximum pressure exceeded 1 min in almost all instances even in early lactation and increased throughout lactation. Despite the normal decrease of milk yield average milk flow fell only slightly while maximum flow rate remained almost constant. Pressure increase, milk yield and milk flow were not different after 1 min and after extended stimulation. Thus there were no indications of a decreasing sensitivity of the milk ejection reflex during lactation, and milking characteristics were positively affected by intense teat stimulation. Suggestions for practical dairying are made.

Mammary cisternal size, cisternal milk and milk ejection in Murrah buffaloes

2004 ◽  
Vol 71 (2) ◽  
pp. 162-168 ◽  
Author(s):  
Chirathalattu S Thomas ◽  
Kerstin Svennersten-Sjaunja ◽  
Madhukar R Bhosrekar ◽  
Rupert M Bruckmaier
Keyword(s):  
Milk Yield ◽  
Cross Sections ◽  
Age Groups ◽  
Latency Period ◽  
Close Correlation ◽  
Milk Ejection ◽  
Murrah Buffaloes ◽  
Oxytocin Release ◽  
Cavity System ◽  
Internal Arrangement

The internal arrangement of the mammary gland cavity system, cisternal and alveolar milk fractions and the characteristics of milk ejection were investigated in buffaloes. Twenty-four Murrah buffaloes in three different stages of lactation and of two age groups were used. Continuous ultrasound cross-sections during milk ejection induced by exogenous oxytocin were performed to record the latency period of milk ejection. Buffaloes had small cisterns and the cavity area in the teat and gland regions were not significantly different (P>0·05). The animals had long teat canals (3·1±0·1 cm), longer in the hind than fore quarters. Cisternal milk yield was low (0·17±0·01 kg) and cisternal fraction was only 4·9±0·1% of the total milk. The cisternal area (cm2) was 69·6±4·6, 51·61±4·8 and 26·01±4·8 while the cisternal yield (kg) was 0·32±0·05, 0·18±0·05 and 0·05±0·05 in early, mid and late lactation, respectively. A close correlation (r=0·87, P<0·05) existed between the ultrasound cisternal area and cisternal milk yield. The latency period of induced milk ejection was similar to that reported for cows (25±1 s) and was negatively correlated with milk yield (r=−0·75, P<0·05). Milk ejection occurred shortly after elevated oxytocin concentrations were present. Delayed milk ejection reported earlier in this species must therefore be due to the absence of cisternal milk and delayed oxytocin release. An increase in teat length and circumference at milk ejection was also evident in the ultrasound cross sections.

Small increases in peripheral noradrenaline inhibit the milk-ejection response by means of a peripheral mechanism

1984 ◽  
Vol 100 (3) ◽  
pp. 337-344 ◽  
Author(s):  
A. M. Lefcourt ◽  
R. M. Akers
Keyword(s):  
Milk Yield ◽  
Bolus Injection ◽  
Fold Increase ◽  
Response To Treatment ◽  
Milk Ejection ◽  
Milk Flow ◽  
Dependent Change ◽  
Peripheral Mechanism ◽  
Oxytocin Release ◽  
Second Peak

ABSTRACT The effects of exogenous noradrenaline on the milk-ejection response were determined for nine Holstein cows. Noradrenaline was injected (0·95 nmol/kg) 15 s after the start of teat stimulation (preparation) or infused (0·13 nmol/kg per min, after bolus injection of 0·47 nmol/kg) starting 10 min before milking for 20 min. Cows were prepared (udder wash and dry) for 1 min before milking. Both injection and infusion resulted in approximately a 3·5-fold increase in peripheral noradrenaline at 1·75 min after the start of milking (baseline noradrenaline 0·83 and 0·89 nmol/l plasma; at 4 min, 2·00 and 3·00 nmol/l). Prolactin release was delayed and oxytocin release enhanced, while milk yield was decreased by 8·6% for both treatments. The maximum rate of milk flow was also depressed by treatment. In contrast, milking time increased for injection and decreased for infusion. In addition, a milk-yield-dependent change in the pattern of milk flow was seen in response to treatment. In medium-yield animals, two distinct milk-flow peaks were apparent and injection delayed the time to the second peak. We conclude that physiologically meaningful increases in peripheral noradrenaline can inhibit milk-ejection response by means of a peripheral mechanism not involving inhibition of release of oxytocin. J. Endocr. (1984) 100, 337–344

