Progesterone and 20-alpha-hydroxypregn-4-en-3-one levels in ovarian vein blood of the rat throughout lactation

Changes in the rate of progesterone and 20α-hydroxypregn-4-en-3-one (20α-OH-P) secretion by the rat ovary during the course of lactation were investigated. The level of progesterone in the ovarian vein blood, which was very low on day 1 of lactation, increased progressively up to day 8 (355 μg./100 ml. blood), then declined to day 18 (45·5 μg./100 ml.) and day 21 of lactation. A high concentration of 20α-OH-P in blood was observed on day 1 and day 21 of lactation, but from day 4 to day 18 the secretion of this steroid was relatively low. The ratio of progesterone to 20α-OH-P exceeded unity from day 4 to day 16, and in the middle of lactation the concentration of progesterone in ovarian venous blood was about four times greater than that of 20α-OH-P. These changes in the secretory pattern of progestins during lactation are discussed in connexion with the effects of the suckling stimulus on prolactin and gonadotrophin secretion from the anterior pituitary gland.

Body weight and food consumption of lactating rats: effects of ovariectomy and of arrest and resumption of suckling

In order to assess the role of the suckling stimulus in the regulatory mechanism of body weight and food consumption of lactating rats, changes in body weight and food intake under various conditions were investigated.

The results of the changes in food intake during the oestrous cycle, pregnancy and lactation, and after weaning were consistent with those reported by previous workers. The rate of increase in body weight was similar during dioestrus, early pregnancy, early lactation and after ovariectomy. Food consumption of mother rats was maintained at the lactating level for 24 hr. after the removal of suckling pups on the 12th day of lactation, then it rapidly decreased. Resumption of suckling by foster litters, 5 days after removal of the original litters, caused increase in body weight and food intake as well as the restoration of lactation in both normal and ovariectomized animals. The rate of increase in body weight arising from the resumption of suckling was similar to that observed in the ovariectomized rats that were not resuckled after removal of the litters. The increase in body weight in the resuckled rats was not necessarily associated with the enhanced food intake. In spite of vigorous suckling by pups, food intake of the resuckled animals did not show a progressive increase as in normal lactating mothers until the function of mammary glands was restored and sufficient milk was produced to increase the weight of the foster litters. After restoration of lactation food consumption of the resuckled mothers increased progressively, the increase being closely related to increased milk secretion.

The greater food intake in the resuckled rats than in the non-resuckled animals, even before restoration of milk secretion, seems to indicate a direct stimulating effect of the suckling stimulus on appetite; consumption of energy associated with milk secretion is also considered to be one of the main factors in inducing the enhanced food intake in lactating rats. A further possibility that the suckling stimulus participates in the regulation of body weight and food consumption in lactating animals by changing the ovarian function is discussed.

Body weight and food consumption of lactating rats nursing various sizes of litters

Changes in body weight and food consumption during lactation in rats nursing various sizes of litters were studied. The rate of increase in body weight of the mother rats during the experimental period (day 3–14 of lactation) was very similar in mothers with different numbers (2, 4, 8 and 12) of suckling pups/litter. It is suggested that the weight increase of adult female rats during lactation is related more closely to the alteration of ovarian function caused by the suckling stimulus than to the enhanced food intake during this period. Both the food intake of mother rats and the daily gain in weight of litters increased as the number of suckling pups/litter increased and as lactation advanced. Linear relationships were observed between the logarithm of the litter size and both the food intake of the mother rats and the weight gain of the litters. The presence of a close correlation between the food intake of mother rats and the quantity of milk produced by them is suggested.

Studies of cellular proliferation in human leukemia. I. Estimation of growth rates of leukemic and normal hematopoietic cells in two adults with acute leukemia given single injections of tritiated thymidine

Two adults with rapidly progressive acute myeloblastic and myelomonoblastic leukemia were given single injections of tritiated thymidine, and measurements were made of the growth rates of their leukemic and normal hematopoietic cells by radioautographic methods. Although almost all leukemic blasts in both marrow and blood were metabolically active as shown by their ability to incorporate tritiated uridine and leucine in vitro, only 5.6% and 6.1% of the blasts in the marrow and even fewer in the blood incorporated tritiated thymidine. The mitotic indexes of the marrow blasts were 0.66% and 0.52%; no circulating blasts were dividing. The mean generation times of the actively proliferating blasts were estimated to be 49 and 83 hours. This cannot be equated with the doubling time of the total leukemic population as there is evidence that many blasts fail to continue dividing and die. The mean durations of the phases of the blasts' mitotic cycles were as follows: DNA synthesis (S) = 22 and 19 hours, premitosis (G(2)) = 3 hours, mitosis (M) = 0.47 and 0.62 hour (minimal estimates), and postmitosis (G(1)) = 24 and 61 hours. In both patients the maximal mean transit time of the blasts in the blood was 36 hours, and the minimal numbers of actively dividing blasts present were 1.6 and 2.6 x 10(9) per kg of body weight.Estimates were also made of the rates of proliferation and maturation of the residual normal erythrocytic and granulocytic cells in these two patients. Although total production was markedly diminished because of reduction in the number of normal elements, the relatively few remaining normal cells appeared to be dividing and maturing at rates that are about the same or only slightly slower than those found in normal subjects. We conclude that main reason leukemic blasts displace normal hematopoietic precursors in acute leukemia is that the blasts largely fail to differentiate. Many die but many others persist in the marrow and elsewhere as primitive cells and continue to proliferate. As the blasts accumulate, they gradually displace the normal hematopoietic cells, most of which continue their normal course of differentiation and leave the marrow as nondividing mature cells. It is not known why the over-all production of normal cells is not adequately increased to compensate for the anemia, granulocytopenia, and thrombocytopenia that develop, but apparently the leukemic cells somehow interfere with the proliferation or differentiation or both of normal stem cells.