Mammary Nucleic Acid Content Research Articles

Effect of Arginine Deficiency on Mammary Gland Development in the Rat

The effect of dietary arginine deficiency on rat mammary gland development was investigated in pregnant rats and ovariectomized nonpregnant rats. Consumption of an arginine-deficient diet from day 0 of pregnancy significantly reduced the total DNA and RNA content of the mammary gland by day 20. Pair-feeding studies revealed that reduced food intake associated with consumption of the arginine-deficient diet was not responsible for the altered nucleic acid content of the gland. Restriction of food intake by pair-feeding did reduce the wet weight of the mammary gland as well as its fat content when compared with ad libitum fed controls, but the degree of reduction did not fully account for the depressing effect on the wet weight and fat content observed when the arginine-deficient diet was fed. The ratio of RNA to DNA in the mammary tissues of rats fed the arginine-deficient diet indicated normal protein synthetic activity per cell. The extent of reduction in mammary nucleic acid content by arginine deficiency was similar for pregnant rats and ovariectomized nonpregnant rats treated with estrogen and progesterone. These studies show that dietary arginine is required for optimal mammary growth. The possible mechanism(s) by which arginine can modify mammary growth are discussed.arginine mammary gland pregnancy estrogen progesterone

MAMMARY NUCLEIC ACIDS AND PITUITARY PROLACTIN SECRETION DURING PROLONGED LACTATION IN MICE

Lactation was prolonged until 61 days by repeated renewal of litters every week after day 12 in primiparous C3H/He strain mice. On days 12, 19, 40, and 61 of lactation, litters were removed for 5 h and after 1 h of resuckling the synthesis of DNA and RNA in the mammary gland was estimated by the incorporation of (3H)thymidine and (14C)uridine into mammary DNA and RNA in vitro respectively. Mammary nucleic acid content and pituitary and plasma levels of prolactin were also assayed. Nulliparous mice were similarly treated on day 19 of pregnancy. The percentage gain in litter weight per week was highest between days 5 and 12 of lactation, declined until days 26-33 and became steady thereafter. Mammary DNA synthesis was extremely high on day 19 of pregnancy, decreased on day 12 of lactation to less than one-fifteenth of that on day 19 of pregnancy and increased linearly therafter. Changes in mammary DNA content were not so marked, but DNA content was high on days 12 and 19 of lactation. RNA synthesis was highest on day 19 of pregnancy, abruptly decreased on days 12 and 19 of lactation and increased again with the advance of lactation. Mammary RNA content, RNA:DNA and 14C:3H ratios increased from day 19 of pregnancy to days 12-19 of lactation and decreased on days 40 and 61. While the pituitary levels of prolactin were almost constant during lactation, they were significantly higher than those on day 19 of pregnancy. There were only slight differences in plasma prolactin levels at any stage.

Effects of ergot drugs on prolactin and growth hormone secretion, and on mammary nucleic acid content in C3H-Bi mice.

Effects of ergot drugs on prolactin and growth hormone secretion, and on mammary nucleic acid content in C3H-Bi mice.

Effects of adrenalectomy and-or deficiency of pituitary prolactin secretion on initiation and maintenance of lactation in mice.

SUMMARY In order to examine the effects of deficiency of adrenal corticosteroids and/or prolactin on the initiation and maintenance of lactation in mice, C3H/He female mice were adrenalectomized and/or implanted during days 13–15 of pregnancy with a pellet of 2-bromo-α-ergocryptine (EC), a potent inhibitor of pituitary prolactin secretion. Average body weights of the young and mammary contents of DNA and RNA were determined on days 0 (day of parturition) and 10 of lactation. On day 0, no differences in these parameters were found among groups, and plenty of milk was present in the stomachs of the young. Furthermore, the treatments did not affect the duration of pregnancy, the number of still-born young or the maternal behaviour at parturition. All young in the group adrenalectomized and implanted with EC died by day 2. Adrenalectomy or implantation of EC retarded the growth of young after day 2 and decreased markedly the mammary nucleic acid content on day 10. These results strongly suggest that adrenal corticosteroids and prolactin play minor roles in the initiation of lactation at parturition, while they are indispensable for the maintenance of lactation in mice.

Effects of administering antisera to mouse growth hormone and prolactin on gain in litter weight and on mammary nucleic acid content of lactating C3H mice.

SUMMARY The effects of administering antiserum to mouse growth hormone (GH) and prolactin on lactation and mammary nucleic acid content of C3H mice were studied. Injections of either antisera to lactating mothers suppressed the gain in body weight of their suckling young, GH antiserum more readily than prolactin antiserum. A combined injection of the two antisera resulted in an immediate retardation of the gain in body weight of the young. Although both antisera reduced DNA and RNA content of the mammary gland, GH antiserum appeared to affect DNA content predominantly whereas prolactin antiserum affected RNA: DNA ratio, suggesting involvement of GH primarily in cell proliferation and of prolactin in protein synthesis. Both antisera abolished the gain in maternal body weight. Mouse GH antiserum decreased maternal adrenal weight whereas both antisera reduced ovarian weight. The results suggest that both GH and prolactin may be involved in normal lactation and in maintenance of body weight in C3H mice.