scholarly journals Milk yield, oxytocin and β-endorphin gradually normalize during repeated milking in unfamiliar surroundings

1996 ◽  
Vol 63 (2) ◽  
pp. 191-200 ◽  
Author(s):  
Rupert M. Bruckmaier ◽  
Hans-Ulrich Pfeilsticker ◽  
Jürg W. Blum
Keyword(s):  
Dairy Cows ◽  
Milk Yield ◽  
Control Level ◽  
Operating Theatre ◽  
Milk Ejection ◽  
Asymptotic Approach ◽  
Blood Samples ◽  
Milk Flow ◽  
Total Milk ◽  
Oxytocin Release

SummaryFor six successive milkings, six dairy cows were relocated immediately before milking to an unfamiliar operating theatre, a procedure previously shown to inhibit oxytocin release and milk ejection. Two control milkings were performed in familiar surroundings. After milk flow had ceased, two i.v. injections of 1 i.u. oxytocin were given to remove the remaining milk. Milk flow was recorded continuously and blood samples were taken every minute during milking and 10 min after milking. During the first milking in unfamiliar surroundings, no oxytocin was released. Thereby, only 13% of the total milk yield, the cisternal milk, was available and the alveolar milk fraction could only be removed after injection of oxytocin. During subsequent relocations oxytocin release steadily increased toward the control level, although the timing of oxytocin release remained delayed as compared with controls. However, the milk fraction available before oxytocin injection increased with increasing number of removals, following an asymptotic approach to control levels. The concentrations of β-endorphin, cortisol (and perhaps also of prolactin) gradually declined with the number of times the animal was moved to unfamiliar surroundings, i.e. hormone concentrations gradually adjusted to control level. During milking, concentrations of prolactin and cortisol increased, while β-endorphin concentrations decreased (except for the first relocation). We conclude that milking-related oxytocin release and therefore milk ejection adapted gradually to repeated relocations to unfamiliar surroundings. This adaptation was inversely related to β-endorphin concentrations, so it is possible that oxytocin release was suppressed by high circulating β-endorphin concentrations.

Machine milking of Ostfriesian and Lacaune dairy sheep: udder anatomy, milk ejection and milking characteristics

1997 ◽  
Vol 64 (2) ◽  
pp. 163-172 ◽  
Author(s):  
RUPERT M. BRUCKMAIER ◽  
GEORG PAUL ◽  
HARALD MAYER ◽  
DIETER SCHAMS
Keyword(s):  
Milk Yield ◽  
Cross Sections ◽  
Ultrasound Measurement ◽  
Delayed Response ◽  
Dairy Sheep ◽  
Milk Ejection ◽  
Flow Curves ◽  
Flow Rates ◽  
Milk Flow ◽  
Oxytocin Release

