Effect of Rise in Plasma Osmotic Pressure on the Milk-ejection Reflex in the Rat
The effect of an increase in plasma osmolality on the milk-ejection reflex of rats was studied. The lactating rats, at day 8-12 of lactation, were anesthetized with urethane (1.1 g/kg, i. p.) and 8-11 pups which had been separated from their mother 16-18 h were put to the nipples to suckle. In 21 of...
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Veröffentlicht in: | Endocrinologia Japonica 1983, Vol.30(3), pp.361-366 |
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Zusammenfassung: | The effect of an increase in plasma osmolality on the milk-ejection reflex of rats was studied. The lactating rats, at day 8-12 of lactation, were anesthetized with urethane (1.1 g/kg, i. p.) and 8-11 pups which had been separated from their mother 16-18 h were put to the nipples to suckle. In 21 of 47 rats studied an intermittent pattern of milk ejection was recorded with a latency of 15-74 min (group-I rats). The mean interval between recurring milk ejections was 8.3±0.6 (S.E.M.) min and the mean amount of oxytocin released at each milk ejection estimated in 11 of them was 0.26±0.04 mU. The remaining 26 rats showed no milk ejection throughout the nursing period of more than 90 min (group-II rats). The intraperitoneal injection of 1.5 M NaCl (1 ml) had no effect on the interval between milk ejections but increased the amount of oxytocin released at each milk ejection by 2.4 times in group-I rats, as the plasma osmolality changed from 297.9±2.7 mOsm/kg to 310.4±3.6 mOsm/kg. On the other hand, the 1.5 M NaCl injection induced recurring reflex milk-ejections in all of the group-II rats, while the plasma osmolality increased from 307±2.8 mOsm/kg to 320±3.1 mOsm/kg. The mean interval was not significantly different from that observed in the group-I rats. The sensitivity of the mammary gland to oxytocin was not altered by the 1.5 M NaCl injection. The injection of isotonic NaCl had no effect on the milk-ejection reflex. These results indicate that an increase in plasma osmolality facilitates the milk ejection reflex in rats by increasing the amplitude but not by changing the rhythmicity. |
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ISSN: | 0013-7219 2185-6370 |
DOI: | 10.1507/endocrj1954.30.361 |