The Foetoplacental Unit and the Initiation of Lactation in the Rat

Abstract

Rats were either Caesarean-sectioned, ovariohysterectomized or ovariectomized on day 19 of gestation anti the role of prolactin and corticosteroids in the initiation of lactation was studied by administering 2~bromo-lX-ergocryptine (CB 154) and prolactin, and by using adrenalectomy and foetectomY. The concentrations of corticosteroids and prolactin in the plasma and the weight and lactose content of the inguinal mammary glands were determined 48 h after Caesarean section, and 24 h after ovariohysterectomy and ovariectomy.The ranges in concentrations of corticosteroids, prolactin and mammary lactose were 207-348 JIg/l plasma, 21·9-65·3 JIg/l plasma and 1·21--4·50mg/g tissue, respectively, in the Caesareansectioned, ovariohysterectomized and ovariectomized rats. The administration of CB 154 after either Caesarean section, ovariohysterectomy or ovariectomy decreased the concentration of prolactin to less than 8· 8 Jig/I. Whereas CB 154 significantly depressed the lactose content of the mammary tissue in Caesarean-sectioned and ovariohysterectomized rats (0·42 and o· 31 mg/g tissue, respectively), no effect was observed in ovariectomized rats (1·39 mg/g tissue). The administration of ovine prolactin reversed the inhibitory effects of CB 154. Furthermore, in two rats which were both ovariectomized and foetectomized, CB 154 did not inhibit lactose accumulation in the mammary tissue (2·02 mg/g tissue).Adrenalectomy of ovariohysterectomized rats decreased corticosteroid concentrations from 348 to 14 JIg/l plasma and the lactose content of mammary tissue from 1 . 31 to O· 19 mg/g tissue. Whereas adrenalectomy of ovariectomized rats decreased corticosteroid concentrations to 53 Jig/I, the lactose content of mammary tissue (1·82 mg/g tissue) remained within the range for ovariohysterectomized rats.These findings show that hormones produced in late pregnancy by the foetus and placenta can support lactogenesis in the rat in the absence of maternal prolactin and corticosteroids.

The yield and nutrient content of colostrum and milk of women from giving birth to 1 month post-partum

“…The increase in milk yield during the first 5 d of lactation was correlated (r 0.76) with the increase in the concentration of lactose in the mammary secretion (Figs 2a and 3). This relationship confirms the conclusion that the increase in the concentration of lactose in milk after birth provides an estimate of the timing of lactogenesis in women as in other species (Hartmann, 1973;Nicholas & Hartmann, 1981). Although the lactose and fat profiles appear similar (Fig.…”

“…The abrupt increase in the concentration of lactose in the mammary secretion just before parturition has been shown to be a useful indicator of the increase in the synthetic activity of the mammary glands of rats (Nicholas & Hartmann, 1981) and cows (Hartmann, 1973) during the initiation of lactation. In contrast to other species, the concentration of lactose in the mammary secretion of women remains low during late pregnancy and increases abruptly between 30 and 40 h after parturition .…”

Effects of uteroplacental insufficiency and reducing litter size on maternal mammary function and postnatal offspring growth

“…It begins in midpregnancy with the synthesis of milk components (lactogenesis I) and is followed by the onset of copious milk secretion associated with the decrease in progesterone and an increase in prolactin and glucocorticoids around parturition (lactogenesis II) (25,35). Progesterone withdrawal has been identified as the initial trigger of lactogenesis II in rodents (10,25,35,42,46,54). This is supported by the finding that lactogenesis II is impaired as a result of delayed progesterone withdrawal when placental fragments are retained within the uterus of humans and dairy cattle (30).…”

Maternal Progesterone Treatment Rescues the Mammary Impairment Following Uteroplacental Insufficiency and Improves Postnatal Pup Growth in the Rat

“…17 It is known that the onset of milk production is associated with a reduction in maternal progesterone, together with an increase in prolactin and glucocorticoids, around the time of parturition. 20,21 Furthermore, the trigger for secretory activation is characterized by maternal progesterone withdrawal. [20][21][22][23][24] The aim of the current study was to determine whether progesterone, compared to vehicle, administration to rat dams for 2 days following the induction of uteroplacental insufficiency can promote or maintain mammary gland development during late pregnancy and result in an improved lactation and offspring growth after birth.…”

“…20,21 Furthermore, the trigger for secretory activation is characterized by maternal progesterone withdrawal. [20][21][22][23][24] The aim of the current study was to determine whether progesterone, compared to vehicle, administration to rat dams for 2 days following the induction of uteroplacental insufficiency can promote or maintain mammary gland development during late pregnancy and result in an improved lactation and offspring growth after birth. Human studies have historically shown that early postpartum progesterone administration increases milk production in uncomplicated pregnancies across the normal birth weight range through yet to be determined mechanisms.…”