Effect of interrupted nursing on lactation in rats.

SummaryInterruption of suckling in rats for a single period of up to 12 hr in the immediate postpartum period or on day 10 of lactation had no significant effect on subsequent litter weights or mammary nucleic acid content. Interruption for 24 hr in both early and midlactation reduced litter weights and mammary gland RNA content but had no significant effect on weight of anterior pituitary, adrenal, or mammary gland DNA content. The results suggest that the effect of interrupted nursing is to reduce mammary gland metabolic activity without altering cell number and furthermore, that the effect probably occurs locally within the mammary gland.

Nursing duration and suckling intensity: effects on plasma corticosterone, circulating leukocytes, and mammary nucleic acids.

Lactating rats were killed after exposure to specific nursing intensities and suckling intervals to examine the effects of these factors on circulating leukocytes, plasma corticosterone, and mammary nucleic acids. Nursing durations of 0.25, 0.5, and 1 hr caused a 3-fold increase in plasma corticosterone when compared to nonnursed levels. In comparison, plasma corticosterone concentrations were similar to nonnursed control values after hours 2, 3, and 4 of nursing. In addition, exteroceptive stimuli associated with nursing provoked increases in plasma corticosterone that were comparable to values obtained from 0.25 or 0.5 hr of nursing. Circulating leukocytes decreased 24% during the first 0.5 hr of nursing with 10 pups; whereas mammary nucleic acid content increased 9%, suggesting an influx of leukocytes into mammary tissue. Histological examination of mammary glands revealed a striking increase in leukocytes within the alveolar lumina of glands within 0.5 hr after nursing. The results from this study indicate that nursing is a dynamic situation which is capable of provoking striking alterations in leukocytic and adrenocortical function.

Lactational performance of rats injected with oxytocin, cortisol-21-acetate, prolactin and growth hormone during prolonged lactation.

The response of the mammary gland of rats to various hormones injected daily between days 16 and 32 of lactation was studied. One unit of oxytocin, given 3 times daily, resulted in 37 and 44 % more mammary DNA and RNA content to day 32 of lactation than in saline-injected controls; however, oxytocin did not significantly increase litter weight gain or mammary RNA/DNA ratio. Cumulative litter weight gain decreased markedly in both oxytocin and saline injected rats as lactation advanced. Consequently, the endogenous supply of oxytocin appeared to be sufficient for removal of the reduced amounts of milk synthesized during advanced lactation. Cortisol-21-acetate (0.5 mg), ovine prolactin (2 mg) and ovine growth hormone (1 mg) were injected singularly and in all possible combinations between days 16 and 32 to determine if these treatments would maintain mammary nucleic acid content and lactational performance. Cortisol-21-acetate maintained mammary DNA and RNA content to day 32 of lactation and markedly retard...

Changes in pituitary prolactin and mammary nucleic acid content during pseudopregnancy in the rat.

SummaryAcute and long-term changes in pituitary prolactin and mammary nucleic acids of rats following induction of pseudopregnancy by cervical vibration were investigated. After maintaining a constant level (0.045-0.047 IU/mg) between 0 and 16 hr of stimulation, prolactin concentration declined progressively to the lowest level (0.012 IU/mg) on day 10 of pseudopregnancy. This decrease was followed by substantial increases in DNA and RNA contents of the mammary gland. Pituitary prolactin and mammary nucleic acid content were highly but negatively correlated. The data suggest that prolactin in rats may be involved in mammogenesis and luteal function during pseudopregnancy.

Contribution of pregnancy, fetuses, fetal placentas and deciduomas to mammary gland and uterine development.

In rats, the influence of pregnancy, fetuses, fetal placentas and pseudopregnancy with and without deciduomas on mammary and uterine development (DNA content) and metabolism (RNA content) was studied. Mammary nucleic acid content increased throughout pregnancy. Removal of fetuses before midpregnancy, but not after, interfered with normal increases in mammary DNA and RNA content. Excision of fetal placentas caused mammary development to regress to nonpregnant control values. Mammary development during the first 12 days of pseudopregnancy was 29–33% less than that observed in 12-day pregnant rats. It is suggested that maternal hormones are the primary stimulant of mammary development during the first half of pregnancy. However, the fetal placentas commence to stimulate mammary development before midpregnancy, and they may be the primary limiting factor for mammary development during the second half of pregnancy. Uterine DNA increased 2.8-fold, whereas uterine RNA and weight increased 5.8- and 4.6-fold, resp...

Regulation of mammary nucleic acid content by various suckling intensities.

Regulation of mammary nucleic acid content by various suckling intensities.