Mammary resistance: a possible controlling factor in milk ejection.

Area of Science:

• Lactation physiology
• Reproductive biology
• Mammalian reproduction

Background:

• Rats exhibit increased milk release in response to suckling at 13 days postpartum compared to 8 days.
• This enhanced milk release may be due to increased oxytocin or mammary gland changes.
• Previous studies suggest oxytocin sensitivity increases with lactation stage.

Purpose of the Study:

• To investigate the role of mammary gland changes in enhanced milk release during advanced lactation.
• To compare milk release and intramammary pressure in rats at different lactation stages.
• To assess mammary gland resistance and compliance in early versus late lactation.

Main Methods:

• Milk release and intramammary pressure were measured in anesthetized rats at 8-9 and 13-15 days postpartum.
• Milk release was quantified by pup weight gain after suckling.
• Intramammary pressure responses to oxytocin and a constant pressure pulse were analyzed.

Main Results:

• Milk release in response to oxytocin was significantly greater in 13-15 day lactators compared to 8-9 day lactators.
• Intramammary peak pressure and its dissipation time were higher in early lactation (8-9 days).
• Mammary glands showed greater resistance in early lactation, indicated by higher pressure peaks from a constant pulse.

Conclusions:

• Reduced mammary gland resistance contributes to increased milk release in later lactation stages.
• Mammary gland physiology adapts during lactation, enhancing milk availability.
• These findings highlight the importance of mammary gland changes alongside hormonal factors in regulating milk ejection.