Mammary cistern anatomy derived from ultrasound measurement, milk ejection in response to exogenous oxytocin and oxytocin release and milking characteristics with and without manual prestimulation in early (months 2–4) and late (months 5–8) lactation were investigated in Lacaune and Ostfriesian dairy ewes. Vertical ultrasound cisternal cross sections of the cisternal cavities did not differ in the two breeds, whereas the cisternal area fraction located lower than the exit into the teat channel was larger in Ostfriesian than in Lacaune sheep. The cisternal area enlarged within 1 min in response to i.v. oxytocin injection, indicating milk ejection. During milking, oxytocin concentrations in Lacaune generally increased dramatically within 0·5 min from the start of prestimulation or milking, whereas only slight or no oxytocin release was detected during milking without prestimulation in Ostfriesian ewes. Prestimulation induced oxytocin release in Ostfriesian sheep within 1–2 min after the start of milking, indicating delayed response to stimulation. Two peaked milk flow curves were observed when oxytocin release and milk ejection occurred only after removal of cisternal milk. This type of milk flow was more frequent in Ostfriesian than in Lacaune ewes and was reduced in both breeds by prestimulation, while the frequency of one peaked milk flow curves increased. During the course of lactation, milk yield, main milk fraction and milk flow rates decreased, while stripping yield was almost unchanged. Although milk yield was similar in both breeds, milk flow was lower and stripping yield was higher in Ostfriesian than in Lacaune ewes. We conclude that milk ejection in ewes occurred in response to elevated oxytocin concentrations. In Ostfriesian ewes reduced and delayed oxytocin response to teat stimulation resulted in milk ejection only during stripping. Therefore, and probably because a larger volume of the cistern was located below the teat exit in the Ostfriesian breed, stripping yield was higher in Ostfriesian than in Lacaune sheep.

Stimulation of milk secretion with inhibition of milk ejection by corticosteroids during extended lactation in the rat

1984 ◽  
Vol 103 (2) ◽  
pp. 213-218 ◽  
Author(s):  
D. J. Flint ◽  
R. A. Clegg ◽  
C. H. Knight
Keyword(s):  
Adipose Tissue ◽  
Mammary Gland ◽  
Milk Yield ◽  
Insulin Receptors ◽  
Insulin Binding ◽  
Serum Prolactin ◽  
Milk Ejection ◽  
Anabolic Activity ◽  
Extended Lactation ◽  
Stimulation Of

ABSTRACT Milk yield declined significantly between days 22 and 28 of lactation in rats, when lactation was extended by frequent replacement of older litters with younger ones. Corticosterone implants but not cortisol injections or implants prevented this decline. Cortisol, however, appeared to inhibit milk ejection since the mammary glands became engorged with milk and milk yield was improved dramatically by oxytocin injections. In both cases corticosteroid concentrations increased approximately threefold above basal concentrations. Both corticosteroids increased total mammary gland RNA content and lipoprotein lipase (LPL) activity of the mammary gland but were without effect on insulin binding. They also decreased LPL activity, lipogenesis and the number of insulin receptors on adipose tissue. Serum prolactin and insulin concentrations were unaffected by any of the treatments. The results suggest that corticosteroids (1) inhibit milk ejection under certain conditions, (2) may be circulating in lower concentrations, which thereby limit milk production, during prolonged lactation and (3) may improve milk yield during extended lactation in part by suppressing anabolic activity in adipose tissue. J. Endocr. (1984) 103, 213–218

Inhibitory effect of adrenaline on oxytocin release in the ewe during the milk-ejection reflex

1979 ◽  
Vol 46 (1) ◽  
pp. 41-46 ◽  
Author(s):  
Tadeusz Barowicz
Keyword(s):  
Blood Plasma ◽  
Milk Yield ◽  
Myoepithelial Cell ◽  
Inhibitory Effect ◽  
Receptor Blocker ◽  
Milk Ejection ◽  
Cell Level ◽  
Oxytocin Release ◽  
Milk Ejection Reflex ◽  
Β Receptor

SUMMARYMilk-ejection activity was determined in the blood plasma of ewes during normal milking and during milking when adrenaline was injected intravenously before or after udder stimulation. It was found that administration of adrenaline either before or after udder washing, decreased the oxytocin concentration and milk yield but increased the yield by hand-stripping. Adrenaline also retards the average time for peak oxytocin concentration. These results and the use of a β-receptor blocker to inhibit the effect of adrenaline at the myoepithelial cell level indicate that in ewes adrenaline can prevent the release of oxytocin from neurohypophysis.

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